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/Å) 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/Å 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.