Hello Nirav, your cyclic voltammogram seems strange. But the first question to ask is "how clean is your WE?" How did you ensure the effective cleaning of the electrode.

The problem is almost certainly your working electrode (plastic?) and the 30 Ohms of resistance (plus any extra Ru). You've got a fairly large current there--it looks like a bit over 5 mA--and 5 mA across 30 Ohms is s 150 mV error in the applied potential. That is neverminding any odd offset/work function issues that are arising within your working electrode due to that much current passing through.

It definitely looks like a problem with the electrode resistance. You can deal with that by several means. 1) Reduce your scan rate to lower the peak current. 2) Decrease the electrode size to reduce the current. 3) reduce the concentration of ferri/ferrocyanide to 1 mM or less. 4) Use resistance compensation if available.

Also, your initial CV potential should be close to the equilibrium potential (about -0.2 here). For results to match theory, the initial Faradaic current should be close to zero, i.e. no electrolysis occurring at the initial potential.

Hello David O Wipf,

I have already tried by reduce scan rate, reduce electrode size and reduce the concentration but the peak is almost same and looks flatter.

Is there any method for resistance compensation?

Check if your potentiostat has iR (or ohmic) compensation. See this note https://www.gamry.com/application-notes/instrumentation/understanding-ir-compensation/

Otherwise, you need to give more information. All the details of the electrode size, composition, scan rate, and the solution concentration must be provided. You say the electrode is "plastic". That is unclear. What do you mean by a plastic electrode? How did you determine the resistance was 30 ohms.

Is the "plastic electrode" a composite material? 30 ohm is a huge resistance in a potentiodynamic experiment. Composite materials can also show resistances that vary across the electrode surface, particularly if you are close to the percolation threshold for conductivity, and this leads to a distribution of potential and consequently smeared peaks. Also, your concentration of background electrolyte is not really high enough at 1:1. Ferri/ ferrocyanide can be sensitive to surface conditions, especially on carbon materials. Your potential limits also seem rather extreme. At near neutral, or just below neutral pH as I'd expect KCl to be, significant solvent decomposition will be taking place at both ends, further perturbing the local pH in the vicinity of the electrode. Electrode oxidation will also occur at the positive end of your scan which will affect the rate constant for electron transfer.

I have had such issues before. Sometimes it is due to wrong voltage window used.

Hello Danny O'Hare,

Yes, plastic electrode is a composite material. The published paper of it is attached here for your kind reference.

Hello David O Wipf,

Please find the detail, as per your suggestion.

Electrode size : Total size is 3.5 cm x 8 mm. Out of it, the active area is 5 mm x 8mm. (All other part i.e. 3 cm x 8 mm is covered by teflon tap )

Working Electrode Composition : Please find the attached copy of published paper regarding working electrode composition (above said plastic electrode).

Scan rate : 50 mV/Sec

Solution concentration : Ferro/Ferri with KCL (1:1)

We have measured the resistance of plastic electrode i.e. working electrode by using digital multimeter. Two probe of multimeter were put at both end of 3.5 cm long plastic electrode.

Please suggest to solve the issue.

You still haven't given the solution concentration. What is the concentration of each species in mol/L. The ferri/ferrocyanide concentration should be 10 to 100x smaller than the KCl to avoid ohmic drop. Especially since your electrode is rather large for an analytical electrode.

Dear Nirav Gadhiya,

could you, please, show a photo of your cell ?

Hi Nirav,

You can run the same CV with a common working electrode, glassy carbon electrode for example, to confirm that everything in the cell is working fine: electrolyte, concentrations, scan rate.... and then check with your electrode. It seems by the shape that this is probably due to the high resistance. I would not use a concentration of ferro/ferri higher than 10 mM.

Good luck and best regards

Hello Ioannis Samaras,

Please find the attached photos of cell.

Hi Nirav Gadhiya,

the WE (Plastic Electrode) should be corroded (aged, Rcorroded >> 30 Ohms); replace the WE, or renew, it's surface (the corroded WE's "skin"), by reducing the initial diameter, from 8mm, to 6mm. Reduce, also, the concentration of the ferri/ferrocyanide. Check, mainly, lower CV-rates, using the fresh WE.