Theoretical design of highly active SrTiO3-based photocatalysts by a codoping scheme towards solar energy utilization for hydrogen production

Abstract

SrTiO₃ is a promising photocatalyst for the production of hydrogen from water splitting under solar light. Cr doping is an effective treatment for adjusting its absorption edge to the visible-light range, although the performance of Cr-doped SrTiO₃ is strongly affected by the oxidation number of the Cr ions. In this study, we theoretically predict that elevating the Fermi level, i.e., n-type carrier doping in SrTiO₃, can stabilize the desirable oxidation number of chromium (Cr³⁺), contributing to a higher activity for H₂ evolution. Our computational results, based on hybrid density-functional calculations, reveal that such an n-type condition is realized by substituting group-V metals (Ta, Sb, and Nb), group-III metals (La and Y), and fluorine atoms for the Ti, Sr, and O sites in SrTiO₃, respectively. From our systematic study of the capability of each dopant, we conclude that La is the most effective donor for stabilizing Cr³⁺. This prediction is successfully evidenced by experiments showing that the La and Cr codoped SrTiO₃ dramatically increases the amount of H₂ gas evolved from water under visible-light irradiation, which demonstrates that our guiding principle based on Fermi level tuning by the codoping scheme is valid for the design of advanced photocatalysts.