Kinetics of reduction of a RuO2(110) film on Ru(0001) by atomic hydrogen

The kinetics and the mechanism of reduction of a RuO"2(110) film, grown thermally on a Ru(0001) surface, has been studied in the temperature range of 60-200^oC by using an atomic hydrogen flux of 2x10^1^9at.Hm^-^2s^-^1. The reduction kinetics is dominated by the creation of oxygen vacancies at the surface (V"b"r) and bulk lattice positions (V"3"f), and by the subsequent diffusion of subsurface oxygen species (O"3"f) to these vacancies. The activation energy associated with this reduction process equals 0.43eV. At 200^oC, about 10 H atoms are required for the removal of an oxygen atom from the RuO"2 lattice. This value is about an order of magnitude lower when compared with the reduction of RuO"2 by molecular hydrogen under similar conditions. Moreover, the reduction proceeds at least 14 times faster when using highly reactive atomic hydrogen species.