Figure 3

Electrochemical performance.

(a), CV curves at a scan rate of 0.2 mV s⁻¹ and, (b), galvanostatic charge/discharge profiles at the current rate of 0.8 A g⁻¹ for the initial three cycles of the S/NP Cu/MnO₂ electrode in the potential window of 0.01–3 V. (c), The reversible capacity retention and Coulombic efficiency of the S/NP Cu/MnO₂ hybrid bulk electrode during the first cycles at 4.2 A g⁻¹ followed by a higher current density of 8.3 A g⁻¹. Inset: SEM micrograph of a S/NP Cu/MnO₂ hybrid bulk electrode after charge/discharge cycling. (d), Charge/discharge profiles of the S/NP Cu/MnO₂ electrode (top) and MnO₂ nanoparticles on Cu foil (middle) and the specific capacities of their constituent MnO₂ as a function of current density (bottom).