Oxidation of metallic Mn thin films prepared in butyimethylpyrrolidinium bis(trifluoromethyisuifony)imide ionic liquid and the pseudo-capacitive performance of the anodized oxide electrodes

Metallic Manganese (Mn) thin films were successfully prepared by electrodeposition in butylmethylpyrrolidinium bis(trifluoromethylsulfony)imide (BMP-NTf₂) ionic liquid, which has a very wide potential window extending over the reduction potential of Mn. Potentiostatic, galvanostatic, and cyclic voltammetric methods were performed to anodize the Mn films in Na ₂SO₄ solution. The surface morphology and crystal structure of the obtained oxides were examined by a scanning electron microscope and X-ray diffractometer, respectively. Moreover, their chemical states were also analyzed with an X-ray photoelectron spectroscopy. It was clearly confirmed that the anodization methods could affect the material characteristics of the Mn oxides and therefore their pseudo-capacitive performance. The Mn oxide anodized by the cyclic voltammetric method showed a promising specific capacitance of 355 F/g (measured in 0.1 M Na₂SO₄ solution at a potential scan rate of 25 mV/s). Its capacitance retained ratio after 500 charge-discharge cycles was as high as 94 %.