I'm testing supercapacitors with some carbon material as electrode, a spike shows up at 1V at slower scan rate in the CV (normalized by scan rate).
My understanding is that the spike is either due to pseudo capacitance or the selected scanning window is too large.
The test is conducted with symmetrical two electrode setup and the electrolyte is 6M KOH.
I have very limited experience in electrochemical test and supercapacitors. Can someone point me to the right direction?
Any help is appreciated! Thanks
The spikes or rather the increase in specific capacitance with the voltage level is observed in carbon based super capacitors because of the porous nature of the electrodes. As you can see, the increasing specific capacitance for higher scan rate is also following the same trend. At lower scan rate, the variation of capacitance is prominently visible.
Dear Yijun Chen
Pleased mention which scale it is for voltage axis. I think it is due to start of oxygen evolution reaction (OER) and at lower scan rate you are holding the electrode for longer time at higher potential, so more current for low scan rate.
All the best.
Best Regards,
Bapi
Dear Geethi Krishnan, if this increase is common in carbon based supercapacitors, what is the reason behind it?
Dear Bapi Bera, the voltage is scanned from 0 to 1 V and the spike occurs at 1V, is this voltage high enough for OER to happen in 6M KOH? How could I confirm if it's OER?
Dear Yijun Chen , Pleased mention which scale it is for voltage axis (Ag/AgCl or RHE).
To confirm if it is OER, go further positive potential and see the onset potential of OER.
One time you go higher positive potential, you will find out is it Spikes or starting of OER.
All the Best.
Bapi Bera it was two electrode system so it’s the device voltage, I don’t have a reference electrode here
Dear Yijun Chen , a porous carbon electrode comprises of several pores having varying range of size and shape (macro,micro, nano pores..). The accessibility of some of the sub nano meter pores is possible only at higher voltage and slower charging rates. The increase in accessibility implies increase in available surface area which in turn leads to increase in capacitance.
Many references are available in the literature. Please check whether the following reference is helpful.
Suss, Matthew E., et al. "Impedance-based study of capacitive porous carbon electrodes with hierarchical and bimodal porosity." Journal of Power Sources 241 (2013): 266-273.
Yijun Chen This is not a cyclic voltammetry record, because you use only two electrodes and the graph is charge (not current) vs voltage. For a 1 V applied voltage, the anode potential is close to 0.3V and the cathode potential is close to - 0.3V: the voltage is close to 1,2 V where the water electrolysis starts (this may explains the "spike"). For 0.1 V applied voltage, the capacitor is completely charged. I suggest you to try a true CV (verify is a redox process is present or not at low potentials).
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