Microscopic Insights into Hydrogen Permeation Through a Model PdCu Membrane from First-Principles Investigations

Palladium-based alloys are commonly used in industry as a membrane material for the purification of hydrogen. In this work, we report a systematic theoretical study of all of the processes associated with permeation of H through a model PdCu membrane. The surface of the membrane is modeled using the most stable (110) surface. Our calculations show that the nuclear quantum effects, due to the light mass of the H atom can significantly affect the stability and reaction rates. On the basis of a microkinetic model of the permeation process, we find that the permeation can be limited by diffusion of H in the membrane bulk or the reassociation of H to form H-2 on the permeate side of the membrane depending on the operation temperature and membrane thickness. At typical operating conditions, for membranes thinner than 0,5 mu m, the permeation at high temperature (T > 500 K) is limited by surface processes, whereas at lower temperatures it can be either diffusion-limited or reassociation-limited.