Hydrous ruthenium oxides (RuO2 center dot xH(2)O) with ultra-stable cycling ability were directly prepared on tantalum substrate by thermolysis of RuCl3 in heated steam environment. Characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and wettability test, the RuO2 center dot xH(2)O showed lower crystallite and better hydrophilic than that are prepared by thermolysis in air. Their specific capacitance is twice as great as the latter. Moreover, this capacitance maintains nearly 100% after 100,000 cycles and its coulombic efficiency is 100% due to its good balance of electron/proton conductivity. (C) 2014 Elsevier B.V. All rights reserved.