CV redox peaks and Gamry Potentiometer

[Erbil]

I'm using Gamry Potentiometer for taking CV measurements for finding the appropriate voltage values for oxidation/reduction peaks and Echem Analyst for analyzing. CV measurements has performed on liquid electrolyte in order to find if working electrode accept Li ions. My question is about interpreting the results.

How can I interpret if potential difference equal or below 1V has no oxidation or reduction peak (or has only one of them) while potential sweep between -2V to 2V bring good results but if I change it to 1 to -3 no reduction peak again. Moreover, going to negative values has a bad consequences such broke the working electrode. What does it mean going to negative values?

That was my first question, my second question is: Is it possible perform Chronoamperometry measurements (in other word, simulate) by using existing CV measurements via Echem analyst script editor?

[jketter]

Hi Erbil,

 

I'm really not sure how to answer your questions, but will try.

 

Note: electrochemistry benefits a lot from a class or background in it. If you have not done electrochemistry before, you can read applications notes and get texts, but it is really useful to have a more in depth interaction with a person/persons who are familiar with it. on to your questions.

 

First question: it is not universal but for most researchers more negative potentials are more cathodic and increase the likelihood and rate of reduction. Conversely more positive potentials are more anodic and increase the likelihood and rate of oxidation. The measure of voltage, however, is a relative measure--i.e. voltage is measured at the working electrode (WE) vs. some reference point (hence: reference electrode) and the nature of that reference point affects what reactions can occur at given voltages. As such it is impossible to say what *should* happen at a given potential without complete knowledge of the system: # electrodes, nature of reference, type of working and the [possible] electoactive species and their existing state (+1, 0, -1...).

 

Second question: no. The Echem Analyst is an analysis program, not an experimental one (Framework is the experimental program) so editing Analyst scripts doesn't let you run any experiment. Now, if you mean is it possible to run chronoamp based off values obtained from running CV's then absolutely, yes. You can run CV, to determine which potential(s) to use for a subesequent chronoamperometry experiment then run chronoamp at the relevant potential(s) to get data, maybe to electrolyze or plate or catalyze...

[Erbil]

Hi jketter,

You are absolutely right with your suggestion but I don't know any person who can I interact about this kind of discussions. Therefore, I need to learn myself as much as I can. Firstly, I want to explain what I'm looking for and what I already have.

My working electrode is TiO₂-Deposited FTO/Glass (thin film). I use LiClO₄-PC aqueous solution as an electrolyte. The method is discussed in several papers (doi: 10.1016/0167-2738(86)90214-6). Upon Li⁺ intercalation due to change in structure TiO₂ expected to change a color (from a transparent to grey). However, there is no discernible change in the color that can human eye recognize in my analysis. As a result, I have doubt about the reactions kinetics. So my questions are, as follows.

1) Does seeing a peak in CV curve guarantees that some redox reactions is happening?
2) I've attached a picture of CV curves for various scan rates. Do you agree that it is a quasi reversible system (also discussed in here:https://www.researchgate.net/post/How_to_interpret_CV_redox_peaks_and_is_it_possible_run_a_Chronoamperometry_simulation_from_existing_CV_data)
3) Since current is proportional to scan rate what is the correct way to calculate inserted charges (Qa and Qc -> Integration in Gamry)

4) After a lot of try, I found going to further from -1.7V broke my working electrode. And also, going to away from +1.9V. Can I consider this, as my limitations?

5) What does max current means in CV measurement? Does changing the value effects the shape of the curve?

 

By the way, by simulating I meant to be able to convert CV curve to Current-Time curve since all parameters are known. İn example: In attached image I have CV's for various scan rates. I also now potential differences. So I can obtain the required time for a full cycle and the integration gives me the total charge inserted and extracted from the electrode. Of course, I will not be sure if this value will reflect the truth until I'll sure where/when does redox reactions happening.

 

I'm looking for a guidance rather than answer to my questions. I know that there is a lot, and it is not possible to cover all of them in here. Waiting for your suggestions.

 

Thank your for your interest/help.

 

Question.tiff

Edited February 23, 2017 by Erbil