DENSITY FUNCTIONAL THEORY STUDY OF H2O ADSORPTION AND DISSOCIATION ON Al (111) SURFACE

Comparative study about the adsorption and dissociation behaviors of H 2 O molecule on clean and vacancy defective Al (111) surface was conducted by extensive density functional theory (DFT) calculations, the interaction mechanisms between H 2 O molecule and Al (111) surface were also figured out. Geometry optimization results indicated that H 2 O molecule was apt to be adsorbed at top site on these two kinds of surfaces, whereas, the adsorption configurations, the adsorption type and inclination of H 2 O molecule planes away from the normal were different. The calculated adsorption energies demonstrated that the adsorption of H 2 O molecule occurred more readily on vacancy defective Al (111) surface. The electron density distribution indicated that the vacancy defect enhanced the interactions between H 2 O molecule and surface Al atoms. Further analysis of the density of states (DOS) showed that the vacancy defect increased the number of bonding electrons between H 2 O molecule and surface Al atoms. The detailed exploration of dissociation pathways demonstrated that the dissociation of H 2 O molecule on these two kinds of surfaces was a two-step process: (1) H 2 O → H + OH , (2) OH → H + O . However, for each step the dissociation pathway variations on vacancy defective Al (111) surface were different with those on clean Al (111) surface. Compared with the first step, the dissociation of hydroxyl group into O atom and H atom was kinetically difficult. The calculated lower activation energy barriers on vacancy defective Al (111) surface showed that the vacancy defect had catalytic effect for the dissociation of H 2 O molecule to some extent, especially for the first step.