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.