A novel chemical synthesis of Mn3O4 thin film and its stepwise conversion into birnessite MnO2 during super capacitive studies

A novel chemical successive ionic layer adsorption and reaction (SILAR) method has been developed for the deposition of Mn3O4 thin films. The as-prepared Mn3O4 thin film showed ideal capacitive behavior after potential cycling within the range of -0.1 to +0.9 V/SCE in a 1 M Na2SO4 electrolyte. Analysis of the X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectroscopy (XPS) during the cycling showed that the as-prepared crystalline Mn3O4 film was electrochemically oxidized to nanowalls of pseudocapacitive birnessite MnO2 film using potential cycling. The water contact angle changed from hydrophilic to superhydrophilic since the surface morphology converted from interlocked cubes to porous nanowalls. Impedance spectroscopy studies revealed that charge transfer resistance of the birnessite MnO2 structure has higher value than that of the Mn3O4 structure. Thus nanowalls of layered birnessite MnO2 are a promising electrode material for electrochemical capacitors. The effect of scan rate on the specific capacitance of so formed birnessite MnO2 has been investigated. It exhibited highest specific capacitance of 314 F g(-1) in 1 M Na2SO4 electrolyte at 5 mV s(-1) scan rate and 90% stability after 10,000 cycles. (C) 2010 Elsevier B.V. All rights reserved.