With regard to interpreting the CVs you provided: We'll probably need some more info before we can say what the peaks are. What's in the membrane? What kind of working electrode are you using? What scan rate are you using?

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More broadly though, when investigating new electrochemical systems the first thing one generally does is find the steady-state potential window limits. This is done by collecting successive CVs at wider and wider potentials until you reach the positive and negative potential window limits: where the current density exceeds 0.4mA/cm^2 (I believe it's 0.4mA/cm^2 – check the literature to be sure). Note: It may take 10, 20, even 100 cycles before the cell reaches steady-state. But that info in and of itself will be useful, and you'll just have to test it to find out how long it takes.

The next step would depend on the purpose of the cell. Are you trying to measure the concentration of some chemical? Measure the discharge rate of a battery or capacitor? Measuring the impedance? Something else? There are several different tests you could use (chronoamperametry, chronocoulometry, impedance spectroscopy, etc) each with infinite combinations of settings. The best one to use, and the settings to use with it, will strongly depend on the purpose of your cell.

Just to let you know that this system is comprised of a Pt counter electrode, Ag/AgCl reference electrode, my working electrode with the material in question, and my electrolyte (KOH in this case - 0.1M)

I am aware that the system appears to change and therefore experiences some irreversible change, after a number of cycles this change ceases to occur and the CV scan remains essentially constant for a large number of cycles before beginning to change once more as my material begins to degrade.

Actually this curves doesnt give and distinctive signal, I mean which is the lowes which is the highest. for example the first one(I mean scan 5) chronoamperometry will give signal for first material, therefore I think you can choose 200mV and go on experiment by adding other concentrations. of course you can choose 150mV this will give also a signal.

Hi thank you for your input. However I do not quite understand.

Would I be choosing 200mV for the chronoamperometry? As if you are saying this is the case it would not work for me as the redox reaction I am initiating does not occur at such low potentials.

Perhaps I should put the direction on this plot, the CV runs clockwise in this case, so the 200mV peak is in the reverse direction.

Dear Dr. Neeves,

Your CV study is not giving a clue about the oxidation potential of your compound. If you would like to working on the oxidation side I can recommend to you, youe can take your CV curves between -0.25 (or 0.0) V and 1.4 or 1.5 V depending on your working electrode and working media pH. If you use carbon based electrodes you can use 1.8V for finishing potential. If I can see right from your CV you have some small wave at about +1.0 V. If it is true (you should confirm it with wider potential range studies) you can use this potential for your studies. But I can recommend you the optimization of pH and nature of the buffer type studies. The best pH and supporting electrolyte should be selected for further studies. In this supporting electrolyte and pH the obtained peak or wave potential can be used for your further studies.

Dear Matthew, I am physicist - theorist and now I was not able to prompt you the optimal conditions of the parameters that are going to measure. I'm able only to interprete the beahvior of the complex dielectric permitivity with respect to frequency and temperature.

There is no distinctive signal in the oxidation part of your CV. Is it possible to scan further with your new working material until +1.4V? May be you generate a new compound which is reduced during the reverse scan in two waves. If you work in amperometry at +0.2V, you will work in reduction mode, but if you didn't generate the oxidized species before, it will not work.

Usually, the first step of a chronoamperometry experiment should be set to about 200 mV past the forward wave observed in a CV. In your case, that might run into the solvent limit so you might want to stick to a potential of about 1.0 Volts. That might not get you complete oxidation if the E°' value is close to 1.0. If you have slow electron-transfer (looks possible), then 1.0 might be sufficiently past E°' to be OK.

If you integrate the chronoamperometry curve (i.e. chronocoulometry) you would get a value for the amount of charge passed which will be better than what you could get from CV. Since you have a film, radial diffusion at a small electrode would not be a problem. Chronoamperometery of a known standard would give you electrode area so you can get charge density for the film, assuming reproducible coverage.

To get charge from a CV, usually one looks at the area under the curve in a CV after converting the x-axis to time using the scan rate. The problem lies in extrapolating the baseline so as to take into account the charging current.

Double potential step chronoamperometry might be useful to determine how much charge recovery you get after a forward-reverse cycle, in which case I would set the first potential to 1.0V and the second to -0.3 V.

