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

An amorphous MnO2 center dot nH(2)O/microporous carbon spheres (alpha-MnO2 center dot nH(2)O/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 alpha-MnO2 center dot nH(2)O 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 alpha-MnO2 center dot nH(2)O. The composite also shows a rather high electrodespecific 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.