If you have an FRA available, you can measure the cell impedance at a high frequency range (20kHz - 1kHz depending on the system). The resistance you can compensate is no more than the real axis high frequency intercept Z_Re(inf) of the Nyquist plot of Z_Re vs. Z_Im.

If you do not have an FRA, you can use the "Positive Feedback" gadget in the software (at least in GPES) to find the approximate value to compensate for. It displays a potential step waveform which gives you an idea of the cell response. As you carefully increase the amount of compensation, you will see this waveform start ringing, which is the point where your potentiostat is starting to see only the capacitance of your system with no resistance to dampen the oscillations. You should lower the amount of compensation to a point where this oscillating behaviour is barely seen. This procedure is also described in the Autolab manual (I assume you are using an Autolab. If not, you can do the same with a waveform generator and an oscilloscope).

I suggest doing these determinations at or around the open circuit voltage to keep the DC current as low as possible.

You can, but you mustn't. At least in GPES there is a tool for "compensating" for the iR-drop, but, in my opinion, this is not the right way of doing it.

The iR-drop changes the scan speed during the measurement, rendering simple analysis impossible. You can check this by subtracting the current multiplied by the solution resistance from your applied potential. You must either compensate for the iR-drop during the measurement, or come up with a numeric model for your system that incorporates the iR-drop.

In the case of Butler-Volmer kinetics, the boundary condition solution is quite tedious, since the current to be solved also serves as an input in the applied potential. I have found this to be computationally expensive, since it requires a non-linear solver.

Dear Tuomas,

I appreciate your answer. One issue is to measure again the samples by compensate the internal resistance. For this I should determine before the exact resistence of the electrolyte which is the resistance between WE and reference electrode right? There is a methode/standard procedure do do that?

If you have an FRA available, you can measure the cell impedance at a high frequency range (20kHz - 1kHz depending on the system). The resistance you can compensate is no more than the real axis high frequency intercept Z_Re(inf) of the Nyquist plot of Z_Re vs. Z_Im.

If you do not have an FRA, you can use the "Positive Feedback" gadget in the software (at least in GPES) to find the approximate value to compensate for. It displays a potential step waveform which gives you an idea of the cell response. As you carefully increase the amount of compensation, you will see this waveform start ringing, which is the point where your potentiostat is starting to see only the capacitance of your system with no resistance to dampen the oscillations. You should lower the amount of compensation to a point where this oscillating behaviour is barely seen. This procedure is also described in the Autolab manual (I assume you are using an Autolab. If not, you can do the same with a waveform generator and an oscilloscope).

I suggest doing these determinations at or around the open circuit voltage to keep the DC current as low as possible.

The equation is Butler-Volmer is complex in case the GPES, used this equation E=E_t -+iRs where R_s is resistance solution, follows the advice Tuomas . To measure the resistance of the solution using Fe (CN)_6^{+2 /+3} 1 mM electrolyte used and also to determine the active area in this electrolyte.

you proceed with mesurement of resistance by impedancemetry ( use more than 30 KHz )and then you correct the potential in data.

I agree with Tuomas's opinion.

Another way to analyze the voltammogram is numerically simulating the curve with the model including the solution resistance. I don't know about GEPES nor NOVA specification, however, the program is not complicated but is a simple expansion of normal cyclic voltammetry.

But. I recommend reexamination using an ultramicroelectrode.

I know it's of little help to suggest a different way of doing the experiment in the first place, as you are asking about compensation in the analysis, but it may be worth looking at using a Nanoflex electrode. This gives the performance of a nano band electrode, but can be used with a conventional potentiostat. I would expect IR drop to be very significantly reduced (though I have no direct experience). www.nanoflex.com

IR drop is created due to very low conducting solvent (THF) used in the present study. This IR drop may not be eliminated by using microelectrode. High resistance offered by the solvent is the main source for IR drop. Hence R of the electrolyte can be measured by impendance spectroscopy or by EIS with appropriate frequency. Then calculate IR drop and make the correction using ORIGIN or MATLAB.

