First principles study of V/Pd interface interactions and their hydrogen absorption properties

Abstract

Hydrogen permeation through vanadium/palladium (V/Pd) metal composite membranes is an effective and practical method of separating hydrogen from gas mixtures. In order to gain an insight into the relation between the interfacial structure and hydrogen adsorption/diffusion properties of the catalytic Pd layer bonded to the metal membrane, and then improve the ability of the alloy membrane to purify hydrogen, the first principle based on the density functional theory is used to study the hydrogen adsorption/diffusion behavior at the V/Pd metal composite membrane interface. The results show that because the charge density at the V/Pd interface increases with the V/Pd bonding increasing, the dissolution energy of hydrogen atom (H) increases with it approaching to the interface, and it has the highest dissolution energy near the V/Pd interface (0.567 eV). Hydrogen migration energy barrier calculations show that compared with the maximum energy barrier for horizontal diffusion of H along the V/Pd interface (0.64 eV), the H vertical V/Pd interface energy barrier (0.56 eV) is small, thus H tends to migrate vertically V/Pd interface and diffuse from the Pd layer to the V substrate side. As the hydrogen solvation energy of the Pd layer at the V/Pd interface (0.238 eV) is higher than that on the V membrane side (–0.165 eV), H will gather on the V film side of the interface, which is easy to cause hydrogen to be embrittled. Calculations of Pd/Fe doping of the V matrix show that comparing with the undoped energy barrier (0.56 eV), Pd/Fe doping can significantly reduce the maximum energy barrier (0.45 eV/0.54 eV) in the diffusion path of the interface, which is favorable for hydrogen permeation and diffusion. And the doped interface can inhibit the interdiffusion of V layer and catalytic Pd layer to a certain extent, which improves the structural stability of the composite film.