Phase transition and electrochemical capacitance of mechanically treated manganese oxides

Mechanical grinding (MG) leads to a sequential phase transition of gamma-MnO2 to form the thennodynamically stable alpha-Mn2O3 and, subsequently, Mn3O4 depending on the duration of MG treatment. By MG treatment for 150h, alpha-Mn2O3 became a predominant species. A subsequent transition to Mn3O4 was observed on further MG treatment for 200h. 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 gamma-MnO, left without phase transition. (c) 2005 Elsevier B.V. All rights reserved.