Electrochemical cyclability mechanism for MnO2 electrodes utilized as electrochemical supercapacitors

The electrochemical cyclability mechanism of nanocrystalline MnO2 electrodes with rock salt-type and hexagonal ɛ-type structures was investigated to determine the relationship between physicochemical feature evolution and the corresponding electrochemical behaviour of MnO2 electrodes. Rock salt MnO2 and hexagonal ɛ-MnO2 electrodes, with fibrous and porous morphologies, evolve into the antifluorite-type MnO2 with a petal-shaped nanosheet structure after electrochemical cycling, similar to that observed in nanocrystalline antifluorite-type MnO2 electrodes after electrochemical cycling. However, a different impedance response was observed for the rock salt MnO2 and hexagonal ɛ-MnO2 electrodes during the charge–discharge cycles, compared with the improved impedance response observed for the cycled antifluorite-type MnO2. A dissolution–redeposition mechanism is proposed to account for the impedance response of the MnO2 electrodes with different morphologies and crystal structures.