Spontaneous Oxygen Vacancy Ionization Enhances Water Oxidation on BiVO$_4$

TL;DR

This study uses hybrid density functional theory to show that ionized oxygen vacancies on BiVO$_4$ surfaces significantly improve water oxidation efficiency by reducing overpotential and facilitating reactive intermediates.

Contribution

It reveals the spontaneous ionization of oxygen vacancies and their role in lowering overpotential, providing new insights into defect engineering for enhanced photoelectrochemical performance.

Findings

Ionized oxygen vacancies lower the thermodynamic overpotential.

Surface-bound peroxide and superoxide are key intermediates.

Spontaneous vacancy ionization influences water oxidation pathways.

Abstract

The influence of surface oxygen vacancies on the oxygen evolution reaction on bismuth vanadate is studied using hybrid density functional theory. Our findings reveal the thermodynamic instability of the neutral unionized defect (${\rm V}_{\rm O}^0$), leading to spontaneous ionization into ${\rm V}_{\rm O}^{2+}$. By investigating the oxygen evolution reaction mechanism on both stoichiometric and oxygen-deficient surfaces, we find that surface oxygen vacancies reduce the reaction's thermodynamic overpotential, but only when the defects are ionized. Moreover, the reaction pathway involves the formation of surface-bound peroxide and superoxide ions as intermediates. Our work provides insight into the nature of surface oxygen vacancies and shines new light on how they may enhance the photoelectrochemical properties of semiconductors.