1. The CV analysis gives you an idea which potential range should be chosen for the charge-discharge experiment. You couldn't choose any potential window beyond the range obtained from the CV, as it would mislead you in terms of capacity.

2. The potential range, chosen for CV or charge-discharge, very much depends on the electrolyte to be used. Although you can choose the potential range as long as you get the rectangular shaped CV or proper capacitance.

3. Again, it depends on the electrolyte. But you can choose if you get proper CV or capacitance.

For my case it is actually a three electrode set up, where the working electrode is modified with nanoparticles.

The stable state was achieved in the window of -0.4V to 0.8 V.

Whether this potential window is acceptable?

In 6M KOH electrolyte solution, always negative potential window gives better result for carbon nanofiber in my charge-discharge analysis. Could you please give me any explanation why this is happening?

This is happening for two-electrode and three-electrode systems also, I am getting more confused as the two-electrode system should give more convincing results with a positive potential window. Please answer both of my questions.

A supercapacitor's potential is defined as the voltage across its electrodes in the charging-discharging curve. The voltage across the electrodes rises as the supercapacitor is being charged, and it falls when the supercapacitor is being drained. A negative potential in a supercapacitor's charging-discharging curve shows that the voltage across the electrodes is less than the beginning voltage. This can happen during the discharge phase, when the supercapacitor's stored charge is discharged.