Sticking of H_2 on Oxygen-Covered Surface of Vanadium Doped with Oxygen to Various Bulk Concentrations

The sticking probability of Hz on the surface of polycrystalline V covered with oxygen was examined as a function of oxygen concentration in the bulk metal (0.4 to 3.3 at.%) at specimen temperatures from 200 to 1000℃. At all temperatures examined, the sticking probability was strongly dependent on the oxygen concentration in the bulk.Such correlation between the reaction rate of Hz on the surface and the oxygen concentration in the bulk was attributed to the dependence of concentration of oxygen vacancies (holes in surface oxygen coverage) on the oxygen bulk concentration. The values of sticking probability were relatively high even at the oxygen bulk concentration of 3.3 at.%; the oxygen coverage on vanadium was rather "holey" even at the oxygen concentration close to the solubility limit. The activation energy for H_2 dissociation on such holes in the coverage was evaluated to be 10 kJ/mol H_2