Rabbia Naz there are several ways to do this:
One is to use the Randles-Sevcik equation for a reversible system such as ferrocyanide/ferricyanide. To do this, you must know the diffusion coefficient of the electroactive species, either ferro or ferricyanide. The diffusion coefficient can be determined experimentally either by cyclic voltammetry, by chronoamperometry, or by another method. In the case of voltammetry and chronoamperometry, you need to know the area of an electrode such as a platinum electrode, whose area you determine using 0.5 M sulphuric acid. With the electrical charge obtained from the hydrogen adsorption or desorption peaks, you can calculate the area and then with that area, calculate the diffusion coefficient of the ferro or ferri, recording voltammograms or chronoamperograms on the same platinum electrode. After you have the diffusion coefficient, you record voltammograms on the same reversible system with your electrode under study and obtain the area using the same Radles-Sevcik equation. The problem with this method is that you must have a reversible system, something that can be affected when experimental aspects are neglected, such as the distance between the electrodes or the supporting electrolyte, which generates ohmic drop and the voltammograms look like those of a quasi-reversible system, which deviates the results from the real value of the diffusion coefficient. One way to check if you have reversible system conditions is to verify that the difference between the anodic and cathodic peaks is 59 mV, and that the ipc/ipa ratio is 1.
Here are some articles on this:
Article Determination of the Real Surface Area of Pt Electrodes by H...
There is a way to determine the electrode area without depending on the value of the diffusion coefficient. You should use the current values at different scan rates in a region of the voltammogram where there is no faradaic current contribution. In this region, the measured current mostly corresponds to the charging current of the electrical double layer. You will get different values of current versus scan rate. If you get a line, the slope is the capacitance (in farads, F). Then you should look for the specific capacitance of your electrode material, which should be reported (F/cm2). Dividing the capacitance by the specific capacitance gives you the electroactive area of your electrode. The disadvantage of this method is that it requires finding the standardized specific capacitance value of the electrode material.
Article Physical and Electrochemical Area Determination of Electrode...
https://www.researchgate.net/deref/https%3A%2F%2Fosf.io%2Fgyexd%2Fdownload
Anyway, here is a link to an article where several methods to determine the electroactive area are presented:
Article International Union of Pure and Applied Chemistry Physical C...
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