I hope this helps!

sorry Matthew not +200mV it can be -200mV or lower(mathematically -250, or -300 etc)

I guess you are studying oxygen evolution?

Then your window to the right could be a bit bigger for the CV.

you have some peak at the right end.

If you study hydrogen evolution then you need to go much further to the right,

also for oxygen reduction, but I am not exactly sure.

The return peak is maybe stripping or reduction of the oxide that is formed during the forward scan.

More info would be helpfull, if you can give us

The common chronoamperometry's theory is not applicable, because you don't have a redoxcouple in your solution.

You need to know what you want to study. With CV you can guess what happens at your electrode. Amperometry is probably for a performance test.(E.G. 1hour at 1.2 V)

Because the reactions are solid state reactions all Theory is not trivial. Maybe you can argue also with some adsorption.

With regard to interpreting the CVs you provided: We'll probably need some more info before we can say what the peaks are. What's in the membrane? What kind of working electrode are you using? What scan rate are you using?

--------

More broadly though, when investigating new electrochemical systems the first thing one generally does is find the steady-state potential window limits. This is done by collecting successive CVs at wider and wider potentials until you reach the positive and negative potential window limits: where the current density exceeds 0.4mA/cm^2 (I believe it's 0.4mA/cm^2 – check the literature to be sure). Note: It may take 10, 20, even 100 cycles before the cell reaches steady-state. But that info in and of itself will be useful, and you'll just have to test it to find out how long it takes.

The next step would depend on the purpose of the cell. Are you trying to measure the concentration of some chemical? Measure the discharge rate of a battery or capacitor? Measuring the impedance? Something else? There are several different tests you could use (chronoamperametry, chronocoulometry, impedance spectroscopy, etc) each with infinite combinations of settings. The best one to use, and the settings to use with it, will strongly depend on the purpose of your cell.

salam

the potential that you must choose is between 0.9 and 1.1 (E1/2 peak)

your new material is it a conducting polymer

pth i have a work about this

[email protected]

It is not clear why you think you should perform chronoamperometry on you electrode material. Is it to characterize the electrode behaviour? or to measure an analyte(s) with the electrode?. Either of these require different approaches. What supporting electrolyte have you used to obtain your CV and at what pH? Both of these, as well as the scan rate and potential range will have effect on your CV responses. You need to get these right, otherwise the response you have obtained may be meaningless and may not reflect the true behaviour of your electrode. As someone already suggested, what you are measuring may just even be oxygen reduction. This may happen if you have not adequately purged your solution with nitrogen or argon to remove oxygen from solution. Not knowing all these things makes it difficult to give you any concrete suggestions. Also you have two peaks, one anodic and the other cathodic. Which one of these do you want to monitor by chronoamperometry? If you want to get a general chronoamperometry over the whole potential range, you could do this by stepping the potential between the initial and final potential with a residence time of 30s or so. I suggest you read the book: Biomembrane Electrochemistry edited by Martin Blank and Igor Vodyanoy - Chapter 23 has some stuff on CV and EIS that you may find useful. Otherwise, other books focusing on electroanalytical techniques will be equally useful.

Hi all, my apologies for the slow reply I have been in a laboratory without internet connection for the last two days!

Thank you all for your kind replies this is indeed very useful for someone inexperienced with the interpreting CV data in detail! Since this will be a very long reply, I will try to reply individually to avoid confusion :-)

@ Prof. Ozkan

I believe I will have to find an alternative electrolyte to perform a wider range since I have an issue with oxygen evolution at greater positive potentials (I am not studying oxygen evolution, simply the redox behavior of the mixed metal oxide deposited on my working electrode.) I will need to select a suitable supporting electrolyte (if this might help) which will not interact with my electrode - so it will have to have large anions and cations to avoid competition between the intercalating species. Do you have any suggestions? (The electrolyte being used is simply 0.1M KOH solution)

@ Prof. Nigmatullin

Would you please be able to elaborate what calculations I might make from my experimental data as it is at the moment or otherwise? Certainly the permitivity and kinetics are of concern to me.

