Orbital Engineering of Phosphidized CoFe Oxide/BiVO ₄ Heterojunctions for Scavenger-Free PEC Water Splitting Revealed by DFT and Multimodal Spectroscopy

BiVO4 photoanodes are limited by short hole-diffusion lengths, bulk recombination, and sluggish surface kinetics. Herein, we report a strategically engineered phosphidized CoFe oxide/BiVO4 heterojunction that coherently modulates the electronic structure, defect chemistry, and interfacial band bending. Controlled phosphidation affords an optimal CoFeOP-2/BVO architecture consisting of crystalline CoFe oxide cores encapsulated by an amorphous P-rich shell, delivering a photocurrent density of 7.14 mA/cm2 at 1.23 VRHE and an enhanced operational stability exceeding 22 h. Spectroscopic analyses reveal Fe3+ stabilization, Co–P covalency, and electron redistribution across the heterointerface, while band diagrams indicate Fermi-level equilibration and strengthened band bending. Dual-electrolyte internal assessment (ΔJ, photocurrent difference with/without scavenger; PRI, performance robustness index) separates intrinsic charge generation from surface kinetics, confirming suppressed recombination without sacrificial agents. Density functional theory validates enhanced Fe-3d/O-2p orbital hybridization, reinforcing covalency to accelerate charge migration. This study demonstrates one of the best performing BiVO4-based photoanodes, setting out general design principles for oxide-phosphide heterojunctions toward large-scale solar hydrogen generation.