Improvement of surface light absorption of ZnO photoanode using a double heterojunction with α–Fe2O3/g–C3N4 composite to enhance photoelectrochemical water splitting

•The Vis. Light absorption of the ZnO/α–Fe2O3/g–C3N4 sample was significantly improved.•Depth and 3D images of the ZnO/α–Fe2O3/g–C3N4 report by TOF-SIMS analysis.•ZnO/α–Fe2O3/g–C3N4 photoanode obtained a photocurrent about 4.8-fold more than ZnO.•The ZnO/α–Fe2O3/g–C3N4 generated 29.28 μmol.cm−2 of H2 after 2 h, at 1.23 VRHE.