Photoelectrochemical (PEC) water splitting is a promising technique for converting solar energy into hydrogen fuels, while its practical applications are mainly restricted by the relatively low photo-conversion efficiencies. Herein, we demonstrated a simple surface fluorination process for drastically promoting the PEC water oxidation activity of BiVO₄ photoanodes, achieving a remarkable photocurrent density of 3.2 mA cm⁻² at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 G illumination, one of the highest values of BiVO₄ electrodes without cocatalysts. After in-situ formation of CoF₂ cocatalysts, the photocurrent density could be further increased up to 5.1 mA cm⁻² (1.23 V_RHE), accompanying by a remarkably negative shift of onset-potential (270 mV). Systematic studies clearly reveal that tuning surface electronegativity of BiVO₄ photoanodes could drastically promote the charge separation efficiencies of both surface and bulk up to nearly 100%. This work may provide a facile but effective approach for constructing the highly efficient BiVO₄ photoanodes for solar water splitting.