Hematite (alpha-Fe2O3) is one of the most promising photoanode materials to realize solar-to-hydrogen energy conversion via photoelectrochemical water splitting. However, alpha-Fe2O3 still suffers from serious charge recombination rate and its practical application in solar water splitting is severely hindered by its low carrier mobility. Hence, Ti-doped alpha-Fe2O3 (Ti-Fe2O3) nanoarrays with surface phosphate ions (Pi) functionalization are successfully synthesized and demonstrate synergistic enhanced photoelectrochemical water oxidation performance. The resulting Ti-Fe2O3/Pi photoanode nanoarrays exhibit an onset potential as low as 0.88 V vs. RHE and a significantly promoted photocurrent density of 1.56 mA/cm(2) at 1.23 V vs. RHE under AM 1.5G illumination in 0.1 M KOH solution, which is much higher than those of Ti-Fe2O3 (0.92 mA/cm(2)) and pristine alpha-Fe2O3 (0.5 mA/cm(2)). Comprehensive structural and photoelectrochemical analysis reveal that the enhanced photoelectrochemical water oxidation performance can be ascribed to the synergistic effect of surface Pi functionalization. The phosphates could not only act passivation effect to enhance the photogenerated voltage and lower the onset potential by suppress the charge recombination, but also improve the surface PEC water oxidation kinetics to increase the photocurrent by accelerating the surface charge separation and utilization. This work along with indepth understanding the role of Pi functionalization is expected to provide new vision for improving the PEC performance of metal oxide photoanodes. (C) 2019 Elsevier Ltd. All rights reserved.