A First Principles Study of H(2) Adsorption on LaNiO(3)(001) Surfaces

The adsorption of H(2) on LaNiO(3) was investigated using density functional theory (DFT) calculations. The adsorption sites, adsorption energy, and electronic structure of LaNiO(3)(001)/H(2) 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, H(2) molecules completely dissociate and then tend to bind with the O atoms, forming two –OH bonds. Second, H(2) molecules partially dissociate with the H atoms bonding to the same O atom to form one H(2)O molecule. These two types are chemical adsorption modes; however, the physical adsorption of H(2) molecules can also occur. When analyzing the electron structure of the H(2)O molecule formed by the partial dissociation of the H(2) molecule and the surface O atom, we found that the interaction between H(2)O and the (001) surface was weaker, thus, H(2)O 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 H(2) molecule and surface is mainly due to the overlap-hybridization among the H 1s, O 2s, and O 2p states. Therefore, the conductivity of LaNiO(3)(001)/H(2) is stronger after adsorption and furthermore, the conductivity of the LaNiO(3) surface is better than that of the LaFeO(3) surface.