Light-Induced Surface Reactions at the Bismuth Vanadate/Potassium Phosphate Interface.

Area of Science:

• Materials Science
• Electrochemistry
• Surface Science

Background:

• Bismuth vanadate (BiVO₄) is a promising photoanode material for photoelectrochemical water splitting.
• Understanding the surface chemistry of BiVO₄ under operating conditions is crucial for improving its efficiency.

Purpose of the Study:

• To investigate the in situ interfacial changes of a bismuth vanadate electrode in contact with an aqueous potassium phosphate solution under illumination.
• To elucidate the role of light in modifying the bismuth vanadate/electrolyte interface and its impact on surface charge and ion distribution.

Main Methods:

• Utilized in situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) with tender X-rays (4.0 keV).
• Employed a 25-30 nm thick electrolyte layer created via the 'dip-and-pull' method for investigating the polycrystalline BiVO₄ electrode.
• Monitored photoelectron signals from phosphate ions and water under dark and light conditions at open circuit potential.

Main Results:

• Illumination induces the formation of a bismuth phosphate layer on the BiVO₄ surface, leading to increased surface negative charge.
• A repulsive interaction between the illuminated surface and phosphate ions causes a redistribution of ions in the electrolyte film, enhancing photoelectron signals.
• These interfacial modifications were observed to be reversible upon returning to dark conditions.

Conclusions:

• Light induces a reversible chemical modification of the BiVO₄/potassium phosphate electrolyte interface.
• The formation of bismuth phosphate passivates surface states and influences ion behavior, providing direct evidence for light-driven surface chemistry.
• Findings offer critical insights into the operational mechanisms of BiVO₄ photoanodes for water splitting applications.