Hi everyone! I am working on measuring cyclic voltammetry (CV) and controlled potential electrolysis (CPE) for my cell. I understand the iR drop can be measured by several technics, such as EIS. So, I use an impedance analyzer to obtain the impedance data and plot the Nyquist plot. However, my potentiostat is unable to conduct real-time iR compensation when it takes CV or CPE measurement. Is it correct to correct the applied potential by using E = E0 - iR after the CV data are obtained?
Some people do say compensating iR drop after acquiring CV data measurement is wrong. Some people say conducting real-time compensation is also wrong. I am not sure which is the correct way to do iR compensation. I really need some advice. Thank you all your help and answers in advance. Thank you!
Dear Wei,
Whether you can correct for iR-drop in a meaningful way depends on the types of reactions you are attempting to study. If the reactions of interest are actively generating electrolyte species, iR-compensation before or after the run may inaccurately distort the voltammogram. However, in most cases the iR-drop across the solvent is essentially constant, meaning that applying the iR-correction to the x-axis of the voltammogram in real-time and after the run ends are equally valid methods.
The "automatic" correction simply applies the equation you outlined in real-time, which is why it is generally required that a method to measure the iR-drop be performed before the iR-corrected measurement. Thus, the real-time program uses this single measured "R" between the WE and RE to apply the correction, which can be accomplished in the same manner manually at the end of the run.
The current-interrupt method was the first widely accepted iR correction methods, the principles of which are detailed here:
Article Automatic ir drop correction for studies of electrochemical systems
Since then, EIS has become the dominant method to measure iR-drop. Hopefully this information is helpful!
Kind Regards,
Matt Glasscott
Hello,
You write "I understand the iR drop can be measured by several technics, such as EIS". This is true. Have a look at the add file: Ohmic Drop Part II: Introduction to Ohmic Drop measurement techniques
You write : "Some people do say compensating iR drop after acquiring CV data measurement is wrong". They are right and it is wrong to correct the applied potential by using E = E0 - iR after the CV data are obtained. Have a look at the Wolfram demonstration https://demonstrations.wolfram.com/CyclicVoltammetryCorruptedByOhmicDrop/ or at the add file "CV Sim: Simulation of the simple redox reaction (E) Part II: The effect of ohmic drop and double layer capacitance".
Most potentiostats now have a method for measuring and correcting the ohmic drop when R is constant.
Best regards
Hello,
I do correct my LSV and CV after acquisition and I have no problem. Why can we not do that?
I do that when I measure the stationary polarisation curves for electroplating bath (e.g. Ni, Au baths...) with low scan rates (1 mV/s).
In these cases, no problem to correct iR drop after data acquisition. In the cases of CV or LSV with higher scan rates, it could be wrong, am I right?
Because linear sweep voltammetry (E(t) = Einit +v t) is no longer linear with ohmic drop (E(t) = Einit +v t -I(t) R)
Hello,
I agree with you Jean-Paul Diard , but when I correct my i vs E curve, I correct with E = E(applied) - R x i for each point of my curve. For a stationary curve, it should be right, is not it? For faster scan rate, I agree, this correct cannot be perform like that. Am I right?
Best Regards
Dear Mr Wang,
If you are comparing CV results for different working electrodes in the same electrochemical conditions and same experimental conditions, there would be no need to consider IR drop compensation because you are going to compare them together in same chemical and electrochemical conditions. But if you want to investigate just on CV curve, in this case you have to consider iR drop. One of the methods to fond out the amount of IR drop is Instant off-potential measurement which applies in field survey of cathodic protection systems by instantaneous zeroing the current for example 2 seconds off and 8 seconds ON and measuring their difference. Take this into consideration that if your test solution has a very low resistance, so, iR drop could be negligible compared to the applied instantaneous potential. By nyquist plot you can measure solution resistance, if it is negligible compared to charge transfer resistance you can neglect it.
Thomas,
I agree, for a stationary curve, for example redox reaction studied on a rotating disk electrode (hydrodynamic CV, with low scan rate) correct each point with E = E(applied) - R x i is right. It is not for classical CV.
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