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 F_total g_electrode⁻¹, volumetric capacitance of 131 and 56 F_total cm⁻³ and areal capacitance of 0.81 and 0.34 F_total 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.