Electronic Defects in Metal Oxide Photocatalysts

TL;DR

This paper reviews the role of electronic defects in metal oxide photocatalysts, highlighting how defects can both hinder and enhance solar energy conversion processes, and explores their implications for designing better photocatalytic materials.

Contribution

It provides a comprehensive analysis of defect behaviour in metal oxides and extends insights to emerging photocatalyst materials like carbon nitrides and perovskites.

Findings

Defects can stabilize charge separation in photocatalysts.

Electronic structure changes due to defects influence catalytic activity.

Lessons from oxide defect chemistry inform new photocatalyst design.

Abstract

A deep understanding of defects is essential for the optimisation of materials for solar energy conversion. This is particularly true for metal oxide photo(electro)catalysts, which typically feature high concentrations of charged point defects that are electronically active. In photovoltaic materials, except for selected dopants, defects are considered detrimental and should be eliminated to minimise charge recombination. However, photocatalysis is a more complex process where defects can play an active role, for example, by stabilising charge separation and mediating rate-limiting catalytic steps. Here, we review the behaviour of electronic defects in metal oxides, paying special attention to the principles underpinning the formation and function of trapped charges in the form of polarons. We focus on how defects alter the electronic structure, statically or transiently upon illumination, and discuss the implications of such changes in light-driven catalytic reactions. Finally, we consider the applicability of lessons learned from oxide defect chemistry to new photocatalysts based on carbon nitrides, polymers and metal halide perovskites.