Oxygen evolution reaction (OER) active sites in BiVO₄ studied using density functional theory and XPS experiments

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Chemistry

Background:

• Bismuth vanadate (BiVO4) is a promising semiconductor for photocatalytic water splitting due to its synthesis ease and 2.4 eV band gap.
• However, BiVO4 suffers from low photocatalytic water oxidation activity, with active sites for the oxygen evolution reaction (OER) remaining unclear.
• Current literature identifies Bi atoms as OER active sites, while V atoms have not been investigated for OER.

Purpose of the Study:

• To investigate the role of V atoms in BiVO4 for the oxygen evolution reaction (OER).
• To elucidate the underlying reasons for the low OER activity in BiVO4.
• To provide fundamental insights into OER activity in vanadium-containing photocatalysts.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to study the electronic structure and surface properties of BiVO4.
• Ab initio molecular dynamics simulations were performed to assess the stability of surface structures and V atom coordination at different temperatures.
• X-ray Photoelectron Spectroscopy (XPS) was used to characterize the surface composition and oxidation states of BiVO4 morphologies.

Main Results:

• DFT and molecular dynamics simulations revealed that the VO4 tetrahedron structure in BiVO4 is highly stable, even under high temperatures (300-673 K).
• Surface reconstruction leads to V atoms maintaining bulk-like coordination, and any theoretically predicted unsaturated V sites readily reform VO4 by incorporating oxygen from water.
• XPS characterization confirmed the presence of unsaturated Bi sites but found no evidence of unsaturated V sites on the BiVO4 surface, supporting the theoretical findings.

Conclusions:

• The stable VO4 structure and its tendency to reform make V sites in BiVO4 unsuitable for OER due to difficulties in adsorbate/intermediate adsorption and desorption.
• This study demonstrates that V atoms are not active sites for OER in BiVO4, contrasting with the established role of Bi sites.
• The findings offer crucial insights for enhancing BiVO4's OER activity and understanding OER mechanisms in related photocatalytic materials.