In the work, we developed an aqueous symmetric Ru-Cr binary oxide (Ru0.83Cr0.17O2 center dot nH(2)O)-based electrochemical capacitor (EC) with unwonted high operating voltage in 1 M KOH aqueous solution. Electrochemical performance of the symmetric EC was investigated by current-potential response and galvanostatic charge-discharge techniques. Electrochemical data demonstrated that the symmetric EC with a specific capacitance (SC) of ca. 148 Fg(-1) surprisingly can operate in a large electrochemical window of 1.4V in 1 M KOH electrolyte, ensuring that the symmetric EC delivered an energy density of ca. 40 Wh kg(-1). Moreover, the extended cycle life and good power property were obtained meanwhile, indicating that the Ru0.83Cr0.17O2 center dot nH(2)O-based EC is a promising candidate for aqueous symmetric devices with high energy density and desirable power property. (c) 2012 Elsevier Ltd. All rights reserved.