Using first-principles calculations to predict surface resistances to H2 transport through metal alloy membranes

The net resistance to hydrogen transport through defect-free metal membranes includes intracrystalline resistance associated with diffusion of H through the bulk of the membrane and other resistances associated with surface processes. We introduce quantitative modeling methods based on plane wave density functional theory calculations that assess the relative role of intracrystalline and surface resistances for membranes made from metal alloys. To demonstrate the method, we examine the permeation of hydrogen through Pd75Cu25 films as a function of film thickness, temperature, feed pressure, and transmembrane pressure drop. For membranes that are 1 μm thick, resistances associated with surface processes play a crucial role at all temperatures lower than ∼700 K.