Facile Conversion of the Surface Layers of Graphite to Capacitive Manganese Oxide Coatings

Abstract

A simple method to convert graphite to manganese oxide coatings is presented in this paper. The as-grown coatings were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analyses, and thus verified to be largely amorphous manganese oxide. The coatings behave typically capacitive in various neutral aqueous solutions of alkali metal salts, e.g., 0.5 M LiCl, 0.5 M NaCl, and 0.5 M KCl. The capacitance per geometric electrode surface area from cyclic voltammetry in 0.5 M NaCl increased to when the conversion time was up to 120 min, obeying the logarithm law very well. In addition, the capacitance per mass of the coating of 362, 385, 380, and was achieved with the manganese coatings grown for 10, 30, 60, and 120 min, respectively. Electrochemical measurements demonstrated evident differences in capacitive behaviors of the coatings in the three above-mentioned electrolyte solutions. It was confirmed that this facile conversion of the surface layers of graphite offers a simple and efficient formation of thin-film supercapacitors promising for industrial applications.