Metal membranes play a vital role in hydrogen purification. Defect-free membranes can exhibit effectively infinite selectivity for hydrogen. Membranes must meet multiple objectives, including providing high fluxes, resistance to poisoning, long operational lifetimes, and low cost. Alloys offer an obvious route to improve upon membranes based on pure metals such as Pd. Development of new membranes is hampered by the large effort required to experimentally test membrane materials. We show how first principles calculations and coarse-grained modeling can accurately predict H2 fluxes through binary alloy membranes as functions of alloy composition, temperature, and H2 pressure. Our approach, which requires no experimental input apart from knowledge of bulk crystal structures, is demonstrated for PdCu alloys, which show nontrivial behavior due to the existence of fcc and bcc structures and have potential for resistance to sulfur poisoning. First, we used plane wave Density Functional Theory to study the binding and local motion of hydrogen for representative alloy compositions. This data was used to generate comprehensive models to predict hydrogen solubility and diffusivity in CuPd alloys over a wide range of compositions, temperatures and pressures. The accuracy of our approach is examined by a comparison with extensive experiments using thick PdCu foils at elevated temperatures performed by our coworkers at the National Energy Technology Laboratory. These experiments also demonstrate the ability of these membranes to resist poisoning by H2S. We extend these methods to develop means to rapidly screen metal additives which when alloyed with CuPd would enhance the net hydrogen permeability. We performed in depth analysis of hydrogen solution and diffusion in CuPdRh alloys using methods analogous to those for binary CuPd alloys. Finally, ongoing work on CuPdRh and CuPdZn alloys is also discussed.
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