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okay um so i wanted to start
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kind of with the i want to share with
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you guys what's going on in
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in my driveway at the moment um this is
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my my younger brother's
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car it's a uh 1978 fiat spider
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and my brother is uh 18 years old
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now and he got this car when he turned
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16 he purchased it from
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our neighbors up the street and when he
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purchased it it was not running
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and of course now it's missing a wheel
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but uh
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i had to push the car down the street to
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get into our driveway and so my
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brother and my father have been working
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on it over the past few years
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and they've had it got it up and running
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um you know it's very
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quick fairly quickly after getting it
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but they've always been
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changing things and they've taken the
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entire engine out of it and
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replaced the transmission and and all
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that um but this is just kind of recent
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work and
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what was interesting why i'm why i'm
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bringing this up is that
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they um they had the engine block
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re-surfaced so they took the engine
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block out and they
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they sent it to a machinist in seattle
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who
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who re finished the engine block so now
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it looks
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nice and clean as you can see here so
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this is the end the
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i don't i'm not too familiar with all
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the the lingo
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um the mechanic lingo
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so i might be making up some words that
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don't make sense but this is the the
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engine the head of the engine block
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and um this these areas are where the
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combustion reaction happens right the
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gas and
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uh oxygen mixture combusts and there's a
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the spark plug comes out here
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and then these areas are where the
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valves open and close to allow the
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oxygen or the the gas in
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and um so this whole thing was uh
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chemically treated and cleaned and then
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resurfaced but
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what i wanted to point out is that this
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these engine blocks
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are are typically sand casted aluminum
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and you guys are familiar with sand
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casting and i wanted to show you some of
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the surface features of this
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resurfaced engine block and
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um you can see the porosity in the sand
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cast
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it has very high porosity just evident
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just through
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visually inspecting it and
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what's what's also interesting is that
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you know fiat
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is also notorious for for having parts
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break down on it and in fact uh my
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father
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that was talking with a a machinist who
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was who's making these parts
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or specializing the fiat parts and he
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said yeah the engine blocks have always
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been notorious for for
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it's uh low quality and i think it's
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pretty evident of this you know high
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porosity that
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these are kind of poor materials but
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also why this is out right now
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is that my brother was adjusting the
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timing of the
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of the of the car the engine
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and um the timing is important because
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the timing
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is uh you know when the spark will will
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ignite
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compared to the height of the cylinder
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that
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the piston and also the valves when they
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come out and so if you want to get it at
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the right spot where
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you have the spark right at the top of
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the cylinder or whatever so you have the
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right compression ratio i'm not i'm not
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too familiar with
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you know the exact uh lingo but what
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happened is if the timing is off by too
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much
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that the head of the cylinder that
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piston that's going up and down
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will bump into the valve that's opening
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which is this
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the valve seat is right here and so what
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happened is my brother
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uh accidentally put the timing a little
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bit too far off time
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and the top of the cylinder bumped into
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this valve that would open
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and broke off and so now it's inside
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this chamber that's
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bouncing around you can see how it's
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deformed the pieces of this cylinder
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valve have broken off and deformed
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inside while while the engine was
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running
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and so if we had to take the whole thing
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they had to take the whole thing apart
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again uh this time the engine could stay
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in the car just taking the the head off
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is easier
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and what they did recently is they went
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to a i guess a scrap yard
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that had the same car and got the same
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part from an
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old your retired car and so here's the
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same kind of part you see these are the
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valve
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uh parts that kind of open and close and
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that's what was destroyed and so they're
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going to clean this up and replace the
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one that was damaged
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which is too bad because it's nice and
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clean already but anyways
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just just a little bit of material
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science uh i thought i would share
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what's kind of going on in in our time
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off
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but that's my brother my father have
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mainly been doing that
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okay so let's um we're going to talk
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about
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a bit more about the electrochemistry i
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wanted to go over some things we learned
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last lecture
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some things that i might have missed and
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clarify some things
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and we'll talk a bit more about
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batteries um so last time i talked about
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the standard reduction potential right
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this list of potentials that these
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different species will
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reduce at i've i failed to emphasize
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that these values are measured at
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standard state
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so they're empirically determined at
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standard state conditions and the
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standard state is at 25 degrees celsius
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one atmosphere
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and then also most importantly is the
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concentration
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of the species so in all of these uh
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these cases with exception for some like
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the the metals like zinc metal
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zinc metal you can't have a
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concentration in solution it's a solid
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but like iron three plus iron two plus
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the concentration of iron three plus is
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equal to the concentration of iron
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two plus and and for standard state i
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think they keep it at one molar which is
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a bit high in my opinion but
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uh so these values are only accurate
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when
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it's at standard state and that's why
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it's called the standard reduction
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potential it's given by this notation
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the
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the e with a little knot above it that's
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the standard
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reduction potential so if we uh in just
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looking back at this example where we
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had the cell
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of the iron two and three plus and the
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zinc two plus and zinc metal
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well this this potential that we
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calculated the standard redox potential
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of the reaction
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it's only accurate if we say that the
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concentration of iron two plus is equal
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to the
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concentration of iron three plus and
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then the concentration of zinc two plus
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is one molar
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uh okay so that that's only the case and
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i
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kind of forgot to mention that i wanted
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to go over that in more detail
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you know what happens to the voltage of
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this cell
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if the concentration is not the same for
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each species okay so what does the
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voltage look like in that case
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and this follows uh what's called the
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nernst equation
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okay so this equation relates the
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voltage the redox potential
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of the species related to its standard
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reduction
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to potential at standard state and then
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how it changes concentration so minus
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rtr is the gas constant t is temperature
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in kelvin
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n is the number of electrons involved in
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the reaction so for iron two plus iron
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three plus it's only one electron
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like zinc two plus the zinc metal is two
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electron reaction
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um f is faraday's constant relates the
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the amount of charge
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in one mole of electrons and then q
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r is the the um i want to say reaction
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quotient
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reaction quotient that is the ratio of
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the products of the reaction
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to the the uh
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reactants of the reaction okay so
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if at standard state the products and
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the reactants are at equal concentration
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and here i've plotted
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the reduction potential versus the
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the ratio of the products to the
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reactants of that reaction of this uh
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this redox reaction and you see if
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they're equal so
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it would be one over one or it would be
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equal to one
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that is the value of the standard
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reduction potential and for iron
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to the three oxide it's 0.77 volts
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but as we increase the amount of
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reactants
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which would be iron in this case would
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be iron three plus if we increase the
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concentration of iron three plus
