Photocatalytic water oxidation on SrTiO$_3$ [001] surfaces

TL;DR

This study combines experimental and computational methods to understand how different surface terminations of SrTiO$_3$ influence its efficiency as a photocatalyst for water splitting under UV light.

Contribution

It provides a detailed atomic-level understanding of the active sites and the role of surface terminations in SrTiO$_3$ photocatalytic water oxidation, which was previously lacking.

Findings

Water splitting occurs only when both SrO and TiO$_2$ terminations are exposed to water.

Oxidation mainly occurs at SrO surfaces through four single hole transfer steps.

TiO$_2$ termination influences the band alignment critical for water oxidation.

Abstract

SrTiO$_3$ 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 TiO$_2$- terminations of aqueous-solvated [001] SrTiO$_3$. Our experimental findings show that the overall water-splitting reaction proceeds on the SrTiO$_3$ 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 TiO$_2$ 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 SrTiO$_3$ surfaces, and has consequent implications for maximizing sustainable solar-driven water splitting.