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학습트랜스크립트
00:01OK, let me continue with electrodes.
00:05In electrochemistry, we saw we are using electrodes for anode and for cathode.
00:17Most likely, we have two electrodes in electrochemistry system.
00:24For application, that's true.
00:29For example, the batteries, it has anode and cathode and plus, negative, plus and minus.
00:36In solar cells, we also have a positive and negative, plus and minus.
00:44What else?
00:46In electrochronic device, when we apply the voltage, that changes the color of the window.
00:55The smart window also has two electrodes.
00:58I don't think we see any three electrode system for regular electrochemical application.
01:07But now, here, we see a little bit different one.
01:12The electrode of interest that we are focusing on, that is called the working electrode.
01:20That's interesting because we already defined a few words for the electrodes, anode and cathode.
01:27Correct?
01:28In Korean, like 양극, 음극, they are regular name of the electrode.
01:36But now here, we have another definition, working electrode.
01:41That anode or cathode, that's true.
01:44But also, let's say we have anode and cathode.
01:50Which one are you interested in?
01:54For specific reaction, for example, if we use that zinc and kappa becomes zinc and kappa,
02:02and this should be zinc 2 plus, and kappa 2 plus should be kappa, this way.
02:08Right?
02:09And then, if we are interested in this zinc electrode, somehow, we would like to do some research
02:18for zinc anodization, or zinc color change, or how much zinc can be dissociated, whatever.
02:28In that case, that is also called that working electrode.
02:36So, if we are interested in anode, oxidation occurs, that's working electrode.
02:44But the anode is working electrode?
02:47That's not true.
02:49If we are interested in cathode, that's working electrode.
02:54Potentials of individual electrodes cannot be measured.
02:58That's an interesting word.
02:59It says, like, potential.
03:02Potential.
03:03You know, potential, that's quite the impressive words for the energy part.
03:11For example, you know, in Korean, that the witch energy.
03:22The witch is in the United States.
03:25In English, that's like a position, or the, sometimes it could be like height.
03:38So, where it is located, right?
03:41But in English, that's actually, it originates from potential.
03:48That's not like obvious value.
03:53It can have some sort of the internal value, which can be, um, the, which can be the, the,
04:04what is that, like, it can be realized, or it can be still stored inside.
04:10We don't know yet.
04:11But that's potential.
04:13But in the case of this, the, this word, we can expect because that position is already defined.
04:25But anyway, that, that potential is something we cannot see actually.
04:31So that's the difference between the original position and the current position, or the current position and possible final position.
04:45Right?
04:46So, for example, let's say I have a ball.
04:49I have a building here.
04:51I'm sorry, I don't have a building.
04:53There is a building, and I'm at the top of this building, and I have a ball at hand.
04:59It can, uh, if I let it fall down to the building, then it may have energy to this amount.
05:10What if somebody catches the ball at some position?
05:15Maybe this one.
05:16The ball is just rolling down to the sea level.
05:18What if it just flow the rolling down until the sea level.
05:25What's the actual energy of this ball?
05:30It can be this one or this one or this one.
05:35That's the potential.
05:42이 한국어로는 이 상황을 설명해 주시기 바랍니다.
05:50아무튼, 이 상황은 이 상황을 설명해 주시기 바랍니다.
06:04그래서 criticizing the height of this building.
06:07Normally we measure, it is not from the ground.
06:11not from the sea level.
06:14But sometimes, you see reports saying that its building can have this kind of height.
06:23compared to the sea level.
06:25I don't know why they measure that one..
06:29maybe they want to measure...
06:34The absolute value from the sea level.
06:39But I don't know why they need it.
06:42But actually, so when we measure the height or any position,
06:48that should have some sort of reference, ground or sea level, whatever.
06:55So potential is that kind of value, it's reference to ground or sea level, whatever.
07:05So without the two-electrode system or more than two-electrode system, we cannot measure
07:13the potential.
07:14So one thing has some voltage and the other one has the counter of the voltage.
07:21That's more possible and reasonable.
07:25And the other electrode can be called a count electrode.
07:28We see like a working electrode and count electrode.
07:32So anything of interest, that's working electrode.
07:37And then the other one is count electrode.
07:40Normally when we measure the potential difference, that's working electrode minus count electrode.
07:47That's the difference.
07:50So normally delta means like a final minus initial, right?
07:55So working electrode minus count electrode.
08:01But in electrochemistry, we often split the count electrode so as to use three electrodes.