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relative to iron two plus
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the voltage of this of this redox
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voltage
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increases okay and the opposite is true
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for if we increase the
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amount of products okay this this should
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be familiar with you should be familiar
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with this
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you've probably learned this in freshman
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chemistry and even high school chemistry
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this is uh a principle called
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le chatelier's principle okay and that
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that
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says you know if you have more product
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then the reaction will be favored to go
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in the reverse or if you have more more
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reactant it'll be favorable in the the
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forward reaction
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all right so all we're saying is that we
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have more reactant versus product and so
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there's going to be a higher a greater
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thermodynamic driving force
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for that reaction to proceed instead if
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it had more
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product than reactive okay i mean even
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if
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even if the amount of product is very
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low
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or excuse me if the amount of product is
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very high there's still a positive
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potential which means there's still a
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thermodynamic driving force for that
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reaction to proceed it's just lower than
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if it was the other way around okay uh
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so here's an example
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of that uh i i've taken two cells
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uh a solution a and solution b and they
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are both made up of
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iron two plus and iron three plus but
286
00:09:20,160 --> 00:09:21,839
the difference is the difference in
287
00:09:21,839 --> 00:09:23,839
concentration of the three plus to two
288
00:09:23,839 --> 00:09:24,399
plus
289
00:09:24,399 --> 00:09:26,800
so in solution a we have a greater
290
00:09:26,800 --> 00:09:27,680
amount of
291
00:09:27,680 --> 00:09:30,880
uh iron three plus solution b solution b
292
00:09:30,880 --> 00:09:33,040
we have a greater amount of iron two
293
00:09:33,040 --> 00:09:35,519
plus so you can use the nernst equation
294
00:09:35,519 --> 00:09:36,640
to calculate the
295
00:09:36,640 --> 00:09:39,680
the redox potential in solution a okay
296
00:09:39,680 --> 00:09:41,200
so we have the standard redox potential
297
00:09:41,200 --> 00:09:42,080
of iron is
298
00:09:42,080 --> 00:09:45,120
0.77 and the natural log
299
00:09:45,120 --> 00:09:48,240
of the concentration in this case is one
300
00:09:48,240 --> 00:09:50,160
the concentration of the product iron
301
00:09:50,160 --> 00:09:52,080
two plus is one in this case and the
302
00:09:52,080 --> 00:09:55,600
reactant is ten okay so it has a a
303
00:09:55,600 --> 00:09:57,680
redox potential that's above its
304
00:09:57,680 --> 00:09:58,959
standard redux potential
305
00:09:58,959 --> 00:10:01,120
and the opposite is true for solution b
306
00:10:01,120 --> 00:10:03,120
as a redox potential that's lower
307
00:10:03,120 --> 00:10:05,839
so if you compare these two together
308
00:10:05,839 --> 00:10:06,880
there is a
309
00:10:06,880 --> 00:10:08,800
potential difference between these two
310
00:10:08,800 --> 00:10:10,240
cells so if you were to take the
311
00:10:10,240 --> 00:10:12,240
multimeter and measure between you you'd
312
00:10:12,240 --> 00:10:14,079
see a voltage and that voltage is the
313
00:10:14,079 --> 00:10:15,440
difference between these two
314
00:10:15,440 --> 00:10:17,279
so the cell voltage is just the
315
00:10:17,279 --> 00:10:18,480
difference between the reduction
316
00:10:18,480 --> 00:10:19,200
potential of
317
00:10:19,200 --> 00:10:21,360
solution a and solution b so you can
318
00:10:21,360 --> 00:10:22,720
always take the
319
00:10:22,720 --> 00:10:25,279
the higher number minus the the smaller
320
00:10:25,279 --> 00:10:26,160
number
321
00:10:26,160 --> 00:10:29,040
and that will be that can indicate which
322
00:10:29,040 --> 00:10:31,200
direction like electrons will flow
323
00:10:31,200 --> 00:10:33,760
and which what species will be reduced
324
00:10:33,760 --> 00:10:35,600
or oxidized so in this case i've used
325
00:10:35,600 --> 00:10:37,519
the reduction potential but in the
326
00:10:37,519 --> 00:10:39,920
previous example of the zinc
327
00:10:39,920 --> 00:10:42,240
i had used oxidation potential which is
328
00:10:42,240 --> 00:10:43,120
just the negative
329
00:10:43,120 --> 00:10:45,040
of reduction potential all right so it
330
00:10:45,040 --> 00:10:46,240
is the the
331
00:10:46,240 --> 00:10:49,680
the opposite here so you have to
332
00:10:49,680 --> 00:10:52,320
add uh the oxidation potential in this
333
00:10:52,320 --> 00:10:53,760
case
334
00:10:53,760 --> 00:10:57,120
um so the question is
335
00:10:57,120 --> 00:11:01,200
is is this when will this uh reaction
336
00:11:01,200 --> 00:11:02,160
stop
337
00:11:02,160 --> 00:11:04,720
all right so if we if we were to short
338
00:11:04,720 --> 00:11:05,839
circuit this you know
339
00:11:05,839 --> 00:11:08,320
just put a wire across this then
340
00:11:08,320 --> 00:11:10,240
electrons will flow from
341
00:11:10,240 --> 00:11:13,040
this side the iron two plus will oxidize
342
00:11:13,040 --> 00:11:13,519
it'll give
343
00:11:13,519 --> 00:11:16,320
electrons and flow into this side and
344
00:11:16,320 --> 00:11:18,399
reduce the iron three plus and that will
345
00:11:18,399 --> 00:11:19,040
continue
346
00:11:19,040 --> 00:11:20,640
until a certain point and that is of
347
00:11:20,640 --> 00:11:22,959
course equilibrium of the entire system
348
00:11:22,959 --> 00:11:25,279
but the question is when does it reach
349
00:11:25,279 --> 00:11:26,399
equilibrium
350
00:11:26,399 --> 00:11:29,839
okay so we know at equilibrium
351
00:11:29,839 --> 00:11:32,800
there is no net prod uh production of
352
00:11:32,800 --> 00:11:34,399
product and there's no there's no net
353
00:11:34,399 --> 00:11:36,240
forward reaction there's no net reverse
354
00:11:36,240 --> 00:11:36,880
reaction
355
00:11:36,880 --> 00:11:40,399
okay so that means that
356
00:11:40,399 --> 00:11:43,200
the potential between these two cells at
357
00:11:43,200 --> 00:11:44,480
equilibrium would be
358
00:11:44,480 --> 00:11:46,959
zero all right so or gibbs free energy
359
00:11:46,959 --> 00:11:48,560
would be zero right there's no
360
00:11:48,560 --> 00:11:51,040
uh thermodynamic driving force to go one
361
00:11:51,040 --> 00:11:52,399
way or the other
362
00:11:52,399 --> 00:11:54,720
and so the question is you know when at
363
00:11:54,720 --> 00:11:56,560
what concentration of these two cells
364
00:11:56,560 --> 00:11:57,120
will that
365
00:11:57,120 --> 00:11:59,279
occur at when will the the reaction stop
366
00:11:59,279 --> 00:12:00,639
uh taking place
367
00:12:00,639 --> 00:12:03,040
and in this example i i should have
368
00:12:03,040 --> 00:12:04,720
started with nine and one to make the
369
00:12:04,720 --> 00:12:05,120
total
370
00:12:05,120 --> 00:12:07,360
10 but the total concentration of iron
371
00:12:07,360 --> 00:12:08,959
is actually 11 so that's kind of my
372
00:12:08,959 --> 00:12:12,320
mistake but that's fine
373
00:12:12,480 --> 00:12:15,440
so the total concentration of iron in
374
00:12:15,440 --> 00:12:16,800
this case is 11
375
00:12:16,800 --> 00:12:20,399
so when this cell has a concentration of
376
00:12:20,399 --> 00:12:24,800
of 5.5 millimolar iron 3 plus and 5.5
377
00:12:24,800 --> 00:12:27,120
iron 2 plus and that's the same as this
378
00:12:27,120 --> 00:12:29,200
cell that's when the voltage between the
379
00:12:29,200 --> 00:12:30,800
two will be zero
380
00:12:30,800 --> 00:12:33,680
okay and so that's when the reaction
381
00:12:33,680 --> 00:12:35,600
will stop the electrons current will
382
00:12:35,600 --> 00:12:36,800
stop flowing
383
00:12:36,800 --> 00:12:39,680
between the two there's no potential to
384
00:12:39,680 --> 00:12:40,320
to drive
385
00:12:40,320 --> 00:12:44,800
the current um so another question is
386
00:12:44,800 --> 00:12:46,240
you know in this example is fairly
387
00:12:46,240 --> 00:12:48,320
simple the concentrations are the same
388
00:12:48,320 --> 00:12:48,880
in both
389
00:12:48,880 --> 00:12:50,720
right the total amount of iron in both
390
00:12:50,720 --> 00:12:52,399
cells is 11 millimolar
391
00:12:52,399 --> 00:12:55,839
what if one of the cells had a much
392
00:12:55,839 --> 00:12:58,240
higher concentration of iron for example
393
00:12:58,240 --> 00:13:00,240
let's say solution a
394
00:13:00,240 --> 00:13:03,760
had a 100 millimolar iron three plus and
395
00:13:03,760 --> 00:13:05,200
one millimeter iron tubeless but
396
00:13:05,200 --> 00:13:06,079
solution b was kept
397
00:13:06,079 --> 00:13:09,200
the same all right then what would the
398
00:13:09,200 --> 00:13:12,079
the final concentration be now before
399
00:13:12,079 --> 00:13:13,440
this lecture i had prepared
400
00:13:13,440 --> 00:13:15,600
the slide but unfortunately i lost it
401
00:13:15,600 --> 00:13:17,600
and it didn't save
402
00:13:17,600 --> 00:13:20,160
and i'm wondering we could go through it
403
00:13:20,160 --> 00:13:20,720
um
404
00:13:20,720 --> 00:13:22,320
but actually this lecture this morning's
405
00:13:22,320 --> 00:13:24,079
lecture was kind of long so i think i'll
406
00:13:24,079 --> 00:13:24,959
skip that
407
00:13:24,959 --> 00:13:28,240
but uh the answer is you know for if
408
00:13:28,240 --> 00:13:31,360
you have to think of um as
409
00:13:31,360 --> 00:13:34,880
you take electrons away from solution b
410
00:13:34,880 --> 00:13:38,079
all right for every like one millimole
411
00:13:38,079 --> 00:13:40,160
of electrons you take away right you're
412
00:13:40,160 --> 00:13:42,240
you're creating one millimole of iron
413
00:13:42,240 --> 00:13:43,839
three plus and then the same for this
414
00:13:43,839 --> 00:13:45,279
solution you're you're giving it one
415
00:13:45,279 --> 00:13:47,040
millimole of electrons you're
416
00:13:47,040 --> 00:13:49,040
you're creating one millimole of iron
417
00:13:49,040 --> 00:13:50,240
two plus so
418
00:13:50,240 --> 00:13:53,839
if this was 100 millimolars the the most
419
00:13:53,839 --> 00:13:55,760
this could change in concentration at
420
00:13:55,760 --> 00:13:57,519
the maximum let's say it took all the
421
00:13:57,519 --> 00:13:59,440
electrons away from these irons
422
00:13:59,440 --> 00:14:01,440
then the most it could be would be it
423
00:14:01,440 --> 00:14:02,480
would be 9
424
00:14:02,480 --> 00:14:05,440
or excuse me 10. it only has 10 electron
425
00:14:05,440 --> 00:14:07,360
millimolars of electrons to give
426
00:14:07,360 --> 00:14:10,000
so this would be become what 90 instead
427
00:14:10,000 --> 00:14:11,360
of 100. so that would be
428
00:14:11,360 --> 00:14:13,040
the maximum but it's not going to reach
429
00:14:13,040 --> 00:14:14,720
that state
430
00:14:14,720 --> 00:14:18,000
because remember the reduction potential
431
00:14:18,000 --> 00:14:19,360
of these solutions
432
00:14:19,360 --> 00:14:21,920
depends on the ratio of product to
433
00:14:21,920 --> 00:14:23,040
reactant
434
00:14:23,040 --> 00:14:26,320
okay so actually uh before it depletes
435
00:14:26,320 --> 00:14:27,920
all those electrons that ratio is going
436
00:14:27,920 --> 00:14:28,399
to create
437
00:14:28,399 --> 00:14:31,600
such a a potential that
438
00:14:31,600 --> 00:14:33,920
the it's going to equilibrate and turn
439
00:14:33,920 --> 00:14:34,639
to zero
440
00:14:34,639 --> 00:14:36,800
it's a bit it's a lot more clear when i
441
00:14:36,800 --> 00:14:38,240
have that extra slide i'll i'll see if i
442
00:14:38,240 --> 00:14:39,600
can upload it and
443
00:14:39,600 --> 00:14:41,279
later it'll make more sense but let's
444
00:14:41,279 --> 00:14:43,440
move on
445
00:14:43,440 --> 00:14:44,959
so this is something i was thinking
446
00:14:44,959 --> 00:14:47,120
about last night when i was making these
447
00:14:47,120 --> 00:14:48,160
slides
448
00:14:48,160 --> 00:14:52,800
is how how is this different
449
00:14:52,800 --> 00:14:56,000
than having just iron and two plus and
450
00:14:56,000 --> 00:14:57,440
three plus in solution right i mean
451
00:14:57,440 --> 00:14:59,120
what's what's stopping from
452
00:14:59,120 --> 00:15:01,760
stopping this iron two plus two for from
453
00:15:01,760 --> 00:15:03,760
giving electrons to this iron three plus
454
00:15:03,760 --> 00:15:04,079
and
455
00:15:04,079 --> 00:15:06,480
reducing it right it's kind of kind of
456
00:15:06,480 --> 00:15:08,240
similar to this and um
457
00:15:08,240 --> 00:15:10,240
if the concentrations are different
458
00:15:10,240 --> 00:15:12,720
right i i i'm embarrassed to admit i
459
00:15:12,720 --> 00:15:13,360
spent
460
00:15:13,360 --> 00:15:16,160
a long time thinking about this and i
461
00:15:16,160 --> 00:15:17,199
was i was
462
00:15:17,199 --> 00:15:21,440
it was driving me nuts thinking why why
463
00:15:21,440 --> 00:15:24,320
it didn't make sense um and the reason
464
00:15:24,320 --> 00:15:24,880
is
465
00:15:24,880 --> 00:15:27,600
well of course in solution you you are
466
00:15:27,600 --> 00:15:28,320
having
467
00:15:28,320 --> 00:15:30,160
this electron transfer between iron two
468
00:15:30,160 --> 00:15:31,839
blocks and iron three plus all the time
469
00:15:31,839 --> 00:15:34,079
right it's it's fine it's natural to to
470
00:15:34,079 --> 00:15:36,079
have some exchange
471
00:15:36,079 --> 00:15:38,480
but the point is that i was missing is
472
00:15:38,480 --> 00:15:40,000
that if you remove
473
00:15:40,000 --> 00:15:43,199
an electron from this iron atom
474
00:15:43,199 --> 00:15:45,279
and give it to this iron atom the
475
00:15:45,279 --> 00:15:47,360
concentration of iron three plus and
476
00:15:47,360 --> 00:15:49,360
iron two plus does not change right you
477
00:15:49,360 --> 00:15:50,800
just removed it from one iron and gave
478
00:15:50,800 --> 00:15:51,759
it to another and
479
00:15:51,759 --> 00:15:53,360
it took me about an hour to figure that
480
00:15:53,360 --> 00:15:55,440
out like oh i'm
481
00:15:55,440 --> 00:15:56,720
i was a little bit embarrassed about
482
00:15:56,720 --> 00:15:58,720
that anyways
483
00:15:58,720 --> 00:16:00,720
so it is different this solution you
484
00:16:00,720 --> 00:16:02,480
could say is at equilibrium it has
485
00:16:02,480 --> 00:16:04,160
equilibrium potential
486
00:16:04,160 --> 00:16:07,279
this system this system is not at
487
00:16:07,279 --> 00:16:08,399
equilibrium
488
00:16:08,399 --> 00:16:11,360
okay until the voltage reads zero but if
489
00:16:11,360 --> 00:16:12,880
you're just looking at individual
490
00:16:12,880 --> 00:16:14,399
solutions you could say yeah that
491
00:16:14,399 --> 00:16:15,920
solution is at equilibrium
492
00:16:15,920 --> 00:16:19,680
but the system is not um
493
00:16:19,680 --> 00:16:21,839
that's you know particularly introducing
494
00:16:21,839 --> 00:16:23,199
the salt bridge
495
00:16:23,199 --> 00:16:26,639
uh will put the the give you this this
496
00:16:26,639 --> 00:16:29,600
potential between the two electrodes uh
497
00:16:29,600 --> 00:16:31,279
in a side note i
498
00:16:31,279 --> 00:16:34,480
i was at a museum in uh germany this is
499
00:16:34,480 --> 00:16:36,000
related it's related i was
500
00:16:36,000 --> 00:16:37,839
in germany with my wife and i when i was
501
00:16:37,839 --> 00:16:40,079
an undergrad and we were vacationing and
502
00:16:40,079 --> 00:16:41,759
i went i think it was in dresden we went
503
00:16:41,759 --> 00:16:43,360
to some science museum and there was
504
00:16:43,360 --> 00:16:45,199
this really cool demo
505
00:16:45,199 --> 00:16:47,360
that talked about the like corrosion
506
00:16:47,360 --> 00:16:49,040
potential between different metals
507
00:16:49,040 --> 00:16:51,279
or the activity between different metals
508
00:16:51,279 --> 00:16:52,639
where they had a metal
509
00:16:52,639 --> 00:16:54,560
like a one type of metal like aluminum
510
00:16:54,560 --> 00:16:55,839
and add another type of metal
511
00:16:55,839 --> 00:16:58,160
copper and they were like plates and it
512
00:16:58,160 --> 00:17:00,639
had a volt meter just like in the setup
513
00:17:00,639 --> 00:17:03,680
okay and
514
00:17:03,680 --> 00:17:05,679
the idea was you would put your hands on
515
00:17:05,679 --> 00:17:06,880
these plates
516
00:17:06,880 --> 00:17:08,240
and then the voltmeter would read a
517
00:17:08,240 --> 00:17:10,000
voltage okay
518
00:17:10,000 --> 00:17:12,720
so how does that work it's it's very
519
00:17:12,720 --> 00:17:13,359
similar
520
00:17:13,359 --> 00:17:17,119
to to this setup where you have
521
00:17:17,119 --> 00:17:18,959
you know say you have the copper plate
522
00:17:18,959 --> 00:17:21,599
on one side the
523
00:17:21,599 --> 00:17:23,119
aluminum plate on another and they're
524
00:17:23,119 --> 00:17:24,640
connected to the voltmeter that we're
525
00:17:24,640 --> 00:17:25,520
looking at
526
00:17:25,520 --> 00:17:28,559
and then you your your own body is
527
00:17:28,559 --> 00:17:30,799
making the salt bridge
528
00:17:30,799 --> 00:17:32,240
to connect the two and that's when the
529
00:17:32,240 --> 00:17:34,320
voltage reads so your body
530
00:17:34,320 --> 00:17:37,200
is the electrolyte to for this uh to
531
00:17:37,200 --> 00:17:38,000
make this
532
00:17:38,000 --> 00:17:39,760
uh to measure this potential difference
533
00:17:39,760 --> 00:17:40,799
and i thought it was really cool because
534
00:17:40,799 --> 00:17:41,840
there's all these different metals and
535
00:17:41,840 --> 00:17:43,039
you put your hands on different things
536
00:17:43,039 --> 00:17:44,720
and it make the volt meter
537
00:17:44,720 --> 00:17:46,720
go to different voltages anyways so
538
00:17:46,720 --> 00:17:48,799
pretty cool demo you can you can try out
539
00:17:48,799 --> 00:17:51,600
if you have a volt meter and see if it
540
00:17:51,600 --> 00:17:52,320
works
541
00:17:52,320 --> 00:17:56,240
okay so here's a method of determining
542
00:17:56,240 --> 00:17:59,280
the the standard reduction potential
543
00:17:59,280 --> 00:18:01,039
uh this is called potentiometric
544
00:18:01,039 --> 00:18:02,320
titration
545
00:18:02,320 --> 00:18:04,640
and there's other types of titrate
546
00:18:04,640 --> 00:18:06,160
titration is when you when you
547
00:18:06,160 --> 00:18:08,960
when you add a species to a solution
548
00:18:08,960 --> 00:18:10,640
like drop by drop
549
00:18:10,640 --> 00:18:13,039
and you're measuring the volume added to
550
00:18:13,039 --> 00:18:14,400
the solution
551
00:18:14,400 --> 00:18:16,880
okay so like there's uh you're probably
552
00:18:16,880 --> 00:18:18,320
familiar with a
553
00:18:18,320 --> 00:18:20,480
acid-base titration right you might have
554
00:18:20,480 --> 00:18:22,400
a solution that has an indicator that
555
00:18:22,400 --> 00:18:23,440
