Study On Photoelectric Properties Of Iron Oxide Semiconductor Materials

With the rapid development of human society,People's demand for energy increases daily.However,the problems of atmospheric and environmental pollution caused by fossil energy have brought significant challenges to the sustainable development of human society.As nature does in photosynthesis,converting solar energy into storable chemical energy is an excellent method to break away from fossil fuel dependence.Photoelectric catalytic water splitting,which converts solar energy into hydrogen,is a perfect energy carrier for achieving a carbon-free economy.Metal oxide semiconductors are frequently utilized because of their low cost of implementation,and they are a promising optoelectronic material because of their ease of synthesis and oxidation stability.In particular,iron oxide(?-Fe2O3),with its low price,narrow bandgap(2.1ev),As a perfect photoanode material,has gotten a lot of attention and investigation because of its high theoretical solar-to-hydrogen conversion efficiency.However,?-Fe2O3 has a short carrier diffusion distance,low carrier concentration,and slow kinetics of the water oxidation reaction,making high performance a tremendous problem.In this paper,novel nanostructured iron oxides are prepared by thermal evaporation(CVD).Surface oxygen vacancies are introduced by annealing in various atmospheres to improve the conductivity of iron oxides,increase the carrier concentration in the photoanodic reaction of iron oxides,and promote the charge separation and conversion efficiency,which can accelerate the kinetic process of the oxidized water reaction and improve its photoelectric catalytic water splitting performance.This paper mainly includes the following parts:(1)Preparation of iron oxide by thermal evaporation and research on its photoelectric catalytic performance:The preparation of iron oxide by traditional hydrothermal methods requires water-phase synthesis,which leads to the adsorption of more hydroxyl groups(-OH)on the surface,which reduces the charge separation ability of ?-Fe2O3,and makes the photogenerated carriers generated by the ?-Fe2O3 photoanode.It is easier to recombine in the bulk phase,and the photoelectric catalytic activity becomes poor.To overcome this limitation,an iron oxide photoanode with a pyramid-shaped or micro-cone-shaped nanostructure was created using a one-step low-temperature thermal evaporation process.Put SnCl2.2H2O and FeCl3 6H2O into a rectangular quartz crucible according to a particular proportion,mix well,and place the cleaned FTO horizontally on the customized quartz crucible to ensure that the conductive surface faces downwards.The quartz crucible was placed in a tube furnace and kept in an air atmosphere at 550?.For 2 hours,cooled to room temperature and washed with deionized water to obtain an ?-Fe2O3 photoanode.X-ray diffraction(XRD),scanning electron microscopy(SEM),and high-resolution transmission electron microscopy(HRTEM)showed its near-single crystal crystallinity and unique micro-conical morphology.X-ray photoelectron spectroscopy(XPS)demonstrated that the thermal evaporation method was synthesized out of the aqueous phase,avoiding the surface-adsorbed hydroxyl groups.The photoelectrochemical test results,such as the current-time curve(IT)and linear voltammetry curve(LSV),show that the thermal evaporation method of ?-Fe2O3 has better performance in photoelectrochemical water splitting than the water-phase synthesized ?-Fe2O3.The significant improvement provides a good idea for the industrialized preparation of iron oxide photoanode.(2)Influence of the introduction of surface oxygen vacancies on the photocatalytic performance of iron oxide photoanode:iron oxide itself has poor electrical conductivity,slow water oxidation kinetics,and poor charge separation and transfer efficiency during the reaction process activity of ?-Fe2O3 photoanode.In response to this problem,since the hightemperature annealing of iron oxide in an oxygen-free environment will generate surface oxygen vacancies(-Ov),by creating a local nitrogen environment and annealing,surface oxygen vacancies were successfully introduced into the ?-Fe2O3 photoanode.Two FeOOH nanofilms were prepared on the FTO substrate by the hydrothermal method,placed in a tube furnace respectively,and annealed at 550? for 2 h under nitrogen and air atmospheres to obtain the samples.XRD and Raman spectroscopy(Raman)test results prove that the samples prepared by annealing in different atmospheres are in the same phase of ?-Fe2O3.SEM and TEM test results show that their morphology is almost the same.The test results of XPS prove that the samples are in a nitrogen environment.After annealing,surface oxygen vacancies can be successfully introduced on the ?-Fe2O3 photoanode.The LSV and incident photoelectron conversion efficiency(LPCE)test showed that surface oxygen vacancies would positively affect the ?-Fe2O3 photoanode,which significantly improved its water oxidation capacity photoelectric conversion efficiency.(3)Secondary hydrothermal optimization constructs branch-type micro-nano Fe2O3 composite structure:Because iron oxide's PEC performance is severely limited by weak electrical conductivity,short hole diffusion distance,and inevitable surface imperfections that hinder the kinetic process of water oxidation,it's critical to figure out how to boost charge transfer efficiency.We optimized the shape of the Fe2O3 photoanode in response to this issue.We started with Fe2O3 micro-rods as the primary structure.We then used secondary hydrothermal to wrap a layer on top of the micro rods that consisted of a disorderly arrangement of nanoparticles and nano-burrs.A branch-type micro-nano composite structure is built using the Fe2O3 secondary structure layer.The prepared four FeOOH precursors were subjected to secondary hydrothermal treatment at 100? for 0 minutes,15 minutes,30 minutes,and 60 minutes,then annealed at 550? to obtain foura-Fe2O3 photoanodes.According to XRD,Raman,and XPS measurements,the secondary nanostructure layer generated by secondary hydrothermal is still the same iron oxide phase.The electric doublelayer capacitance(Cd1)test demonstrates its enhanced photoelectrochemical surface area.The Fe2O3 photoanode with a micro-nano composite structure has a shorter carrier transport distance,higher charge transfer efficiency,and a considerable increase in photoelectrochemistry,according to photo-electrochemical I-T and LSV experiments.