The geometrical surface of the included electrode is 0.45cm² but the active or the real surface of an electrode often differs from the geometrical one.
The current efficiency based on the geometrical value becomes too high and I suspect the active surface has to be much larger.
Dear Dr. Javad Hikmati,
in general, the counter electrode is optimized by increasing its area and facilitating current flowing through the cell. Personally I use Pt electrodes in the form of a flat grid (for samples with the same geometry) and in the form of a cyclindrical grid (for samples of different shapes, eg small cylindrical samples), which are visible in the attached photos. The results were excellent, both in tests of potentiodynamic polarization curves and in EIS measurements.
Best regards, Pierluigi Traverso
Hello Javad Hikmati
I agree with Pierluigi Traverso . The counter electrode (CE) needs to have a bigger surface area (than your WE) to allow current to flow, and so that your results are more precise. I usually use a platinum wire that I coil (in a spiral shape) for a bigger surface area. Just to make sure, have you consider both side of your electrode to determine the surface or is it platinum on one side only?
You can actually calculate the electrochemical surface area using cyclic voltammetry (CV) and a redox probe like ferrocene methanol or ferricynide(III) (or ferrocyanide (II)). For that, you would need to perform a few CVs (at least 4 to have a correct estimation) at different scan rates, and then, depending on the redox probe that you are using, you would need to plot Ipa or Ipc as a function of the square root of the scan rate. This linear fit will allow you to access the electrochemical surface using Randles-Sevcik equation.
https://en.wikipedia.org/wiki/Randles–Sevcik_equation
Best regards,
Marie B.
Please look at the following below links which may help you in your analysis:
http://www.electrochemsci.org/papers/vol11/110604442.pdf
Thanks
Dear Javad,
The active surface area is always larger than the geometric surface area. This can arise from many sources, porosity, microroughness, nanoparticles etc. I have found that if I use polished platinum electrodes (typical for RDE experiments), that the Roughness (Active area/Geometric area) is between 1.5 and 2. On unpolished samples or nanostructured samples, it can be orders of magnitude higher.
Regarding surface area determination, I integrate the hydrogen adsorption peaks during cyclic voltammetry in sulfuric acid solution to determine the area assuming one H adsorbed pr surface site. This method is well-described for platinum, and, as all other methods of surface area determination, has its strengths and weaknesses.
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