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Dissociation mechanism of H₂ molecule on the Li₂O/hydrogenated-Li₂O (111) surface from first principles calculations

Kong, Xianggang, Yu, You, Ma, Shenggui, Gao, Tao, Xiao, Chengjian, Chen, Xiaojun
RSC advances 2017 v.7 no.56 pp. 35239-35250
adsorption, ceramics, dissociation, electrons, energy, gases, lithium, molecular dynamics, tritium
Hydrogen molecules in a purge gas are known to enhance the release of tritium from lithium ceramic materials, which has been demonstrated in numerous in-pile experiments. The static computational results suggest that the molecular adsorption of H₂ on the “ideal” Li₂O/hydrogenated-Li₂O (111) surface encounters high dissociation barriers in various entrance channels. The surface chemical inertness of the plane can be broken by introducing vacancy defects. In the present work, a combination of static DFT calculations and ab initio molecular dynamics has been performed to investigate the H₂ dissociative mechanism. Our theoretical results, that the end-on oriented H₂ could dissociate on the hydrogen monomer vacancy surface with one hydrogen atom ejected into the gas phase by the abstraction channel and the parallel H₂ molecule dissociates on the hydrogen dimer vacancy surface with two hydroxyls forming, suggest that hydrogen vacancy defects facilitate the adsorption and dissociation of H₂ molecule. The presence of the O²⁻ ion induced by the hydrogen vacancy provides some low energy states in which the H₂ electrons can be accommodated. This is very instructive for the comprehension of phenomena that occur during the operation of a thermonuclear reactor.