Figure 6

(a) Voltammograms recorded for the Ni-foam, NiCo₂S₄, and NiCo₂S₄@PPy nanomaterials at a scan rate of 50 mV s⁻¹, (b) comparison of the GCD curves of NiCo₂S₄@PPy, NiCo₂S₄, and Ni foam at a current density of 2.54 A g⁻¹, (c) CV curves of NiCo₂S₄@PPy electrode at different scan rates, (d) GCD curves of the NiCo₂S₄@PPy electrode at different current densities, (e) plots of specific capacitance and Coulombic efficiency against current density, (f) The plots of i(v)/v^1/2 versus v^1/2 at various potentials, (g) Surface capacitive and diffusion-controlled contribution to the capacitance at various scan rates, (h) cycling life test of the NiCo₂S₄@PPy electrode at a scan rate of 100 mV s⁻¹, and (i) the SEM image of NiCo₂S₄@PPy electrode at a scan rate of 100 mV s⁻¹ after 2100 cycles.