Herein, in situ zirconium-doped hematite nanocoral (Zr-Fe2O3 (I) NC) photoanode was prepared via a specially designed diluted hydrothermal approach and modified with Al3+ co-doping and electrodeposited cobalt-phosphate ("Co-Pi") cocatalyst. Firstly, an unintentional in situ Zr-Fe2O3 (I)) NC photoanode was synthesized, which achieved an optimum photocurrent density of 0.27 mA/cm(2) at 1.0 V vs. RHE but possessed a more positively shifted onset potential than conventionally prepared hematite nanorod photoelectrodes. An optimized amount of aluminum co-doping suppresses the bulk as well as surface defects, which causes a negative shift in the onset potential from 0.85 V to 0.8 V vs. RHE and enhances the photocurrent density of Zr-Fe2O3 (I) NC from 0.27 mA/cm(2) to 0.7 mA/cm(2) at 1.0 V vs. RHE. The electrodeposited Co-Pi modification further reduce the onset potential of Al co-doped Zr-Fe2O3 (I) NC to 0.58 V vs. RHE and yield a maximum photocurrent of 1.1 mA/cm(2) at 1.0 V vs. RHE (1.8 mA/cm(2) at 1.23 V vs RHE). The improved photocurrent at low onset potential can be attributed to synergistic effect of Al co-doping and Co-Pi surface modification. Further, during photoelectrochemical water-splitting, a 137 and 67 mu mol of hydrogen (H-2) and oxygen (O-2) evolution was achieved over the optimum Co-Pi-modified Al-co-doped Zr-Fe2O3 (l) NC photoanode within 6 h. The proposed charge transfer mechanism in optimum Co-Pi-modified Al-co-doped Zr-Fe2O3 (I) NC photoanodes during the photoelectrochemical water splitting was also studied. (C) 2020 Elsevier Inc. All rights reserved.