To overcome the tradeoff between the gravimetric capacitance and loading density of pseudocapacitive MnO2, we electrodeposited MnO2 nanoparticles on the carbon nanotube (CNT) surfaces in 18-37 μm-thick self-supporting CNT papers. We examined the electrodeposition conditions including constant potential, constant current, and potential pulses, and obtained MnO2-CNT hybrid electrodes containing MnO2 nanoparticles uniformly deposited at 60-90 wt% with an expanded CNT matrix. The MnO2-CNT hybrid electrode with a thickness of 62 μm, density of 1.09 g cm-3, areal mass of 6.75 mg cm-2, and 82 wt% MnO2 load showed a total gravimetric capacitance of 120 and 51 Ftotal gelectrode-1, volumetric capacitance of 131 and 56 Ftotal cm-3 and areal capacitance of 0.81 and 0.34 Ftotal cm-2 at scan rates of 2 and 200 mV s-1, respectively. The large thickness, moderately high mass density, and fairly conductive CNT matrix realized such high values of gravimetric, areal and volumetric capacitances that are important for practical devices.
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