Dear Sonal Gupta

The CV curves are overlapped. Therefore, it is hard to see how they are changing cycle-to-cycle. Can you tell what exactly do you mean by the "variation" or highlight it on the scheme?

Thank you for your reply Maciej Cieplak

I have marked the region in the attached image.

Dear Sonal Gupta

This peak at about 0.2-0.4 V vs. AgCl it is rather not polythiophene oxidation. It is to sharp and appears at to low potentials. Polythiophene oxidation you may observe on your CV above 0.5 V.

Therefore, I see two possible sourses of this peak:

1) Your monomer may contain some other than thiophene moiety, that is electroactive, i.e., some metal center, pyrol, carbazole, phenol, aniline???

It seems resonable because this additional peak is increasing with each cycle.

2) Your polymerization solution is being contaminated with electroactive species. Is such a case you should find source of this contamination. Check H1 and C13 NMR of your monomer to see if it is pure? Clean carefully your electrochemical setup. Once I had problem with hexaferrocyjanide redox probe that went into the frit of the reference electrode (this frit became blue). Later this frit was slowly realising Fe ions to the solutions and additional peak at 0.2 V vs. Ag/ACl was appearing even if Fe2+ shouldn't be present. Change working electrode, etc.

With best,

Thank you Maciej Cieplak for your useful suggestions.

I will work and find out the reason.

Dear Sonal Gupta

Along side the suggestion of Maciej Cieplak , I would actually interpret the peak at 0.4V as the oxidation of the thiophene monomer because bear in mind that the potential of the reference electrode can also change if the electrode is leaking or old... So maybe use another Ag/AgCl reference electrode to confirm the potentials that you are reading.

I agree with your suggestion.Thank you Amir Bzainia