Study On The Construction Of α-Fe₂O₃ Heterojunction Photoanode And The Performance Of Photoelectrochemical Water Splitting

Photoelectrochemical technology can realize the conversion of scattered solar energy into easily stored hydrogen energy,and the large-scale use of hydrogen energy can solve the current energy crisis and environmental pollution.The key of hydrogen production by photoelectrochemical technology is to develop efficient,cheap and environmentally friendly photoanode materials.Among many semiconductor materials,α-Fe₂O₃ has attracted much attention due to its suitable optical band gap（2.1 e V）,chemical stability and corrosion resistance,and high earth abundance.However,the defects of short lifetime of photogenerated charge,high recombination rate of photogenerated charge and low light absorption coefficient lead to the photoelectrochemical performance ofα-Fe₂O₃ far below the theoretical value.Based on this,Bi₂S₃,Zn Fe₂O₄ andα-Fe₂O₃ were selected to form the heterojunction in this paper.The interfacial electric field of the heterojunction was used to promote the separation of photogenerated charge and inhibit the recombination of photogenerated charge,so as to improve the PEC performance.On the basis of this,the effects of heterojunction interface composition,element doping,coated photothermal materials,coated oxygen generation cocatalyst and other methods on the photochemical properties ofα-Fe₂O₃ and the mechanism of action were studied.The main research contents and results of this paper are as follows:（1）In this paper,Bi₂S₃/Sn:Fe₂O₃ heterojunction nanorods were prepared by hydrothermal method,and the effects of Sn doping and heterojunction on the morphology,crystal structure,light absorption capacity,photogenerated charge separation and transmission efficiency,photocurrent density,initial potential and other PEC performance were studied.Scanning electron microscope（SEM）image,X-ray diffraction（XRD）and Raman spectroscopy（Raman）characterization results show that the sample films prepared by the experiment are nano rod shape,good crystallinity.The photochemical test showed that Sn doping improved the conductivity and reaction kinetics ofα-Fe₂O₃,and the photocurrent density ofα-Fe₂O₃ increased from 0.08m A/cm²(1.23 V_RHE)to 0.47 m A/cm²(1.23 V_RHE),and the initial potential also decreased by 130 m V.By constructing Bi₂S₃/Sn:Fe₂O₃ heterojunction,the light absorption capacity ofα-Fe₂O₃ samples was enhanced,the specific surface area was increased,the photogenerated charge transfer rate and separation efficiency were promoted,and the photocurrent density ofα-Fe₂O₃ reached 4.0 m A/cm²(1.23 V_RHE).Moreover,the stability of the sample was improved.（2）In this paper,Ti:Zn Fe₂O₄/Ti:Fe₂O₃ heterojunction nanorods were prepared by hydrothermal method,and the effects of Ti doping and heterojunction on sample morphology,crystal structure and PEC performance were studied.Through scanning electron microscope（SEM）image,X-ray diffraction spectrum（XRD）,Raman spectrum（Raman）and other characterization,it is proved that Ti doping and the construction of heterojunction has little influence on the morphology and crystal structure of the sample,but the heterojunction can improve the light absorption performance of the sample.Ti doping can increase the carrier concentration and conductivity ofα-Fe₂O₃,and thus increase the photocurrent density from 0.11 m A/cm²(1.23V_RHE)to 0.34m A/cm²(1.23V_RHE).In addition,The Ti:Zn Fe₂O₄/Ti:Fe₂O₃ heterojunction is constructed.Due to their well-matched lattice size and energy band structure,they can form a tight heterojunction interface,which is conducive to promoting the separation and transfer of photogenerated charge by electric field at the interface of the heterojunction.The photocurrent density reaches 0.62 m A/cm²(1.23 V_RHE).（3）In this paper,a layer of CQDs and Co-Pi was loaded on the surface of Ti:Zn Fe₂O₄/Ti:Fe₂O₃ heterojunction by soaking and photoassisted electrochemical deposition,and the action law and mechanism of photothermal materials and oxygen-producing cocatalyst on the performance of Ti:Zn Fe₂O₄/Ti:Fe₂O₃ heterojunction were studied.After loading CQDs and Co-Pi,the photocurrent density of the sample increased from 0.62 m A/cm²(1.23 V_RHE)to 0.8 m A/cm²(1.23 V_RHE).After CQDs was excited by 808nm near-infrared light to produce photothermal effect,the photocurrent density of the sample increased to 1.06 m A/cm²(1.23 V_RHE)。This is because the photothermal effect enhances the carrier concentration in the Ti:Zn Fe₂O₄/Ti:Fe₂O₃heterojunction,improves the bulk injection efficiency and surface separation efficiency of the photogenerated charge,and significantly improves the charge transfer efficiency.