BiVO₄ photoanodes are promising for solar-driven water oxidation, but their performance is often limited by inefficient interfacial hole utilization and inadequate operational stability. Herein, via Mo modification, a conventional passive Nb₂O₅ protective layer on FeOOH/BiVO₄ is converted into a functional interfacial layer, simultaneously enhancing photoelectrochemical activity and stability. The resulting Mo:Nb₂O₅/FeOOH/BiVO₄ photoanode delivers a photocurrent density of 6.27 mA/cm² at 1.23 V vs. RHE under AM 1.5G illumination and maintains stable operation for over 100 h at 0.7 V. Electrochemical analyses reveal markedly suppressed charge recombination and improved interfacial hole utilization. Combined Kelvin probe force microscopy, in situ light-assisted X-ray photoelectron spectroscopy, surface photovoltage measurement and density functional theory calculation demonstrate that Mo incorporation modulates the light-induced interfacial potential redistribution, reconstructs near-Fermi-level electronic states, and promotes a more favorable oxygen evolution reaction pathway. These findings provide an effective strategy for constructing high-performance BiVO₄ photoelectrodes by functionalizing a passive protective layer.