Nanostructure And Surface Optimization Of Hematite Nanorod-array Photoanodes For Photoelectrochemical Water Oxidation

Photoelectrochemical?PEC?water splitting system is an important means to provide clean and renewable energy via converting solar energy and water to hydrogen fuels.Oxygen evolution reaction?OER?is regarded as the core problem because the water oxidation of photoanode involves a four electron transfer process,which limits the efficiency of PEC water splitting.Here,the?-Fe₂O₃ nanorods array was used as the photoanodes.The Fe₂O₃ nanorods array was prepared on the macroporous substrate to increase the light absorption,and the efficiencies of electron collection and transfer;The PEC performance of?-Fe₂O₃ nanorods photoanode was improved via decreasing the surface state by O₂ plasma treatment.The main research contents are as follows:1.The coral-like?-Fe₂O₃ nanorods array photoanode was prepared on porous Sb doped SnO₂?ATO?substrate?ATO-Fe₂O₃?to improve the PEC water oxidation performance.A two-layer of polystyrene microspheres?PS?with the diameter of 500 nm film was prepared as the templates,where the macroporous ATO was spin coated.The coral-like Fe₂O₃ photoanode was prepared on the macroporous ATO substrate via the hydrothermal method.Compared with the Fe₂O₃ prepared on planar FTO substrate?FTO-Fe₂O₃?,ATO-Fe₂O₃ exhibits a 2.4 times higher Fe₂O₃ content,a 13.6-fold increased surface area,and a 5 times reduced charge transfer resistance.In addition,ATO-Fe₂O₃ also showed the better wettability to water and less photocurrent dependence on light angle than FTO-Fe₂O₃.These contributed to the improved PEC water oxidation performance.The photocurrent density of ATO-Fe₂O₃ achieved 1.32m A/cm²?1.23 V vs.RHE?,which was 8.8-fold higher than FTO-Fe₂O₃.The PEC performance of the coral-like?-Fe₂O₃ was further enhanced,and the photocurrent density reached 1.81 mA/cm²at 1.23 V vs.RHE after the Ti Cl4 treatment.Coral-like nanostructure is of great significance in solving the contradiction between the big depth penetration of the photon and the short diffusion length of minority carriers of hematite.2.The?-Fe₂O₃ NR photoanode was treated with O₂ plasma to decrease the defect states on the surface of hematite.Fe₂O₃ has large surface area,and a serious charge combination was caused by the oxygen vacancies related defect states,thus O₂ plasma treatment of titanium doped Fe₂O₃ was explored to enhance the PEC water oxidation performance.The results showed that the concentration of surface oxygen vacancies was decrease by 6.7%,and the surface charge transfer efficiency was increased by 1.66-fold after the optimum O₂ plasma conditions of 100?,200 W,and 70 s.At the potential of 1.23 V vs.RHE,the photocurrent density reached 2.14m A/cm²,which was 1.95 times that of the untreated nanorods.Surface O₂ plasma treatment reduced the surface defect states of the photoanode and provided a new method for controlling the surface defect states of photoanode.