Origin of H2 Formation on Perfect SrTiO3 (001) Surface: A First principles Study

We systematically investigate saturated adsorption of H atoms on the SrTiO3 (001) surface to reveal the origin of H-2 molecule formation using density functional theory methods. We find that H atoms prefer to adsorb on O sites at low coverage, while adsorbing on Ti sites at higher coverage. Interestingly, H on O sites and H on neighboring Ti sites (H-Ti) dimerize to form H-2 molecules provided that enough electrons are doped in the conduction bands of SrTiO3. Bader charges and electronic structures show that negatively charged H-Ti plays a decisive role in the formation of H-2. Both calculated hydrogen coverage and electron density at saturated adsorption are in good agreement with experimental values. Our results provide an illuminating instance of H-2 formation on perfect oxide surface, which shall pave the way to further understanding the detailed mechanism of H-2 evolution on more complex oxide surfaces.