First-principles study of palladium-based metal alloys as hydrogen purification membranes

Hydrogen is a good candidate as a future energy source. Current technologies generate hydrogen from hydrocarbons as mixtures with other species like CO and CO2. High flux and resistance to contaminants are required for membranes used to separate hydrogen from these mixtures, as well as other requirements such as long operation standard and low cost. Development of new membranes is hampered by the large effort and time required to experimentally develop and test these membranes. I show how first-principles Density Functional Theory (DFT) calculations combined with coarse-grained modeling can be used to predict the performance of metal alloys as H2 purification membranes. I introduce quantitative modeling methods based on DFT calculations that assess the relative role of surface resistances for metal alloy membranes, the bulk permeation rate through alloy membranes, and the selectivity of metal membranes. In my study, I first examined the importance of surface processes for thin membranes. The possibility of using new materials such as PdCuAg ternary alloys and metal sulfides as hydrogen purification membranes were examined. Finally I predicted the absorption and diffusion of another atomic species, carbon, in the membranes. My methods require no experimental input apart from the knowledge of the bulk crystal structure, so they provide an alternate way to explore new materials as hydrogen purification membranes. My results will be a useful guide for future experimental studies.