changes color
556
00:18:23,440 --> 00:18:25,760
when it reaches a certain ph and then
557
00:18:25,760 --> 00:18:27,360
you titrate it with an acid and you're
558
00:18:27,360 --> 00:18:28,559
measuring the volume
559
00:18:28,559 --> 00:18:30,960
added to that solution and you're modern
560
00:18:30,960 --> 00:18:32,480
monitoring it and then all of a sudden
561
00:18:32,480 --> 00:18:33,520
it hits that that
562
00:18:33,520 --> 00:18:35,600
that ph and it changes color so that's a
563
00:18:35,600 --> 00:18:37,120
acid-base titration
564
00:18:37,120 --> 00:18:39,360
in this type of titration you have a
565
00:18:39,360 --> 00:18:40,320
species
566
00:18:40,320 --> 00:18:43,760
of redox active ions in solution so in
567
00:18:43,760 --> 00:18:44,880
this example we have
568
00:18:44,880 --> 00:18:48,240
a tin two plus in iron two plus just a
569
00:18:48,240 --> 00:18:49,120
hundred percent
570
00:18:49,120 --> 00:18:51,440
two plus hundred percent iron two plus
571
00:18:51,440 --> 00:18:53,200
and we're titrating it with
572
00:18:53,200 --> 00:18:57,520
this this ion this is um
573
00:18:57,520 --> 00:18:59,679
and correct me if i'm wrong i think a
574
00:18:59,679 --> 00:19:00,559
cerium
575
00:19:00,559 --> 00:19:02,720
i believe cerium i could be saying that
576
00:19:02,720 --> 00:19:04,880
wrong cerium four plus
577
00:19:04,880 --> 00:19:07,679
um so cerium four plus it has a very
578
00:19:07,679 --> 00:19:09,360
high reduction potential
579
00:19:09,360 --> 00:19:12,799
1.6 volts so that means if it comes in
580
00:19:12,799 --> 00:19:15,120
contact with any of these ions
581
00:19:15,120 --> 00:19:18,000
it's going to easily oxidize those ions
582
00:19:18,000 --> 00:19:19,440
so those ions are going to oxidize
583
00:19:19,440 --> 00:19:21,200
they're going to
584
00:19:21,200 --> 00:19:24,400
they're going to iron cesium four plus
585
00:19:24,400 --> 00:19:26,320
is going to steal an electron from those
586
00:19:26,320 --> 00:19:27,919
ions
587
00:19:27,919 --> 00:19:31,120
okay so if we start
588
00:19:31,120 --> 00:19:34,000
with this solution of two plus ions and
589
00:19:34,000 --> 00:19:34,480
what
590
00:19:34,480 --> 00:19:36,640
you do is that you measure the redox
591
00:19:36,640 --> 00:19:37,760
potential
592
00:19:37,760 --> 00:19:40,080
so the potential between the platinum
593
00:19:40,080 --> 00:19:42,160
and the a reference electrode such as
594
00:19:42,160 --> 00:19:44,320
a standard hydrogen electrode so you're
595
00:19:44,320 --> 00:19:45,679
measuring the whatever reaction is
596
00:19:45,679 --> 00:19:46,960
happening at the surface of this
597
00:19:46,960 --> 00:19:48,240
electrode
598
00:19:48,240 --> 00:19:50,720
as you titrate it okay so this this is
599
00:19:50,720 --> 00:19:52,160
very much at equilibrium
600
00:19:52,160 --> 00:19:54,799
you add a little bit of cerium you you
601
00:19:54,799 --> 00:19:55,760
let it mix up
602
00:19:55,760 --> 00:19:58,799
together and so it
603
00:19:58,799 --> 00:20:00,799
goes to equilibrium and you measure the
604
00:20:00,799 --> 00:20:02,720
voltage and so you take these
605
00:20:02,720 --> 00:20:05,120
different points as you add the cerium
606
00:20:05,120 --> 00:20:06,720
and you measure the volume of cerium and
607
00:20:06,720 --> 00:20:07,200
that's
608
00:20:07,200 --> 00:20:08,720
relative to the concentration of the
609
00:20:08,720 --> 00:20:11,039
cerium okay and you'll get a plot like
610
00:20:11,039 --> 00:20:11,600
this
611
00:20:11,600 --> 00:20:14,720
and this plot very much is the nernst
612
00:20:14,720 --> 00:20:15,520
equation
613
00:20:15,520 --> 00:20:18,720
for each species so all i did as i
614
00:20:18,720 --> 00:20:20,000
modeled the nernst equation
615
00:20:20,000 --> 00:20:22,320
for 10 2 plus the 4 plus and then i also
616
00:20:22,320 --> 00:20:23,840
modeled the neurons equation 2 plus the
617
00:20:23,840 --> 00:20:25,200
3 plus and i just kind of added them
618
00:20:25,200 --> 00:20:26,400
together
619
00:20:26,400 --> 00:20:29,200
and the at the inflection point is the
620
00:20:29,200 --> 00:20:29,919
standard
621
00:20:29,919 --> 00:20:31,840
reduction potential and remember
622
00:20:31,840 --> 00:20:33,760
standard reduction potential is when
623
00:20:33,760 --> 00:20:35,679
the concentration of the product is
624
00:20:35,679 --> 00:20:37,520
equal to the concentration of the
625
00:20:37,520 --> 00:20:38,400
reactant
626
00:20:38,400 --> 00:20:40,400
all right so at this potential and or
627
00:20:40,400 --> 00:20:41,919
that this volume added
628
00:20:41,919 --> 00:20:44,960
you have reduced half excuse me you have
629
00:20:44,960 --> 00:20:47,600
oxidized half of the tin
630
00:20:47,600 --> 00:20:50,559
ions in solution all right and then you
631
00:20:50,559 --> 00:20:52,080
continue and then at this point you've
632
00:20:52,080 --> 00:20:54,320
oxidized all of the tin ions
633
00:20:54,320 --> 00:20:56,159
and then you start oxidizing the iron
634
00:20:56,159 --> 00:20:58,000
ions and then this at the halfway point
635
00:20:58,000 --> 00:20:59,280
as the standard redux
636
00:20:59,280 --> 00:21:02,480
potential is a half of the iron
637
00:21:02,480 --> 00:21:04,640
ions have been oxidized now one question
638
00:21:04,640 --> 00:21:06,960
is uh you know when you drop the cerium
639
00:21:06,960 --> 00:21:09,440
in why why is it that only the tin
640
00:21:09,440 --> 00:21:11,600
oxidizes and not the iron
641
00:21:11,600 --> 00:21:14,880
okay because i mean iron is also lower
642
00:21:14,880 --> 00:21:18,799
in reduction potential than the cerium
643
00:21:18,799 --> 00:21:20,799
so you know both of these are are fair
644
00:21:20,799 --> 00:21:23,520
game to being oxidized right
645
00:21:23,520 --> 00:21:25,440
but but if you were you were to measure
646
00:21:25,440 --> 00:21:26,799
it you'd only see the tin
647
00:21:26,799 --> 00:21:29,760
oxidized um so in reality when when we
648
00:21:29,760 --> 00:21:31,840
drop this liquid in and the cerium
649
00:21:31,840 --> 00:21:33,919
reacts with the the liquid it could very
650
00:21:33,919 --> 00:21:35,600
well yeah it's very possible that it
651
00:21:35,600 --> 00:21:36,880
does oxidize
652
00:21:36,880 --> 00:21:39,280
the iron two plus the iron three plus
653
00:21:39,280 --> 00:21:40,240
however
654
00:21:40,240 --> 00:21:43,120
iron three plus also has a higher
655
00:21:43,120 --> 00:21:46,080
reduction potential than tin four plus
656
00:21:46,080 --> 00:21:48,400
okay so that means the iron three plus
657
00:21:48,400 --> 00:21:50,480
is oxidizing any
658
00:21:50,480 --> 00:21:53,440
tin two plus that's uh present as well
659
00:21:53,440 --> 00:21:54,000
so any
660
00:21:54,000 --> 00:21:57,200
iron iron two plus that gets oxidized
661
00:21:57,200 --> 00:21:59,679
it goes forward and oxidizes tin two
662
00:21:59,679 --> 00:22:00,960
plus and becomes reduced again
663
00:22:00,960 --> 00:22:04,559
anyways okay so that's potentiometric
664
00:22:04,559 --> 00:22:05,600
titration and again
665
00:22:05,600 --> 00:22:07,520
the important of this type of technique
666
00:22:07,520 --> 00:22:09,520
is that it's at equilibrium
667
00:22:09,520 --> 00:22:12,080
all right each data point we collect is
668
00:22:12,080 --> 00:22:13,360
at equilibrium
669
00:22:13,360 --> 00:22:15,679
now we'll talk about cyclic voltometry
670
00:22:15,679 --> 00:22:17,280
and i introduced this before
671
00:22:17,280 --> 00:22:18,880
but what's different with cyclical
672
00:22:18,880 --> 00:22:21,039
optometry is that we're not
673
00:22:21,039 --> 00:22:23,600
we are no longer at equilibrium all
674
00:22:23,600 --> 00:22:24,080
right so
675
00:22:24,080 --> 00:22:25,280
in this type of test you might have a
676
00:22:25,280 --> 00:22:26,880
three electrode cell like this where you
677
00:22:26,880 --> 00:22:28,720
have the working electrode and that's
678
00:22:28,720 --> 00:22:30,320
that's going to be the reaction that
679
00:22:30,320 --> 00:22:31,760
you're you're interested in
680
00:22:31,760 --> 00:22:33,280
so you're measuring the voltage of that
681
00:22:33,280 --> 00:22:35,760
reaction against a reference electrode
682
00:22:35,760 --> 00:22:39,600
and then you're applying a current
683
00:22:39,600 --> 00:22:41,360
between that and the counter electro so
684
00:22:41,360 --> 00:22:43,039
all the purpose of the counter electrode
685
00:22:43,039 --> 00:22:45,200
is only only to provide electrons or
686
00:22:45,200 --> 00:22:46,640
take away electrons but we're not really
687
00:22:46,640 --> 00:22:47,200
interested
688
00:22:47,200 --> 00:22:49,360
at what whatever redox reaction is
689
00:22:49,360 --> 00:22:50,960
happening on that surface
690
00:22:50,960 --> 00:22:53,520
because we're not measuring the voltage
691
00:22:53,520 --> 00:22:54,720
now i said with the
692
00:22:54,720 --> 00:22:56,080
we're supplying our current but i mean
693
00:22:56,080 --> 00:22:58,320
really we're controlling the voltage so
694
00:22:58,320 --> 00:22:59,440
this type of test
695
00:22:59,440 --> 00:23:02,720
we we have we we control the voltage
696
00:23:02,720 --> 00:23:05,760
and we set it so that it it linearly
697
00:23:05,760 --> 00:23:07,840
increases at a certain rate and then
698
00:23:07,840 --> 00:23:09,679
decreases a certain rate between
699
00:23:09,679 --> 00:23:12,000
you know arbitrary points that we select
700
00:23:12,000 --> 00:23:14,000
uh it's important that these voltages
701
00:23:14,000 --> 00:23:15,039
are within like the
702
00:23:15,039 --> 00:23:17,039
electrolyte rate range so if you're
703
00:23:17,039 --> 00:23:18,159
working with water
704
00:23:18,159 --> 00:23:21,120
and if you push the voltage too far then
705
00:23:21,120 --> 00:23:22,799
the water or the electrolyte will start
706
00:23:22,799 --> 00:23:24,640
breaking down as well and you'll get
707
00:23:24,640 --> 00:23:25,440
other
708
00:23:25,440 --> 00:23:29,039
things that you're not interested in um
709
00:23:29,039 --> 00:23:32,559
okay so here's a
710
00:23:32,559 --> 00:23:35,280
this should be a video if i click or a
711
00:23:35,280 --> 00:23:36,080
um
712
00:23:36,080 --> 00:23:38,640
let's see yeah this happened in the
713
00:23:38,640 --> 00:23:40,159
morning too oh there we go
714
00:23:40,159 --> 00:23:43,520
so this is the the test okay so we start
715
00:23:43,520 --> 00:23:44,400
out
716
00:23:44,400 --> 00:23:46,799
uh at a negative potential okay let's
717
00:23:46,799 --> 00:23:48,640
say we're starting with iron
718
00:23:48,640 --> 00:23:50,960
ferrous chloride it's a hundred percent
719
00:23:50,960 --> 00:23:52,159
iron two plus
720
00:23:52,159 --> 00:23:54,000
and we've set the potential to negative
721
00:23:54,000 --> 00:23:55,279
four so again we're
722
00:23:55,279 --> 00:23:57,760
in this test we're applying a potential
723
00:23:57,760 --> 00:23:58,559
rather than
724
00:23:58,559 --> 00:24:01,679
uh just measuring it at equilibrium so
725
00:24:01,679 --> 00:24:02,159
it might
726
00:24:02,159 --> 00:24:04,559
it's not necessarily at equal this is
727
00:24:04,559 --> 00:24:06,080
below the equilibrium
728
00:24:06,080 --> 00:24:08,240
potential of the iron but iron has
729
00:24:08,240 --> 00:24:10,159
already been reduced completely so
730
00:24:10,159 --> 00:24:11,520
you're not going to see any current yeah
731
00:24:11,520 --> 00:24:13,360
the y-axis is current
732
00:24:13,360 --> 00:24:15,039
going through and the x-axis is the
733
00:24:15,039 --> 00:24:16,559
applied potential
734
00:24:16,559 --> 00:24:18,400
so we're not at equilibrium at negative
735
00:24:18,400 --> 00:24:19,840
0.4 and this is
736
00:24:19,840 --> 00:24:21,760
voltage versus the standard reduction
737
00:24:21,760 --> 00:24:23,520
potential so at zero volts that's just
738
00:24:23,520 --> 00:24:24,880
going to be for iron
739
00:24:24,880 --> 00:24:28,159
0.77 volts versus she um
740
00:24:28,159 --> 00:24:30,480
so yeah so we're below the equilibrium
741
00:24:30,480 --> 00:24:31,760
potential but again
742
00:24:31,760 --> 00:24:33,440
all the iron has already been reduced so
743
00:24:33,440 --> 00:24:34,799
it's no it can't
744
00:24:34,799 --> 00:24:38,240
be reduced anymore and we sweep the
745
00:24:38,240 --> 00:24:39,200
voltage
746
00:24:39,200 --> 00:24:40,960
we increase the voltage and then we
747
00:24:40,960 --> 00:24:42,880
start to reach the reduction potential
748
00:24:42,880 --> 00:24:44,559
and that's when we see current and the
749
00:24:44,559 --> 00:24:46,400
current corresponds to the reaction the
750
00:24:46,400 --> 00:24:47,600
electrons are being
751
00:24:47,600 --> 00:24:49,600
delivered to the iron or taken away from
752
00:24:49,600 --> 00:24:51,440
the iron two plus and it's oxidizing at
753
00:24:51,440 --> 00:24:52,559
that surface
754
00:24:52,559 --> 00:24:56,320
okay and then we reach a maximum point
755
00:24:56,320 --> 00:24:59,520
the reason why we reach a maximum limit
756
00:24:59,520 --> 00:25:02,799
in this case is that the concentration
757
00:25:02,799 --> 00:25:05,200
of iron two plus at the surface of this
758
00:25:05,200 --> 00:25:06,559
platinum electrode
759
00:25:06,559 --> 00:25:09,279
is decreasing as as we're as we're
760
00:25:09,279 --> 00:25:10,640
oxidizing the iron two plus the
761
00:25:10,640 --> 00:25:12,640
concentration decreases
762
00:25:12,640 --> 00:25:15,039
okay and eventually we reach a limit
763
00:25:15,039 --> 00:25:15,760
where there's no
764
00:25:15,760 --> 00:25:18,320
longer any any iron two plus available
765
00:25:18,320 --> 00:25:19,039
but there's still
766
00:25:19,039 --> 00:25:21,120
there's still plenty of iron two plus in
767
00:25:21,120 --> 00:25:22,480
the bulk of the
768
00:25:22,480 --> 00:25:24,480
electrolyte it's just not at the surface
769
00:25:24,480 --> 00:25:26,000
of the the electrode
770
00:25:26,000 --> 00:25:27,919
and so what happens is we've reached a
771
00:25:27,919 --> 00:25:29,039
diffusion limit
772
00:25:29,039 --> 00:25:32,080
so we're we're waiting for the ions in
773
00:25:32,080 --> 00:25:33,760
solution to diffuse
774
00:25:33,760 --> 00:25:35,520
to the surface and then also the iron
775
00:25:35,520 --> 00:25:37,200
three plus in the uh
776
00:25:37,200 --> 00:25:39,279
against the surface to diffuse away from
777
00:25:39,279 --> 00:25:41,200
the surface all right so that's why the
778
00:25:41,200 --> 00:25:42,000
current starts to
779
00:25:42,000 --> 00:25:44,159
go down even though there's plenty of
780
00:25:44,159 --> 00:25:45,840
iron two plus still in the solution the
781
00:25:45,840 --> 00:25:47,279
current starts to go down
782
00:25:47,279 --> 00:25:49,279
because of a diffusion limit so it's a
783
00:25:49,279 --> 00:25:50,720
it's a kinetic
784
00:25:50,720 --> 00:25:53,200
limitation and this peak current also
785
00:25:53,200 --> 00:25:55,279
can depend on you know the size
786
00:25:55,279 --> 00:25:57,360
of this electrode if you have a higher
787
00:25:57,360 --> 00:25:58,720
surface area of course you're going to
788
00:25:58,720 --> 00:25:59,679
have more
789
00:25:59,679 --> 00:26:03,200
more uh a higher current um than a
790
00:26:03,200 --> 00:26:06,480
smaller like a wire a platinum wire
791
00:26:06,480 --> 00:26:09,760
okay so we're continuing to push this uh
792
00:26:09,760 --> 00:26:13,120
this voltage let's see if i can
793
00:26:13,120 --> 00:26:15,840
go up and then we reach the the final
794
00:26:15,840 --> 00:26:17,279
voltage and reverse it
795
00:26:17,279 --> 00:26:19,760
okay so we've reached our end voltage
796
00:26:19,760 --> 00:26:21,360
which is would be this point here and
797
00:26:21,360 --> 00:26:23,120
then we start to sweep the voltage down
798
00:26:23,120 --> 00:26:24,880
okay so at this point we still have
799
00:26:24,880 --> 00:26:26,720
positive current
800
00:26:26,720 --> 00:26:29,039
see it's above zero if we have positive
801
00:26:29,039 --> 00:26:30,720
current that means that
802
00:26:30,720 --> 00:26:33,919
electrons are flowing away from this
803
00:26:33,919 --> 00:26:35,440
electrode they're flowing out of that
804
00:26:35,440 --> 00:26:37,200
electrode we're oxidizing it so we're
805
00:26:37,200 --> 00:26:38,159
still oxidizing
806
00:26:38,159 --> 00:26:39,840
the iron because there's still plenty of
807
00:26:39,840 --> 00:26:41,919
iron available until we reach
808
00:26:41,919 --> 00:26:44,080
zero and at that point then we switch
809
00:26:44,080 --> 00:26:45,600
from oxidation
810
00:26:45,600 --> 00:26:48,480
to reduction okay so now the electrons
811
00:26:48,480 --> 00:26:49,840
are flowing to
812
00:26:49,840 --> 00:26:52,480
the platinum electrode here and reducing
813
00:26:52,480 --> 00:26:54,400
the iron three plus species
814
00:26:54,400 --> 00:26:56,080
and then the same thing happens that you
815
00:26:56,080 --> 00:26:58,400
you have a diffusion limit of the iron
816
00:26:58,400 --> 00:27:00,400
three plus available at the surface
817
00:27:00,400 --> 00:27:04,320
and then it continues to go okay
818
00:27:04,320 --> 00:27:05,760
so that's that's an interesting to think
819
00:27:05,760 --> 00:27:08,640
about and this kind of um
820
00:27:08,640 --> 00:27:10,640
the fact that you know we're at we're at
821
00:27:10,640 --> 00:27:12,080
a positive potential
822
00:27:12,080 --> 00:27:14,559
versus she so remember this zero it
823
00:27:14,559 --> 00:27:15,600
should be really just
824
00:27:15,600 --> 00:27:19,760
0.77 actually we're at 0.77 volts above
825
00:27:19,760 --> 00:27:23,039
she and we
826
00:27:23,039 --> 00:27:25,679
we have both you know pot we can have
827
00:27:25,679 --> 00:27:26,880
positive current
828
00:27:26,880 --> 00:27:28,960
or negative current and you know for the
829
00:27:28,960 --> 00:27:30,399
longest time
830
00:27:30,399 --> 00:27:32,320
i i forget when i learned this but i
831
00:27:32,320 --> 00:27:33,520
always thought you know if you have a
832
00:27:33,520 --> 00:27:34,240
battery
833
00:27:34,240 --> 00:27:36,240
and you discharge the battery right
834
00:27:36,240 --> 00:27:37,279
you're getting current out of the
835
00:27:37,279 --> 00:27:38,960
battery and then if you want to recharge
836
00:27:38,960 --> 00:27:40,799
the battery all you have to do is apply
837
00:27:40,799 --> 00:27:42,240
a reverse
838
00:27:42,240 --> 00:27:44,799
uh current you know if if your if your
839
00:27:44,799 --> 00:27:46,640
battery discharges at three volts and
840
00:27:46,640 --> 00:27:47,919
you want to recharge it you apply
841
00:27:47,919 --> 00:27:49,120
negative 3 volts
842
00:27:49,120 --> 00:27:51,360
and that is entirely incorrect if you do
843
00:27:51,360 --> 00:27:52,320
that you're going to you're going to
844
00:27:52,320 --> 00:27:53,679
blow up the battery
845
00:27:53,679 --> 00:27:55,120
all right if you want to recharge a
846
00:27:55,120 --> 00:27:57,200
battery let's say your lithium ion
847
00:27:57,200 --> 00:27:59,279
battery discharges at 3 or 4 volts
848
00:27:59,279 --> 00:28:01,360
to recharge it you actually want to
849
00:28:01,360 --> 00:28:03,279
apply a higher voltage across the same
850
00:28:03,279 --> 00:28:04,720
terminals you're going to
851
00:28:04,720 --> 00:28:07,360
increase it to 4 volts or 5 volts okay
852
00:28:07,360 --> 00:28:08,559
so it's kind of interesting to think
853
00:28:08,559 --> 00:28:09,120
about
854
00:28:09,120 --> 00:28:10,880
you know even though in both cases we
855
00:28:10,880 --> 00:28:12,799
have positive voltage
856
00:28:12,799 --> 00:28:16,000
across the electrodes it's
857
00:28:16,000 --> 00:28:18,960
it's um the current can be either
858
00:28:18,960 --> 00:28:20,399
positive or negative which is
859
00:28:20,399 --> 00:28:23,279
kind of strange now now the that's
860
00:28:23,279 --> 00:28:25,200
versus a references
861
00:28:25,200 --> 00:28:29,360
of course versus the other electrode
862
00:28:29,360 --> 00:28:33,039
um the potential is does change
863
00:28:33,039 --> 00:28:35,840
so that's that's where it that's a bit
864
00:28:35,840 --> 00:28:36,240
different
865
00:28:36,240 --> 00:28:38,080
so here's another thing to think about
866
00:28:38,080 --> 00:28:39,840
let's say we're running our test
867
00:28:39,840 --> 00:28:42,159
and we start increasing the current and
868
00:28:42,159 --> 00:28:44,559
we we hit this zero volts all right they
869
00:28:44,559 --> 00:28:46,080
were at the standard state
870
00:28:46,080 --> 00:28:49,120
if we were to stop the test let's say
871
00:28:49,120 --> 00:28:49,679
let's say
872
00:28:49,679 --> 00:28:51,919
uh we'll not necessarily stop but we we