08:08So the textbook says this way, like split the count electrode, not working electrode.
08:17The count electrode can be divided into three electrodes, working, that's the word we already
08:24have of interest.
08:26And the count electrode can be dissociated into reference electrode and the count electrode.
08:36In this case, in the previous slide, when we have two electrode systems, we measure the
08:42voltage difference by checking the voltage of the working electrode and count electrode.
08:49But now when we have this three electrode system, reference electrode is the base.
08:57So we measure the potential difference between working electrode and reference electrode, not count electrode.
09:10So reference electrode is that much important.
09:13Then why do we have this count electrode?
09:18Because the reference electrode is for measuring the voltage, but that doesn't have the large area
09:29of the cell, the electrode itself, because, you know, we don't know who's going to do what
09:38kind of experiments.
09:42So that electrode cannot be made like with large size electrode, the surface.
09:51So since this reference electrode is only for the measuring the voltage, it doesn't have
09:57to be large.
09:58It doesn't have to be large area electrode.
10:09But in that case, we also need one electrode, which can supply the electron.
10:18Because without flowing the electron, that circuit is not well defined and well working.
10:28So here, the counter electrode is only for supplying the current by making other kinds of reaction.
10:37That's Faraday current.
10:40So reference electrode may supply a small amount of electrons and current, but most likely the
10:49counter electrode plays a very important role for supplying the electrons or current.
10:56electron.
10:56I'm sorry.
10:58Depending on the situation, it may supply electron or positron, whatever.
11:08Okay, this is just a regular, the potential stat.
11:13You know, there are many well known company for making this potential stat and it has something
11:22inside.
11:24Large size.
11:25And also, they have a very compact size device.
11:31But, you know, if you open that potential stat, they do not have much parts inside.
11:39Maybe they, they are selling at very high price.
11:43And then, if they make a very small device, then the customer may not agree to the price.
11:51So, they are making like a large size.
11:55So, they are making like a large size and now with many channels inside.
11:59And that's how they can make money with potential stat.
12:03So, every potential stat has three electrodes and with the same color like here, red, white,
12:12and green.
12:15Which one does it look like working electrode?
12:17Which is the electrode for the interest.
12:24So, here it says like a working electrode can be connected to this, the green one.
12:31But most likely, in my case, I was very confused for this kind of experiments.
12:38When I did all this electrochemistry related experiments, it looks like this white one could be working electrode.
12:51Because, you know, this one, this, these colors are quite the, what is that, common.
13:00Right?
13:00So, we see this kind of color very often, but not green color.
13:04So, I thought these two colors might be something related to the working electrode and the counter electrode.
13:15But somehow, this is the setting.
13:20Here, working electrode, green.
13:24And the reference electrode, white.
13:27And counter electrode, red.
13:31In most cases, that system has the labeling on it.
13:38So, CE, and here, WE, something like this.
13:47This is very important because when we apply the voltage by changing the knob or set the values inside,
13:56that potential can be applied to this working electrode.
14:01This green one, not other colors.
14:04You cannot just switch them without knowing the system.
14:10Okay?
14:11So, that's what I'm saying.
14:12Green, working electrode.
14:15And white, reference electrode.
14:18And then red, counter electrode.
14:22I took this picture from the company, the EST.
14:29Then, we, actually, we observed a few, like, reference, just one reference electrode in the previous basic, the electrochemistry part.
14:42That's the standard hydrogen electrode.
14:44So, I mentioned that reference electrode is quite important to measure the voltage.
14:51So, in electrochemistry, the binding voltage is kind of like 50% or almost 90% of the research of
15:00the work.
15:03Theoretically, it is the most important electrode for use in aqueous solution.
15:07So, this has been developed at a very early time to make the situation clear.
15:17Remember that K-Ka-Nama, R-A-P-N is something, and then hydrogen.
15:20That's reference, right?
15:23So, it should be used to make the reference electrode.
15:28And the electrode consists of a platinum wire immersed in a solution.
15:35Platinum wire here, and the connect wire.
15:39Solution containing hydrogen ions.
15:42So, inside, the, you know, this could be, like, blocked somehow, making design.
15:52It's up to the condition.
15:53Or, this hole could be standard hydrogen electrode in a separate way.
15:59The electrode, then, consisting hydrogen ion, that's proton, right?
16:02So, this is the hydrogen ion, that's also called like a proton.
16:10And saturated with the hydrogen gas.
16:13Normally, one mole or the one activity.
16:18This way.
16:20I don't know, maybe just this way.
