Carbon-coated tungsten and molybdenum carbides for electrode of electrochemical capacitor

New electrode materials for electrochemical capacitor, tungsten carbide WC and molybdenum carbide Mo2C coated by porous carbon, were prepared through a simple heat treatment of the mixture of K2WO4 and K2MoO4, respectively, with hydroxy propyl cellulose. Carbide changed to hydroxide during the 1st charge–discharge cycle in H2SO4 aqueous electrolyte, which showed redox reaction in further charge–discharge cycles, in addition to electric double layers of the carbon formed on its surface. The carbon-coated carbide gave a high capacitance in 1 mol L−1 H2SO4 electrolyte, as about 350 F cm−3 for carbon-coated WC and 550–750 F cm−3 for carbon-coated Mo2C. Coating of carbon inhibits the growth of carbide particles during their formation, of which the small particle size make possible to complete transformation to hydroxides during the 1st charge–discharge cycle, and also disturbs the agglomeration of tungsten and molybdenum hydroxides during charge–discharge cycles, as well as porous carbon coated act as electrode material for electric double layers of electrolyte ions.