First principles calculation of hydrogen adsorption, dissociation and diffusion on Cr/Ni/Mn doped α-Al_2O_3 (0001) surface

摘要

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 alpha-Al2O3 surface, energies and geometric structures of H-2 adsorption, dissociation and diffusion on Cr/Ni/Mn doped alpha-Al2O3 (0001) surface have been investigated by first-principles. It's found that Cr and Ni have slight effect on H-2 adsorption and dissociation on alpha-Al2O3 (0001) surface due to the similar adsorption and dissociation behavior and close activation energies before and after doping. On Mn doped alpha-Al2O3 (0001) surface, the adsorption energies for H-2 are close to that on undoped surface, while the lowest activation energies for H-2 dissociation and H atoms recombination are 0.32 eV and 0.24 eV, which are obviously lower than that for H-2 dissociation on undoped alpha-Al2O3 (0001) surface. This finding reveals that Mn doping is favor to H-2 dissociation and also beneficial to H atoms recombination on alpha-Al2O3 (0001) surface. The lowest activation energy is 1.36 eV for H atom diffusion from surface to bulk on Mn doped alpha-Al2O3 (0001) surface and obviously higher than that of H diffusion through RAFM steels measured through H-2 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. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.