Fig. 4

(a) CV curves of NMCSs electrodes at scan rate of 10 mV s^− 1, (b) CV curves of the NMCSs-600 electrode at different scan rates from 10 to 100 mV s^− 1, (c) GCD curves of NMCSs electrodes at current density of 1 A g^− 1, (d) GCD curves of the NMCSs-600 electrode at different current densities, (e) Specific capacitance of NMCSs electrodes as a function of current densities, and (f) Cycling performance of the NMCSs-600 electrode at current density of 10 A g^− 1 for 10,000 cycles and the inset shows the GCD curves of the first five and last five cycles, with a three-electrodes system in 6 M KOH aqueous solution