Effect of specific surface area on capacitance in asymmetric carbon/α-MnO2 supercapacitors

alpha-MnO2 has been made using a solid state synthesis and the specific surface area then modified through milling. The formation of alpha-MnO2 (specific surface area 96 m(2) g(-1)) has been studied by SEM and powder XRD prior to milling. Electrode films (cast using MnO2, graphite and PVDF) have been investigated using N-2 sorption at 77 K and show a more complex relationship than their parent oxides. Specific capacitances of 235 Fg(-1) were observed in cyclic voltammetry studies in (NH4)(2)SO4 (aq.) electrolyte. Good cyclability was observed in hybrid C/MnO2 cells investigated through both galvanostatic and electrochemical impedance techniques. The specific capacitances of the cells were found to correlate with S-BET of the electrode films and not that of the parent MnO2 powders. (C) 2010 Elsevier Ltd. All rights reserved.