Faradaic contributions in the supercapacitive charge storage mechanisms of manganese dioxides

Electrode materials based on four different manganese dioxides, amorphous, birnessite, crytpomelane and spinel were fabricated and their electrochemical behaviors compared in two electrolytes, Li2SO4 and (NMe4)2SO4. With respect to the structural characteristics of the various prepared MnO2, these electrolytes can be differentiated by their cation size. Voltammetric studies showed that these electrode materials presented distinct capacitive behaviors depending on the electrolyte used. Modeling of the electrode capacitances measured at various scan rates allowed to discriminate the surface and material bulk contributions to the overall specific capacitance of the fabricated electrodes.