Study On Modification Of Fe₂O₃ Photoanode And Photoelectrochemical Performance

Utilization of solar energy to produce clean and green energy has been regarded as an ideal approach to solve the current energy shortage on earth ever since 1970s,and H₂generated from photoelectrochemical（PEC）water splitting has been thought as a sustainable energy carrier.However,the actual efficiency of PEC process is far from the requirement of industrial application,and the key factor that limits PEC performance is semiconductor photoanode.At present,photoelectric catalysis（PEC）technology,which utilizes abundant solar energy resources to catalyze water splitting to obtain hydrogen energy,has been widely studied.The band gap ofα-Fe₂O₃ is only 2.2 e V,which can utilize visible light in solar spectrum efficiently and thus exhibits a theoretical solar to hydrogen（STH）efficiency of as high as 15.8%.Unfortunately,due to the lower electron mobility and short hole diffusion length,the charge carriers are easily to recombine and the surface oxidation kinetics is slow,which makes the real performance ofα-Fe₂O₃ is far from the theoretical efficiency.In this paper,α-Fe₂O₃ was modified by doping,defect regulation,construction of heterojunction and other methods,and the effect of these methods on the photoelectrochemical performance ofα-Fe₂O₃ was studied.First,Fe₂O_3-x@p-Ti O₂ heterojunctions are constructed to achieve efficient spatial separation of charge carriers.The effects of different defect types on the performance and charge transfer mode of the heterojunction,and the effect of the amount of p-Ti O₂ on the performance of the heterojunction were explored.The results show that the reaction time of6 h can obtain the optimal photoanode.When the oxygen-vacancies（O_V）Fe₂O_3-xrecombines with the metal-vacancies p-Ti O₂,a p-n junction with Z-type charge transfer is formed,showing the best performance.At 1.23 V vs.RHE,the photocurrent is 1.05m A·cm^-2,which is 4.04-fold than that of pureα-Fe₂O₃;and the hydrogen production rate is16.37μmol·cm^-2·h^-1.The Faradaic efficiency can be maintained above 80%.Secondly,the Fe₂O_3-x@Mo S₂ system was constructed to realize the rapid participation of charge carriers in the surface reaction.The amount of Mo S₂ was regulated by controlling the reaction time,and the effect of Mo S₂ on the performance of the photoanode was explored.The results showed that the optimal reaction time was 6 h.The Mo S₂ helps to expand the light absorption range ofα-Fe₂O₃,provides more reaction sites,and acts as a charge transport layer to ensure that the carriers quickly reach the electrode/electrolyte interface and participate in the OER reaction.The photocurrent of the optimal photoanode Fe₂O_3-x@Mo S₂-6h is as high as 0.99 m A·cm^-2（1.23 V vs.RHE）,which is 3.81-fold than that of pureα-Fe₂O₃.The hydrogen production rate is 16.34μmol·cm^-2·h^-1,and the Faraday efficiency has always remained above 85%.Finally,a Ti-Fe₂O₃-In₂O₃/Co OOH photoanode with synergistic promotion of heterojunction and cocatalyst was constructed to realize the spatial separation of charge carriers and accelerate the kinetics of the surface OER reaction.The results show that In₂O₃improves the light absorption capacity of the photoanode in the ultraviolet region.The cocatalyst Co OOH effectively reduces the overpotential of PEC water splitting so that the onset potential exhibits a significant negative shift,and a photocurrent appears at 0.75 V vs.RHE,indicating improved surface reaction kinetics.The photocurrent of Ti-Fe₂O₃-In₂O₃/Co OOH is 1.33 m A·cm^-2（at 1.23 V vs.RHE）,which is 5.11-fold than that of pureα-Fe₂O₃.The hydrogen production rate is 22.8μmol·cm^-2·h^-1,and the Faradaic efficiency reaches 90%above.More importantly,the performance of all the above photoanodes in simulated seawater is slightly reduced,but still maintains excellent stability.