I understand that electrodes have different resistance but not quite sure if it's safe to assume that the overpotential of an electrode with resistance of 4 ohms and compensation of 50% would be comparable to the one with 2 ohms of 100%.
And is there maximum/optimum least square smoothing? Since a graph would scatter if it's overly compensated but would look ok using the smoothing technique, not sure how much I can manipulate the least square point value.
I am using CHI Electrochemical Analyzer.
1. The iR compensation in a voltammetric experiment is something about the potential drop in solution (electrolyte), not about the potential drop in electrodes. In an electrochemical cell a potential is measured between WE and RE and is reported vs RE: the electrolyte is supposed to be at 0 V (in fact it is possible to ground the solution using a Pt electrode). This is true if no current is passing through the cell (at OCP). If a small current is passing through the cell, the potential profile in solution is modified: the RE potential vs solution is always constant, but the solution potential has a variation in the space between WE and CE; the absolute potential of RE now depends on its position in solution.
I suggest you to observe how the potential profile changes when a current is passing through the cell (black line in Fig.4 and Fig. 5 from:
https://www.comsol.com/blogs/does-the-current-flow-backwards-inside-a-battery/ ).
If, by some method, the solution resistance between WE and CE is measured, iR is the potential drop in solution, in the space between WE and CE. If the three electrodes in a cell are equidistant, then iR is also the potential drop in solution in the space between WE and RE (or a good approximation for it). This iR is subject to compensation.
2. Smoothing (even at high values) is an accepted processing method: you may "manipulate" the record. Sometimes the record is incorrectly processed near the low and the high potential limits (if the record is a CV and the software is not well prepared for this task). In practice use smoothing only to eliminate the measurement noise: compare the two records -after and before processing- to observe/avoid artifacts.
Dr. Cornel Radu Thank you so much for this. I totally thought wrong about the iR but this was such great help.
Although, specifically, I was wondering as to how to compare my electrodes (overpotential) properly since I'm using 2 different materials. Both would have resistance of 3-4 ohms (varying), as you've mentioned having the same equidistant 3-electrode set-up, but one would scatter at 90% compensation and the other at approximately 80% as you can see in the images.
Browsing through Youtube, one tutorial (Autolab - Nova 2), mentions that the best practice is compensating for 90-95% mentioning 90 ohms. Using a CHI Electrochemical Analyzer, mine would come to 3-4 ohms and previous seniors would compensate around 90-95% of 1-2 ohms.
I'm not sure if I was supposed to compare it:
(1) all having the same iR compensation with less smoothing needed (all of them at 80%)
(2) all having same iR compensation with higher smoothing for some (least square point)
(3) where the data points of each material would not scatter (90% vs 80% etc.) since I'm not sure if or which of the 3rd or 4th picture would be comparable to the 1st one. 2nd and 4th picture are the same electrode but at different iR compensation, 80% & 85%, respectively, and smoothed at the 3rd & 5th image (least square point of 21 and 47, respectively) or
(4) where they would supposedly have the same ohmic resistance compensated (all specifically 2.9 ohms for example)
1. I suggest you to observe Fig. 3 a) in this paper
Article A highly-efficient oxygen evolution electrode based on defec...
and to use the same method to compare your electrode materials, i.e. to compare the potential needed to achieve a given small current (10 mA is also good for you, but you can also choose 15 or 20 mA).
2. Your potentiostat indicates a resistance of 4 ohm for the compensation scope. iR=4 ohm x 0.050A = 0.2 V (it is a max. value). This value is very small and I think you may ignore any need for iR compensation.
3. Alternative method for comparison: read this discussion
https://www.researchgate.net/post/How_to_obtain_onset_overpotential_from_LSV_plot
with my recommendation to use the method associated to the green line.
4. Smoothing has no effect on the proposed procedures to be used for comparison.
5. Observe Fig. 4 a and b in this paper:
Article Electrocatalysis for the oxygen evolution reaction: Recent d...
to understand how important is to use, for comparison, current density vs potential, not current vs potential plots (i.e., be sure that the electrode active surface area is appropriately considered in your analysis).
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