Water induced redistribution of polarons in rutile TiO₂(011)-(2 × 1)

The interaction between water and TiO₂ is a widely discussed topic due to its direct relevance to green hydrogen production. In addition to the impact of TiO₂ substrate structure on the adsorption of water, adsorbates have also been found to affect the distribution of excess electrons, which form polaron-like bandgap states (BGS) in the substrate for rutile TiO₂(110) and anatase TiO₂(101). In order to further investigate the adsorbate induced redistribution of polarons in TiO₂, we measured water coverage-dependent BGS and surface species on rutile TiO₂(011) [R-TiO₂(011)], another model metal oxide surface, using ultraviolet and x-ray photoelectron spectroscopy (UPS and XPS). We found the increase in BGS magnitude and surface hydroxyl quantity with increasing water coverage below 1 monolayer (ML). Ab initio molecular dynamics simulations suggested that excess electrons in the bulk of R-TiO₂(011) are abstracted to the surface and induce water dissociation. Our results expand the applicable systems for the adsorbate induced polaron redistribution and indicate that it might be a general phenomenon. Knowledge about the adsorbate–polaron interaction in semiconductors may contribute to the understanding and optimization of surface processes involving molecule–substrate interaction, such as photocatalysis and photovoltaics.