Quantitative computational screening of Pd-based intermetallic membranes for hydrogen separation

Abstract

One of the most important processes in producing high purity hydrogen is separating hydrogen from a mixture of gas streams. This work looks at intermetallics, stoichiometric compounds of two or more metals, as prospective membranes for these applications. We describe a systematic computational screening approach based on calculation of key properties like solubility, diffusivity and permeability of hydrogen through these materials using quantitatively accurate Density Functional Theory calculations. Solubility was used as a screening parameter and solubility data has been calculated for 78 Pd-based binary intermetallics. Permeability calculations were performed for the shortlisted candidates. After systematically examining all Pd-based intermetallics, no material was found to have higher hydrogen permeability than pure Pd. To investigate the potential influence of hydrogen on the stability of metastable phases, we examined a number of metastable structures of Pd3Mn. Two metastable Pd3Mn phases are stabilized in the presence of hydrogen, but these phases are predicted to have low permeability. We also explored whether an empirical relationship could be found to rapidly predict H solubility in intermetallics using a QSPR approach. Unfortunately, the values calculated using this empirical approach cannot be used to make useful predictions.