Crystalline tungsten oxide mixtures WO3-WO3 0 5H(2)O prepared by microwave-assisted hydrothermal (MAH) synthesis at 180 C for various periods show capacitive-like behavior at 200 mV s(-1) and Cs approximate to 290 Fg(-1) at 25 mV s(-1) in 0 5 M (HSO4)-S-2 between -0 6 and 0 2 V Oxide rods can be obtained via the MAH process even when the synthesis time is only 0 75 h while WO3 05H(2)O sheets with poor capacitive performances are obtained by a normal hydrothermal synthesis process at the same temperature for 24 h The aspect ratio of tungsten oxide rods is found to increase with prolonging the MAH time while all oxides consist of WO3 and WO3 05H(2)O The oxide mixtures prepared by the MAH method with annealing in air at temperatures <= 400 degrees C show promising performances for electrochemical capacitors (ECs) Due to the narrow working potential window of the oxide mixtures an aqueous EC of the asymmetric type consisting of a WO3-WO3 05H(2)O anode and a RuO2 xH(2)O cathode with a potential window of 1 6V is demonstrated in this work which shows the device energy and power densities of 23 4W kg(-1) and 5 2 kW kg(-1) respectively (C) 2010 Elsevier B V All rights reserved