Hematite has been receiving increasing attention for its application in photoelectrochemical(PEC)water oxidation,but usually exhibits poor efficiency.We fabricated stable gradient structured FeOx(PO4)y layer on hematite by diffusively incorporating phosphate into the surface layer of hematite films at a low temperature.XPS depth profile and Fe K-edge grazing incidence X-ray absorption near edge structure(GI-XANES)and extended X-ray absorption fine structure(EXAFS)analysis demonstrated the formation of a~50 nm overlayer with a gradient phosphorus distribution and structural evolution from the outer surface to the depth.The as-prepared photoanodes showed highly improved PEC water oxidation performance.Up to 8.5-fold enhancement in photocurrent density at 1.23 V vs.RHE was achieved relative to the pristine anode.This strategy is applicable for hematite photoanodes prepared by different methods and with different morphologies and structures.The improvement in water oxidation activity is mainly attributed to the enhanced separation of photogenerated electron-hole pairs,which is derived from the increased hole diffusion length in the gradient structured overlayer.This work develops a simple and universal method to boost the PEC water oxidation efficiency with versatile hematite photoanodes.