i want to calculate specific capacitance (F/g) from cyclic voltammetry.
cyclic voltaammetry is carried out for five cycles and their graph (except first cycle) is attached here. i used three electrode configuration and to calculate the specific capacitance i used the formula:
Cs = area under the cycle/v*E*m
where, v= scan rate
E= potential window
m= mass of the material
it is clear from CV (in attachment) that each cycle has different area so corresponding capacitance is also different. Cycle 2 give specific capacitance of 212.6 F/g and cycle 5 give 122.1 F/g.
My question is that which value of specific capacitance i have to consider, i.e., of cycle 2 or cycle 5?
Thanks
From the CV response, it is clear that the both the current density and peak potential get altered significantly. But this should not be happened for a good Pseudocapacitor. Also the Specific capacitance value should not change this much extent for different cycles. A true pseducapacitors have satisfactory cycling stability upto 500 or 1000 cycles. You can only observe the change in specific capacitance at different scan rates for supercapacitors. Probably your materials get discharge from the electrode surface or the redox property of the materials get affected during cycling. You need to first settle this issue.
And answer to your question is you have to take the last cycle value where you will observe a steady specific capacitance value. For that you may have to run more cycles where the current response not changed significantly.
Subrata Mondal
Yes during CV material is discharged from the electrode.
Thanks for reply
Hi Sachin Kumar ,
I am not sure if it is a good idea to measure the capacitance using this CV curve because your electrode is showing a lot of activity in the scan range which means it starts to oxidize and corrode from first so in each instant of time your material is changing and the numbers you report are not truly your materials capacitance.
the best condition to use CV curve in order to measure capacitance is the time it is nearly rectangular shaped without showing any activity in the scan range(no peaks), although sometimes people report capacitance from these kind of CV curves in their articles, but it is not really right. maybe it is more prudent you measure capacitance using GCPL(charge/discharge) test.
Regards,
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