A First Principles Study of H₂ Adsorption on LaNiO₃(001) Surfaces

The adsorption of H₂ on LaNiO₃ was investigated using density functional theory (DFT) calculations. The adsorption sites, adsorption energy, and electronic structure of LaNiO₃(001)/H₂ systems were calculated and indicated through the calculated surface energy that the (001) surface was the most stable surface. By looking at optimized structure, adsorption energy and dissociation energy, we found that there were three types of adsorption on the surface. First, H₂ molecules completely dissociate and then tend to bind with the O atoms, forming two -OH bonds. Second, H₂ molecules partially dissociate with the H atoms bonding to the same O atom to form one H₂O molecule. These two types are chemical adsorption modes; however, the physical adsorption of H₂ molecules can also occur. When analyzing the electron structure of the H₂O molecule formed by the partial dissociation of the H₂ molecule and the surface O atom, we found that the interaction between H₂O and the (001) surface was weaker, thus, H₂O was easier to separate from the surface to create an O vacancy. On the (001) surface, a supercell was constructed to accurately study the most stable adsorption site. The results from analyses of the charge population; electron localization function; and density of the states indicated that the dissociated H and O atoms form a typical covalent bond and that the interaction between the H₂ molecule and surface is mainly due to the overlap-hybridization among the H 1s, O 2s, and O 2p states. Therefore, the conductivity of LaNiO₃(001)/H₂ is stronger after adsorption and furthermore, the conductivity of the LaNiO₃ surface is better than that of the LaFeO₃ surface.