Dear Vadiyar,

Thanks for your question.

Basically, if you have obtained nonlinear GCD curves for your materials, it means that your materials are not capacitive in terms of charge storage. As a result, the non-linear GCD curve CANNOT be used for capacitance analysis.

I know that there are many publications in high profile journals claiming high specific capacitance values for materials exhibiting non-linear GCD curves, particularly those showing a plateau on the GCD curve. Such behaviour is of that of battery electrode and should not be used for capacitance analysis. These papers are really misleading the community.

The correct way for analysing your data is the specific charge capacity. This is easy to measure from the GCD curve as follow.

Specific charge capacity = current x time / electrode mass.

Note that you cannot use the GCD curve of a single electrode to calculate the energy value. The energy calculation must be based on GCD curves recorded from a two electrode cell.

However, if you obtained linear or approximately linear GCD curves, they can be used for capacitance analysis. The equation is very simple as follow.

Specific capacitance = current x time / (potential range x electrode mass)

Again for calculation of energy, it can be based on the linear GCD curves of a two electrode cell. From the GCD curves, you can obtain the specific capacitance of the cell using the equation below.

Cell specific capacitance = current x time / (maximum cell voltage x total mass of both electrodes)

The cell specific capacitance can then be used for calculation of specific energy by the following equation.

specific energy = specific cell capacitance x (cell voltage)2 / 2

I shall emphasise again that if your GCDs are non-linear, particularly if they show a plateau, you should not attempt to calculate capacitance.

I hope the above is of some help to you.

(For publication purposes, you can claim your materials to be suitable for supercapattery, instead of supercapacitor.)

Dear Prof. George Zheng Chen,

Thank you for your answer. Really, it is helpful for calculation of specific capacity charge instead of capacitance. 

Sir What is the unit for specific capacity charge whether it is mAh g-1 or C g-1

Thank you once again

Madagonda Vadiyar: Both units are for specific charge capacity, although mAh/g is more commonly used.

Dear Prof. George Zheng Chen Sir,

Thank you for your kind help and answer. 

I agree with Prof. George Zheng Chen Sir

Prof. George Zheng Chen,

Thanks for nice explanation of this fact.

Can you further explain

How to calculate the slope of discharge curve using origin or area under discharge curve?

Could you please drop me the link(s) of paper(s) that use this formula in supercapacitor or supercapattery application. Thank you.