Effect of point defects on water adsorption on the ThO2{111} surface: A first-principles computational study

Abstract

H adatom and O vacancy point defects, and their effects on water adsorption, are studied computationally on the ThO2 {111} surface. Comparisons are made with the perfect {111} surface. For H adatoms, two different coverages (1/8 and ¼ ML) are investigated. H adatoms increasingly tend to bond at the nearby Osub position with increasing H coverage. The surface work function linearly increases with H coverage, resembling the classic catalytic transition metals Pt, W, Ni and Pd. For the O vacancies, those formed in the bulk are energetically favoured over those formed at the surface. Due to these point defects, the surface symmetry breaks, and hence water adsorptions at different sites are compared. The adsorption energy is linearly correlated with the bonded Th f band centre in the conduction band, similar to the d band theory for transition metal catalysts.