873
00:28:51,919 --> 00:28:54,240
hold the voltage at zero if we were to
874
00:28:54,240 --> 00:28:54,880
hold
875
00:28:54,880 --> 00:28:57,360
the voltage at zero what would happen
876
00:28:57,360 --> 00:28:59,360
okay we hold the voltage at zero we
877
00:28:59,360 --> 00:28:59,760
don't
878
00:28:59,760 --> 00:29:01,840
we don't progress any higher or lower
879
00:29:01,840 --> 00:29:03,919
what happens is the current will decay
880
00:29:03,919 --> 00:29:07,120
along zero okay until it reaches zero
881
00:29:07,120 --> 00:29:08,080
volts
882
00:29:08,080 --> 00:29:09,520
all right and at that point we know that
883
00:29:09,520 --> 00:29:11,919
zero volts the the versus the standard
884
00:29:11,919 --> 00:29:13,360
reduction potential
885
00:29:13,360 --> 00:29:17,520
that is when the product is equal to
886
00:29:17,520 --> 00:29:20,960
the reactant okay and actually in this
887
00:29:20,960 --> 00:29:22,000
case because
888
00:29:22,000 --> 00:29:24,240
uh in this setup it doesn't make too
889
00:29:24,240 --> 00:29:25,440
much sense actually i'll show in the
890
00:29:25,440 --> 00:29:26,320
next setup
891
00:29:26,320 --> 00:29:28,240
but because there's a bulk solution of
892
00:29:28,240 --> 00:29:30,399
iron two plus we would probably never
893
00:29:30,399 --> 00:29:33,600
reach we might not ever reach a
894
00:29:33,600 --> 00:29:35,120
zero because there's still going to be
895
00:29:35,120 --> 00:29:37,600
plenty of iron two plus
896
00:29:37,600 --> 00:29:39,440
in the bulk that's diffusing so we'll
897
00:29:39,440 --> 00:29:41,120
probably reach its current limit i
898
00:29:41,120 --> 00:29:42,640
i want to correct myself there but the
899
00:29:42,640 --> 00:29:44,880
next slide it makes more sense
900
00:29:44,880 --> 00:29:46,799
um so yeah this type of cyclic
901
00:29:46,799 --> 00:29:49,440
voltometry has this diffusion limit
902
00:29:49,440 --> 00:29:51,360
okay but there's another type if you
903
00:29:51,360 --> 00:29:53,840
take this electrode and you move it
904
00:29:53,840 --> 00:29:57,600
around for example this is called a
905
00:29:57,600 --> 00:29:58,480
spinning
906
00:29:58,480 --> 00:30:02,000
disc electrode so
907
00:30:02,000 --> 00:30:03,840
if you it's basically electro a platinum
908
00:30:03,840 --> 00:30:05,120
electrode that's a
909
00:30:05,120 --> 00:30:07,760
disc and it spins in solution and as it
910
00:30:07,760 --> 00:30:09,520
spins it's creating a convection
911
00:30:09,520 --> 00:30:11,520
current in the solution so you're always
912
00:30:11,520 --> 00:30:12,799
delivering fresh
913
00:30:12,799 --> 00:30:15,200
iron two plus to the solution and so it
914
00:30:15,200 --> 00:30:17,039
no longer has that diffusion limit where
915
00:30:17,039 --> 00:30:18,320
the current goes back down
916
00:30:18,320 --> 00:30:20,240
but still has a current limit and this
917
00:30:20,240 --> 00:30:21,520
current limit
918
00:30:21,520 --> 00:30:23,039
depends on factors like the
919
00:30:23,039 --> 00:30:24,559
concentration of ions
920
00:30:24,559 --> 00:30:27,039
the the size of the electrode the the
921
00:30:27,039 --> 00:30:29,200
speed that's spinning at
922
00:30:29,200 --> 00:30:30,799
and also what's important is the
923
00:30:30,799 --> 00:30:32,240
diffusion
924
00:30:32,240 --> 00:30:36,000
of the the redox active
925
00:30:36,000 --> 00:30:38,559
species right so you can use this type
926
00:30:38,559 --> 00:30:39,440
of test
927
00:30:39,440 --> 00:30:40,480
and if you know all those other
928
00:30:40,480 --> 00:30:42,080
parameters you can calculate the
929
00:30:42,080 --> 00:30:42,960
diffusion
930
00:30:42,960 --> 00:30:46,240
coefficient of that ion in solution so
931
00:30:46,240 --> 00:30:46,640
that
932
00:30:46,640 --> 00:30:48,480
is kind of an interesting test to do if
933
00:30:48,480 --> 00:30:50,240
you need to find diffusion coefficient
934
00:30:50,240 --> 00:30:52,000
of ionic species
935
00:30:52,000 --> 00:30:55,360
in uh redox ionic species in the um
936
00:30:55,360 --> 00:30:58,960
the solution okay so again
937
00:30:58,960 --> 00:31:01,120
these this type of cyclic voltmeter this
938
00:31:01,120 --> 00:31:02,080
type of test
939
00:31:02,080 --> 00:31:05,679
we're taking it away from equilibrium
940
00:31:05,679 --> 00:31:09,360
and driving the reaction so in these
941
00:31:09,360 --> 00:31:11,279
what i've showed is that we have a redox
942
00:31:11,279 --> 00:31:12,880
active species as part of the
943
00:31:12,880 --> 00:31:15,039
electrolyte it's in the solution
944
00:31:15,039 --> 00:31:18,960
but batteries and other materials
945
00:31:18,960 --> 00:31:21,279
the redox active solution is not you
946
00:31:21,279 --> 00:31:22,080
know it's not an
947
00:31:22,080 --> 00:31:24,799
aqueous ion it's actually a part of a
948
00:31:24,799 --> 00:31:25,519
solid
949
00:31:25,519 --> 00:31:28,159
okay so in this case the all the species
950
00:31:28,159 --> 00:31:31,039
are already present at the platinum so
951
00:31:31,039 --> 00:31:32,480
depending on what the material is you
952
00:31:32,480 --> 00:31:34,240
don't have to worry about diffusion
953
00:31:34,240 --> 00:31:37,840
of of your redox active species to the
954
00:31:37,840 --> 00:31:38,880
surface
955
00:31:38,880 --> 00:31:40,640
anymore it's already on the surface and
956
00:31:40,640 --> 00:31:42,399
if it has high electrical conductivity
957
00:31:42,399 --> 00:31:43,519
then it has no
958
00:31:43,519 --> 00:31:45,600
no problem and then you would expect a
959
00:31:45,600 --> 00:31:47,039
curve like this where
960
00:31:47,039 --> 00:31:49,760
uh you'll have zero uh when if the
961
00:31:49,760 --> 00:31:51,679
entire species is reduced
962
00:31:51,679 --> 00:31:53,519
and then you start oxidizing and then
963
00:31:53,519 --> 00:31:56,080
you're starting to run out of uh
964
00:31:56,080 --> 00:31:58,559
the material is starting to become fully
965
00:31:58,559 --> 00:32:00,240
oxidized and then at this point
966
00:32:00,240 --> 00:32:03,919
c all the redox active species on the
967
00:32:03,919 --> 00:32:06,320
electrode have been fully oxidized so it
968
00:32:06,320 --> 00:32:07,440
should reach a
969
00:32:07,440 --> 00:32:09,200
current of zero and then you can do the
970
00:32:09,200 --> 00:32:11,200
opposite as well
971
00:32:11,200 --> 00:32:14,080
but oftentimes in uh electrode materials
972
00:32:14,080 --> 00:32:15,279
like battery materials
973
00:32:15,279 --> 00:32:18,000
there's still an influence of diffusion
974
00:32:18,000 --> 00:32:19,440
so you'll still see
975
00:32:19,440 --> 00:32:21,840
that these peaks will shift away from
976
00:32:21,840 --> 00:32:24,080
zero and because of the diffusion limit
977
00:32:24,080 --> 00:32:25,760
and that's because you know if you have
978
00:32:25,760 --> 00:32:27,279
a lithium ion battery
979
00:32:27,279 --> 00:32:29,600
you're still relying on the lithium from
980
00:32:29,600 --> 00:32:31,279
solution to diffuse
981
00:32:31,279 --> 00:32:33,840
into the material and so you can you can
982
00:32:33,840 --> 00:32:35,440
still deplete the concentration of
983
00:32:35,440 --> 00:32:36,720
lithium at the surface
984
00:32:36,720 --> 00:32:38,399
and so you're still limited by that and
985
00:32:38,399 --> 00:32:40,559
not only that that's the
986
00:32:40,559 --> 00:32:43,919
the solution resistance but also the
987
00:32:43,919 --> 00:32:46,000
the diffusion resistance inside the
988
00:32:46,000 --> 00:32:47,600
material right so you can you can
989
00:32:47,600 --> 00:32:49,440
intercalate lithium or sodium right into
990
00:32:49,440 --> 00:32:50,960
the surface of the material but it still
991
00:32:50,960 --> 00:32:52,799
needs to diffuse throughout the material
992
00:32:52,799 --> 00:32:55,039
to make room for more lithium or sodium
993
00:32:55,039 --> 00:32:58,159
and so that can also limit the limit
994
00:32:58,159 --> 00:32:59,279
this reaction
995
00:32:59,279 --> 00:33:01,279
and so if that happens you'll see a
996
00:33:01,279 --> 00:33:02,559
splitting of the peaks
997
00:33:02,559 --> 00:33:05,840
okay and in general if if you increase
998
00:33:05,840 --> 00:33:08,720
the scan speed right if you if we if
999
00:33:08,720 --> 00:33:10,559
we're sweeping the voltage faster
1000
00:33:10,559 --> 00:33:13,679
you'll see a bigger split in the peaks
1001
00:33:13,679 --> 00:33:15,039
and also the current will also
1002
00:33:15,039 --> 00:33:17,440
increase but you'll see a bigger split
1003
00:33:17,440 --> 00:33:19,360
because diffusion is uh
1004
00:33:19,360 --> 00:33:22,840
more limited at faster scan speeds
1005
00:33:22,840 --> 00:33:25,840
okay
1006
00:33:26,640 --> 00:33:28,159
um oh yeah so in this example this is
1007
00:33:28,159 --> 00:33:29,919
where i can talk more about you know if
1008
00:33:29,919 --> 00:33:31,279
you were to take this uh
1009
00:33:31,279 --> 00:33:33,600
material and bring it you know measure
1010
00:33:33,600 --> 00:33:36,399
it up to this point at zero volts
1011
00:33:36,399 --> 00:33:38,080
uh versus its standard reduction
1012
00:33:38,080 --> 00:33:41,039
potential and you were to stop the test
1013
00:33:41,039 --> 00:33:43,519
okay what would happen well remember
1014
00:33:43,519 --> 00:33:45,039
even even if we have
1015
00:33:45,039 --> 00:33:48,559
are applying uh zero volts versus the
1016
00:33:48,559 --> 00:33:51,039
standard reduction potential
1017
00:33:51,039 --> 00:33:54,000
it's not at equilibrium even if we're
1018
00:33:54,000 --> 00:33:55,120
applying the standard reduction
1019
00:33:55,120 --> 00:33:56,080
potential it's not
1020
00:33:56,080 --> 00:33:57,840
equilibrium yet because we have current
1021
00:33:57,840 --> 00:33:59,200
we still have current if you have
1022
00:33:59,200 --> 00:34:00,720
current it means there's a reaction
1023
00:34:00,720 --> 00:34:02,720
undergoing and so that means it's not
1024
00:34:02,720 --> 00:34:04,720
equilibrium but over time if you hold it
1025
00:34:04,720 --> 00:34:06,240
at zero volts the current will
1026
00:34:06,240 --> 00:34:09,359
decay the current will go down and then
1027
00:34:09,359 --> 00:34:11,119
reach zero current and then once it has
1028
00:34:11,119 --> 00:34:12,399
reached zero current
1029
00:34:12,399 --> 00:34:14,960
then you're at equilibrium okay another
1030
00:34:14,960 --> 00:34:16,480
thing to think about is you know what if
1031
00:34:16,480 --> 00:34:17,679
we had taken this
1032
00:34:17,679 --> 00:34:20,719
material pushed it to zero volts and
1033
00:34:20,719 --> 00:34:22,079
then stop the test
1034
00:34:22,079 --> 00:34:24,639
and then do no longer control the
1035
00:34:24,639 --> 00:34:25,599
voltage if we
1036
00:34:25,599 --> 00:34:29,280
if we if we no longer uh apply a current
1037
00:34:29,280 --> 00:34:31,679
basically if we disconnect this wire you
1038
00:34:31,679 --> 00:34:33,440
know we push it to zero volts and we
1039
00:34:33,440 --> 00:34:34,079
disconnect
1040
00:34:34,079 --> 00:34:35,918
this wire what would happen to the
1041
00:34:35,918 --> 00:34:38,719
voltage the voltage would go back down
1042
00:34:38,719 --> 00:34:40,320
because when we had brought it to zero
1043
00:34:40,320 --> 00:34:43,119
volts by forcing electrons in or out of
1044
00:34:43,119 --> 00:34:44,320
the solution
1045
00:34:44,320 --> 00:34:46,000
that's not at equilibrium remember this
1046
00:34:46,000 --> 00:34:48,079
cyclophotometry is not at equilibrium
1047
00:34:48,079 --> 00:34:50,000
we're pushing it away from equilibrium
1048
00:34:50,000 --> 00:34:52,079
in order for the reaction to proceed
1049
00:34:52,079 --> 00:34:53,839
and if we had stopped it at this point
1050
00:34:53,839 --> 00:34:55,520
it would go back the voltage would go
1051
00:34:55,520 --> 00:34:56,000
back
1052
00:34:56,000 --> 00:34:57,760
to whatever its equilibrium voltage
1053
00:34:57,760 --> 00:34:59,119
would be would probably be it depends on
1054
00:34:59,119 --> 00:35:00,640
the number of species that had already
1055
00:35:00,640 --> 00:35:01,440
been reduced
1056
00:35:01,440 --> 00:35:04,400
would be probably somewhere and again if
1057
00:35:04,400 --> 00:35:04,800
we had
1058
00:35:04,800 --> 00:35:06,400
if we had driven it all the way to zero
1059
00:35:06,400 --> 00:35:07,920
held it there the current goes down to
1060
00:35:07,920 --> 00:35:08,480
zero
1061
00:35:08,480 --> 00:35:11,920
left it then at zero half the species
1062
00:35:11,920 --> 00:35:13,599
are reduced and half the species are
1063
00:35:13,599 --> 00:35:17,440
oxidized okay okay um oh yes another
1064
00:35:17,440 --> 00:35:18,000
question
1065
00:35:18,000 --> 00:35:19,599
to think about is in these three
1066
00:35:19,599 --> 00:35:21,280
electrode cells
1067
00:35:21,280 --> 00:35:23,280
i mentioned this before you know we're
1068
00:35:23,280 --> 00:35:24,320
taking electro
1069
00:35:24,320 --> 00:35:26,400
electrons away or giving electrons to
1070
00:35:26,400 --> 00:35:27,839
the counter electrode
1071
00:35:27,839 --> 00:35:31,040
so there's some sort of redox reaction
1072
00:35:31,040 --> 00:35:33,119
occurring at the counter electrode but
1073
00:35:33,119 --> 00:35:34,560
like i said we don't really care about
1074
00:35:34,560 --> 00:35:35,599
it
1075
00:35:35,599 --> 00:35:39,280
but in my research i was interested in
1076
00:35:39,280 --> 00:35:42,240
learning what exactly it was going on at
1077
00:35:42,240 --> 00:35:42,960
that
1078
00:35:42,960 --> 00:35:45,119
um in part of my research i was
1079
00:35:45,119 --> 00:35:46,640
investigating mixing
1080
00:35:46,640 --> 00:35:49,119
uh non-aqueous and aqueous solvents
1081
00:35:49,119 --> 00:35:50,079
together
1082
00:35:50,079 --> 00:35:52,000
and doing three electrode tests but one
1083
00:35:52,000 --> 00:35:53,839
of the problems was i wanted i wanted to
1084
00:35:53,839 --> 00:35:55,760
keep the concentration of water
1085
00:35:55,760 --> 00:35:58,960
in my non-aqueous solvent consistent
1086
00:35:58,960 --> 00:36:02,320
and but the problem is in a three
1087
00:36:02,320 --> 00:36:04,160
electrode test if you have your
1088
00:36:04,160 --> 00:36:07,040
counter electrode providing or taking
1089
00:36:07,040 --> 00:36:07,920
electrons
1090
00:36:07,920 --> 00:36:09,839
it means that something is breaking down
1091
00:36:09,839 --> 00:36:10,960
at that side
1092
00:36:10,960 --> 00:36:12,720
which meant that the water was breaking
1093
00:36:12,720 --> 00:36:14,240
down i wanted to keep that consistent so
1094
00:36:14,240 --> 00:36:14,560
i
1095
00:36:14,560 --> 00:36:16,720
in this experiment i just had a
1096
00:36:16,720 --> 00:36:18,160
completely aqueous
1097
00:36:18,160 --> 00:36:20,400
cell so it's all water and i had a
1098
00:36:20,400 --> 00:36:21,440
electrolyte
1099
00:36:21,440 --> 00:36:23,520
i had my material on carbon cloth
1100
00:36:23,520 --> 00:36:24,480
electrode
1101
00:36:24,480 --> 00:36:26,079
okay and what's different about this
1102
00:36:26,079 --> 00:36:27,760
cell is that you know typically right i
1103
00:36:27,760 --> 00:36:28,720
have my voltage
1104
00:36:28,720 --> 00:36:30,640
against the reference electrode which is
1105
00:36:30,640 --> 00:36:32,480
in this case with silver silver chloride
1106
00:36:32,480 --> 00:36:34,720
is a different type of electro reference
1107
00:36:34,720 --> 00:36:35,520
and the
1108
00:36:35,520 --> 00:36:38,000
material and then the current between
1109
00:36:38,000 --> 00:36:39,760
that and the counter electron
1110
00:36:39,760 --> 00:36:43,280
electrode but also on another channel i
1111
00:36:43,280 --> 00:36:44,640
was measuring the voltage
1112
00:36:44,640 --> 00:36:46,720
between platinum and reference which is
1113
00:36:46,720 --> 00:36:47,839
kind of unusual
1114
00:36:47,839 --> 00:36:49,920
this is the typical cv curve of my
1115
00:36:49,920 --> 00:36:51,040
material which again was
1116
00:36:51,040 --> 00:36:54,880
prussian blue and this is in water
1117
00:36:54,880 --> 00:36:57,680
so it's uh you have two different
1118
00:36:57,680 --> 00:36:59,839
species of iron and that's why you get
1119
00:36:59,839 --> 00:37:00,400
two
1120
00:37:00,400 --> 00:37:03,280
different peaks on cv because you have
1121
00:37:03,280 --> 00:37:03,760
they're
1122
00:37:03,760 --> 00:37:06,240
two different chemical chemical
1123
00:37:06,240 --> 00:37:06,880
environments
1124
00:37:06,880 --> 00:37:08,560
what's surrounding them is one is is
1125
00:37:08,560 --> 00:37:10,320
carbon the other one is nitrogen
1126
00:37:10,320 --> 00:37:12,560
so that changes the energy of the iron
1127
00:37:12,560 --> 00:37:13,440
so that changes the
1128
00:37:13,440 --> 00:37:15,680
reduction potential of the iron for each
1129
00:37:15,680 --> 00:37:16,560
one
1130
00:37:16,560 --> 00:37:18,240
and so what i did this is a little bit
1131
00:37:18,240 --> 00:37:20,240
confusing but i'll go through it
1132
00:37:20,240 --> 00:37:23,280
so on the first graph is the measuring
1133
00:37:23,280 --> 00:37:26,480
in blue this is the cyclic voltometry
1134
00:37:26,480 --> 00:37:28,079
scan all right so we're just controlling
1135
00:37:28,079 --> 00:37:28,880
the voltage
1136
00:37:28,880 --> 00:37:30,960
we're pushing it away from equilibrium
1137
00:37:30,960 --> 00:37:32,240
and uh
1138
00:37:32,240 --> 00:37:34,880
and it's sweeping it and then the red
1139
00:37:34,880 --> 00:37:35,280
curve
1140
00:37:35,280 --> 00:37:37,280
is the current of the cell okay the
1141
00:37:37,280 --> 00:37:38,640
current between the
1142
00:37:38,640 --> 00:37:41,040
carbon my my active material and the
1143
00:37:41,040 --> 00:37:42,160
counter electrode
1144
00:37:42,160 --> 00:37:44,880
the second graph is the voltage in blue
1145
00:37:44,880 --> 00:37:45,839
again
1146
00:37:45,839 --> 00:37:48,240
from the counter electrode to the
1147
00:37:48,240 --> 00:37:49,680
reference electrode during the same
1148
00:37:49,680 --> 00:37:52,720
during the same time during the test
1149
00:37:52,720 --> 00:37:55,520
okay and what you'll see is during high
1150
00:37:55,520 --> 00:37:56,240
peaks of
1151
00:37:56,240 --> 00:37:59,359
current when we when we we need to
1152
00:37:59,359 --> 00:38:00,320
supply
1153
00:38:00,320 --> 00:38:02,640
a lot of electrodes or receive
1154
00:38:02,640 --> 00:38:03,520
electrodes
1155
00:38:03,520 --> 00:38:06,640
you see the voltage against the counter
1156
00:38:06,640 --> 00:38:07,680
electrode
1157
00:38:07,680 --> 00:38:11,280
uh is negative and then when we switch
1158
00:38:11,280 --> 00:38:11,920
the current
1159
00:38:11,920 --> 00:38:14,240
it goes to the positive and so if you
1160
00:38:14,240 --> 00:38:16,079
see this plateau here i measure that
1161
00:38:16,079 --> 00:38:17,040
plateau
1162
00:38:17,040 --> 00:38:20,160
that potential at these two plateaus for
1163
00:38:20,160 --> 00:38:22,160
the counter electrode that corresponds
1164
00:38:22,160 --> 00:38:23,599
to the the
1165
00:38:23,599 --> 00:38:25,440
the breaking down of water the
1166
00:38:25,440 --> 00:38:27,280
electrolysis of water
1167
00:38:27,280 --> 00:38:29,920
okay so that's what is happening on this
1168
00:38:29,920 --> 00:38:32,000
counter electrode during our test
1169
00:38:32,000 --> 00:38:33,920
is that we're breaking down water and
1170
00:38:33,920 --> 00:38:35,520
either giving away electrons or
1171
00:38:35,520 --> 00:38:36,800
receiving electrons
1172
00:38:36,800 --> 00:38:38,880
so if we look at that in more detail so
1173
00:38:38,880 --> 00:38:40,079
during the
1174
00:38:40,079 --> 00:38:43,760
oxidation of my my material i need to
1175
00:38:43,760 --> 00:38:46,079
take electrons away from the material so
1176
00:38:46,079 --> 00:38:47,839
this is reaction a on the counter
1177
00:38:47,839 --> 00:38:49,760
electrode or on the counter electrode
1178
00:38:49,760 --> 00:38:52,000
the water is receiving electrons at this
1179
00:38:52,000 --> 00:38:53,119
negative potential
1180
00:38:53,119 --> 00:38:55,520
and breaking down into hydrogen gas and
1181
00:38:55,520 --> 00:38:57,520
hydroxide ions
1182
00:38:57,520 --> 00:38:59,599
okay and then on the reverse during
1183
00:38:59,599 --> 00:39:01,200
reduction of my material
1184
00:39:01,200 --> 00:39:03,440
i'm giving it electrons so that means
1185
00:39:03,440 --> 00:39:05,040
that the counter electrode needs to
1186
00:39:05,040 --> 00:39:06,320
supply electrons
1187
00:39:06,320 --> 00:39:08,640
so we have positive potential where we
1188
00:39:08,640 --> 00:39:09,599
break down
1189
00:39:09,599 --> 00:39:12,960
water into oxygen gas and hydrogen
