Mechanisms for adsorption, dissociation and diffusion of hydrogen in hydrogen permeation barrier of α-Al2O3: The role of crystal orientation

The mechanisms of adsorption of hydrogen on alpha-Al2O3(1-102) surface and of its diffusion in bulk are investigated, using first principles thermodynamics and kinetics, and compared with similar results obtained for the diffusion of hydrogen on alpha-Al2O3(0001) surface. Because of the different oxygen environments on both surfaces, the H binding energies on the (1-102) surface are 0.3-1.2 eV smaller than in the (0001) surface. The H-2 binding energies on (1-102) and (0001) surfaces are resembled. We have identified four main mechanisms, leading to dissociation of H-2, H migration on the surface, H diffusion into and inside the bulk. Equilibrium constant and activation barrier show that H-2 dissociation is the most favorable process and significant diffusion of H into the bulk can occur more readily from the (1-102) surface compared to the (0001) surface. Based on the hydrogen interaction with alpha-Al2O3(1-102) surface, a mechanism of alpha-Al2O3 suppressing H-permeation is identified. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.