Structure of the photo-catalytically active surface of SrTiO3

TL;DR

This study investigates the surface structural changes of SrTiO3 during water splitting, revealing irreversible surface reordering and increased activity after training, using operando X-ray reflectivity, SECM, and first-principles simulations.

Contribution

It provides the first detailed in-situ analysis of SrTiO3 surface evolution under operational conditions, linking structural changes to enhanced photo-catalytic activity.

Findings

Training causes irreversible surface reordering.

Surface reordering triples water splitting activity.

An anatase-like structure is identified on the active surface.

Abstract

A major goal of energy research is to use visible light to cleave water directly, without an applied voltage, into hydrogen and oxygen. Since the initial reports of the ultraviolet (UV) activity of TiO2 and SrTiO3 in the 1970s, researchers have pursued a fundamental understanding of the mechanistic and molecular-level phenomena involved in photo-catalysis. Although it requires UV light, after four decades SrTiO3 is still the gold standard for splitting water. It is chemically stable and catalyzes both the hydrogen and the oxygen reactions without applied bias. While ultrahigh vacuum (UHV) surface science techniques have provided useful insights, we still know relatively little about the structure of electrodes in contact with electrolytes under operating conditions. Here, we report the surface structure evolution of a SrTiO3 electrode during water splitting, before and after training with a positive bias. Operando high-energy X-ray reflectivity measurements demonstrate that training the electrode irreversibly reorders the surface. Scanning electrochemical microscopy (SECM) at open circuit correlates this training with a tripling of the activity toward photo-induced water splitting. A novel first-principles joint density-functional theory (JDFT) simulation constrained to the X-ray data via a generalized penalty function identifies an anatase-like structure for the more active, trained surface.