@ Dr. Blankert

Unfortunately I believe I will have to find an alternative electrolyte to perform a wider potential range since I have an issue with oxygen evolution at greater positive potentials. Oxidation does seem to occur at potentials greater than 0.6V but is very slow until approximately 0.8v, beyond which oxygen evolution becomes apparent :-(

@ Dr. Shaw

I believe I do have slow electron-transfer, and as you suspect I can not perform a wider potential range since I have an issue with oxygen evolution beyond +1.0V. In fact when using longer CA investigations I have found (since posting) that oxygen evolution becomes apparent on the surface of the electrode beyond 0.8V.

Integration of the CA curve is exactly what I have been doing prior to investigating my CV behavior in more detail. I shall stick with this since it is more accurate. The setup is a custom made cell so I have designed this and deposit the films with specific area. The nature of my experiments call for double potential step CA which is indeed what I have been performing. The issue I have found is presumably what you describe as the charge recovery - in oxidation the layer or any subsequent devices constructed consume more current than in reduction. My suspicion is that this is again due to oxygen evolution - should I simply integrate the reduction curve (since it is the smaller value) and present this as the charge capacity?

Yes extremely helpful thank you :-)

@ Dr. Boyd

This is indeed very interesting as I have not considered the methods you suggest. I have performed some potential dependent CA, and was not sure how to use my findings - i.e. if simply selecting the value I found to perform well being sufficiently scientific, hence my questions.

The solvent is UHP water.

The electrolyte is 0.1M KOH

I would like to attempt another electrolyte but my issue is that for comparison either 1M or 0.1M KOH is the generally employed standard. I have been looking to test 1M Lithium Perchlorate in PC however my setup needs some modifications before I can do this.

The scan is very similar and does not seem to be effected by scan direction. This one is clockwise.

Scan rate is 10mV/s - I have attempted 100mV/s, 50mV/s, 25mV/s also. the 25mV is very similar but the 50 and 100 display even less information. Slower scans experience oxygen evolution and early film breakdown.

It is a mixed metal oxide film approximately 150nm thick deposited on an ITO glass electrode.

I expected it to be similar to the single metal oxide which is the major constituent in this film (80%) - this material has oxidation peaks at approximately +0.3 and +0.7V and reduction peaks at -0.2V and -0.6V - the +0.7 and -0.2 being the more major and apparent peaks.

@ Dr. Schmachtel

I am not studying any gas evolution, only the redox behavior of the mixed metal oxide film which is deposited upon my electrode.

As you have guessed, the use of CA thus far has been a performance test. By oxidizing and reducing my film I modify its bandgap absorbance and as such its optical transmittance (which is simultaneously being measured using a custom in-situ broadband spectroscopy setup). The change in transmittance, charge consumed, speed of reaction and charge capacity are all of concern. I would like to extract more data on the electrical bandgap, permitivity and reaction kinetics if possible, once I have decided upon the appropriate potentials for CA.

@ Dr. Sheppard

I have no membrane, the working electrode is a mixed metal oxide deposited on a glass ITO electrode.

Scan rate is 10mV/s - I have attempted 100mV/s, 50mV/s, 25mV/s also. the 25mV is very similar but the 50 and 100 display even less information. Slower scans experience oxygen evolution and early film breakdown.

I work on electrochromics, so by oxidizing and reducing my film I modify its bandgap absorbance and as such its optical transmittance (which is simultaneously being measured using a custom in-situ broadband spectroscopy setup). The change in transmittance, charge consumed, speed of reaction and charge capacity are all of primary concern. I would like to extract more data on the electrical bandgap, permitivity and reaction kinetics if possible, once I have decided upon the appropriate potentials for CA.

@ Dr. Bahoul

The working electrode is a mixed metal oxide deposited on a glass ITO electrode.

@ Dr. Adeloju

I wish to characterize electrode behavior.

The solvent is UHP water, and the electrolyte is 0.1M KOH, so the PH is 13

I have been performing double potential step CA since bothe oxidation and reduction are to be studied.

Thank you for your literature suggestion I shall look at acquiring that hopefully tomorrow.

@ Dr. Micheli

This is interesting, I shall attempt this later on this evening and see what I obtain. Thank you :-)

Again thank you to everyone for your answers, they have been most useful, I shall update once I have tried any suggestions you have made.