H₂Adsorption On Nb(100)and Nb(110)Surfaces By Using Ab-initio Investigation

Hydrogen (H) is an important element in nature, and Hydrogen (H2) is the lightest gas, which has very strong reducibility. The properties that make it become a natural reducing agent. At the same time, the hydrogen, as a clean energy, is also a very important industrial gas. The interaction between H2and transition metals has attracted more and more attention from the surface scientists because of their importance in both scientific researches and applications. Nb is a kind of important hydrogen adsorbing elements. It is very meaningful for understanding the hydrogen on the surface of the catalyst behavior for us to make it clear on the Nb surface adsorption mechanism.This work adopts the first principle calculation based on density-function theory, studying the interaction between H2and both Nb(100) surface and Nb(110) surface. We have calculated the structure relations with horizontal and vertical H2in different coverages and height symmetrical adsorption sites, discussing geometric structure, adsorption energy, work function and so on. The conclusions we have got from this work could be outlined as follows:Single hydrogen molecules can be adsorbed on Nb(100) and Nb(110) surfaces. The adsorption energy of hydrogen molecule adsorbed on niobium surface horizontally, is significantly less than the hydrogen molecule adsorbed on the surface vertically, which shows that hydrogen molecule level adsorption is more stable than vertical adsorption. For Nb(100) surface, the adsorption energy and geometric structure are changed little along with the impact of coverage change. Hydrogen molecules prefer occupying on the top site. On the hollow site and bridge site, the adsorption phenomenon is not very obvious. For Nb(110) surface, the adsorption effect varies with coverage dramatically. Hydrogen is favored to adsorb on the hollow site of Nb(110) at the low coverage, while H2can't adsorb on bridge site. At the low coverage, adsorption effect becomes stronger on hollow site, while weaker on top site.