16:29Okay, the electrode is composed of a silver wire.
16:33Oh, that's like a standard hydrogen electrode.
16:35That's showing the zero.
16:37And also, another reference electrode is a silver chloride electrode.
16:42That electrode is composed of a silver wire with a silver chloride coating,
16:47and immersed in the solution of chloride ions.
16:51And that could be like potassium chloride.
16:54The chloride equilibrium is given by this one.
17:01And also, this value, E0 value, E0 value, E0 value is 0.024 volt.
17:15Normally, we have some saturated chloride ion, because if we change this pH or chloride ion,
17:26that the voltage can be changing.
17:29See?
17:30So, for the reference electrode, it's very important to keep everything in normal condition.
17:39It is the most commonly used saturated calumet electrode we will see.
17:44So, I mentioned that the standard hydrogen electrode,
17:48and the next one is the silver chloride,
17:51and the third one is saturated calumet electrode.
17:54It's the most commonly used.
17:56See?
17:57It's the most commonly used.
17:58When I have done all these experiments for a physics degree,
18:07at that time, we were using the silver chloride,
18:11and that was quite cheap.
18:14Sometimes less than 10,000 won.
18:18So, it's very common to use it.
18:23But, normally, that's not applicable to any organic solvent system.
18:32But, this mercury and the saturated calumet electrode,
18:35it's working a little bit, much better than the silver silver chloride,
18:40the reference electrode.
18:43The electrode basically consists of a platinum wire in the same way as we saw in the previous silver silver
18:50chloride electrode.
18:51I will show you the picture in the next slide.
18:56While dipped into pure mercury, which rests in a paste of mercury chloride and mercury.
19:04You will see here.
19:05Here, mercury accepts electron, mercury ion becomes mercury,
19:11and then mercury chloride accepts two electrons, makes mercury and chloride ion.
19:19Then, this potential can be used, rewritten like this one.
19:27So, the calumet is kind of, instead of pH, it's related to PCl, right?
19:37So, the same thing.
19:39And then, later, if we change the concentration of chloride, then the voltage is changing.
19:50So, normally, we should have this saturated one.
19:54Otherwise, the potential may be changing a lot.
19:58This value and this value, this difference is quite large, right?
20:04So, this is the saturated calumet electrode, SC, and silver silver chloride.
20:13I'm sorry, silver chloride.
20:15And they look almost the same with the porous frit.
20:22No, the frit is kind of a glassy wool.
20:28You may see that.
20:30Sometimes, that can be replaced by some polymer membrane.
20:37And then, there are some other kinds of reference electrode, too.
20:41So, silver chloride, that's what I mentioned before.
20:44And the standard hydrogen electrode, that's most common one.
20:50And that can be replaced.
20:51This one, quite cheap.
20:52And also, calumet electrode.
20:55Those three reference electrodes are very common.
20:59And most textbooks mention those three.
21:03And then, recently, they have some other reference electrode, which can be applied to a special system.
21:12Or just a regular system, including some sulfate ion or any other way.
21:20See, these are all mercury-related or copper-related parts.
21:27So, you can check.
21:30And then, if we change the temperature, the potential has been a little bit changed.
21:38So, if you want to do very accurate experiments with this reference electrode, you might want to keep the temperature
21:49to the set value all the time.
21:54Or you can just calibrate the value with this kind of table.
22:08According to the Encyclopedia of Electrochemistry, that value based on the hydrogen, that's some sort of electron volt or the
22:24voltage due to that hydrogen reaction.
22:28They can be converted to the absolute value.
22:33You know, when we have the hydrogen atom, the electron is confined with the specific distance.
22:43If we kick out this electron to a certain limit that's free from the proton atom, that energy is around
22:5413.6 electron volt.
22:57Correct?
22:58So, this is the absolute value.
23:05So, that matching the proton in the solution system, that can be matching to, here, negative 4.4, negative 4
23:19.44.
23:22So, that standard hydrogen electron electron moving is corresponding to this one.
23:31Because that's in the solution part.
23:35It's much lower than the regular, this value.
23:43Much lower.
23:46So, from this electrochemistry, we can find some value, which can be converted to this physically absolute value.
24:01Okay, that's it.
24:03Then, this is the regular system.
24:07That's what I said before.
24:09So, that between this working electrode and reference electrode, we measure the potential.
24:16And then, the current will be measured by between this working electrode to a counter electrode.
24:24Okay.
24:27Thank you for listening, and we will see something else after this.
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