Sol–gel MnO2 as an electrode material for electrochemical capacitors

MnO2 was synthesized by the sol–gel method. Two forms of MnO2, namely xerogel and ambigel, were prepared by reduction of NaMnO4 and KMnO4 with sodium fumarate. The synthesized products were characterized using X-ray diffraction (XRD), Brunauer–Emmet–Teller (BET), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and chemical analysis. Electrochemical characterization was carried out using cyclic voltammetry by a three electrode system consisting of saturated calomel electrode as reference electrode, platinum mesh as a counter electrode, and sol–gel prepared MnO2 mounted on Ti mesh used as working electrode. Aqueous NaCl, KCl, Na2SO4 and LiCl solutions were used as electrolytes. The ambigel form of MnO2 showed high capacitance compared to that of the xerogel form of MnO2. Maximum capacitance of 130 F/g was obtained at a scan rate of 5 mV/s for the ambigel form of MnO2 in a 2 M NaCl solution. Effect of NaCl concentration on the capacitance of MnO2 was studied. Stability of MnO2 was studied up to 800 cycles.