New information about the electrochemical behaviour of Ru(0001) in perchloric acid solutions

Clean and well-ordered Ru(0 0 0 1) surfaces were prepared by inductive heating in an argon stream. The electrochemical behaviour of Ru(0 0 0 1) was studied with perchloric acid solutions of different concentration. The reversible process at -0.2 V in 0.01 M HClO4, which had been assigned to hydrogen adsorption on an oxide covered Ru(0 0 0 1) surface, is related to OH adsorption as demonstrated by CO charge displacement experiments. While CO adsorption on Ru(0 0 0 1) in 0.01 M HClO4 at -0.27 V leads to a blocking of adsorption peaks, CO adsorption at -0.08 V results in a mixed CO + OH phase, which is not reactive. A voltammetric peak in the hydrogen evolution region is ascribed to OH reduction and hydrogen adsorption, as suggested by CO displacement. This peak is dependent on the pH of the solution and on the presence of specifically adsorbing anions. In contrast to recent reports, surface oxidation of Ru(0 0 0 1) is related to processes involving two electrons per Ru surface atom until the onset of bulk oxidation. (C) 2002 Elsevier Science B.V. All rights reserved.