1190
00:39:12,960 --> 00:39:15,280
ions and we give away electrons all
1191
00:39:15,280 --> 00:39:17,440
right so that that these this is uh
1192
00:39:17,440 --> 00:39:19,920
you know the where these electrons are
1193
00:39:19,920 --> 00:39:20,720
coming from
1194
00:39:20,720 --> 00:39:23,760
in the circuit right but again we're not
1195
00:39:23,760 --> 00:39:24,800
too interested in this
1196
00:39:24,800 --> 00:39:27,839
and as long as the cell is a large
1197
00:39:27,839 --> 00:39:28,720
volume
1198
00:39:28,720 --> 00:39:32,079
you know any changes in ph should be
1199
00:39:32,079 --> 00:39:35,280
rather insignificant okay unless you're
1200
00:39:35,280 --> 00:39:36,560
going to run the test for you know a
1201
00:39:36,560 --> 00:39:37,920
very long time
1202
00:39:37,920 --> 00:39:39,680
or if the cell size is very small then
1203
00:39:39,680 --> 00:39:42,800
it could influence it um
1204
00:39:42,800 --> 00:39:45,280
one more thing you know so i drew these
1205
00:39:45,280 --> 00:39:47,200
lines the lines represent the standard
1206
00:39:47,200 --> 00:39:49,440
reduction potential or the the reduction
1207
00:39:49,440 --> 00:39:50,320
potential
1208
00:39:50,320 --> 00:39:53,680
of uh water either reducing or
1209
00:39:53,680 --> 00:39:56,720
oxidizing but you notice that the actual
1210
00:39:56,720 --> 00:39:57,520
voltage
1211
00:39:57,520 --> 00:40:00,079
is either lower or higher than those
1212
00:40:00,079 --> 00:40:00,560
lines
1213
00:40:00,560 --> 00:40:02,960
corresponding to the amount of current
1214
00:40:02,960 --> 00:40:05,200
that is needed to supply
1215
00:40:05,200 --> 00:40:07,760
and so this this uh either over
1216
00:40:07,760 --> 00:40:09,359
potential under potential
1217
00:40:09,359 --> 00:40:12,319
we call it over potential and it's an
1218
00:40:12,319 --> 00:40:13,920
additional thermodynamic you know
1219
00:40:13,920 --> 00:40:15,040
driving force to
1220
00:40:15,040 --> 00:40:18,079
increase the the rate of the reaction i
1221
00:40:18,079 --> 00:40:18,720
like to
1222
00:40:18,720 --> 00:40:22,079
think about it in related to
1223
00:40:22,079 --> 00:40:24,160
how phase diagrams work for like for
1224
00:40:24,160 --> 00:40:26,000
example the iron carbon phase diagram
1225
00:40:26,000 --> 00:40:27,839
the steel phase diagram you guys are
1226
00:40:27,839 --> 00:40:28,960
familiar with this
1227
00:40:28,960 --> 00:40:30,880
you know if you're going from austenite
1228
00:40:30,880 --> 00:40:32,960
to um
1229
00:40:32,960 --> 00:40:34,960
perlite for example or austenite to
1230
00:40:34,960 --> 00:40:36,400
alpha ferrite
1231
00:40:36,400 --> 00:40:38,880
right you at high temperature the y-axis
1232
00:40:38,880 --> 00:40:40,240
is temperature
1233
00:40:40,240 --> 00:40:42,800
and you start an austenite and you lower
1234
00:40:42,800 --> 00:40:43,760
the temperature
1235
00:40:43,760 --> 00:40:45,920
and you reach that line right that line
1236
00:40:45,920 --> 00:40:47,440
is the equilibrium line
1237
00:40:47,440 --> 00:40:50,640
and then in order to transform austenite
1238
00:40:50,640 --> 00:40:53,359
into perlite you need to go take bring
1239
00:40:53,359 --> 00:40:55,760
the temperature below that line
1240
00:40:55,760 --> 00:40:57,599
and so that's that's called under
1241
00:40:57,599 --> 00:40:59,280
cooling is the amount of temperature
1242
00:40:59,280 --> 00:41:01,359
below that phase equilibrium they have
1243
00:41:01,359 --> 00:41:02,240
to bring it
1244
00:41:02,240 --> 00:41:04,319
to increase the thermodynamic driving
1245
00:41:04,319 --> 00:41:06,000
force for this transformation to
1246
00:41:06,000 --> 00:41:07,839
occur and you guys know if you bring it
1247
00:41:07,839 --> 00:41:09,200
if you quench the material if you bring
1248
00:41:09,200 --> 00:41:09,839
it down
1249
00:41:09,839 --> 00:41:12,560
faster and faster more and more that's a
1250
00:41:12,560 --> 00:41:14,560
higher thermodynamic driving force
1251
00:41:14,560 --> 00:41:16,720
for that transformation to occur the
1252
00:41:16,720 --> 00:41:18,560
same idea can be applied to these
1253
00:41:18,560 --> 00:41:19,440
voltages
1254
00:41:19,440 --> 00:41:21,680
is that you know this line represents
1255
00:41:21,680 --> 00:41:23,680
the phase
1256
00:41:23,680 --> 00:41:25,760
equilibrium between you know the
1257
00:41:25,760 --> 00:41:27,119
breaking down of water
1258
00:41:27,119 --> 00:41:29,119
and we need to bring the voltage lower
1259
00:41:29,119 --> 00:41:31,119
than that to increase the thermodynamic
1260
00:41:31,119 --> 00:41:33,359
driving force for this reaction to occur
1261
00:41:33,359 --> 00:41:35,599
so we can either supply or receive more
1262
00:41:35,599 --> 00:41:36,480
or less
1263
00:41:36,480 --> 00:41:38,560
electrons okay so that's called
1264
00:41:38,560 --> 00:41:39,760
overpotential
1265
00:41:39,760 --> 00:41:42,079
and the amount of overpotential is
1266
00:41:42,079 --> 00:41:43,680
related to the resistance
1267
00:41:43,680 --> 00:41:45,760
in the cell for example diffusion
1268
00:41:45,760 --> 00:41:47,359
resistance
1269
00:41:47,359 --> 00:41:48,960
water is kind of different because water
1270
00:41:48,960 --> 00:41:50,480
is everywhere in the cell but let's say
1271
00:41:50,480 --> 00:41:52,160
there's a different reaction happening
1272
00:41:52,160 --> 00:41:54,400
where you needed ions from the solution
1273
00:41:54,400 --> 00:41:55,760
to come to the surface
1274
00:41:55,760 --> 00:41:57,680
right and just like before we had
1275
00:41:57,680 --> 00:41:59,200
diffusion limits
1276
00:41:59,200 --> 00:42:01,440
you know that can add additional
1277
00:42:01,440 --> 00:42:02,319
resistance
1278
00:42:02,319 --> 00:42:04,079
and you might see this voltage drop even
1279
00:42:04,079 --> 00:42:06,079
lower in order to get that required
1280
00:42:06,079 --> 00:42:07,359
current that you need because
1281
00:42:07,359 --> 00:42:09,200
of the slow diffusion of ions to the
1282
00:42:09,200 --> 00:42:10,560
surface
1283
00:42:10,560 --> 00:42:15,200
that's one i one way there's other other
1284
00:42:15,200 --> 00:42:16,560
other things that can increase this
1285
00:42:16,560 --> 00:42:19,680
resistance such as the the surface area
1286
00:42:19,680 --> 00:42:22,720
of your electrode okay if you use a
1287
00:42:22,720 --> 00:42:24,240
small wire
1288
00:42:24,240 --> 00:42:26,400
that has very small surface area as your
1289
00:42:26,400 --> 00:42:27,839
counter electrode you have
1290
00:42:27,839 --> 00:42:30,480
you don't have too many active sites for
1291
00:42:30,480 --> 00:42:31,760
electron transfer
1292
00:42:31,760 --> 00:42:34,880
but if you use a large sheet a larger
1293
00:42:34,880 --> 00:42:37,040
film of platinum for example has a
1294
00:42:37,040 --> 00:42:38,640
larger surface area
1295
00:42:38,640 --> 00:42:41,119
you know you have more active redox
1296
00:42:41,119 --> 00:42:41,680
sites
1297
00:42:41,680 --> 00:42:45,119
on the surface so uh the you don't have
1298
00:42:45,119 --> 00:42:46,079
to have as much
1299
00:42:46,079 --> 00:42:48,160
over potential to create the same amount
1300
00:42:48,160 --> 00:42:49,839
of current
1301
00:42:49,839 --> 00:42:52,560
okay i i like to think of it and i'm not
1302
00:42:52,560 --> 00:42:53,440
sure if this is correct
1303
00:42:53,440 --> 00:42:55,119
although i i'm pretty sure you can be
1304
00:42:55,119 --> 00:42:57,599
thought of this way as ohm's law
1305
00:42:57,599 --> 00:43:00,640
so if if we require a certain amount of
1306
00:43:00,640 --> 00:43:01,200
current
1307
00:43:01,200 --> 00:43:02,640
but there's a certain amount of
1308
00:43:02,640 --> 00:43:04,480
resistance in our
1309
00:43:04,480 --> 00:43:06,160
cell for example the diffusion
1310
00:43:06,160 --> 00:43:07,760
resistance or the the
1311
00:43:07,760 --> 00:43:10,560
the electrical resistance then that
1312
00:43:10,560 --> 00:43:11,440
creates
1313
00:43:11,440 --> 00:43:14,079
a certain amount of over potential which
1314
00:43:14,079 --> 00:43:15,520
is the potential drop
1315
00:43:15,520 --> 00:43:18,319
in the cell uh beyond of like this
1316
00:43:18,319 --> 00:43:19,200
equilibrium
1317
00:43:19,200 --> 00:43:22,240
position okay so as i
1318
00:43:22,240 --> 00:43:25,040
goes up as i goes up like this red line
1319
00:43:25,040 --> 00:43:27,760
has a peak then the voltage drop
1320
00:43:27,760 --> 00:43:31,599
also goes up okay
1321
00:43:31,599 --> 00:43:33,359
oh okay so since we were talking about
1322
00:43:33,359 --> 00:43:34,480
prussian blue this would be the last
1323
00:43:34,480 --> 00:43:35,680
thing we talked about actually
1324
00:43:35,680 --> 00:43:38,960
all right um
1325
00:43:38,960 --> 00:43:41,040
uh i'll let me introduce a little bit
1326
00:43:41,040 --> 00:43:42,160
more history about
1327
00:43:42,160 --> 00:43:44,079
this material that i've been doing
1328
00:43:44,079 --> 00:43:45,359
research on
1329
00:43:45,359 --> 00:43:48,240
um suppression blue is the the trade
1330
00:43:48,240 --> 00:43:48,800
name
1331
00:43:48,800 --> 00:43:50,440
the chemical name is iron
1332
00:43:50,440 --> 00:43:52,160
hexacyanopherate
1333
00:43:52,160 --> 00:43:54,880
and it's a quite quite interesting
1334
00:43:54,880 --> 00:43:56,000
history
1335
00:43:56,000 --> 00:43:58,640
it was discovered in the early 1700s by
1336
00:43:58,640 --> 00:43:59,200
a
1337
00:43:59,200 --> 00:44:01,839
paint maker okay who is mixing chemicals
1338
00:44:01,839 --> 00:44:03,680
together to make a paint
1339
00:44:03,680 --> 00:44:06,079
and it was first the the synthesis was
1340
00:44:06,079 --> 00:44:08,720
first published in 1731
1341
00:44:08,720 --> 00:44:11,920
and by this guy george stahl and i
1342
00:44:11,920 --> 00:44:13,599
i could be wrong i thought george stahl
1343
00:44:13,599 --> 00:44:15,200
might have been from from
1344
00:44:15,200 --> 00:44:18,480
england working in berlin
1345
00:44:18,480 --> 00:44:21,680
and what was interesting is i found the
1346
00:44:21,680 --> 00:44:22,960
original
1347
00:44:22,960 --> 00:44:26,319
publication that includes the synthesis
1348
00:44:26,319 --> 00:44:27,920
of what was called at the time berlin
1349
00:44:27,920 --> 00:44:29,839
blue is discovered
1350
00:44:29,839 --> 00:44:32,400
named after the city it was made in
1351
00:44:32,400 --> 00:44:33,599
which at the time
1352
00:44:33,599 --> 00:44:37,119
berlin was part of the prussian empire
1353
00:44:37,119 --> 00:44:38,880
which is why it's called prussian blue
1354
00:44:38,880 --> 00:44:42,720
and not german blue and
1355
00:44:44,240 --> 00:44:45,920
you guys know have any idea what
1356
00:44:45,920 --> 00:44:49,280
language this was published in
1357
00:44:49,280 --> 00:44:51,440
so again it was i think a english guy
1358
00:44:51,440 --> 00:44:52,960
working in
1359
00:44:52,960 --> 00:44:55,760
germany and what language did he publish
1360
00:44:55,760 --> 00:44:56,160
this
1361
00:44:56,160 --> 00:44:59,040
this article in
1362
00:45:02,720 --> 00:45:06,240
i'll have the chat open hold on
1363
00:45:06,240 --> 00:45:07,680
if you guys have been asking questions i
1364
00:45:07,680 --> 00:45:08,880
haven't seen any of them because the
1365
00:45:08,880 --> 00:45:11,680
chat wasn't open
1366
00:45:12,880 --> 00:45:15,760
okay no no question okay well if you
1367
00:45:15,760 --> 00:45:16,960
can't read it
1368
00:45:16,960 --> 00:45:19,440
yes that's correct aaron uh the the
1369
00:45:19,440 --> 00:45:20,480
language
1370
00:45:20,480 --> 00:45:23,520
is latin and if you if you know the
1371
00:45:23,520 --> 00:45:26,000
the language of science during this time
1372
00:45:26,000 --> 00:45:26,640
period
1373
00:45:26,640 --> 00:45:28,640
was latin even though this guy was
1374
00:45:28,640 --> 00:45:30,480
english and he was in germany
1375
00:45:30,480 --> 00:45:33,839
uh he everything was published in latin
1376
00:45:33,839 --> 00:45:35,839
and so now now these days the language
1377
00:45:35,839 --> 00:45:36,880
of science is english
1378
00:45:36,880 --> 00:45:41,440
so yeah convenient for us um
1379
00:45:41,440 --> 00:45:42,720
that was kind of interesting so i found
1380
00:45:42,720 --> 00:45:44,720
this paper on like the google books and
1381
00:45:44,720 --> 00:45:45,839
you know how you can search through
1382
00:45:45,839 --> 00:45:46,720
google books like
1383
00:45:46,720 --> 00:45:49,280
word by word and so i i had translated
1384
00:45:49,280 --> 00:45:50,480
berlin blue into
1385
00:45:50,480 --> 00:45:52,640
latin to find exactly what page it was
1386
00:45:52,640 --> 00:45:53,680
on which was kind of
1387
00:45:53,680 --> 00:45:55,280
kind of cool i don't know what the rest
1388
00:45:55,280 --> 00:45:58,079
of it says but um anyway so
1389
00:45:58,079 --> 00:46:00,160
it's significant this material was
1390
00:46:00,160 --> 00:46:01,280
discovered because
1391
00:46:01,280 --> 00:46:04,640
it became the first synthetic
1392
00:46:04,640 --> 00:46:08,079
paint pigment uh before for at least for
1393
00:46:08,079 --> 00:46:10,720
blue i mean for blue paint pigment
1394
00:46:10,720 --> 00:46:12,560
before the blues were made out of
1395
00:46:12,560 --> 00:46:14,240
crushed up minerals which
1396
00:46:14,240 --> 00:46:16,560
could be uh quite expensive and this was
1397
00:46:16,560 --> 00:46:17,760
provided a cheaper
1398
00:46:17,760 --> 00:46:19,040
alternative that can also be mass
1399
00:46:19,040 --> 00:46:21,280
produced and so it's used in a lot of
1400
00:46:21,280 --> 00:46:22,640
different famous paintings a lot of
1401
00:46:22,640 --> 00:46:24,400
paintings it's very common paint pigment
1402
00:46:24,400 --> 00:46:25,839
actually
1403
00:46:25,839 --> 00:46:27,520
such as the starry night by vincent van
1404
00:46:27,520 --> 00:46:29,119
gogh
1405
00:46:29,119 --> 00:46:31,200
and there's a bunch of these different
1406
00:46:31,200 --> 00:46:33,760
paints are named after the materials
1407
00:46:33,760 --> 00:46:35,359
that are used to make them like a
1408
00:46:35,359 --> 00:46:36,880
titanium oxide white or
1409
00:46:36,880 --> 00:46:38,960
lead oxide white if you guys remember a
1410
00:46:38,960 --> 00:46:40,640
couple weeks ago i was talking about
1411
00:46:40,640 --> 00:46:43,119
gerocite as a material gyrocyte has a
1412
00:46:43,119 --> 00:46:44,560
yellow color and
1413
00:46:44,560 --> 00:46:46,240
it also has a paint pigment called
1414
00:46:46,240 --> 00:46:48,640
gerocite yellow or something like that
1415
00:46:48,640 --> 00:46:51,599
so kind of interesting
1416
00:46:52,000 --> 00:46:54,640
so this is oh let me go back here this
1417
00:46:54,640 --> 00:46:56,000
is the crystal structure
1418
00:46:56,000 --> 00:46:59,119
of uh the prussian blue
1419
00:46:59,119 --> 00:47:02,240
um and it has a cage-like structure
1420
00:47:02,240 --> 00:47:02,560
where
1421
00:47:02,560 --> 00:47:05,920
where you have uh iron fcc
1422
00:47:05,920 --> 00:47:08,079
lattice so face-centered cubic lattice
1423
00:47:08,079 --> 00:47:09,760
of iron
1424
00:47:09,760 --> 00:47:11,599
in the high spin state so these are the
1425
00:47:11,599 --> 00:47:13,520
corners in the face center and then also
1426
00:47:13,520 --> 00:47:13,839
it's
1427
00:47:13,839 --> 00:47:17,359
another fcc lattice of low spin iron and
1428
00:47:17,359 --> 00:47:19,520
the low spin iron is coordinated
1429
00:47:19,520 --> 00:47:24,400
uh octahedrally by six cyanide ligands
1430
00:47:24,400 --> 00:47:27,440
so cyanide as you probably know is a
1431
00:47:27,440 --> 00:47:30,880
toxic material and the reason why it's
1432
00:47:30,880 --> 00:47:31,520
toxic
1433
00:47:31,520 --> 00:47:34,480
is is similar to carbon monoxide so if
1434
00:47:34,480 --> 00:47:36,240
we breathe in carbon monoxide
1435
00:47:36,240 --> 00:47:38,960
it it binds to the iron in our in our
1436
00:47:38,960 --> 00:47:39,839
blood
1437
00:47:39,839 --> 00:47:43,119
uh the heme group and that prevents it
1438
00:47:43,119 --> 00:47:44,800
from delivering oxygen to different
1439
00:47:44,800 --> 00:47:46,400
parts of our body
1440
00:47:46,400 --> 00:47:49,119
and uh the same idea for cyanide is it
1441
00:47:49,119 --> 00:47:50,880
binds the iron in our blood if we
1442
00:47:50,880 --> 00:47:51,599
breathe it in
1443
00:47:51,599 --> 00:47:55,440
and then prevents the oxygen transport
1444
00:47:55,839 --> 00:47:59,520
however the iron prussian blue
1445
00:47:59,520 --> 00:48:03,920
is relatively non-hazardous
1446
00:48:03,920 --> 00:48:05,520
okay even though it contains this
1447
00:48:05,520 --> 00:48:07,200
cyanide ion and it's exactly the same
1448
00:48:07,200 --> 00:48:09,119
reason because this the bonding between
1449
00:48:09,119 --> 00:48:11,520
the iron the cyanide is very strong
1450
00:48:11,520 --> 00:48:14,720
so it's very safe to handle um
1451
00:48:14,720 --> 00:48:17,440
unless you unless you eat it and then
1452
00:48:17,440 --> 00:48:18,160
maybe
1453
00:48:18,160 --> 00:48:21,440
perhaps uh the it can break down in your
1454
00:48:21,440 --> 00:48:25,520
your stomach acid but um i'm not sure
1455
00:48:25,520 --> 00:48:27,200
actually actually i could be i might be
1456
00:48:27,200 --> 00:48:28,720
wrong actually i i think i'm wrong
1457
00:48:28,720 --> 00:48:29,119
because
1458
00:48:29,119 --> 00:48:31,680
i know for a fact that prussian blue or
1459
00:48:31,680 --> 00:48:33,599
at least this kind of the material is
1460
00:48:33,599 --> 00:48:34,400
used
1461
00:48:34,400 --> 00:48:37,839
as a medicine for radioactive poisoning
1462
00:48:37,839 --> 00:48:39,920
so for example if you ingest a
1463
00:48:39,920 --> 00:48:41,520
radioactive element
1464
00:48:41,520 --> 00:48:43,280
particularly it's just for i think
1465
00:48:43,280 --> 00:48:46,000
cesium a radioactive cesium
1466
00:48:46,000 --> 00:48:47,839
and if it's in your body you would take
1467
00:48:47,839 --> 00:48:49,599
this medicine prussian blue
1468
00:48:49,599 --> 00:48:52,400
and eat it i i guess you eat it eat it
1469
00:48:52,400 --> 00:48:53,680
this is not medical advice i'm not a
1470
00:48:53,680 --> 00:48:55,280
doctor so don't
1471
00:48:55,280 --> 00:48:57,119
don't be eating this stuff that you
1472
00:48:57,119 --> 00:48:58,880
encounter radioactive poisoning
1473
00:48:58,880 --> 00:49:02,240
but the idea is just like in a lithium
1474
00:49:02,240 --> 00:49:04,319
or sodium ion battery it has these large
1475
00:49:04,319 --> 00:49:06,000
cage-like structures i have another
1476
00:49:06,000 --> 00:49:06,720
slide here
1477
00:49:06,720 --> 00:49:10,000
large cage structures that can absorb uh
1478
00:49:10,000 --> 00:49:14,079
large monovalent and even divalent ions
1479
00:49:14,079 --> 00:49:17,440
okay so cesium is monovalent cesium plus
1480
00:49:17,440 --> 00:49:19,200
and so it's a very large ion so this
1481
00:49:19,200 --> 00:49:21,839
this material can absorb the radioactive
1482
00:49:21,839 --> 00:49:23,920
cesium from it and then i guess you
1483
00:49:23,920 --> 00:49:26,160
pee or poop it out layer and gets rid of
1484
00:49:26,160 --> 00:49:27,200
it from your body
1485
00:49:27,200 --> 00:49:28,960
uh but that's why how it's used as a
1486
00:49:28,960 --> 00:49:32,559
medicine for radio radiation poisoning
1487
00:49:32,559 --> 00:49:34,720
but the same idea you know the advantage
1488
00:49:34,720 --> 00:49:36,559
of this structure is that has these very
1489
00:49:36,559 --> 00:49:38,079
open cages
1490
00:49:38,079 --> 00:49:40,480
so there's a lot of volume interstitial
1491
00:49:40,480 --> 00:49:43,200
volume for large ions to be intercalated
1492
00:49:43,200 --> 00:49:45,760
in and out of it at very fast rates
1493
00:49:45,760 --> 00:49:47,520
right so the diffusion coefficient of
1494
00:49:47,520 --> 00:49:49,200
these ions in the material
1495
00:49:49,200 --> 00:49:51,359
are fairly high which is good for a
1496
00:49:51,359 --> 00:49:53,280
battery material
1497
00:49:53,280 --> 00:49:55,280
and not only that but such a large space
1498
00:49:55,280 --> 00:49:57,280
you can you can incorporate even larger
1499
00:49:57,280 --> 00:49:59,520
ions other than like lithium
1500
00:49:59,520 --> 00:50:01,040
for example sodium plus has good
1501
00:50:01,040 --> 00:50:03,280
diffusion potassium ion has been
1502
00:50:03,280 --> 00:50:05,200
investigated for this material potassium
1503
00:50:05,200 --> 00:50:06,720
ion battery that is
1504
00:50:06,720 --> 00:50:09,839
um i forget that also there's a there's
1505
00:50:09,839 --> 00:50:11,599
a research group in portland i figure
