Synthesis,Modification And Performance Study On The Nano-ɑ-Fe₂O₃ During Photoelectrochemical Water Splitting

Performed as the alternative approach of utilizing solar energy,α-Fe₂O₃,which with the efficiencies like appropriate band gap（～2.1 e V）,resourceful deposit,stable and low-cost,has been considered as a distinctive photoanode material.However,its poor electrical conductivity,short hole diffusion distance,easy recombination of electrons and holes,and slow oxygen evolution reaction and other factors reduce its photoelectric performance.Therefore,improved light absorption,promoted charge separation and accelerated surface reaction helps to improve the photoelectric performance.First,nano-flower-like hematite（α-Fe₂O₃）depositing on Nickel foam was prepared by hydrothermal method Theα-Fe₂O₃nanoflowers consist of nanosheets and attain a photocurrent density of 0.42 m A/cm~2 at 1.23 V vs.reversible hydrogen electrode（RHE）.Theα-Fe₂O₃ modified by Co O_x layer still keeps the nano-flower-like structure,and prepared by the one-step in-situ hydrothermal process.As the concentration of Co²⁺is 0.01M,the Fe₂O₃/Co O_x attains a photocurrent density of 1.87 m A/cm~2 at 1.23 V_RHE,with the onset potential of 266 m V negative shift.The results of characterizations indicated that the reduced charge transfer resistance of nanoflower-like Fe₂O₃/Co O_x photoanode accelerates the water oxidation kinetics at the interface between photoanode and electrolyte.Simultaneously,Co doping and the conversion between high and low valence of Co element,which increases the carrier density and hole consumption,improves the charge separation efficiency,thereby effectively improving the photoelectrochemical performance.Then,based on the Fe₂O₃/Co O_x,surface plasmon Au nanoparticles（10 nm）are deposited on the surface of Fe₂O₃/Co O_x by electrochemical reduction method.The results of electron microscopy show that a beaded structure composed of nanoparticles and nanorods appears at the top of Fe₂O₃/Co O_x nanoflowers,due to corrosion and agglomeration happened during the electrochemical reduction deposition process.The photocurrent density of Fe₂O₃/Co O_x/Au photoanode reaches 3.88 m A/cm~2 at 1.23 V_RHE,which is 9.24 times that of originalα-Fe₂O₃.The maximum bias photon-current conversion efficiency of Fe₂O₃/Co O_x/Au photoanode at 1.18 V_RHE is 0.10%,which is 5 times that ofα-Fe₂O₃,the charge separation efficiency is 2.3 times that ofα-Fe₂O₃,and the charge injection efficiency is 3.96 times that ofα-Fe₂O₃.The synergistic effect of the catalytic effect of Co O_x and the surface plasmon resonance effect of Au reduces the charge resistance at the interface,promotes light absorption,thereby improves the efficiency of charge separation and charge injection,and enhances the photoelectrochemical performance ofα-Fe₂O₃.Thirdly,α-Fe₂O₃ nanorods are prepared on the surface of FTO substrate by hydrothermal method,and Co-Pi was deposited by two-part dipping method.The photocurrent density ofα-Fe₂O₃ andα-Fe₂O₃/Co-Pi at 1.23 V_RHE is 1.02 and 1.95 m A/cm2,respectively.The onset potential decreases by 80 m V.Through physical chemistry,photoelectrochemical and electrochemical characterizations,the PEC mechanism is studied.It is found that the modification of Co-Pi improves the bias photon-current efficiency,the charge separation efficiency and the charge injection separation,and reduces the charge transfer resistance,thereby effectively improving the photoelectrochemical performance ofα-Fe₂O₃ photoanode.Finally,α-Fe₂O₃ nanoparticles are prepared by the electrochemical method,and Ni Fe OOH as oxygen evolution cocatalyst was deposited on the surface by the dipping method.The photoelectric performance results show that the photocurrent density ofα-Fe₂O₃ andα-Fe₂O₃/Ni Fe OOH photoanodes at 1.23 V_RHE is 0.95 m A/cm~2 and 1.39 m A/cm~2,respectively.The onset potential decreases by 140 m V.Through electrochemical characterization and analysis,it is found that Ni Fe OOH acts as cocatalyst and accelerates the water oxidation kinetics of the surface reaction between the photoanode and the electrolyte,thereby effectively improving the photoelectrochemical performance ofα-Fe₂O₃.