Preparation and electrochemistry of hydrous ruthenium oxide/active carbon electrode materials for supercapacitor

Amorphous hydrous ruthenium oxide/active carbon (RuO2. xH(2)O/C) powders we re prepared by a simple procedure based on the sol-gel process. The precurs or was obtained by mixing an aqueous solution of RuCl3 and active carbon po wders at pH 7. When annealing the precursor at 150 degreesC for 7-9.5 h, th e RuO2. xH(2)O/C powders obtained had the highest specific capacitance. Tra nsmission electron microscopy photographs showed that the RuO2. xH(2)O prim ary particles were about 10-15 nm diam. They adhered to form large porous s econdary particles. A modeling capacitor was made with electrodes comprised of RuO2. xH(2)O/C powder and 30% H2SO4 electrolyte. At 10-20 wt % rutheniu m in the electrodes, the specific capacitance remained almost unchanged at 243 F/g, which included both the electric double-layer capacitance associat ed with the high surface area of active carbon and redox capacitance associ ated with ruthenium oxide. About 52% of the RuO2 in the RuO2. xH(2)O/C powd ers was utilized. More than 50% of the capacitance in the electrode with 12 .1% ruthenium was due to the formation of the double layer, but for the ele ctrode with 21.1% ruthenium, the capacitance attributed to the double layer dropped to 16.8% of the total capacitance. When the electrodes contained r uthenium from 35 wt % to pure RuO2. xH(2)O, the specific capacitance increa sed from 350 to 715 F/g. The specific capacitance was proportional to the m ass of the ruthenium in the electrodes. This enabled the specific capacitan ce to be controlled by changing the mass ratio of RuCl3 to active carbon in the preparation. Physical properties of the material and electrochemical c haracteristics of electrodes are also reported along with the capacitor per formance. (C) 2001 The Electrochemical Society.