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

α-MnO2 has been made using a solid state synthesis and the specific surface area then modified through milling. The formation of α-MnO2 (specific surface area 96 m2 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 N2 sorption at 77 K and show a more complex relationship than their parent oxides. Specific capacitances of 235 F g−1 were observed in cyclic voltammetry studies in (NH4)2SO4 (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 SBET of the electrode films and not that of the parent MnO2 powders.