Electrocatalysis of H2 oxidation on Ru(0001) and Ru(10−10) single crystal surfaces

The hydrogen oxidation reaction kinetics have been measured as a function of temperature on Ru(0001) and Ru(10−10) surfaces in H2SO4 and HClO4 solutions by using a rotating disk electrode. The reaction is essentially under kinetic control at temperatures between 25 and 60 °C. It has a pronounced structural sensitivity, having higher rates on a Ru(10−10) than on a Ru(0001) surface. The reaction is strongly inhibited by Ru oxide formation at low overpotentials for hydrogen oxidation, which causes a current peak in the polarization curve and a negligible oxidation current at large overpotentials. The structural dependence appears to be predominantly determined by the properties of the oxidized surfaces of Ru(0001) and Ru(10−10). The kinetics are faster in H2SO4 than in HClO4 solution due to a slower surface oxidation in the former acid. The apparent electrochemical activation energy for the Ru(0001) surface is about 120 kJ mol−1, while 80 kJ mol−1 is observed for the Ru(10−10) surface. The exchange current densities of 0.13 and 0.16 mA cm−2 at 40 °C for Ru(0001) and Ru(10−10), respectively have been determined from the linear part of the polarization curves. The origin of the structural effects on the hydrogen oxidation kinetics on Ru surfaces has been discussed. In sharp contrast to hydrogen oxidation, the hydrogen evolution kinetics shows a very small structural dependence.