Fig. 4

a Cyclic voltammetry (CV) profiles of the OMC-700, OMC-800, OMC-900, OMC-1000, and HOPC electrodes at a scan rate of 2 mV s⁻¹ using the three-electrode configuration and b corresponding specific capacitance. c CV profiles of the HOPC electrode in the symmetric two-electrode supercapacitor at scan rates varying from 2 mV s⁻¹ to 100 mV s⁻¹ in 6 M KOH aqueous electrolyte. d Charge-discharge curves at different current density from 0.5 A g⁻¹ to 10 A g⁻¹. e Specific capacitance calculated from the discharge curves from the charge-discharge testing. f Ragone plots showing the energy density as a function of power density