1506
00:50:11,599 --> 00:50:12,079
out what
1507
00:50:12,079 --> 00:50:15,359
university or in oregon
1508
00:50:15,359 --> 00:50:17,760
and they're they're investigating
1509
00:50:17,760 --> 00:50:18,800
ammonium
1510
00:50:18,800 --> 00:50:21,920
ion batteries so instead of a single
1511
00:50:21,920 --> 00:50:22,880
atom
1512
00:50:22,880 --> 00:50:26,079
it's a molecule of nh4 plus that gets
1513
00:50:26,079 --> 00:50:27,040
intercalated
1514
00:50:27,040 --> 00:50:29,520
in and out of this material and the
1515
00:50:29,520 --> 00:50:31,119
advantage of using
1516
00:50:31,119 --> 00:50:35,359
um different well one of the factors
1517
00:50:35,359 --> 00:50:39,040
uh changing the intercalation
1518
00:50:39,040 --> 00:50:42,319
ion well the size of it changes the
1519
00:50:42,319 --> 00:50:44,000
redox potential
1520
00:50:44,000 --> 00:50:47,280
of this material and the larger the ion
1521
00:50:47,280 --> 00:50:48,720
this has been studied that the larger
1522
00:50:48,720 --> 00:50:49,599
the ion
1523
00:50:49,599 --> 00:50:52,319
that's intercalated the higher the redox
1524
00:50:52,319 --> 00:50:53,440
potential which is
1525
00:50:53,440 --> 00:50:55,839
is good for a cathode material you want
1526
00:50:55,839 --> 00:50:56,960
higher potential
1527
00:50:56,960 --> 00:50:59,040
and the ammonium ions the largest of
1528
00:50:59,040 --> 00:51:01,040
them all and it has the highest redox
1529
00:51:01,040 --> 00:51:01,920
potential for
1530
00:51:01,920 --> 00:51:05,599
prussian blue if you intercalated it
1531
00:51:05,920 --> 00:51:08,079
and one one thing i should point out is
1532
00:51:08,079 --> 00:51:10,319
that you know in this diagram i i draw
1533
00:51:10,319 --> 00:51:11,040
the
1534
00:51:11,040 --> 00:51:15,280
the metal plus ion the monovalent ion
1535
00:51:15,280 --> 00:51:17,200
right in the center of these cages which
1536
00:51:17,200 --> 00:51:19,599
is is not necessarily true
1537
00:51:19,599 --> 00:51:22,720
um because these cages are really open
1538
00:51:22,720 --> 00:51:24,800
and it's just if you guys remember from
1539
00:51:24,800 --> 00:51:27,119
like msc 170 when you calculate the
1540
00:51:27,119 --> 00:51:28,400
coordination of different
1541
00:51:28,400 --> 00:51:31,359
uh materials you know if if the ion size
1542
00:51:31,359 --> 00:51:33,920
is a certain ratio to the cation size
1543
00:51:33,920 --> 00:51:35,920
anion the cation size it'll either be
1544
00:51:35,920 --> 00:51:37,359
tetrahedral octahedral
1545
00:51:37,359 --> 00:51:39,119
right basically you don't want to have a
1546
00:51:39,119 --> 00:51:41,440
small ion surrounded in a big cage
1547
00:51:41,440 --> 00:51:43,040
because then it's it can rattle around
1548
00:51:43,040 --> 00:51:45,200
it's not very energetically favorable
1549
00:51:45,200 --> 00:51:46,800
and so the same cases here is that this
1550
00:51:46,800 --> 00:51:49,359
cage is so big it's not necessarily the
1551
00:51:49,359 --> 00:51:50,599
most energetic
1552
00:51:50,599 --> 00:51:52,800
energetically favorable site is in the
1553
00:51:52,800 --> 00:51:54,880
middle actually there's a lot of studies
1554
00:51:54,880 --> 00:51:55,200
that
1555
00:51:55,200 --> 00:51:58,800
show simulations that the most energetic
1556
00:51:58,800 --> 00:52:01,200
sites might actually be you know inside
1557
00:52:01,200 --> 00:52:02,640
one of these squares or against one of
1558
00:52:02,640 --> 00:52:03,920
these squares or against one of these
1559
00:52:03,920 --> 00:52:05,119
corners so
1560
00:52:05,119 --> 00:52:06,559
it's kind of just a simplification in
1561
00:52:06,559 --> 00:52:08,400
this diagram
1562
00:52:08,400 --> 00:52:11,359
and also well i'll get into that later
1563
00:52:11,359 --> 00:52:13,599
there's a lot going on here
1564
00:52:13,599 --> 00:52:16,880
okay so like i said before uh the energy
1565
00:52:16,880 --> 00:52:18,559
state of
1566
00:52:18,559 --> 00:52:21,599
the two different irons or excuse me the
1567
00:52:21,599 --> 00:52:23,520
yeah the electron energies of two
1568
00:52:23,520 --> 00:52:25,040
different irons are different
1569
00:52:25,040 --> 00:52:27,040
because of what's coordinated to them so
1570
00:52:27,040 --> 00:52:29,359
the iron on the outside of this equation
1571
00:52:29,359 --> 00:52:30,079
here that's
1572
00:52:30,079 --> 00:52:32,400
bonded to the nitrogen of the cyanide
1573
00:52:32,400 --> 00:52:33,200
complex
1574
00:52:33,200 --> 00:52:35,680
that is in what's called the high spin
1575
00:52:35,680 --> 00:52:37,680
state okay so these are the d
1576
00:52:37,680 --> 00:52:40,800
orbitals the electron orbitals and if
1577
00:52:40,800 --> 00:52:42,160
you take a single
1578
00:52:42,160 --> 00:52:44,960
ion ion that's not surrounded by
1579
00:52:44,960 --> 00:52:45,760
anything
1580
00:52:45,760 --> 00:52:47,920
all the energy is symmetric all around
1581
00:52:47,920 --> 00:52:49,040
and there's nothing around it if you
1582
00:52:49,040 --> 00:52:50,480
take a single iron ion
1583
00:52:50,480 --> 00:52:52,240
all the energies are equivalent they're
1584
00:52:52,240 --> 00:52:53,760
all equal they're all lined up
1585
00:52:53,760 --> 00:52:55,520
with each other but as soon as you start
1586
00:52:55,520 --> 00:52:56,960
putting things around it
1587
00:52:56,960 --> 00:52:58,800
like ligands for example the cyanide
1588
00:52:58,800 --> 00:53:01,040
ligand then that's going to change the
1589
00:53:01,040 --> 00:53:02,480
energy states of these different
1590
00:53:02,480 --> 00:53:05,119
orbitals and for octahedral symmetry
1591
00:53:05,119 --> 00:53:07,440
it makes these this kind of deviation of
1592
00:53:07,440 --> 00:53:08,640
energy states
1593
00:53:08,640 --> 00:53:11,680
of the the d orbital electrons
1594
00:53:11,680 --> 00:53:15,440
okay and so depending on what is bonded
1595
00:53:15,440 --> 00:53:16,480
to it and also like
1596
00:53:16,480 --> 00:53:18,960
the bond length of the ligands that
1597
00:53:18,960 --> 00:53:21,280
changes the energy splitting
1598
00:53:21,280 --> 00:53:23,599
of these two energy levels of the d
1599
00:53:23,599 --> 00:53:25,839
orbitals and if that energy splitting is
1600
00:53:25,839 --> 00:53:29,520
large enough then you start to
1601
00:53:29,520 --> 00:53:31,839
start to pair up these electrons because
1602
00:53:31,839 --> 00:53:34,319
it's more energetically favorable
1603
00:53:34,319 --> 00:53:36,960
to make pairs of electrons before
1604
00:53:36,960 --> 00:53:39,920
distributing them to all these single
1605
00:53:39,920 --> 00:53:42,720
unoccupied states and this is called the
1606
00:53:42,720 --> 00:53:43,119
low
1607
00:53:43,119 --> 00:53:45,760
spin state i think i go into that a bit
1608
00:53:45,760 --> 00:53:46,880
more
1609
00:53:46,880 --> 00:53:51,040
later so this is a schematic of how the
1610
00:53:51,040 --> 00:53:52,960
sodium ion battery works for prussian
1611
00:53:52,960 --> 00:53:53,520
blue
1612
00:53:53,520 --> 00:53:55,440
so actually when i synthesize the
1613
00:53:55,440 --> 00:53:57,680
material most often it's
1614
00:53:57,680 --> 00:54:00,559
synthesized as the partially reduced
1615
00:54:00,559 --> 00:54:01,040
state
1616
00:54:01,040 --> 00:54:02,640
all right so it already has a sodium
1617
00:54:02,640 --> 00:54:04,480
inside of it and it's in the mixed
1618
00:54:04,480 --> 00:54:06,559
valence between three plus and two plus
1619
00:54:06,559 --> 00:54:09,119
for the different irons and so usually
1620
00:54:09,119 --> 00:54:10,000
the first step
1621
00:54:10,000 --> 00:54:12,800
when i uh characterize my battery is i
1622
00:54:12,800 --> 00:54:14,559
have to either discharge it or charge it
1623
00:54:14,559 --> 00:54:15,119
first
1624
00:54:15,119 --> 00:54:17,520
but so the charging process is when
1625
00:54:17,520 --> 00:54:18,319
we're taking
1626
00:54:18,319 --> 00:54:21,839
sodium ions out of the material and
1627
00:54:21,839 --> 00:54:22,800
we're also taking
1628
00:54:22,800 --> 00:54:24,720
electrons out remember i said we have to
1629
00:54:24,720 --> 00:54:26,000
maintain charged
1630
00:54:26,000 --> 00:54:28,319
neutrality that's the golden rule about
1631
00:54:28,319 --> 00:54:29,040
everything
1632
00:54:29,040 --> 00:54:30,800
you have to if you take an electron out
1633
00:54:30,800 --> 00:54:32,400
of a system you also have to take a
1634
00:54:32,400 --> 00:54:33,440
positive ion
1635
00:54:33,440 --> 00:54:36,160
out of the system so we take a sodium
1636
00:54:36,160 --> 00:54:37,680
out we also take an electron out
1637
00:54:37,680 --> 00:54:39,760
that would that oxidizes this iron two
1638
00:54:39,760 --> 00:54:41,599
plus iron three plus so it's empty
1639
00:54:41,599 --> 00:54:44,000
this is the fully charged state or fully
1640
00:54:44,000 --> 00:54:45,359
oxidized state
1641
00:54:45,359 --> 00:54:47,119
i i guess i should be using the terms
1642
00:54:47,119 --> 00:54:48,720
oxidized versus reduced or
1643
00:54:48,720 --> 00:54:50,880
instead of charged versus discharge
1644
00:54:50,880 --> 00:54:53,119
because
1645
00:54:53,680 --> 00:54:54,880
you could be saying talking about the
1646
00:54:54,880 --> 00:54:56,960
same thing for an anode material and
1647
00:54:56,960 --> 00:54:58,319
it'd be the opposite but this is a
1648
00:54:58,319 --> 00:54:59,680
cathode material so when we take the
1649
00:54:59,680 --> 00:55:00,400
ions out
1650
00:55:00,400 --> 00:55:03,680
it's charged and uh and then we
1651
00:55:03,680 --> 00:55:05,280
go through the test of discharging the
1652
00:55:05,280 --> 00:55:07,359
battery okay and so the
1653
00:55:07,359 --> 00:55:09,520
there's different potentials like i said
1654
00:55:09,520 --> 00:55:11,760
the first the low spin has the higher
1655
00:55:11,760 --> 00:55:12,559
potential
1656
00:55:12,559 --> 00:55:14,720
so we introduce an electron and the
1657
00:55:14,720 --> 00:55:16,319
sodium intercalates
1658
00:55:16,319 --> 00:55:19,359
and that reduces the low spin iron and
1659
00:55:19,359 --> 00:55:20,480
then we have another
1660
00:55:20,480 --> 00:55:23,760
step where we introduce a second sodium
1661
00:55:23,760 --> 00:55:24,559
ion
1662
00:55:24,559 --> 00:55:26,880
and that reduces the high spin state and
1663
00:55:26,880 --> 00:55:28,240
so those are the two
1664
00:55:28,240 --> 00:55:33,119
redox steps in this material
1665
00:55:33,359 --> 00:55:36,480
this is a bit more explanation about the
1666
00:55:36,480 --> 00:55:38,559
crystal field splitting which is the you
1667
00:55:38,559 --> 00:55:40,240
know the energy splitting of these d
1668
00:55:40,240 --> 00:55:43,599
orbitals i think i was just showing
1669
00:55:43,599 --> 00:55:46,000
um i don't have to go in too much detail
1670
00:55:46,000 --> 00:55:48,160
but showing that the chemical species
1671
00:55:48,160 --> 00:55:51,359
the ligand that surrounds this iron ion
1672
00:55:51,359 --> 00:55:53,440
affects that energy splitting and
1673
00:55:53,440 --> 00:55:54,480
eventually get to
1674
00:55:54,480 --> 00:55:57,440
a high a large enough splitting that
1675
00:55:57,440 --> 00:55:58,960
these electrons uh
1676
00:55:58,960 --> 00:56:02,319
will go into the low spin state
1677
00:56:02,319 --> 00:56:05,280
um you guys remember from chemistry
1678
00:56:05,280 --> 00:56:06,079
class
1679
00:56:06,079 --> 00:56:08,079
what this uh principle is called when
1680
00:56:08,079 --> 00:56:09,760
you're you're adding electrons to
1681
00:56:09,760 --> 00:56:12,160
orbitals it's um
1682
00:56:12,160 --> 00:56:14,799
the poly exclusion principle i think i
1683
00:56:14,799 --> 00:56:16,240
think that's it poly exclusion
1684
00:56:16,240 --> 00:56:18,160
paulie's exclusion poly exclusion
1685
00:56:18,160 --> 00:56:20,799
principle um where you know you're
1686
00:56:20,799 --> 00:56:23,440
when you add electrons to these orbitals
1687
00:56:23,440 --> 00:56:25,280
it's more energetically favorable to
1688
00:56:25,280 --> 00:56:26,960
have them unoccupied so you're just
1689
00:56:26,960 --> 00:56:29,359
going to add one to each orbital
1690
00:56:29,359 --> 00:56:32,160
but in this case for low spin right it's
1691
00:56:32,160 --> 00:56:34,079
more energetically favorable
1692
00:56:34,079 --> 00:56:37,760
to pair them before adding them to the
1693
00:56:37,760 --> 00:56:40,880
this empty higher energy state okay
1694
00:56:40,880 --> 00:56:44,079
so that when you add electron when you
1695
00:56:44,079 --> 00:56:45,760
pair an electron together
1696
00:56:45,760 --> 00:56:48,079
there's a pairing energy involved so you
1697
00:56:48,079 --> 00:56:50,160
know when i add this electron in here
1698
00:56:50,160 --> 00:56:51,680
the energy state of these orbitals
1699
00:56:51,680 --> 00:56:53,520
actually increases
1700
00:56:53,520 --> 00:56:55,040
and which is not indicated by these
1701
00:56:55,040 --> 00:56:57,280
diagrams but in general you know if that
1702
00:56:57,280 --> 00:56:58,079
that
1703
00:56:58,079 --> 00:57:01,200
added energy is larger than what these
1704
00:57:01,200 --> 00:57:02,160
energies are at
1705
00:57:02,160 --> 00:57:03,599
then it'll go into the high spin because
1706
00:57:03,599 --> 00:57:05,119
it's more energetically favorable to put
1707
00:57:05,119 --> 00:57:06,480
in that position
1708
00:57:06,480 --> 00:57:08,559
anyways this is kind of a more advanced
1709
00:57:08,559 --> 00:57:10,640
inorganic chemistry that
1710
00:57:10,640 --> 00:57:12,000
we don't need to know too much about
1711
00:57:12,000 --> 00:57:14,880
just kind of skim over
1712
00:57:15,440 --> 00:57:17,920
um oh there's more there's more i made
1713
00:57:17,920 --> 00:57:19,119
these slides so i like to show them
1714
00:57:19,119 --> 00:57:20,559
because i spent a lot of work you know
1715
00:57:20,559 --> 00:57:22,079
putting in the fine detail
1716
00:57:22,079 --> 00:57:23,119
it's important when you make
1717
00:57:23,119 --> 00:57:26,480
presentations that the extra detail um
1718
00:57:26,480 --> 00:57:28,400
like for example i put a lot of work
1719
00:57:28,400 --> 00:57:30,400
into these these are all handmade these
1720
00:57:30,400 --> 00:57:32,720
diagrams these reference electrodes so
1721
00:57:32,720 --> 00:57:34,640
you spend you know 30 minutes to an hour
1722
00:57:34,640 --> 00:57:36,079
maybe less or more
1723
00:57:36,079 --> 00:57:37,599
making these diagrams and then you can
1724
00:57:37,599 --> 00:57:39,359
use them throughout your you know your
1725
00:57:39,359 --> 00:57:41,040
entire career you just recycle them
1726
00:57:41,040 --> 00:57:42,480
right so it's
1727
00:57:42,480 --> 00:57:45,599
it's nice to have nice nice diagrams but
1728
00:57:45,599 --> 00:57:47,680
in this case i talk about how the
1729
00:57:47,680 --> 00:57:49,920
octahedral splitting energy which is
1730
00:57:49,920 --> 00:57:50,880
this this uh
1731
00:57:50,880 --> 00:57:53,359
this energy gap depends on different
1732
00:57:53,359 --> 00:57:54,799
things like the metal ion that you're
1733
00:57:54,799 --> 00:57:56,160
looking at so in general
1734
00:57:56,160 --> 00:57:58,559
uh i think you might be able to relate
1735
00:57:58,559 --> 00:58:00,640
this to the periodic table
1736
00:58:00,640 --> 00:58:02,240
but valence state is definitely one of
1737
00:58:02,240 --> 00:58:03,760
them so like manganese two plus versus
1738
00:58:03,760 --> 00:58:05,119
manganese four plus
1739
00:58:05,119 --> 00:58:07,440
uh that energy gap will change depending
1740
00:58:07,440 --> 00:58:09,040
on if the valence state
1741
00:58:09,040 --> 00:58:11,119
and then i think more importantly is the
1742
00:58:11,119 --> 00:58:12,640
ligand okay
1743
00:58:12,640 --> 00:58:14,720
so what is being surround what is
1744
00:58:14,720 --> 00:58:16,960
surrounding these ions either in liquid
1745
00:58:16,960 --> 00:58:18,160
or in solid
1746
00:58:18,160 --> 00:58:21,200
it will change that energy and so you
1747
00:58:21,200 --> 00:58:21,440
know
1748
00:58:21,440 --> 00:58:23,359
typically you're used to seeing all the
1749
00:58:23,359 --> 00:58:25,040
d orbitals lined up like this
1750
00:58:25,040 --> 00:58:27,599
right in this case there's the it's
1751
00:58:27,599 --> 00:58:28,480
symmetric
1752
00:58:28,480 --> 00:58:30,640
uh electric field there's nothing around
1753
00:58:30,640 --> 00:58:32,160
it coordinated to it
1754
00:58:32,160 --> 00:58:33,680
and then you start coordinating things
1755
00:58:33,680 --> 00:58:36,079
to it and then that changes the energy
1756
00:58:36,079 --> 00:58:39,040
okay yeah so here's carbon monoxide and
1757
00:58:39,040 --> 00:58:39,920
cyanide as
1758
00:58:39,920 --> 00:58:43,119
strong uh ligands
1759
00:58:43,119 --> 00:58:45,520
oh here's some more some more diagrams
1760
00:58:45,520 --> 00:58:47,520
uh this just talks about the
1761
00:58:47,520 --> 00:58:49,839
different orbitals between the the metal
1762
00:58:49,839 --> 00:58:51,520
ion the metal center
1763
00:58:51,520 --> 00:58:54,160
and the ligand and what pairs they make
1764
00:58:54,160 --> 00:58:55,040
and whether it's
1765
00:58:55,040 --> 00:58:56,960
you know if you have these pi orbitals
1766
00:58:56,960 --> 00:58:58,880
that make a pi bond
1767
00:58:58,880 --> 00:59:02,000
um right so if you have an empty pi
1768
00:59:02,000 --> 00:59:03,760
orbital for the ligand and then it's
1769
00:59:03,760 --> 00:59:05,599
accepting electrons from the
1770
00:59:05,599 --> 00:59:08,720
or from the metal pi uh t2g
1771
00:59:08,720 --> 00:59:10,799
orbitals then it's a pi acceptor and
1772
00:59:10,799 --> 00:59:12,799
that that correlates with the larger
1773
00:59:12,799 --> 00:59:13,680
energy gap
1774
00:59:13,680 --> 00:59:17,760
anyways don't need to uh
1775
00:59:17,760 --> 00:59:21,280
there's one more this is a molecular
1776
00:59:21,280 --> 00:59:23,760
orbital diagram of iron cyanide
1777
00:59:23,760 --> 00:59:25,839
uh so you have your iron ion your six
1778
00:59:25,839 --> 00:59:27,119
cyanides and how
1779
00:59:27,119 --> 00:59:29,760
how the orbitals of the cyanides pair up
1780
00:59:29,760 --> 00:59:31,520
with the orbitals of the
1781
00:59:31,520 --> 00:59:33,520
the iron to make these bonds right so
1782
00:59:33,520 --> 00:59:34,799
you have sigma bonds and
1783
00:59:34,799 --> 00:59:38,559
pi bonds and then the energy gap
1784
00:59:38,559 --> 00:59:41,119
and so on
1785
00:59:44,960 --> 00:59:48,000
oh one thing i want to bring up is uh
1786
00:59:48,000 --> 00:59:51,359
not it's it's loosely related
1787
00:59:51,359 --> 00:59:52,640
when i was when i was making these
1788
00:59:52,640 --> 00:59:54,160
orbital diagrams learning more about
1789
00:59:54,160 --> 00:59:54,640
this
1790
00:59:54,640 --> 00:59:57,760
these energies um you know in chemistry
1791
00:59:57,760 --> 00:59:59,440
like high school chemistry and freshman
1792
00:59:59,440 --> 01:00:01,680
chemistry we we always learn
1793
01:00:01,680 --> 01:00:03,440
you know when we're adding the the
1794
01:00:03,440 --> 01:00:05,839
energies like counting up the electrons
1795
01:00:05,839 --> 01:00:07,119
in these different energies
1796
01:00:07,119 --> 01:00:09,839
in orbitals we always learn to fill the
1797
01:00:09,839 --> 01:00:10,319
four
1798
01:00:10,319 --> 01:00:14,079
s orbitals before the 3d
1799
01:00:14,079 --> 01:00:16,799
orbitals and i was wondering i was
1800
01:00:16,799 --> 01:00:19,280
trying to figure out why that was
1801
01:00:19,280 --> 01:00:22,480
and because you know i actually i found
1802
01:00:22,480 --> 01:00:23,760
some papers
1803
01:00:23,760 --> 01:00:27,760
related to chemic chemistry education
1804
01:00:27,760 --> 01:00:29,839
saying that why we should not teach it
1805
01:00:29,839 --> 01:00:31,280
that way
1806
01:00:31,280 --> 01:00:34,960
um and the proof
1807
01:00:34,960 --> 01:00:39,599
that i mean 4s has higher energy than 3d
1808
01:00:39,599 --> 01:00:40,799
and that's the controversy
1809
01:00:40,799 --> 01:00:42,960
right i'm saying this is 4s has a higher
1810
01:00:42,960 --> 01:00:44,559
energy than 3d
1811
01:00:44,559 --> 01:00:46,559
and the proof is that if you had let's
1812
01:00:46,559 --> 01:00:48,640
say a neutral iron
1813
01:00:48,640 --> 01:00:51,359
atom so you have uh you have two
1814
01:00:51,359 --> 01:00:53,440
electrons in the 4s
1815
01:00:53,440 --> 01:00:55,599
and you have you know these or the six
1816
01:00:55,599 --> 01:00:56,880
electrons in the 3d
1817
01:00:56,880 --> 01:00:58,240
so you know of course yeah that makes
1818
01:00:58,240 --> 01:00:59,920
sense you're filling the 4s before you
1819
01:00:59,920 --> 01:01:02,799
