High-voltage aqueous symmetric electrochemical capacitor based on Ru0.7Sn0.3O2•nH2O electrodes in 1 M KOH

A mild hydrothermal process is applied to synthesize hydrous ruthenium-tin binary oxides (Ru0.7Sn0.3O2 center dot nH(2)O) with good capacitive performance in alkaline system. Then, a symmetric electrochemical capacitor (EC) is fabricated based on the as-synthesized Ru0.7Sn0.3O2 center dot nH(2)O material and 1 M KOH aqueous electrolyte. Electrochemical performance of the symmetric EC is investigated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy tests. Electrochemical tests demonstrate that the symmetric EC surprisingly can operate with a high upper cell voltage limit of 1.45 V in 1 M KOH electrolyte. Maximum specific capacitance and energy density of the symmetric aqueous EC are approximately 160 F/g and 21 Wh/kg, respectively, delivered at a current density of 1.25 A/g. And the specific energy density decreases to approximately 15 Wh/kg when the specific power density increases up to approximately 1,770 W/kg. The promising specific energy and power densities are obtained simultaneously for the unwonted symmetric EC due to its larger operating potential range. Moreover, the symmetric EC exhibits electrochemical stability with 85.2% of the initial capacitance over consecutive 1,000 cycle numbers.