Combining density functional theory and cluster expansion methods to predict H2 permeance through Pd-based binary alloy membranes

First-principles calculations offer a useful complement to experimental approaches for characterizing hydrogen permeance through dense metal membranes. A challenge in applying these methods to disordered alloys is to make quantitative predictions for the net solubility and diffusivity of interstitial H based on the spatially local information that can be obtained from first-principles calculations. In this study, we used a combination of density functional theory calculations and a cluster expansion method to describe interstitial H in alloys of composition Pd96M4, where M=Ag, Cu, and Rh. The cluster expansion approach highlights the shortcomings of simple lattice models that have been used in the past to study similar systems. We use Sieverts' law to calculate, H solubility and a kinetic Monte Carlo scheme to find the diffusivity of H in PdAg, PdCu, and PdRh alloys at a temperature range of 400 <= T <= 1200 K. From these results, we are able to predict the permeability of hydrogen through membranes made from these Pd-based binary alloys. (C) 2008 American Institute of Physics.