filled the 3d
1820
01:01:03,119 --> 01:01:06,240
but which electron has the highest
1821
01:01:06,240 --> 01:01:08,319
energy is the question and i'm saying
1822
01:01:08,319 --> 01:01:09,839
the 4s has higher
1823
01:01:09,839 --> 01:01:13,359
energy than 3d and the proof is that if
1824
01:01:13,359 --> 01:01:14,000
you were to
1825
01:01:14,000 --> 01:01:16,480
ionize this iron let's say we're
1826
01:01:16,480 --> 01:01:18,960
ionizing it to iron two plus or iron one
1827
01:01:18,960 --> 01:01:19,280
plus
1828
01:01:19,280 --> 01:01:22,079
which doesn't exist which electron do
1829
01:01:22,079 --> 01:01:23,119
you take away
1830
01:01:23,119 --> 01:01:26,720
are you taking away the 3d electron
1831
01:01:26,720 --> 01:01:28,480
because according to what we learned in
1832
01:01:28,480 --> 01:01:29,920
chemistry class we would take away the
1833
01:01:29,920 --> 01:01:30,319
3d
1834
01:01:30,319 --> 01:01:31,839
electron because it has a higher energy
1835
01:01:31,839 --> 01:01:33,680
but i'm saying well actually 4s has a
1836
01:01:33,680 --> 01:01:35,359
higher length g anyways that's the proof
1837
01:01:35,359 --> 01:01:35,680
that
1838
01:01:35,680 --> 01:01:38,319
yeah you take away from the 4s orbital
1839
01:01:38,319 --> 01:01:39,680
when you ionize something you always
1840
01:01:39,680 --> 01:01:41,680
take away the highest energy electron
1841
01:01:41,680 --> 01:01:42,960
and it's coming from the forest and
1842
01:01:42,960 --> 01:01:45,040
that's a brief aside
1843
01:01:45,040 --> 01:01:46,480
but it's something you might want to
1844
01:01:46,480 --> 01:01:49,440
investigate for yourself
1845
01:01:49,520 --> 01:01:52,000
here's another related side note by it's
1846
01:01:52,000 --> 01:01:53,920
it's related to like these energy levels
1847
01:01:53,920 --> 01:01:54,160
in
1848
01:01:54,160 --> 01:01:57,280
in materials as well so we have three uh
1849
01:01:57,280 --> 01:01:59,359
materials here corundum ruby and
1850
01:01:59,359 --> 01:02:00,880
sapphire do you guys know
1851
01:02:00,880 --> 01:02:04,880
what what chemical equation this is
1852
01:02:04,880 --> 01:02:06,559
for these materials what's the chemical
1853
01:02:06,559 --> 01:02:08,240
formula of these materials or at least
1854
01:02:08,240 --> 01:02:11,359
corundum for example
1855
01:02:13,520 --> 01:02:15,200
and it's okay if you don't know but i
1856
01:02:15,200 --> 01:02:18,640
hope after today you'll know
1857
01:02:19,440 --> 01:02:21,920
or ruby or sapphire you know if i say
1858
01:02:21,920 --> 01:02:23,039
hey what's what's the
1859
01:02:23,039 --> 01:02:25,359
chemical equation for sapphire anyway
1860
01:02:25,359 --> 01:02:27,599
the chemical equation
1861
01:02:27,599 --> 01:02:30,240
is aluminum oxide for all three of these
1862
01:02:30,240 --> 01:02:31,200
materials
1863
01:02:31,200 --> 01:02:33,359
okay so the base material is all
1864
01:02:33,359 --> 01:02:34,799
aluminum oxide and it
1865
01:02:34,799 --> 01:02:36,400
is evident you know they all have
1866
01:02:36,400 --> 01:02:37,839
similar crystal
1867
01:02:37,839 --> 01:02:39,520
crystallographic orientations in the
1868
01:02:39,520 --> 01:02:40,960
crystal shapes so
1869
01:02:40,960 --> 01:02:42,720
they're all the same material the
1870
01:02:42,720 --> 01:02:44,400
difference between ruby and sapphire is
1871
01:02:44,400 --> 01:02:45,520
that we've added
1872
01:02:45,520 --> 01:02:48,640
a dopant so a dopant is a small
1873
01:02:48,640 --> 01:02:50,880
concentration of ions
1874
01:02:50,880 --> 01:02:53,280
that's substituted with the aluminum in
1875
01:02:53,280 --> 01:02:55,200
this material
1876
01:02:55,200 --> 01:02:57,200
and the dopant for ruby is chromium so
1877
01:02:57,200 --> 01:02:58,720
adding a little bit of chromium like
1878
01:02:58,720 --> 01:03:00,160
less than one percent
1879
01:03:00,160 --> 01:03:03,200
will make corundum red ruby
1880
01:03:03,200 --> 01:03:05,440
okay and then for sapphire to make it
1881
01:03:05,440 --> 01:03:06,640
blue it's uh
1882
01:03:06,640 --> 01:03:08,799
you have to add both titanium and iron
1883
01:03:08,799 --> 01:03:09,680
two plus
1884
01:03:09,680 --> 01:03:11,200
and there's some kind of exchange in
1885
01:03:11,200 --> 01:03:12,799
electrons when it absorbs light so
1886
01:03:12,799 --> 01:03:14,480
that's why you need two
1887
01:03:14,480 --> 01:03:18,319
um so i guess the the question is
1888
01:03:18,319 --> 01:03:20,400
well let me move on so here's another
1889
01:03:20,400 --> 01:03:22,480
example
1890
01:03:22,480 --> 01:03:25,119
where we compare corundum and another
1891
01:03:25,119 --> 01:03:26,640
mineral called barrel
1892
01:03:26,640 --> 01:03:28,839
okay another the beryllium aluminum
1893
01:03:28,839 --> 01:03:30,480
silicate
1894
01:03:30,480 --> 01:03:32,640
in both of these materials if you
1895
01:03:32,640 --> 01:03:34,640
substitute i believe it's aluminum from
1896
01:03:34,640 --> 01:03:35,119
barrel
1897
01:03:35,119 --> 01:03:37,200
that could be wrong substitute about one
1898
01:03:37,200 --> 01:03:38,799
percent chromium
1899
01:03:38,799 --> 01:03:41,280
into both of these materials it turns
1900
01:03:41,280 --> 01:03:41,920
the
1901
01:03:41,920 --> 01:03:44,960
corndom red but it turns barrel green
1902
01:03:44,960 --> 01:03:47,039
and that's called emerald
1903
01:03:47,039 --> 01:03:49,520
so the question is why how can the same
1904
01:03:49,520 --> 01:03:50,400
ion
1905
01:03:50,400 --> 01:03:52,559
that is being substituted into these two
1906
01:03:52,559 --> 01:03:53,680
materials
1907
01:03:53,680 --> 01:03:58,559
turn one red and one green okay
1908
01:03:58,559 --> 01:04:01,680
and uh it has to do with the
1909
01:04:01,680 --> 01:04:05,440
the the d orbital splitting of the
1910
01:04:05,440 --> 01:04:07,520
chromium which is responsible for the
1911
01:04:07,520 --> 01:04:08,640
absorbing the light
1912
01:04:08,640 --> 01:04:10,559
in the material okay just like i talked
1913
01:04:10,559 --> 01:04:12,079
before you know it's all about these
1914
01:04:12,079 --> 01:04:15,200
energy levels of these d electrons and
1915
01:04:15,200 --> 01:04:18,559
what is around it affects that energy
1916
01:04:18,559 --> 01:04:19,760
level
1917
01:04:19,760 --> 01:04:22,640
uh this is a tanabe sugano diagram
1918
01:04:22,640 --> 01:04:24,079
that's used often with these
1919
01:04:24,079 --> 01:04:27,680
uh kind of kind of uh light absorbent
1920
01:04:27,680 --> 01:04:28,880
materials
1921
01:04:28,880 --> 01:04:31,359
um and actually uh uh ta from the
1922
01:04:31,359 --> 01:04:32,000
morning group
1923
01:04:32,000 --> 01:04:33,760
helped explain this because i i wasn't
1924
01:04:33,760 --> 01:04:35,599
too familiar i made these slides a long
1925
01:04:35,599 --> 01:04:37,280
time ago i knew it at the time but
1926
01:04:37,280 --> 01:04:38,960
i i can explain it a little bit so but
1927
01:04:38,960 --> 01:04:40,480
i'm i'm kind of paraphrasing what he
1928
01:04:40,480 --> 01:04:41,359
said
1929
01:04:41,359 --> 01:04:44,960
so the x-axis is the ligand field energy
1930
01:04:44,960 --> 01:04:46,960
okay or crystal field energy you could
1931
01:04:46,960 --> 01:04:48,240
also say is is the
1932
01:04:48,240 --> 01:04:50,720
is the energy splitting of these d
1933
01:04:50,720 --> 01:04:52,559
electrons
1934
01:04:52,559 --> 01:04:55,200
in the this is the octahedral
1935
01:04:55,200 --> 01:04:56,400
configuration of the
1936
01:04:56,400 --> 01:04:59,839
d electrons so if you're at a
1937
01:04:59,839 --> 01:05:02,400
crystal field energy of zero what that
1938
01:05:02,400 --> 01:05:04,079
essentially is saying is that nothing is
1939
01:05:04,079 --> 01:05:05,039
surrounding
1940
01:05:05,039 --> 01:05:06,960
your metal ion you know it's just it's
1941
01:05:06,960 --> 01:05:08,880
just saying it's like this this has a
1942
01:05:08,880 --> 01:05:10,960
splitting energy of zero all these
1943
01:05:10,960 --> 01:05:12,799
energy orbitals are at the same level
1944
01:05:12,799 --> 01:05:15,599
there's nothing surrounding the ion but
1945
01:05:15,599 --> 01:05:17,200
as soon as you start surrounding
1946
01:05:17,200 --> 01:05:19,920
the ion then you start splitting that
1947
01:05:19,920 --> 01:05:21,440
those energy levels
1948
01:05:21,440 --> 01:05:23,599
and depending on the ligand strength and
1949
01:05:23,599 --> 01:05:26,160
the bond length the bond strength of the
1950
01:05:26,160 --> 01:05:29,039
the ions and ligands that affects the
1951
01:05:29,039 --> 01:05:30,559
ligand field energy
1952
01:05:30,559 --> 01:05:34,079
okay and then this is the energy
1953
01:05:34,079 --> 01:05:38,720
of light that's absorbed by the material
1954
01:05:38,720 --> 01:05:41,599
okay so for a chromium i found i found
1955
01:05:41,599 --> 01:05:42,079
these
1956
01:05:42,079 --> 01:05:44,480
uh this information for chromium that
1957
01:05:44,480 --> 01:05:45,920
the ligand field energy
1958
01:05:45,920 --> 01:05:48,720
of chromium in aluminum oxide is you
1959
01:05:48,720 --> 01:05:50,160
know 2.2 volts and then
1960
01:05:50,160 --> 01:05:53,119
in the barrel it's a little bit less and
1961
01:05:53,119 --> 01:05:54,160
that affects
1962
01:05:54,160 --> 01:05:57,280
the the energy level of the light
1963
01:05:57,280 --> 01:05:58,480
absorbed
1964
01:05:58,480 --> 01:06:00,559
so in aluminum oxide you're absorbing
1965
01:06:00,559 --> 01:06:02,319
these two like spectrums of light and
1966
01:06:02,319 --> 01:06:03,200
then
1967
01:06:03,200 --> 01:06:04,880
beryllium you're absorbing different
1968
01:06:04,880 --> 01:06:06,799
colors of light which means different
1969
01:06:06,799 --> 01:06:08,559
colors of light is transmitted
1970
01:06:08,559 --> 01:06:10,960
all right so this helps explain why
1971
01:06:10,960 --> 01:06:12,000
chromium
1972
01:06:12,000 --> 01:06:13,680
is responsible for both the red light
1973
01:06:13,680 --> 01:06:15,119
and green light in both of these
1974
01:06:15,119 --> 01:06:15,760
materials
1975
01:06:15,760 --> 01:06:17,039
and is different because the ligand
1976
01:06:17,039 --> 01:06:19,599
field energy and liquid field energy is
1977
01:06:19,599 --> 01:06:21,680
different because the local environment
1978
01:06:21,680 --> 01:06:25,200
surrounding the chromium atom ion
1979
01:06:25,200 --> 01:06:26,559
is different in these two different
1980
01:06:26,559 --> 01:06:28,799
materials all right
1981
01:06:28,799 --> 01:06:30,839
so now you kind of see how everything is
1982
01:06:30,839 --> 01:06:34,160
related i talked about
1983
01:06:34,160 --> 01:06:37,839
you know how it's related in the battery
1984
01:06:37,839 --> 01:06:38,799
materials
1985
01:06:38,799 --> 01:06:41,680
right that changes the redox potential
1986
01:06:41,680 --> 01:06:43,039
of the battery materials
1987
01:06:43,039 --> 01:06:45,039
it changes the optical properties of
1988
01:06:45,039 --> 01:06:46,400
these materials
1989
01:06:46,400 --> 01:06:48,400
there's one more i thought but i forget
1990
01:06:48,400 --> 01:06:49,920
anyways
1991
01:06:49,920 --> 01:06:51,599
and here's another chart it just relates
1992
01:06:51,599 --> 01:06:54,319
the dopant concentration the color
1993
01:06:54,319 --> 01:06:55,839
so i guess chromium oxide is green
1994
01:06:55,839 --> 01:06:57,599
aluminum oxide is clear but you add
1995
01:06:57,599 --> 01:07:00,400
chromium makes it red
1996
01:07:00,400 --> 01:07:03,839
um so just uh quickly go over we're
1997
01:07:03,839 --> 01:07:07,119
about about a bit over time that's fine
1998
01:07:07,119 --> 01:07:08,640
i'll just kind of talk about some of the
1999
01:07:08,640 --> 01:07:09,599
data from my
2000
01:07:09,599 --> 01:07:12,960
my publication so again this was
2001
01:07:12,960 --> 01:07:14,880
looking at prussian blue is looking at
2002
01:07:14,880 --> 01:07:17,200
the synthesis of prussian blue
2003
01:07:17,200 --> 01:07:19,280
now and typically the synthesis if you
2004
01:07:19,280 --> 01:07:20,280
add a
2005
01:07:20,280 --> 01:07:22,640
ferrocyanide salt such as sodium
2006
01:07:22,640 --> 01:07:24,799
ferrocyanide and dissolve it in water
2007
01:07:24,799 --> 01:07:28,480
and then add a ferric or ferrous salt
2008
01:07:28,480 --> 01:07:30,960
uh the pres it undergoes a precipitation
2009
01:07:30,960 --> 01:07:31,680
reaction
2010
01:07:31,680 --> 01:07:34,400
okay the the solubility product of
2011
01:07:34,400 --> 01:07:35,280
prussian blue
2012
01:07:35,280 --> 01:07:37,760
in water is very low it's like 10 to the
2013
01:07:37,760 --> 01:07:39,920
negative 200 it's
2014
01:07:39,920 --> 01:07:42,319
very very low so that means as soon as
2015
01:07:42,319 --> 01:07:44,160
these ions are in contact
2016
01:07:44,160 --> 01:07:46,400
they're going to precipitate into a
2017
01:07:46,400 --> 01:07:47,760
solid okay
2018
01:07:47,760 --> 01:07:50,559
and because of such high precipitation
2019
01:07:50,559 --> 01:07:52,079
or low solubility product
2020
01:07:52,079 --> 01:07:55,200
what ends up happening happening is you
2021
01:07:55,200 --> 01:07:55,520
get
2022
01:07:55,520 --> 01:07:57,440
very small nano particles you get very
2023
01:07:57,440 --> 01:07:59,599
high nucleation
2024
01:07:59,599 --> 01:08:01,920
and if you have high nucleation you
2025
01:08:01,920 --> 01:08:03,119
usually have
2026
01:08:03,119 --> 01:08:04,720
low growth all right because you're
2027
01:08:04,720 --> 01:08:06,559
taking the ions away from solution
2028
01:08:06,559 --> 01:08:09,680
ions allow you to uh to grow the the
2029
01:08:09,680 --> 01:08:10,319
crystal
2030
01:08:10,319 --> 01:08:11,760
and so you what ends up having you have
2031
01:08:11,760 --> 01:08:13,599
these really uh
2032
01:08:13,599 --> 01:08:17,279
rough nanoparticles um and
2033
01:08:17,279 --> 01:08:20,238
they're more or less not grown under
2034
01:08:20,238 --> 01:08:22,158
thermodynamic conditions so they don't
2035
01:08:22,158 --> 01:08:22,719
have
2036
01:08:22,719 --> 01:08:25,120
nice facets or cubic structure and
2037
01:08:25,120 --> 01:08:26,719
there's a lot of vacancies in water
2038
01:08:26,719 --> 01:08:28,399
because of the fast reaction as well
2039
01:08:28,399 --> 01:08:31,759
so the idea was to add a collating agent
2040
01:08:31,759 --> 01:08:34,479
to this reaction that would collate to
2041
01:08:34,479 --> 01:08:35,679
one of the iron
2042
01:08:35,679 --> 01:08:38,000
ions so essentially we're reducing the
2043
01:08:38,000 --> 01:08:39,279
activity
2044
01:08:39,279 --> 01:08:42,560
of the iron species in solution and that
2045
01:08:42,560 --> 01:08:44,799
would help slow down the precipitation
2046
01:08:44,799 --> 01:08:45,759
reaction
2047
01:08:45,759 --> 01:08:48,399
and then also adjust the ph because the
2048
01:08:48,399 --> 01:08:50,000
chelation strength of this
2049
01:08:50,000 --> 01:08:53,040
chelate is uh affected by uh
2050
01:08:53,040 --> 01:08:56,960
the ph uh and so what ended up happening
2051
01:08:56,960 --> 01:08:57,920
right you get
2052
01:08:57,920 --> 01:08:59,520
a different ph you get different sized
2053
01:08:59,520 --> 01:09:01,679
particles you get different uh
2054
01:09:01,679 --> 01:09:03,600
vacancy content different water content
2055
01:09:03,600 --> 01:09:04,719
and then more imports
2056
01:09:04,719 --> 01:09:06,880
most importantly you had a different uh
2057
01:09:06,880 --> 01:09:08,560
redox
2058
01:09:08,560 --> 01:09:11,600
characterization so here's another view
2059
01:09:11,600 --> 01:09:12,158
of it
2060
01:09:12,158 --> 01:09:14,319
these are the particles growing at lower
2061
01:09:14,319 --> 01:09:16,479
ph at higher ph the particles were
2062
01:09:16,479 --> 01:09:18,238
much larger but what's interesting if
2063
01:09:18,238 --> 01:09:19,520
you look at these particles
2064
01:09:19,520 --> 01:09:22,238
they're not necessarily cubic right i
2065
01:09:22,238 --> 01:09:22,640
mean
2066
01:09:22,640 --> 01:09:25,120
they're definitely faceted and if it's
2067
01:09:25,120 --> 01:09:25,839
faceted
2068
01:09:25,839 --> 01:09:27,359
it means that like i said it's grown
2069
01:09:27,359 --> 01:09:29,679
under thermodynamic conditions you're
2070
01:09:29,679 --> 01:09:32,158
you're you're when you grow a crystal
2071
01:09:32,158 --> 01:09:33,759
you're going to grow
2072
01:09:33,759 --> 01:09:36,319
you're going to expand the surfaces that
2073
01:09:36,319 --> 01:09:37,279
have the lowest
2074
01:09:37,279 --> 01:09:40,399
surface energy okay and this
2075
01:09:40,399 --> 01:09:42,238
in this uh crystal structure it's going
2076
01:09:42,238 --> 01:09:43,439
to be a cube
2077
01:09:43,439 --> 01:09:45,359
but like just looking at it you know you
2078
01:09:45,359 --> 01:09:47,359
have like a rectangular prism here you
2079
01:09:47,359 --> 01:09:49,040
have something with like a step
2080
01:09:49,040 --> 01:09:51,198
you have like an l shape here it's kind
2081
01:09:51,198 --> 01:09:52,399
of weird and
2082
01:09:52,399 --> 01:09:53,520
you can see the same thing in the
2083
01:09:53,520 --> 01:09:54,960
smaller one but they're just much
2084
01:09:54,960 --> 01:09:56,000
smaller
2085
01:09:56,000 --> 01:09:59,600
and so the what i had done some
2086
01:09:59,600 --> 01:10:02,000
literature research and it seems like
2087
01:10:02,000 --> 01:10:03,600
it's fairly common with the prussian
2088
01:10:03,600 --> 01:10:04,560
blue material
2089
01:10:04,560 --> 01:10:07,120
grown under thermodynamic conditions to
2090
01:10:07,120 --> 01:10:08,640
make a what's called a
2091
01:10:08,640 --> 01:10:10,960
meso crystal a mesocrystal is when you
2092
01:10:10,960 --> 01:10:12,560
take smaller crystals
2093
01:10:12,560 --> 01:10:15,440
and then they they aggregate together in
2094
01:10:15,440 --> 01:10:15,679
an
2095
01:10:15,679 --> 01:10:17,679
oriented manner and then they can fuse
2096
01:10:17,679 --> 01:10:19,199
together to make another bigger
2097
01:10:19,199 --> 01:10:21,520
single crystal out of these small nano
2098
01:10:21,520 --> 01:10:22,880
crystals okay
2099
01:10:22,880 --> 01:10:25,760
and so that that's sure that makes sense
2100
01:10:25,760 --> 01:10:27,440
and it's supported by literature
2101
01:10:27,440 --> 01:10:29,199
but the other question was you know why
2102
01:10:29,199 --> 01:10:31,199
why do i have small
2103
01:10:31,199 --> 01:10:35,760
mesocrystals versus large mesocrystals
2104
01:10:35,920 --> 01:10:37,360
and also saying that they're
2105
01:10:37,360 --> 01:10:39,440
mesocrystals of speculation i haven't i
2106
01:10:39,440 --> 01:10:40,960
don't have any hard evidence that they
2107
01:10:40,960 --> 01:10:42,640
are mesocrystals but other than
2108
01:10:42,640 --> 01:10:45,600
laser but the question why is this small
2109
01:10:45,600 --> 01:10:46,719
and why are these big
2110
01:10:46,719 --> 01:10:49,920
and so my my proposal my proposed
2111
01:10:49,920 --> 01:10:51,679
mechanism was well
2112
01:10:51,679 --> 01:10:55,679
uh because the the solubility product of
2113
01:10:55,679 --> 01:10:57,040
this material is so low and they
2114
01:10:57,040 --> 01:10:58,960
precipitate so fast or there's such high
2115
01:10:58,960 --> 01:10:59,920
nucleation
2116
01:10:59,920 --> 01:11:02,400
that the particles growing at low ph
2117
01:11:02,400 --> 01:11:04,480
have much higher nucleation
2118
01:11:04,480 --> 01:11:06,560
and then that results in very small
2119
01:11:06,560 --> 01:11:09,199
crystals and then those small crystals
2120
01:11:09,199 --> 01:11:11,679
together can aggregate to form smaller
2121
01:11:11,679 --> 01:11:12,800
mesocrystals
2122
01:11:12,800 --> 01:11:14,800
on the other hand the higher ph would
2123
01:11:14,800 --> 01:11:16,560
have low nucleation
2124
01:11:16,560 --> 01:11:19,120
okay and that allow for more growth
2125
01:11:19,120 --> 01:11:20,239
larger particles
2126
01:11:20,239 --> 01:11:22,000
and then that would aggregate into
2127
01:11:22,000 --> 01:11:23,600
larger mesocrystals
2128
01:11:23,600 --> 01:11:27,440
and i wanted to i wanted to prove that
2129
01:11:27,440 --> 01:11:30,800
at ph 3.8 you know i had some faster
2130
01:11:30,800 --> 01:11:32,320
growth is what i wanted to show and then
2131
01:11:32,320 --> 01:11:33,840
at 4.4 i had
2132
01:11:33,840 --> 01:11:36,960
slower growth so what i did is i took a
2133
01:11:36,960 --> 01:11:37,600
uv
2134
01:11:37,600 --> 01:11:40,159
vis spectrum of the material so these
2135
01:11:40,159 --> 01:11:41,760
are actually four different ph's but i
2136
01:11:41,760 --> 01:11:43,440
only showed two on here
2137
01:11:43,440 --> 01:11:47,120
