Improved photoelectrochemical water splitting performance of Sn-doped hematite photoanode with an amorphous cobalt oxide layer

Hematite with a suitable band gap is a promising candidate as the photoanode for photoelectrochemical water splitting, but it suffers from low catalytic activity and severe electron-hole recombination. Herein, a novel two-step solvothermal synthetic strategy is developed to fabricate a uniform CoO_x amorphous layer with a thickness of 5 nm on Sn-doped Fe₂O₃ nanowire photoanode. The CoO_x surface layer increases the roughness of the photoanode significantly, and thus enlarges the electrochemical active area. Furthermore, the CoO_x layer brings Co²⁺/Co³⁺ redox couples, enhances the concentration of oxygen vacancies and increases the charge carrier density. The bulk and surface charge separation efficiencies are both improved. The surface charge transfer process and the oxygen evolution reaction are accelerated. The photocurrent density of the Sn–Fe₂O₃ photoanode at 1.23 V (vs. reversible hydrogen electrode) is improved from 0.83 to 1.40 mA cm⁻² after the deposition of the CoO_x surface layer.