Cooperative Interactions between Surface Terminations Explain Photocatalytic Water Splitting Activity on SrTi O3

SrTiO3 is a highly efficient photocatalyst for the overall water splitting reaction under UV irradiation. However, an atomic-level understanding of the active surface sites responsible for the oxidation and reduction reactions is still lacking. Here we present a unified experimental and computational account of the photocatalytic activity at the SrO and TiO2 terminations of aqueous solvated [001] SrTiO3. Our experimental findings show that the overall water-splitting reaction proceeds on the SrTiO3 surface only when the two terminations are simultaneously exposed to water. Our simulations explain this, showing that the photogenerated hole-driven oxidation primarily occurs at SrO surfaces in a sequence of four single hole transfer reactions, while the TiO2 termination effects the crucial band alignment of the photocatalyst relative to the water oxidation potential. The present work elucidates the interdependence of the two chemical terminations of SrTiO3 surfaces, and has consequent implications for maximizing sustainable solar-driven water splitting.