Study On The Performance Of Iron Oxide Photoanode In Photoelectrolysis Of Water

The human society is in a stage of rapid development.At present,the traditional fossil energy is facing problems such as resource shortage and environmental pollution,which makes the demand for clean and renewable energy increasing day by day.As a green energy,hydrogen energy is an ideal solution to this problem,and people have also made in-depth research on it.In a series of energy schemes,photoelectrochemical water decomposition technology has great application potential due to the use of continuous solar energy to split water into hydrogen.Unfortunately,its further development is limited by efficient and stable photo anode materials.Among many photocatalytic semiconductor materials,α-Fe2O3 has become one of the ideal photoanode materials with low price,suitable band gap(2.1 eV),excellent light absorption coefficient and good stability.However,due to its poor conductivity,short hole diffusion length,and slow water oxidation kinetics process,its performance is limited,making its photocatalytic water splitting efficiency far lower than the theoretical value.In order to solve these problems,in this paper,Fe2O3/Fe3O4 heterojunction was constructed to increase the absorption coefficient and photothermal effect,Sn and Ru doping improved the conductivity of iron oxide,promoted the increase of carrier concentration,and surface modified the passivation layer to make holes more easily diffuse to the surface of iron oxide,reduce the photogenerated electron hole recombination,thus improving the performance of photoelectric catalytic water splitting.The main contents of this paper are as follows:(1)The influence of different amount of Sn doping on the photocatalysis of iron oxide photoanode and the mechanism analysis:One of the main factors limiting the performance of iron oxide is its poor conductivity,which makes it difficult for holes to diffuse to the sample surface and react with the electrolyte to generate hydrogen.To solve this problem,this study enhanced the The unique feature of Fe2O3 in its photoelectric catalytic water splitting performance is that,in this experiment,by constantly introducing Sn element,it is observed that Effect of Fe2O3 on photoelectric properties.The specific implementation process is as follows:The Fe2O3 sample is immersed in an alcohol solution containing tin chloride crystals,and then annealed at 550℃ for 5 minutes to obtain a sample of iron oxide doped with Sn element once.In this way,it can be recycled for 6 times to introduce different amounts of Sn element.Motschottky curve shows that the flat band potential of doped samples has a tendency to shift to the right,which proves that the conduction band has a positive shift relative to NHE.At the fourth time of doping,the carrier concentration is the highest.At the same time,the corresponding EIS diagram shows that the conductivity at this time is better than that of the other times of doping α-Fe2O3 sample.Thus,the charge transfer inside the iron oxide is improved,the dynamic reaction of water oxidation is enhanced,and the photoelectric performance of iron oxide as the photo anode is improved.(2)The surface modification passivation layer and Ru doping jointly enhance the photocatalysis of iron oxide:nanorod iron oxide has quantum confinement effect due to its structural advantages,which slightly increases the hole diffusion length,but there are still problems of poor conductivity and too fast photogenerated electron-hole recombination.Here,the use of noble metal Ru element doping improves the conductivity of iron oxide nanorods.Photogenerated electron holes will not be easily compounded and annihilated.A very thin layer of TiO2 passivation layer is modified on its surface to reduce the composite center on the surface.The ultra-thin structure will not reduce the conductivity.At the same time,it can make the surface energy band structure bend,the electrons easily migrate to FTO,and the holes diffuse into the electrolyte,The catalytic ability of iron oxide as photoanode was further improved.(3)Photoelectric properties and research of multilayer Fe2O3/Fe3O4 heterostructures with wide spectrum absorption:using one-step hydrothermal method,by changing the reaction time under liquid conditions,respectively,to 1,2.5,4 hours,and then annealing at 500℃ for two hours,to form nano flake pure iron oxide,semi paved Fe2O3/Fe3O4,and fully paved Fe2O3/Fe3O4 heterostructures,and conducted photoelectrochemical tests.The research shows that as long as Fe3O4 is loaded,the light absorption coefficient of the sample outside 800 nm will increase,which makes Fe2O3,which can only absorb visible light,broaden the spectral absorption range to the near-infrared region,and improve the utilization efficiency of solar light.At the same time,this is also proved and reflected in the photothermal effect.In addition,Fe3O4 obviously enhanced the overall conductivity of the sample due to its internal ferrous ion,showing a smaller semicircle figure in the EIS spectrum,which is consistent with the guess through equivalent circuit fitting.The linear voltammetric scanning curves(LSV)of the three samples show that the photocurrent is 0.08 mA/cm2,0.68 mA/cm2 and 0.20 mA/cm2 respectively at the corresponding 1.23 V RHE.Among them,the performance of fully covered heterostructures is degraded due to excessive Fe3O4 hindering the light absorption ability of Fe2O3.