Photoelectrochemical Performance Of Iron Oxide And Its Composites

Iron oxide（α-Fe₂O₃）is a kind of photocatalyst with good application prospect,owing rich resources,environment friend,good chemical stability and suitable energy band.The morphologies of iron oxide are various,and the morphology of nanorods is beneficial to electrons and holes transport along the rod axial and radial direction,respectively,which can reduce electron-hole pairs recombination and improve the photocatalytic performance.At present,α-Fe₂O₃ can be widely used in hydrogen production by water splitting,photocatalytic reduction of CO₂,as well as sensors and so on.Therefore,it is very prospectable to improve photoelectrochemical performances of theα-Fe₂O₃ through optimizing preparation process.In this paper,α-Fe₂O₃ nanorods were prepared based on hydrothermal method,and the best preparation technology to improve photoelectrochemical performances was found out by modifying and compositingα-Fe₂O₃ nanorods.The crystal types,apparent morphologies,and contents of samples were characterized by XRD,SEM and EDS.Phase structures of samples were characterized by Raman spectra,optical properties of samples were studied by the UV-Vis diffuse reflectance spectra;surface charge recombination situations of samples were studied by PL spectra.Finally,a series of photoelectrochemical performances of composites were characterized.The main research work is divided into the following points:1.α-Fe₂O₃ nanorods were prepared by hydrothermal reaction,and the diameter of the nanorods is about 80¹20 nm.Reduced graphene oxide（RGO）thin films and Ag nanoparticles were composited on the surface ofα-Fe₂O₃ nanorods by hydrothermal reaction and light deposition method,respectively.Fe₂O₃/RGO/Ag composite shows the minimum impedance,and the maximum electron concentration(1.14×10²² cm^-3).Light current density is up to 0.72 mA/cm² under the 0.23 V（1.23 V vs RHE）conditions and its maximum optical conversion efficiency is 0.15%,which is more than 2 times than that ofα-Fe₂O₃（0.07%）.The improved photoelectrochemical performances can be attributed to that RGO promotes the electrons transfer,Ag surface plasmon resonance effect generates large numbers of light-induced electrons transferring to semiconductor,and synergistic effect of Ag and RGO increases light absorption intensity and range.2.α-Fe₂O₃/NiFe₂O₄ composites with p-n type transformation were prepared with method of hydrothermal and high temperature dipping.UV-Vis diffuse reflectance spectroscopy shows that composites significantly improve light absorption intensity and absorption range.Photoelectrochemical performances ofα-Fe₂O₃/NiFe₂O₄ composites increase firstly and then decrease with the increase of the dipping recycle times.Fe₂O₃/NiFe₂O₄ composite prepared for the high temperature dipping recycle 3 times shows the highest photoelectrochemical performances,decreases the onset potential,and reduces impedance,which is ascribe to the thickness of NiFe₂O₄.With the increase of the dipping recycle times,the thickness of NiFe₂O₄ increases,leading to the improved photoelectrochemical performances.However,thicker NiFe₂O₄ hinders the light absorption,resulting in the decreased photoelectrochemical performances.3.α-Fe₂O₃/FeS₂ composite was prepared by hydrothermal method and high temperature gas phase reaction.Electrochemical studies show that the photoelectrochemical performances of composites increase firstly and then decrease,with improved temperature and prolonging calcination time.Among them,α-Fe₂O₃/FeS₂ composite prepared under 500℃for 2 h,shows the optimum photoelectrochemical performances.The light current density is up to 3.68 mA/cm² under the 0.23 V（1.23 V vs RHE）conditions,and the electron concentration is 5.56×10²⁴cm^-3,which is about 2000 times than that of pureα-Fe₂O₃(2.25×10²¹ cm^-3).After composition with FeS₂,the initial potential decreased,the flat band potential increased,the concentration of carrier improved,which can be attributed to the narrow band gap of FeS₂ that increases the absorption of visible light,and the formation of heterojunction that promotes the charge separation.