Hydrogen evolution reaction on RuO2 electrodes in alkaline solutions

The hydrogen evolution was studied on ruthenium oxide electrodes prepared by thermal decomposition of RuCl3 and by electrocodeposition of RuO2 powder with nickel in 1 M NaOH at 25 degrees C and 70 degrees C. It was found that RuO2 electrodes prepared by thermal decomposition are slightly more active than the RuO2-Ni electrode. The obtained electrodes were characterized by extremely high capacitances of similar to 0.5 F cm(-2), high charging currents (0.6 A cm(-2) at 1 V s(-1)), high surface area and high electrocatalytic activity. Two semicircles were observed on the complex plane plots obtained from ac impedance measurements. The equivalent model containing a series connection of two parallel CPE-R elements was used to explain the results. The second semicircle was connected with the hydrogen evolution reaction and the first one was attributed to the surface porosity. Double layer capacities obtained by ac impedance spectroscopy and by cyclic voltammetry are similar.