If I do not understand this wrong. I think the concentration is double.

Ip = 268600n3/2AD1/2Cv1/2

• ip = current maximum in amps

• n = number of electrons transferred in the redox event (usually 1)

• A = electrode area in cm2

• F = The Faraday Constant in C mol−1

• D = diffusion coefficient in cm2/s

• C = concentration in mol/cm3

• ν = scan rate in V/s

This is Randles-Sevicik equation. In the solutiong of ferricyanide-ferrocyanide mixed solution, ferricyanide is 5mM and ferrocyanide is 5 mM, potassium chloride is 0.1 M.

Thanks a lot for your answers and discussions.

I dicussed this problem with another professor. He thought when it scan from 0.6V , ferrycyanide is reduced to ferrocyanide and at the same time ferrocyanide is also oxidized to ferricyanide. So the concentration of ferricyanide has been changed to 10 mM.

But it is strange that the detected electrochemical surface area is less than geometric surface area. The result is not accepted.

Thanks a lot for your answer. In solutionf of ferricyanide-ferrocyanide mixed solution, i use C=5mM to caculate the area value. In solution of ferricyanide solution, I also use C=5mM to caculate the area value. But the results are different. How do you give comments on this?

Yeah, you right. I will have a try according to your recommendation. Thanks for your suggestions.

only method  is EIS -  from the calculation of capacitance  in the Warburg region

Thanks a lot. I have soleved it. The method is ok. And the result is approximate to geometric surface area.

To

Willey John

May i know how u solved the problem. bcoz i am also getting the 0.11cm2 for GC electrode

Dear Lavany, you just use only one kind ferricyanide-ferrocyanide. the result is ok.

The electrode geometric area can be lower than the electrochemical surface area, It depends of the type of materials used to make the working electrode, it's different when the glassy carbon electrode is made from nanotubes or carbon fibers, you must think about the working electrode tridimensionality. And evidently in your mix, you have a ferrocyanide oxidation due a potential.  

Thanks for your kind answer.

Dear Yun

We are also admitted to calculate the geometric electrode area of GC using randles equation which results in negative results. Can you please guide us to solve this answer using the same concentration as discussed above in the conversation.

You could use 0.91 M K3Fe(CN)6 +0.1 M KCl, you could substract the background current. And then you could obtain a satisfying result. Good luck.

I have a question about how to recover catalyst that we are going to deposit on GC electrode for ORR/OER? I want to recover that catalyst to do XPS analysis.