Synergistic O-V-O covalent bonding at a BiVO₄/FeNiO_x interface boosts charge transfer for efficient photoelectrochemical water splitting

Efficient charge separation at a BiVO₄/cocatalyst interface is crucial for high-performance photoelectrodes, as it directly determines the availability of surface charges for solar water oxidation. However, achieving robust molecular-level connections to ensure superior interfacial quality remains challenging. Herein, we report a two-step photo-assisted deposition method followed by calcination to introduce vanadyl ions (VO²⁺) to form an O-V-O covalent structure at a BiVO₄/FeNiO_x interface (denoted as BiVO₄/VOFeNiO_x), thereby enabling a strong interfacial interaction. For comparison, direct FeNiO_x deposition yields 4.23 mA cm^-2 at 1.23 V vs. RHE, whereas the optimized BiVO₄/VOFeNiO_x photoanode achieves 6.69 mA cm^-2 under AM 1.5 G illumination, corresponding to a 3.9-fold enhancement over pristine BiVO₄. Furthermore, this architecture exhibits a 3.5-fold improvement in the hole migration rate and excellent operational stability exceeding 30 hours. Systematic studies reveal that the introduction of O-V-O interfacial bonds induces a redistribution of electron density and strong electronic coupling between BiVO₄ and FeNiO_x. This optimized interfacial configuration facilitates charge transport, culminating in a substantial 76% reduction in charge transfer resistance. This work highlights the potential of interfacial engineering in facilitating charge transport, providing insights into the rational design of efficient photoanodes for solar energy conversion.