Surface sulfurization activating hematite nanorods for efficient photoelectrochemical water splitting

Surface treatment is an effective method to improve the photoelectrochemical (PEC) performance of photoelectrodes. Herein, we introduced a novel strategy of surface sulfurization to modify hematite (α-Fe₂O₃) nanorods grown in an aqueous solution, which triggered encouraging improvement in PEC performances. In comparison to the solution-grown pristine α-Fe₂O₃ nanorod photoanode that is PEC inefficient and always needs high temperature (>600 °C) activation, the surface sulfurized α-Fe₂O₃ nanorods show photocurrent density increased by orders of magnitude, reaching 0.46 mA cm^-2 at 1.23 V vs. RHE (reversible hydrogen electrode) under simulated solar illumination. This improvement in PEC performances should be attributed to the synergy of the increased carrier density, the reduced surface charge carrier recombination and the accelerated water oxidation kinetics at the α-Fe₂O₃/electrolyte interface, as induced by the incorporation of S ions and the formation of multi-state S species (Fe-S_x-O_y) at the surface of α-Fe₂O₃ nanorods. This study paves a new and facile approach to activate α-Fe₂O₃ and even other metal oxides as photoelectrodes for improved PEC water splitting performances, by engineering the surface structure to relieve the bottlenecks of charge transfer dynamics and redox reaction kinetics at the electrode/electrolyte interface.