Conversion of Chemically Prepared Interlocked Cubelike Mn3O4 to Birnessite MnO2 Using Electrochemical Cycling

Interlocked cubelike Mn3 O4 thin films have been prepared by a simple and low temperature chemical bath deposition method. These interlocked cubelike Mn3 O4 thin films are further converted into nanoflakes of birnessite MnO2 using voltammetric cycling in aqueous Na2 SO4 electrolyte. The process is dynamic potential activated, which causes the formation of sheet-shaped nanoflakes. The films are characterized by X-ray diffraction, field-emission-scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform IR spectrum, and wettability test. Impedance spectroscopy studies revealed that charge-transfer resistance of the birnessite MnO 2 structure has a lower value than that of the Mn3 O 4 structure. The effect of different numbers of potential cycles on structure, surface morphology, valence states, and contact angles has been investigated. During the cycling process, the supercapacitance of manganese oxide increased by more than 10 times. The maximum supercapacitance achieved at 5 mV s-1 is 223 F g-1. The effect of scan rate on the specific capacitance of birnessite MnO2 electrode has been studied. © 2010 The Electrochemical Society