uh and it shows the peak at 700
2138
01:11:47,120 --> 01:11:49,520
nanometers 700 nanometers is the main
2139
01:11:49,520 --> 01:11:51,679
absorption peak of prussian blue and so
2140
01:11:51,679 --> 01:11:54,239
700 nanometers is like a red
2141
01:11:54,239 --> 01:11:55,920
right so it's kind of almost infrared
2142
01:11:55,920 --> 01:11:57,760
yeah and um
2143
01:11:57,760 --> 01:11:59,840
so if you're absorbing red that means
2144
01:11:59,840 --> 01:12:01,600
you transmit all the other colors and it
2145
01:12:01,600 --> 01:12:03,040
ends up being blue that's why prussian
2146
01:12:03,040 --> 01:12:04,320
blue is blue
2147
01:12:04,320 --> 01:12:08,239
but what i did is i took my my material
2148
01:12:08,239 --> 01:12:12,000
and i put it into a cuvette and uh
2149
01:12:12,000 --> 01:12:14,320
i added the two components together and
2150
01:12:14,320 --> 01:12:15,360
started the test
2151
01:12:15,360 --> 01:12:18,800
right away as it was reacting and then
2152
01:12:18,800 --> 01:12:21,040
every five seconds or so i think it was
2153
01:12:21,040 --> 01:12:22,239
either five or ten seconds
2154
01:12:22,239 --> 01:12:24,320
10 seconds every 10 seconds i would take
2155
01:12:24,320 --> 01:12:26,000
a scan
2156
01:12:26,000 --> 01:12:28,560
or a measurement just at 700 nanometers
2157
01:12:28,560 --> 01:12:29,840
of the intensity
2158
01:12:29,840 --> 01:12:32,640
of the solution because as this material
2159
01:12:32,640 --> 01:12:33,920
precipitates
2160
01:12:33,920 --> 01:12:37,040
it's going to uh absorb more light
2161
01:12:37,040 --> 01:12:38,400
or it's going to absorb blue light or
2162
01:12:38,400 --> 01:12:39,600
excuse me it's going to absorb the red
2163
01:12:39,600 --> 01:12:41,920
light at 700 nanometers
2164
01:12:41,920 --> 01:12:45,280
so here we see a ph 3.8 as soon as i add
2165
01:12:45,280 --> 01:12:46,640
the two solutions together
2166
01:12:46,640 --> 01:12:48,480
you know it becomes saturated very
2167
01:12:48,480 --> 01:12:49,920
quickly
2168
01:12:49,920 --> 01:12:51,520
so that means that the the the
2169
01:12:51,520 --> 01:12:53,679
nucleation growth is very quick
2170
01:12:53,679 --> 01:12:56,800
but at lower higher ph it's much more
2171
01:12:56,800 --> 01:12:58,800
gradual which means that the growth of
2172
01:12:58,800 --> 01:13:00,480
the particles and nucleation is much
2173
01:13:00,480 --> 01:13:01,280
more slow
2174
01:13:01,280 --> 01:13:03,520
and that makes sense because at higher
2175
01:13:03,520 --> 01:13:05,520
ph the chelation strength of this
2176
01:13:05,520 --> 01:13:08,239
chelate is higher so it's it's more it's
2177
01:13:08,239 --> 01:13:08,960
inhibiting
2178
01:13:08,960 --> 01:13:11,360
the nucleation of this reaction so it
2179
01:13:11,360 --> 01:13:12,159
slows it down
2180
01:13:12,159 --> 01:13:15,840
and that's why you get larger growth
2181
01:13:15,840 --> 01:13:17,920
okay so moving on to electrochemical
2182
01:13:17,920 --> 01:13:18,960
properties
2183
01:13:18,960 --> 01:13:22,239
um so here is uh
2184
01:13:22,239 --> 01:13:24,480
the the capacity the discharge and
2185
01:13:24,480 --> 01:13:25,760
charge capacity
2186
01:13:25,760 --> 01:13:28,560
uh for many cycles and then also i
2187
01:13:28,560 --> 01:13:29,120
increase
2188
01:13:29,120 --> 01:13:31,600
the current rate after every 10 cycles
2189
01:13:31,600 --> 01:13:33,840
so remember this is galvanostatic
2190
01:13:33,840 --> 01:13:35,199
cycling so this is like the
2191
01:13:35,199 --> 01:13:37,840
the profile of each one of these dots is
2192
01:13:37,840 --> 01:13:38,560
like this and
2193
01:13:38,560 --> 01:13:40,880
this is actually the last dot of each of
2194
01:13:40,880 --> 01:13:43,360
each series is this profile
2195
01:13:43,360 --> 01:13:45,679
so if you just look at one curve this is
2196
01:13:45,679 --> 01:13:47,440
the discharge curve you start at high
2197
01:13:47,440 --> 01:13:49,440
voltage after charging
2198
01:13:49,440 --> 01:13:52,560
you're discharging at a constant rate
2199
01:13:52,560 --> 01:13:54,719
so the first section is only 100
2200
01:13:54,719 --> 01:13:56,480
milliamps per gram
2201
01:13:56,480 --> 01:13:58,080
right and you measure the voltage as it
2202
01:13:58,080 --> 01:14:00,000
discharges and like i said there's two
2203
01:14:00,000 --> 01:14:02,320
different iron species in this material
2204
01:14:02,320 --> 01:14:04,080
and that represent two different redox
2205
01:14:04,080 --> 01:14:06,320
reactions so here's one redox reaction
2206
01:14:06,320 --> 01:14:07,600
is a higher voltage
2207
01:14:07,600 --> 01:14:10,320
corresponds to low spin iron and then a
2208
01:14:10,320 --> 01:14:12,320
lower redox potential corresponding the
2209
01:14:12,320 --> 01:14:13,280
high spin iron
2210
01:14:13,280 --> 01:14:15,280
and then the other the other chart the
2211
01:14:15,280 --> 01:14:16,560
other plot
2212
01:14:16,560 --> 01:14:19,760
line is just the the charge profile of
2213
01:14:19,760 --> 01:14:20,159
the
2214
01:14:20,159 --> 01:14:23,360
the same material okay and
2215
01:14:23,360 --> 01:14:26,719
um i said before you know as we increase
2216
01:14:26,719 --> 01:14:29,760
the current of the battery
2217
01:14:29,760 --> 01:14:32,719
as we're drawing more current uh things
2218
01:14:32,719 --> 01:14:33,199
become
2219
01:14:33,199 --> 01:14:36,560
there's at there's the capacity
2220
01:14:36,560 --> 01:14:37,280
decreases
2221
01:14:37,280 --> 01:14:39,440
and the voltage decreases i remember i
2222
01:14:39,440 --> 01:14:41,440
said you know i was kind of relating it
2223
01:14:41,440 --> 01:14:43,199
to v equals ir
2224
01:14:43,199 --> 01:14:45,360
that there's these resistances inside
2225
01:14:45,360 --> 01:14:46,320
the battery
2226
01:14:46,320 --> 01:14:48,239
such as diffusion resistance or
2227
01:14:48,239 --> 01:14:49,840
electrical resistance
2228
01:14:49,840 --> 01:14:52,400
and as we increase the current you know
2229
01:14:52,400 --> 01:14:53,920
resistance more or less stays the same
2230
01:14:53,920 --> 01:14:54,719
but as we increase
2231
01:14:54,719 --> 01:14:57,199
current that means the voltage in this
2232
01:14:57,199 --> 01:14:58,080
case voltage
2233
01:14:58,080 --> 01:15:01,120
drop increases so that's why
2234
01:15:01,120 --> 01:15:02,960
you see this voltage as we increase
2235
01:15:02,960 --> 01:15:05,040
current rate the voltage drops
2236
01:15:05,040 --> 01:15:07,360
okay
2237
01:15:09,600 --> 01:15:13,120
so if we just one one idea
2238
01:15:13,120 --> 01:15:14,800
i mean obviously you'll see that the
2239
01:15:14,800 --> 01:15:17,280
capacity of the smaller particles
2240
01:15:17,280 --> 01:15:19,440
is larger than the capacity of the
2241
01:15:19,440 --> 01:15:20,800
larger particles
2242
01:15:20,800 --> 01:15:24,239
okay and now
2243
01:15:24,239 --> 01:15:26,320
i've said this before in a previous
2244
01:15:26,320 --> 01:15:28,320
lecture you know it's always
2245
01:15:28,320 --> 01:15:31,440
better to make nano materials okay
2246
01:15:31,440 --> 01:15:33,679
if you make something nano it means the
2247
01:15:33,679 --> 01:15:35,840
diffusion distance of lithium ions or
2248
01:15:35,840 --> 01:15:37,600
sodium ions in solution
2249
01:15:37,600 --> 01:15:40,080
into the materials shorter all right it
2250
01:15:40,080 --> 01:15:41,520
doesn't have to travel as far
2251
01:15:41,520 --> 01:15:44,480
and that results in less resistance for
2252
01:15:44,480 --> 01:15:45,600
diffusion
2253
01:15:45,600 --> 01:15:47,760
uh during discharge okay and that would
2254
01:15:47,760 --> 01:15:50,080
result in higher capacity as well
2255
01:15:50,080 --> 01:15:52,800
so you know right away you look at this
2256
01:15:52,800 --> 01:15:54,239
and you look at the different
2257
01:15:54,239 --> 01:15:56,159
materials and you say well you know this
2258
01:15:56,159 --> 01:15:58,080
has higher capacity because these are
2259
01:15:58,080 --> 01:15:58,719
smaller
2260
01:15:58,719 --> 01:16:00,960
smaller smaller particles it makes sense
2261
01:16:00,960 --> 01:16:02,000
right
2262
01:16:02,000 --> 01:16:05,280
and so if that was the case
2263
01:16:05,280 --> 01:16:09,120
if if capacity was kinetically limited
2264
01:16:09,120 --> 01:16:12,480
by the diffusion of ions and due to the
2265
01:16:12,480 --> 01:16:14,159
particle size
2266
01:16:14,159 --> 01:16:16,480
you would expect to see as we increase
2267
01:16:16,480 --> 01:16:17,920
the current rate
2268
01:16:17,920 --> 01:16:21,600
that the cur the capacity retention
2269
01:16:21,600 --> 01:16:24,239
of larger particles would decrease even
2270
01:16:24,239 --> 01:16:24,719
more
2271
01:16:24,719 --> 01:16:26,640
but if you compare the initial
2272
01:16:26,640 --> 01:16:28,239
capacities at slow rate
2273
01:16:28,239 --> 01:16:31,360
to the capacities at high rate between
2274
01:16:31,360 --> 01:16:33,040
the small particles and the large
2275
01:16:33,040 --> 01:16:34,800
particles so the ratio of this number to
2276
01:16:34,800 --> 01:16:36,080
this number basically
2277
01:16:36,080 --> 01:16:38,080
they're they're pretty much the same all
2278
01:16:38,080 --> 01:16:39,520
right which would show
2279
01:16:39,520 --> 01:16:42,320
which would indicate that kinetics did
2280
01:16:42,320 --> 01:16:43,679
not play a
2281
01:16:43,679 --> 01:16:47,360
major role in this material as far as
2282
01:16:47,360 --> 01:16:49,600
the capacities go
2283
01:16:49,600 --> 01:16:52,000
however if you investigate it a little
2284
01:16:52,000 --> 01:16:53,520
bit more in detail
2285
01:16:53,520 --> 01:16:56,640
but in these charts here i separate
2286
01:16:56,640 --> 01:16:59,760
an estimated capacity contribution
2287
01:16:59,760 --> 01:17:01,120
you know for each one of these lines
2288
01:17:01,120 --> 01:17:02,880
just the the discharge ignoring the
2289
01:17:02,880 --> 01:17:04,800
charge
2290
01:17:04,800 --> 01:17:06,960
of the low spin iron which is this
2291
01:17:06,960 --> 01:17:08,560
higher voltage
2292
01:17:08,560 --> 01:17:12,239
uh plateau here versus the high spin
2293
01:17:12,239 --> 01:17:14,159
iron which is the lower voltage plateau
2294
01:17:14,159 --> 01:17:15,840
here and so the red
2295
01:17:15,840 --> 01:17:17,520
is the low spin iron capacity
2296
01:17:17,520 --> 01:17:19,440
contribution you see it's this is a bit
2297
01:17:19,440 --> 01:17:21,280
smaller than this line here
2298
01:17:21,280 --> 01:17:23,440
and the black is the high spin and if
2299
01:17:23,440 --> 01:17:24,719
you compare the two
2300
01:17:24,719 --> 01:17:27,679
uh particle sizes together you'll see
2301
01:17:27,679 --> 01:17:28,560
that
2302
01:17:28,560 --> 01:17:31,360
as you increase the current the capacity
2303
01:17:31,360 --> 01:17:32,560
contribution of the
2304
01:17:32,560 --> 01:17:35,040
high spin iron is is more or less
2305
01:17:35,040 --> 01:17:36,640
constant
2306
01:17:36,640 --> 01:17:38,800
okay and the same for the larger
2307
01:17:38,800 --> 01:17:40,800
particles it's more or less constant
2308
01:17:40,800 --> 01:17:42,960
which would indicate that the redox
2309
01:17:42,960 --> 01:17:45,520
mechanism related to the high spin
2310
01:17:45,520 --> 01:17:48,640
iron is not dependent or
2311
01:17:48,640 --> 01:17:50,159
largely dependent everything is
2312
01:17:50,159 --> 01:17:51,920
dependent but it's not largely
2313
01:17:51,920 --> 01:17:54,880
dominated by kinetics of the reaction
2314
01:17:54,880 --> 01:17:55,440
all right
2315
01:17:55,440 --> 01:17:57,760
it's a we're able to supply electrons
2316
01:17:57,760 --> 01:17:59,199
and we're able to supply it
2317
01:17:59,199 --> 01:18:01,440
ions through fast diffusion uh
2318
01:18:01,440 --> 01:18:03,120
effectively
2319
01:18:03,120 --> 01:18:05,360
okay there's no big decrease in that
2320
01:18:05,360 --> 01:18:07,280
that level but if you look at the low
2321
01:18:07,280 --> 01:18:08,080
spin
2322
01:18:08,080 --> 01:18:09,760
capacity contribution that's where you
2323
01:18:09,760 --> 01:18:11,199
see a decrease
2324
01:18:11,199 --> 01:18:13,199
all right which is is kind of unusual
2325
01:18:13,199 --> 01:18:15,199
because you have one material
2326
01:18:15,199 --> 01:18:18,239
and there's a difference in uh
2327
01:18:18,239 --> 01:18:20,960
redox mechanism between the you know
2328
01:18:20,960 --> 01:18:21,920
this plateau and
2329
01:18:21,920 --> 01:18:24,960
the second plateau which is uh a bit
2330
01:18:24,960 --> 01:18:26,000
interesting in my
2331
01:18:26,000 --> 01:18:28,640
opinion and i don't have i i don't have
2332
01:18:28,640 --> 01:18:29,840
an explanation
2333
01:18:29,840 --> 01:18:33,440
for why this redox mechanism of low spin
2334
01:18:33,440 --> 01:18:34,159
is different
2335
01:18:34,159 --> 01:18:38,400
other than that perhaps um
2336
01:18:38,400 --> 01:18:40,320
it's not what we think it is so we
2337
01:18:40,320 --> 01:18:42,320
always think you know we add sodium ions
2338
01:18:42,320 --> 01:18:43,679
in and we're reducing iron
2339
01:18:43,679 --> 01:18:45,520
three plus to iron two plus and it was
2340
01:18:45,520 --> 01:18:47,520
the same for the both but perhaps that's
2341
01:18:47,520 --> 01:18:49,280
not the case for this uh
2342
01:18:49,280 --> 01:18:52,960
higher voltage case so i'm looking into
2343
01:18:52,960 --> 01:18:53,520
this
2344
01:18:53,520 --> 01:18:55,120
when i get back to lab this is the next
2345
01:18:55,120 --> 01:18:56,800
thing i'm going to look at is
2346
01:18:56,800 --> 01:18:59,440
investigate this redox potential at
2347
01:18:59,440 --> 01:19:01,440
different rates of different materials
2348
01:19:01,440 --> 01:19:04,000
and i speculate that actually the water
2349
01:19:04,000 --> 01:19:05,040
content
2350
01:19:05,040 --> 01:19:06,800
might have something to do with it
2351
01:19:06,800 --> 01:19:08,880
actually because if you if you compare a
2352
01:19:08,880 --> 01:19:10,320
non-aqueous
2353
01:19:10,320 --> 01:19:12,400
prussian blue to aqueous prussian blue
2354
01:19:12,400 --> 01:19:13,360
battery you
2355
01:19:13,360 --> 01:19:16,239
always see that this plateau is much
2356
01:19:16,239 --> 01:19:16,880
higher
2357
01:19:16,880 --> 01:19:18,800
in the aqueous state than the
2358
01:19:18,800 --> 01:19:20,960
non-nyquist so it makes me think that
2359
01:19:20,960 --> 01:19:23,040
water plays a large role in the redox
2360
01:19:23,040 --> 01:19:24,159
reaction of this
2361
01:19:24,159 --> 01:19:26,719
material even in this non-aqueous
2362
01:19:26,719 --> 01:19:28,320
battery because i still have water
2363
01:19:28,320 --> 01:19:31,280
inside my material
2364
01:19:32,320 --> 01:19:36,159
so anyways so the point is uh
2365
01:19:36,159 --> 01:19:39,280
is that well there's still a lot to
2366
01:19:39,280 --> 01:19:40,000
learn
2367
01:19:40,000 --> 01:19:42,320
and i think once i figure this out i can
2368
01:19:42,320 --> 01:19:43,120
publish that
2369
01:19:43,120 --> 01:19:45,120
next paper and i can get out of this
2370
01:19:45,120 --> 01:19:47,440
university and then
2371
01:19:47,440 --> 01:19:51,040
move on to the next big thing
2372
01:19:51,040 --> 01:19:53,280
i'm going to end it here it's been about
2373
01:19:53,280 --> 01:19:55,440
an hour and a half
2374
01:19:55,440 --> 01:20:05,040
any questions before we we leave
2375
01:20:05,040 --> 01:20:10,400
well thanks for uh sticking with me
2376
01:20:10,400 --> 01:20:14,560
um i believe on friday
2377
01:20:14,560 --> 01:20:18,239
you have um a journal review
2378
01:20:18,239 --> 01:20:21,679
uh due excuse me a literature literature
2379
01:20:21,679 --> 01:20:22,239
summary
2380
01:20:22,239 --> 01:20:25,760
is due on friday uh so remember
2381
01:20:25,760 --> 01:20:27,760
for your your review paper you need to
2382
01:20:27,760 --> 01:20:30,080
have at least 10
2383
01:20:30,080 --> 01:20:34,800
literature sources since uh 2019
2384
01:20:34,800 --> 01:20:37,520
but there's only five literature uh
2385
01:20:37,520 --> 01:20:38,560
summaries
2386
01:20:38,560 --> 01:20:40,960
summary assignments so if you want to be
2387
01:20:40,960 --> 01:20:43,360
proactive you can actually make two
2388
01:20:43,360 --> 01:20:46,400
summaries each assignment
2389
01:20:46,400 --> 01:20:48,800
but you're only you only need to submit
2390
01:20:48,800 --> 01:20:50,400
one to get full credit and it
2391
01:20:50,400 --> 01:20:53,120
is for credit so please write out uh a
2392
01:20:53,120 --> 01:20:55,199
summary i'm going to try to
2393
01:20:55,199 --> 01:20:57,199
write a summary example tonight and send
2394
01:20:57,199 --> 01:20:58,880
it to you guys just show you what you
2395
01:20:58,880 --> 01:20:59,280
know
2396
01:20:59,280 --> 01:21:01,199
what i'm kind of expecting but basically
2397
01:21:01,199 --> 01:21:02,800
the more the more you do
2398
01:21:02,800 --> 01:21:04,480
the easier it's going to be for when you
2399
01:21:04,480 --> 01:21:08,560
want to compile your your review paper
2400
01:21:08,880 --> 01:21:12,800
okay yeah
2401
01:21:12,800 --> 01:21:14,960
and then tuesday will be the first day
2402
01:21:14,960 --> 01:21:15,920
of lab
2403
01:21:15,920 --> 01:21:17,760
so we'll meet here again at the same
2404
01:21:17,760 --> 01:21:19,120
time uh
2405
01:21:19,120 --> 01:21:21,840
in that day the ta will lead most of the
2406
01:21:21,840 --> 01:21:22,560
lecture
2407
01:21:22,560 --> 01:21:25,120
and i'll be here in support um so we'll
2408
01:21:25,120 --> 01:21:26,159
go through
2409
01:21:26,159 --> 01:21:27,840
some discussion questions there's no
2410
01:21:27,840 --> 01:21:29,840
pre-lab so you don't need to prepare
2411
01:21:29,840 --> 01:21:30,880
anything
2412
01:21:30,880 --> 01:21:32,960
but uh you know just just be ready to
2413
01:21:32,960 --> 01:21:34,239
learn i guess
2414
01:21:34,239 --> 01:21:36,239
be let ready to learn and be sure you
2415
01:21:36,239 --> 01:21:38,719
you can take notes during the lecture
2416
01:21:38,719 --> 01:21:41,440
uh so that at by the end of the lecture
2417
01:21:41,440 --> 01:21:42,320
you can submit
2418
01:21:42,320 --> 01:21:45,600
a summary of of our lab lab
2419
01:21:45,600 --> 01:21:49,280
lecture so the ta will discuss uh some
2420
01:21:49,280 --> 01:21:51,679
some background and discussion questions
2421
01:21:51,679 --> 01:21:52,960
of the topic
2422
01:21:52,960 --> 01:21:55,360
then we will have a video of the
2423
01:21:55,360 --> 01:21:56,560
experiment
2424
01:21:56,560 --> 01:21:59,679
that tatiana has uh has
2425
01:21:59,679 --> 01:22:02,790
been busy putting together these videos
2426
01:22:02,790 --> 01:22:05,040
[Music]
2427
01:22:05,040 --> 01:22:08,080
and now there's an issue with
2428
01:22:08,080 --> 01:22:10,000
streaming the video i tried streaming
2429
01:22:10,000 --> 01:22:11,120
videos on
2430
01:22:11,120 --> 01:22:14,159
zoom and it doesn't really work because
2431
01:22:14,159 --> 01:22:16,400
there's like a lag so i think what we're
2432
01:22:16,400 --> 01:22:17,679
going to have to do is
2433
01:22:17,679 --> 01:22:19,360
once we get to that point you know we're
2434
01:22:19,360 --> 01:22:21,199
going to say okay take 20 minutes to
2435
01:22:21,199 --> 01:22:22,639
watch the video and they'll
2436
01:22:22,639 --> 01:22:24,480
regroup and you watch it on your own and
2437
01:22:24,480 --> 01:22:25,600
then we'll regroup and then we'll have
2438
01:22:25,600 --> 01:22:26,880
discussion questions
2439
01:22:26,880 --> 01:22:29,440
and then the ta has data you'll be given
2440
01:22:29,440 --> 01:22:30,159
the data
2441
01:22:30,159 --> 01:22:32,239
and the ta will go over a data set on
2442
01:22:32,239 --> 01:22:35,040
how to like plot or analyze the data
2443
01:22:35,040 --> 01:22:37,679
and you guys do that together so it'll
2444
01:22:37,679 --> 01:22:39,360
be it'll be interesting how it goes
2445
01:22:39,360 --> 01:22:41,280
i'm quite curious myself it'll be the
2446
01:22:41,280 --> 01:22:43,360
first time okay any questions and
2447
01:22:43,360 --> 01:22:47,120
if not we'll uh you guys can get out of
2448
01:22:50,840 --> 01:22:53,840
here
2449
01:22:55,760 --> 01:22:58,560
okay well i'll see you guys uh next week
2450
01:22:58,560 --> 01:23:00,480
have a good weekend everyone
2451
01:23:00,480 --> 01:23:03,600
try to get some sunlight but you know
2452
01:23:03,600 --> 01:23:06,159
stay away from other people but try to
2453
01:23:06,159 --> 01:23:07,040
get outdoors
2454
01:23:07,040 --> 01:23:21,840
do some exercise yeah
2455
01:23:29,920 --> 01:23:32,000
you
161613
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