Preventing H2S poisoning of dense Pd membranes for H2 purification using an electric-field: An Ab initio study

High purity (> 99.9%) H2 is required across a breadth of fields from the energy, chemicals, and semiconductor processing industries and the current multi-step pressure swing adsorption processes are both high cost and inefficient. Dense Pd membranes are highly permeable and selective to H2, but their deployment after steam methane reformation (SMR) is hampered by their vulnerability to poisoning by S species (e.g., H2S). Here, we use Density Functional Theory (DFT) to investigate the use of an applied electric field (AEF) to prevent S poisoning by altering the energetics of H2S adsorption and decomposition on the Pd(111) surface. We find that strong, negative AEFs (<-1.5 V/angstrom) prevent H2S adsorption without negatively impacting the adsorption or intercalation of H2 into the Pd membrane. Microkinetic simulations of the surface with high strength AEF show long-term (> 80 days) stability even under high 1000 ppm H2S exposure at -1.5 & -2 V/angstrom E-fields. Although the field strength identified here may be challenging to achieve in operation, these findings suggest that E-fields could provide a pathway for gas phase membrane protection in general and, possibly, more cost-effective H2 purification via stable Pd membrane systems.