In the presence of the uncompensated resistance the voltage at the electrode surface changes nonlinearly with time (instead of linearly in the absence of R), therefore you cannot correct for the IR simply by correcting the voltage. There are three ways to deal with it:

1) use ultramicroelectrode to avoid IR

2) use digital simulations for the exact experimental conditions (with Rsol)

3) use convolution and correct the convoluted current (see old paper by Savéant, the reference is in Bard-faulkner)

All these methods are well documented in the literature. There are no other ways to deal with the problem.

This is with reference to the answer given by Dr. Andrzej. I want to know how microelectrode helps to avoid IR drop. If so what is the reason for that? Moreover when electrolyte property, it self, brings out high resistance how it can be eliminated by using microelectrode?

The use of a ultramicroelectrode makes the absolute magnitude of the current very small. That's all. Electrochemistry in low-conductive media, such as organic solvents with low supporting electrolyte concentration, polymer electrolytes, have been extensively studied using ultramicroelectrodes.

So, the use of an ultramicroelectrode ensemble, such as Nanoflex, does not help iR drop problems.

hello,

i have a new question. first i want to explain my set up and problem simply. i am studying on PEM fuel cell electrocatalysis. and i make cyclic voltammetry analysis in order to determine the electrochemical surface area. i have 3 electrode cell. my reference electrode is Ag/AgCl and i fill it with 0.1 M KCl. my electrolyte is 0.1 M HClO4. and i load 28 micrograms/cm2 on GC electrode. my area on GC electrode is 0.1963 cm2.

in order to get the full ads/des of H2 on the electrode i have to decrease the potential to -400mVs. however most of the papers i have read they sweep the potential between -200mV to 1200mV.

i understand that i have an additional (?) resistance in my system. i changed the concentration of the electrolyte and the solution of the reference electrode. i have get the best results with 3.5 M KCl and 0.5M HClO4. but i have alreasy sweep between -300mv to 1200mV. i have already used H2SO4 but i could not decrease that resistance.

what should i do??

thank you.

I mean what should i do to decrease the voltage in my system?

If an estimate of resistance is available it is possible to correct voltammogram for IR drop using the formula described e.g. in Saveant's book Elements of molecular electrochemistry p. 24. A nice Labview routine is available from M.J. Shaw

(https://decibel.ni.com/content/people/roadchem?view=overview), section

Dimensionless and Convoluted Cyclic Voltammograms. Be, however careful when using this software, the E-I data have to follow suitable sign convention.

Yes, there is an ir drop compensation in GPES' software. In "Data presentation" window, you should select "Edit data" and, inside of the pop menú, there is "iR drop compensation". This option opens a small window where you have to type the resistance value... but you have to know this value previously and it only modifies the registered CVs. I don`t know if you can introduce a resistance value before running the scan (there is a option in the "manual control" window but I nerver used it).

this is the response to Parashuram Sahoo subquestion. With microelectrodes, much smaller currents flow for a given electrode process compared to conventionally sized electrodes. Smaller current i, hence smaller iR product.

Thank you Jan for your nice explanation.

IR drop post acquisition processing is available in the eL-ChemViewer software.

More information at:

http://www.mdpi.com/1424-8220/14/8/13943

Free download from:

www.lchem.cz/elchemviewer.htm

 `Hi every one Iam padmini Iam working on La2NiMnO6 Oxygen evolution reactions.

In Nova software I have doubt on how to compensate the iR and how to caluclate the ohmic resistance for that. I was searching the google but I couldnot get the correct approach . I can understand the iR but by using software how can i get my E-iR corrected data.I am looking for the answers.Please any one help me out wth this.

Thanks in advance.

You can easily determine the solution resistance using impedance spectroscopy.

The cyclic voltammograms usually cannot be corrected after registration (see e.g. Saveant's papers for corrections for IR using semiintegration for diffusing speccies). Plan your experiment to avoid IR, use smaller electrodes, positive feedback in the potentiostat, and Luggin capillary.