Preparation and Electrochemistry of Hydrous Ruthenium Oxide/Active Carbon Electrode Materials for Supercapacitor

Amorphous hydrous ruthenium oxide/active carbon (RuO 2 .xH 2 O/C) powders were prepared by a simple procedure based on the sol-gel process. The precursor was obtained hy mixing an aqueous solution of RuCl 3 and active carhon powders at pH 7. When annealing the precursor at 150°C for 7-9.5 h, the RuO 2 .xH 2 O/C powders obtained had the highest specific capacitance. Transmission electron microscopy photographs showed that the RuO 2 .xH 2 O primary particles were about 10-15 nm diam. They adhered to form large porous secondary particles. A modeling capacitor was made with electrodes comprised of RuO 2 .xH 2 O/C powder and 30% H 2 SO 4 electrolyte. At 10-20 wt % ruthenium in the electrodes, the specific capacitance remained almost unchanged at 243 F/g, which included both the electric double-layer capacitance associated with the high surface area of active carbon and redox capacitance associated with ruthenium oxide. About 52% of the RuO 2 in the RuO 2 .xH 2 O/C powders 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 electrode with 21.1% ruthenium, the capacitance attributed to the double layer dropped to 16.8% of the total capacitance. When the electrodes contained ruthenium from 35 wt % to pure RuO 2 .xH 2 O, the specific capacitance increased from 350 to 715 F/g. The specific capacitance was proportional to the mass of the ruthenium in the electrodes. This enabled the specific capacitance to be controlled by changing the mass ratio of RuCl 3 to active carbon in the preparation. Physical properties of the material and electrochemical characteristics of electrodes are also reported along with the capacitor performance.