Continuum Transport Modeling of Hydrogen Adsorption, Absorption, and Transport Across Buried Interfaces in Pd and Pd-Composite Materials

Palladium, alone, alloyed with other metals, or as part of a multi-layered structure, has received significant attention as a material for dense-metal membrane separation of hydrogen from synthesis gases derived from thermochemical conversion of hydrocarbon feeds. To better understand the performance of palladium based systems in these applications, we have constructed a COMSOL-based continuum model which describes hydrogen's interaction with their surfaces and transport through their bulk structures. The transient nonlinear model accounts for dissociative adsorption, penetration into the subsurface, diffusion through the bulk lattice, diffusion across buried interfaces in layered systems, and associative desorption. We used the model to interpret thermal desorption spectra of H2 from Pd single crystals and Pd thin films of varying thickness to provide context for the differences observed among these systems.