First-principles studies of gas molecule adsorption on a LaB6(100) surface

Abstract

First-principles calculations were employed to study the molecular and dissociative adsorption of CO₂, H₂O, O₂ and N₂ on a LaB₆(100) surface. The adsorption energy calculation results indicate that these gas molecules can form thermodynamically stable adsorption structures. Dissociative adsorption is always accompanied by more electron transfer compared to molecular adsorption, which is one of the necessary conditions for dissociation to occur. Bader charge analysis indicates that the adsorption of gas molecules on the LaB₆(100) surface is always accompanied by electron transfer from the surface to the adsorbed molecules. This electron transfer forms a dipole moment from the adsorbed molecule towards the surface, leading to an increase in the work function of LaB₆(100). This mechanism is a crucial aspect of the LaB₆(100) poisoning effect. Additionally, LaB₆(100) sometimes exhibits a certain degree of resistance to poisoning. In such cases, after the adsorption of gas molecules, local regions of the LaB₆(100) surface become negatively charged, which counteracts the poisoning effect to some extent. Using electronic density of states and electron localization function analyses, we examined the nature of the chemical bonds. It was found that La tends to form non-covalent bonds with the adsorbates, whereas B tends to form covalent bonds with them. The 2p orbitals of B play a significant role in the formation of these covalent bonds in most cases.