Preparation Of Bismuth Vanadate Based Photoanode Material And Research On Its Optical And Electrical Properties

With the development of industry,energy consumption is also increasing rapidly.The excessive abuse of fossil fuels has made the environment and energy crisis more and more serious.Therefore,an environmentally friendly approach that can effectively utilize solar energy to solve the energy problem is urgently needed.The most prospective of the solar energy converting technologies is the photoelectrochemical（PEC）water separation technology.BiVO₄is composed of cheap elements,simple preparation method,high stability in aqueous electrolytes,and proper energy level positions.And its forbidden band width is also small,about 2.4～2.5 e V,and it can absorb visible light well.This has led to the widespread use of single-crystal BiVO₄as a photoanode material for photoelectrochemical water separation.But the actual PEC activity of BiVO₄is at low level,and there are various limitations,such as severe composite of photogenerated carriers,poor electron mobilities(about 10^-2·cm²·V^-1·s^-1),and slow reaction dynamics.In this essay,the BiVO₄photoanode with porous structure was prepared by electrodeposition method combined with metal organic decomposition method.On this basis,the BiVO₄photoanode was retrofitted through a series of procedures,thus enhancing the PEC behavior of BiVO₄.The main elements are as shown below:（1）BiOI photoanode was prepared by electrodeposition method,and then the vanadium source solution was added dropwise to the BiOI film and annealed to convert BiOI into BiVO₄,thereby preparing BiVO₄photoanode.CuFeO₂was deposited on the surface of BiVO₄photoanode to construct a p-n-type heterojunction to explore its effect on the performance of BiVO₄,and a BiVO₄/CuFeO₂photoanode material was obtained.Then,Ni Fe-LDH was deposited on the surface of the BiVO₄/CuFeO₂photoanode by the same approach to obtain the BiVO₄/CuFeO₂/Ni Fe-LDH photoanode.The photo-current intensity was 4.34 m A·cm^-2at 1.23 V vs.RHE,which was 3.78fold higher than that of the pristine BiVO₄photoanode,and it can be found that its PEC performance has been greatly improved.The performance improvement can be attributed to two points.One is the deposition of p-structured CuFeO₂semiconductor film on the surface of n-structured BiVO₄,the two structures are compounded and constitute a p-n heterojunction.The strong built-in electric field in the p-n heterojunction accelerates the separation of photoexcited electron-hole pairs and inhibits the compounding of photogenerated carriers;another reason is that after deposition of Ni Fe-LDH,Ni Fe-LDH film increases the specific surface area of surface oxidation reaction,improves the utilization rate of holes,and accelerates the process of water oxidation.The synergy of the two improves the rate of charge separation in the semiconductor,while enabling the kinetics to be enhanced,and also alleviate the recombination of photogenerated carriers,thereby enhancing its PEC performance.（2）The basic bismuth vanadate photoanode was prepared by the same method as（1）,and then Fe OOH semiconductor material with amorphous structure was introduced as the first layer of catalyst deposited on the surface of the bismuth vanadate photoanode to obtain BiVO₄/Fe OOH photoanode.The final BiVO₄/Fe OOH/Zn Fe photoanode was produced by depositing Zn Fe oxygen release co-catalyst on the surface of BiVO₄/Fe OOH photoanode in the same way.However,the stability of the BiVO₄/Fe OOH/Zn Fe photoanode is not very good because both the amorphous structure of Fe OOH and the stability of the Zn Fe co-catalyst itself are not very good,which makes the stability performance of the final sample poor.However,the combination of the two catalysts greatly improved the PEC performance of the photoanode material,improved the charge separation efficiency and increased the water oxidation active sites.