Unraveling and Compensating Surface Vanadium Vacancies in BiVO 4 Photoanodes via a Hydrothermal Diffusion Strategy for Enhanced Photoelectrochemical Water Oxidation

Overview

This work addresses the role of surface defects in BiVO4 photoanodes for photoelectrochemical water oxidation by employing a hydrothermal diffusion strategy to compensate surface vanadium vacancies. The study clarifies that photoelectrochemical performance improvements in BiVO4-based systems derive primarily from suppressed charge recombination at the surface rather than from enhanced oxygen evolution reaction kinetics alone. A hybrid BVO(V)/VOx photoanode architecture was constructed through simultaneous V5+ incorporation into the BiVO4 lattice during vanadium oxide deposition.

Methods and approach

A hydrothermal diffusion strategy was employed to deposit vanadium oxide overlayers while simultaneously introducing V5+ species into the BiVO4 lattice, thereby compensating surface vanadium vacancies. The optimized configuration incorporated a dual-overlayer architecture with FeNiOx as an additional cocatalyst layer. Comprehensive characterization techniques were applied to analyze the electronic structure, defect states, charge carrier dynamics, and electrochemical properties of the resulting photoanodes. Photoelectrochemical measurements were conducted to determine photocurrent density, charge separation efficiency, and operational stability under illumination.

Results

The optimized dual-overlayer BVO(V)/VOx/FeNiOx photoanode exhibited a photocurrent density of 5.82 mA cm-2 at 1.23 V versus the reversible hydrogen electrode, representing a 5.18-fold enhancement relative to pristine BiVO4. The photoanode demonstrated near-unity charge separation efficiency and maintained excellent long-term durability under sustained operation. Analytical findings indicated that the primary mechanism for performance enhancement was suppression of interfacial charge recombination rather than acceleration of surface oxygen evolution reaction kinetics.

Implications

The identification of surface vanadium vacancies as the primary source of interfacial charge recombination establishes a mechanistic foundation for defect engineering in BiVO4 photoanodes. The hydrothermal V-source diffusion approach provides a generalizable defect compensation strategy applicable to photoelectrochemical materials, offering an alternative to cocatalyst deposition for performance enhancement. The work delineates the distinct contributions of charge recombination suppression and OER kinetic acceleration, informing rational design of photoanode architectures for solar fuel synthesis. This defect compensation strategy may extend to other metal oxide photoanodes plagued by structural vacancies that mediate non-radiative carrier loss pathways.