First principles study of hydrogen adsorption on the surface of PdO(101)

Abstract

Liquid hydrogen storage equipment is insulated using high-vacuum multi-layer insulation. This insulation is manufactured from materials that emit hydrogen gas, which degrades the insulating properties. Palladium oxide is widely used in liquid hydrogen storage as an effective hydrogen absorber. This study investigates the adsorption principle of H2 molecules on the surface of PdO(101) crystals. The mechanism of hydrogen adsorption on the PdO(101) surface was investigated by analyzing the adsorption energy, stable adsorption configuration, and electronic structure of the H2/PdO(101) system. The dissociative chemisorption of hydrogen on the PdO (101) surface has been investigated using temperature-programmed desorption (TPD) and density functional theory (DFT) calculations. It is determined that greater than 90% of the hydrogen dissociation occurs at temperatures below ∼100K. The dissociative chemisorption of hydrogen on the PdO(101) surface was found to occur at temperatures below ∼100K. The majority of the dissociated hydrogen reacts and produces water on the surface during TPD, which desorbs above ∼300K. The results indicate that Pdcus is the most stable adsorption site for H2 on the PdO(101) surface, with an adsorption energy of −0.56 eV, resulting in weak chemisorption. Once the activation energy is reached, H2 and Pdcus form a stable structure. The movement of H atoms between Pdcus sites generates a negative heat of reaction. The adsorption energy of H atoms at the Ocus site (−3.26 eV) is higher than that at the Pdcus site (−3.21 eV). Hydroxylated PdO(101) promotes water production. The combination of H atoms and hydroxides to produce water overcomes the potential barrier of 0.69 eV, resulting in the production of Pd and H2O.