Hello

i think there is some oxidation and reduction happening in the material.  But you did not mention anything about the material and the electrolyte. Usually pseudocapacitive material shows such a graph. If your material is something like CNT or graphene, functionalization can lead to small redox peaks and at high scan rates the graph may distort. One more thing is to be noticed is that your working eletrode itself shows fairly high capacitance. You can check for the interaction between working electrode and active material also.

Hello

I am sorry I don't mention the material I used.

The working electrode is graphene synthesized by CVD and electrolyte is 1M H2SO4.

Where can you judge that it has oxidation and reduction reactions?(

A few more questions: (1) What is the substrate of your CVD graphene (Cu, Ni or what) ?  (2) Are you using your CVD graphene whiles still on this substrate ? (3) Was the reference CV obtained with this substrate or another electrode (say another carbon material) ?

If you are using your CVD graphene whiles still on a metallic substrate and the reference CV was not obtained with a sample of this substrate, then my best guess is that your CVD graphene is not uniform over the metallic substrate and exposed portions of the substrate are producing what seems like Faradaic current.

To your question: There is an oxidation peak around 0.3V though with a steady state current and a reduction peak around 0.1V. Note that assuming Cu is your substrate and it is participating in this CV, the following reactions are possible;

Cu 2+ + e  = Cu +       E = 0.159 V vs SHE

Cu 2+ + 2e  = Cu        E = 0.340 V vs SHE

Lastly, If your CVD graphene was actually transferred unto another substrate whose CV is the reference, note that Cu contaminations like you suspect (maybe from the synthesis process), can be responsible for the peaks.

Hello Isaiah

Actually, I use graphite foil as the substrate and also the reference.

As you described

Cu 2+ + e = Cu + E = 0.159 V vs SHE

Cu 2+ + 2e = Cu E = 0.340 V vs SHE

But I am using the Ag/AgCl as the reference electrode. It has a potential difference (0.2V) with SHE. Do you still think that these two peaks come from the redox peaks of copper? Thank you very much.

Hi Arthur,

If only you are convinced that there is Cu contaminant in your graphene sample, then it is likely the peaks are due to Cu redox. Considering your RE, the peak positions will be different but please note that the values above are standard values (under standard conditions). Any deviations from standard conditions (concentration, temperature and pressure) will cause experimental potentials to deviate from ideal standard ones. The purity of the Cu too can cause deviations in the potential positions.

I think you can troubleshoot your system. Try riding your graphene of the Cu impurities and see what happens.

Hi Isaiah

Thank you for your advice.