Hi everyone. I make linear sweep voltammetry measurements for a Pt electrode in sulfuric acid. I think I need to make some iR compensation during the measurements. My potentiostat has such a function. For the iR compensation test I need to specify a test potential (the potential at which no electrochemical reaction occurs). How to determine it? Is it the same as the open circuit potential? Can I measure it using open circuit potential - time technique? Which time interval to choose (minutes, tens of minutes, or something like until getting the steady value). And the last question, how the iR compensation technique is related to the data obtained using the electrochemical impendace spectroscopy (EIS)? Is the resistance compensated using the iR compensation tool is the same as the one determined from the EIS? Or vice versa. Can I use the resistance determined using EIS to make a manual iR compensation? Thanks!
The potential at which no electrochemical reaction occurs means no FARADIC reaction takes place. For your case, any potential before water reduction wave starts.
You can use the resistance determined using EIS to make a manual iR compensation
Hello Ievgen,
What potentiostat and software are you using? Sometimes there are different methods of implementing the iR compensation.
Here are a few examples of manufacturer guidelines:
http://www.gamry.com/application-notes/instrumentation/understanding-ir-compensation/
http://www.ecochemie.nl/download/NovaTutorials/iR_compensation_tutorial.pdf
https://www.basinc.com/manuals/EC_epsilon/Setup/ir_comp
http://www.bio-logic.net/wp-content/uploads/Application-note-27.pdf
You may wish to look at Bard & Faulkner, Electrochemical Methods, Section 15.6, pp 645 - 650, particularly section 15.6.3, Electronic compensation of resistance:
http://glearning.tju.edu.cn/pluginfile.php/74331/mod_resource/content/0/%E5%8F%82%E8%80%83%E4%B9%A6/Electrochemical_methods_2ed_2001_-_Bard_Faulkner.pdf
+1 Jules answer, but a bit of a note: it is possible to measure Ru at any potential, as in most systems it does not change--iR compensation done either by positive feed back or, in most cases, post run correction require that. In cases where Ru does change during an experiment (more common in low ionic strength solutions) then more dynamic techniques like current interrupt are necessary to accurately compensate for iR drop.
Note that all methods for doing iR comp have drawbacks associated with them, so you need to balance those against your reason for doing iR comp in the first place.
Many potentiostats offer the option to correct for the uncompensated resistance during the measurement, often dynamically. While it seems attractive, we caution that the potentiostat may run into resonance, which would render the recorded data unustable and may even harm the hardware or electrodes if no voltage limits are set in the potentiostat. I recommend data analysis after extraction of LSV rather than doing iR compensation during the experiment. Here are the procedures:
The Ohmic resistance is corrected according to E=E(RHE)-iR, where E is the iR-corrected potential, E(RHE) is the measured potential with respect to RHE, i is the measured current, and R is the uncompensated resistance as determined by EIS. The typical EIS method for resistance determination is conducted by collecting the ac impedance spectra from 100 kHz to 0.1 Hz with a voltage perturbation of 10 mV versus open-circuit potential. The uncompensated resistance is either found as the magnitude of the impedance where the phase angle is closest to zero in a Bode plot or equivalently as the real part of the impedance where the imagi-nary part of the impedance is zero in a Nyquist plot. While direct determination from the measured graphs is often sufficient for compensation, higher accuracy can be achieved by fitting the measured impedance spectrum to a suitable circuit model (most commonly the Randles circuit.
How to perform manual iR compensation? For eg. 80 %, 90 % iR compensation. Thank you
Yeah, I have the same query as like Priyanka Aggarwal asked. I was reading a paper where author said that the iR drop was compensated 85% for OER and 90% for HER. What doses it actually mean and how to perform it?
Thank you.
After going through extensive literature survey, Md Mahbubul Alam I got my answer. Actually, the percentage of iR compensation should be decided in such a way that the shape of LSV or CV don't get disturbed (For instance, getting 2 current values at a particular potential). Then, R known as solution resistance is calculated from Nyquist plot while current (i) is obtained from LSV or CV. After this, we simply multiply i * R * x% (x represents the percentage value of iR compensation). We calculate iR corrected overpotential as niR = Ew/o iR (vs RHE) - 0 - (i*R*x%) (0 is the equilibrium potential in case of HER).
The selected potential should be in the non-FARADIC region.
You can use the resistance determined using EIS (measured at OCP) to make a manual iR compensation.
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