Oxidation of Metallic Mn Thin Films Prepared in Butylmethylpyrrolidinium Bis(trifluoromethylsulfony)imide Ionic Liquid and the Pseudo-Capacitive Performance of the Anodized Oxides

Abstract

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 Na2SO4 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 o f 25 mV/s). Its capacitance retained ratio after 500 charge- discharge cycles was as high as 94 %.