Facile conversion of the surface layers of graphite to capacitive manganese oxide coatings

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 (C-a) from cyclic voltammetry in 0.5 M NaCl increased to 67.2 mF/cm(2) when the conversion time was up to 120 min, obeying the logarithm law very well. In addition, the capacitance per mass of the coating (C-m) of 362, 385, 380, and 374 F g(-1) 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. (c) 2008 The Electrochemical Society.