Figure 4

Performances of NiCo2O4 double-shell sphere-based supercapacitors. (a) CV curves of different samples at a scan rate of 10 mV S−1. (b) Calculated specific capacitances of different samples as a function of current density. (c) Cycling performance of different electrodes as a function of cycle number at 2 A g−1. (d) Nyquist plots of different samples. (It means that the sample was annealed at 300 °C and hydrogenated at 300 °C for D-NiCo2O4–300 °C and D-NiCo2O4–300 °C-H, respectively).