Origin of Improved Photoelectrochemical Water Splitting in Mixed Perovskite Oxides

TL;DR

This study investigates how mixing BiFeO3 with SrTiO3 enhances photoelectrochemical water splitting by modifying electronic structures and trap states, leading to significantly increased photocurrent densities.

Contribution

It reveals the intrinsic electronic mechanisms behind improved water splitting in mixed perovskite oxides using ideal epitaxial films, contrasting with polycrystalline studies.

Findings

Adding SrTiO3 raises the conduction band minimum.

Trap states from hybridized Ti 3d and Fe 3d orbitals suppress recombination.

Photocurrent density increases up to 16 times at 0 VRHE.

Abstract

Owing to the versatility in their chemical and physical properties, transition metal perovskite oxides have emerged as a new category of highly efficient photocatalysts for photoelectrochemical water splitting. Here, to understand the underlying mechanism for the enhanced photoelectrochemical water splitting in mixed perovskites, we explore ideal epitaxial thin films of the BiFeO3-SrTiO3 system. The electronic struture and carrier dynamics are determined from both experiment and density-functional theory calculations. The intrinsic phenomena are measured in this ideal sytem, contrasting to commonly studied polycrstalline solid solutions where extrinsic structural features obscure the intrinsic phenomena. We determined that when SrTiO3 is added to BiFeO3 the conduction band minimum position is raised and an exponential tail of trap states from hybridized Ti 3d and Fe 3d orbitals emerges near the conduction band edge. The presence of these trap states strongly suppresses the fast electron-hole recombination and improves the photocurrent density in the visible-light region, up to 16 times at 0 VRHE compared to the pure end member compositions. Our work provides a new design approach for optimising the photoelectrochemical performance in mixed perovksite oxides.