Computational study of hydrogen induced lattice rearrangement and its influence on hydrogen permeance in Pd-Au alloys

Pd-Au alloys are known to undergo lattice rearrangement in the presence of H and exhibit short range order (SRO). Pd-Au alloys also have favorable H permeabilities making them suitable membrane materials for hydrogen separation. In this work a method to study the influence of H induced lattice rearrangement on the H permeability of Pd96Au4 and Pd85Au15 was developed. We used cluster expansion methods in combination with density functional theory and Monte Carlo simulations to predict the extent of ordering induced in the alloys due to hydrogen at various pressures and temperatures. Our calculations predict that H-induced ordering leads to an increase in H solubility and permeability in comparison to alloys that have not been hydrogen heat treated, in agreement with previous experimental results. At 600 K and 1 atm H2, the permeability is found to increase by a factor of 5.4 (2.6) in Pd96Au4 (Pd85Au15) after hydrogen heat treatment (HHT). At higher temperatures, the influence of H-induced ordering is smaller.