Photoelectrochemical Properties Of Hematite Films Deposited By Spray Pyrolysis

Since 1972,photoelectrochemical solar energy to decompose water into hydrogen has attracted more and more attention.Semiconductor photoelectrode materials are the core of photoelectrochemical decomposition of water to make hydrogen.It is generally believed that for a suitable photoelectrode material,its ideal semiconductor bandgap is around 2.0 eV.Iron oxides（all iron oxides mentioned herein areα-Fe₂O₃）have the advantages of low cost,non-toxicity,and good light stability.Especially,the bandgap is about 2.0 eV,and most of sunlight can be used.Therefore,iron oxide is a very promising photoelectrode material.Iron oxide is rich in resources,environment-friendly,chemically stable,with suitable energy band,etc.It is a photocatalyst with good application prospects.The morphology of iron oxides is diverse.The morphology of the thin films favors electron and hole transport,reduces the recombination of electron-hole pairs,and improves photocatalytic performance.At present,iron oxide has been widely studied in many aspects such as hydrogen production from photolysis of water,photodegradation of pollutants,photoelectrocatalytic reduction of CO₂,and sensors.Therefore,it is particularly important to improve the photoelectrochemical performance of iron oxide through the optimization of the preparation process.However,iron oxide photoelectrode material has poor conductivity,slow surface reaction rate,and small hole diffusion length,resulting in a low solar energy conversion efficiency,which limits its practical application.We have conducted a series of researches from the viewpoint of improving the conductivity of iron oxide and increasing the surface reaction rate.In this dissertation,iron oxide thin films were prepared on the basis of spray pyrolysis.Through the modification and compounding of iron oxide thin films,the preparation process for improving the photoelectrochemical performance of materials was identified.The optical properties of the sample were studied by UV-Vis diffuse reflectance spectroscopy,the charge recombination of the sample surface was studied by PL spectroscopy,and finally the composite sample was analyzed.Photoelectrochemical performance characterization.The main research work of the thesis is divided into the following points:1.FTO was prepared by spray pyrolysis,and the test parameters of the best conductivity and light transmission performance were obtained by controlling the temperature of the heating platform,the different proportions of the precursor,and the amount of the precursor.Then,by controlling the concentration of the FTO precursor and the concentration of the iron oxide film precursor,a thin film of iron oxide and fluorine-doped tin oxide（FTO）was prepared on the heated platform by spray pyrolysis,and the Fe₂O₃/FTO composite sample was prepared.When the concentration of the current flooding solution is 0.4 mol/L Fe（NO₃）₃,the prepared film has better performance,up to 0.01 mA/cm²,and has a special surface topography structure of"Flowered cabbage".When the proportion of FTO in the film is increased,the carrier concentration in the composite film can be increased,and the photoelectric conversion efficiency is greatly improved.This is attributed to the fact that FTO promotes the separation of electrons and holes by the absorption of sunlight by iron oxide films,reduces the recombination of electron holes,increases the current,and promotes the photoelectric conversion efficiency.2.The urea is calcined at a high temperature of 500 degrees Celsius for 3 hours by a high-temperature calcination method to obtain a light yellow powdered carbon nitride material,which is collected after centrifugal drying of the carbon nitride and passed through a spray pyrolysis technique.The iron nitrate solution containing carbon nitride was sprayed on the titanium sheet to obtain a composite film of carbon nitride and iron oxide,and better photoelectrochemical performance was obtained.Fe₂O₃/C₃N₄ composite samples exhibited the smallest resistance.Photoelectrochemical measurements were performed on the prepared iron oxide films and the composite films of iron oxide and carbon nitride.It was found that after the addition of carbon nitride,the impedance of the films has increased significantly,but the composite The photocurrent of the film is larger than that of the pure iron oxide film.This is because the added carbon nitride forms a heterojunction with iron oxide,which is advantageous for the separation of photoelectron-hole pairs.Experiments have shown that when 0.3 g of carbon nitride is added,the photoelectrochemical performance is best,the generated photocurrent is about 3 times that of the pure iron oxide film,and the photoelectric conversion efficiency is 3 to 4 times that of the pure iron oxide film.This is attributed to the fact that C₃N₄ promotes the absorption of sunlight by iron oxide films.The surface plasmon resonance effect of C₃N₄ generates a large amount of photo-excited electrons into the semiconductor.The effect of C₃N₄ increases the absorption of light and broadens the absorption range of light..3.The graphite oxide was prepared by the Hummers method,and then spray pyrolysis was performed to prepare a composite film of iron oxide and graphene with excellent performance by constantly adjusting the concentration of the graphene oxide and the concentration of iron nitrate.Iron oxide and graphene composite samples exhibited minimal resistance,and the photoelectrochemical performance was greatly improved.This was attributed to the fact that reduced graphene oxide increased the electrical conductivity of the iron oxide film and promoted the absorption of sunlight by the iron oxide film.The recombination of electron holes is reduced,and current is increased,leading to the photoelectric conversion efficiency is promoted.