50-100 μm-thick pseudocapacitive electrodes of MnO2 nanoparticles uniformly electrodeposited in carbon nanotube papers

Abstract

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.