Phase transition and electrochemical capacitance of mechanically treated manganese oxides

Mechanical grinding (MG) leads to a sequential phase transition of γ-MnO2 to form the thermodynamically stable α-Mn2O3 and, subsequently, Mn3O4 depending on the duration of MG treatment. By MG treatment for 150 h, α-Mn2O3 became a predominant species. A subsequent transition to Mn3O4 was observed on further MG treatment for 200 h. The particle size of the resultant manganese oxides was reduced to as small as 20 nm after 300 h of MG treatment. The change in the specific capacitance of manganese oxides obtained was monitored by XRD and electrochemical experiments. It was observed that the specific capacitance of MG-treated manganese oxides depends on the amount of γ-MnO2 left without phase transition.