Enhancement of the electrocapacitive performance of manganese dioxide by introducing a microporous carbon spheres network

Abstract

An amorphous MnO₂·nH₂O/microporous carbon spheres (α-MnO₂·nH₂O/MCS) composite electrode material is prepared by a chemical co-precipitation method. It is observed that the amorphous MnO₂ particles are deposited on the surface of the MCS, which form a network with a uniquely developed three-dimensional open porous system containing macropores, mesopores and micropores. The electrochemical measurements reveal that the composite electrode material presents a much more stable and reversible capacitance behavior compared to the pure α-MnO₂·nH₂O in 1 M of Na₂SO₄ electrolyte. The composite containing 25 wt% MCS exhibits optimal specific capacitance of 218.2 F g⁻¹ at 2 mV s⁻¹, and is still as high as 112.4 F g⁻¹ at 100 mV s⁻¹, while a drastic reduction from 197.0 F g⁻¹ at 2 mV s⁻¹ to only 40.7 F g⁻¹ at 100 mV s⁻¹ occurs for the pure α-MnO₂·nH₂O. The composite also shows a rather high electrode-specific capacitance of 3.13 F cm⁻² and a long cycle life. The remarkable enhancement in the electrochemical performance is mainly attributed to the microporous structure of the MCS contributing to the deposition of MnO₂ particles on the surface of the MCS, and the uniquely developed porous network of the composite facilitating the rapid transport of the electrolyte. These factors result in the high electrochemical utilization of MnO₂, a great reduction of the equivalent series resistance, and hence the relatively high and stable electrochemical behavior.