Metal oxide perovskite materials show promise for use as hydrogen separation membranes, but metal oxides can dehydrate in the presence of hydrogen to the point of decomposition. The stability of a material in the presence of hydrogen is necessary for an effective hydrogen separation membrane. The stability of a mixed phase metal oxide perovskite (BaCe0.85Fe0.15O3-δ-BaCe0.15Fe0.85O3-δ) was investigated using first-principles thermodynamics calculations based on density functional theory to examine the possible reduction processes on the surface of the material. It was found that for either phase of the material, the loss of H2 becomes thermodynamically favorable over the formation of oxygen vacancies once oxygen vacancy defects exist on the surface. Additionally, both phases of the material become more stable with respect to the dehydration or loss of oxygen with increasing concentrations of surface oxygen vacancies. Under the conditions of commercial hydrogen production (~400-1100 K), it is more thermodynamically favorable for H2 to desorb from the BaCe0.85Fe0.15O3-δ phase. Examination of the atomic-scale structure indicates that the degree of coordination of surface metal atoms in this material may control the stability of the material in reducing environments.
Keywords: DFT; hydrogen; membrane; perovskite oxide; separation; stability.