First principles calculation of hydrogen adsorption, dissociation and diffusion on Cr/Ni/Mn doped α-Al2O3 (0001) surface

Abstract

Cr, Ni and Mn are common impurities observed in Al2O3 tritium permeation barrier in experiments, to acquire influence of these metal impurities on the interaction of hydrogen isotopes with α-Al2O3 surface, energies and geometric structures of H2 adsorption, dissociation and diffusion on Cr/Ni/Mn doped α-Al2O3 (0001) surface have been investigated by first-principles. It's found that Cr and Ni have slight effect on H2 adsorption and dissociation on α-Al2O3 (0001) surface due to the similar adsorption and dissociation behavior and close activation energies before and after doping. On Mn doped α-Al2O3 (0001) surface, the adsorption energies for H2 are close to that on undoped surface, while the lowest activation energies for H2 dissociation and H atoms recombination are 0.32 eV and 0.24 eV, which are obviously lower than that for H2 dissociation on undoped α-Al2O3 (0001) surface. This finding reveals that Mn doping is favor to H2 dissociation and also beneficial to H atoms recombination on α-Al2O3 (0001) surface. The lowest activation energy is 1.36 eV for H atom diffusion from surface to bulk on Mn doped α-Al2O3 (0001) surface and obviously higher than that of H diffusion through RAFM steels measured through H2 gas evolution permeation experiment, indicating that Mn surface doping prevents H permeation in Al2O3 tritium permeation barrier from the view of diffusion activation energy. The results are constructive for optimization the preparation technique of TPBs.