The electrochemical behavior of manganese dioxide based supercapacitor electrocdes was studied by cyclic voltammetry.The peak is not always appear in figure of cyclic voltammetry.How to determine the redox potential ?
I think that there are 3 key parameters that you should optimize, in order to detect redox Peaks in CVs:: 1) the loading amount of MnO2 on working electrode (do you use GCE?), 2) Scan rate (you can go high scan rates such as 2 V/s or 5 V/s or 10 V/s) and 3) electrolyte (di you use KOH?). Good luck.
If you can not observe the obvious redox peaks in MnO2 based supercaps electrodes, it's very normal. I guess you used the K2SO4 or Na2SO4 solution as electrolyte. From 0-1V in a CV pattern, the MnO2 will undergo a series of reversible successive surface redox reactions according to the following equation:
Please read "Manganese oxide-based materials as electrochemical supercapacitor electrodes", "Manganese Oxides: Battery Materials Make the Leap to Electrochemical Capacitors" and "Nanostructured Mn-based oxides for electrochemical energy storage and conversion" for more information.