Fig. 3.

a CV curves at a scan rate of 5 mV s⁻¹ within a potential window from 0 to 1 V, b GCD curves at a current density of 1 mA cm⁻², and c areal capacitances at different current densities from 1 to 30 mA cm⁻² of GCC, CNT/MnO₂-25/ECC, and CNT/MnO₂-25/GCC electrodes. d Nyquist plots of CNT/MnO₂-25/ECC and CNT/MnO₂-25/GCC electrodes. Inset: the fitted equivalent circuit. R_s, R_ct, W, and C_dl denote equivalent series resistance, charge transfer resistance, Warburg diffusion impedance, and electrochemical double-layer capacitance, respectively. e Capacitive contribution (gray region) to the total charge storage at 1 mV s⁻¹, and f capacitive (red) and diffusion-controlled (green) contribution versus scan rates of the CNT/MnO₂-25/GCC electrode. g Capacitance comparison of the CNT/MnO₂-25/GCC electrode with previous reports. MnO₂/carbon fiber paper [22], MnO₂/CNT/carbon tape [23], MnO₂/CNT film [24], MnO₂/anodic aluminum oxide (AAO) [25], MnO₂/Ni nanorod array [26], MnO₂/Ni foil [27], MnO₂/CC [15]. h The schematic illustration of the CNT/MnO₂-25/GCC structure. (Color figure online)