Construction Of BiVO₄/Bi₂S₃/rGO And α-Fe₂O₃/ZnFe₂O₄/Co-Pi Photoanodes For Solar Photoelectrochemical Water Splitting

To meet the various energy challenges of this century,there is an urgent need to develop a low-cost,sustainable and clean energy source that can replace fossil fuels to meet the growing energy demand.Solar energy is considered as one of the most promising renewable energy sources to effectively solve energy problems due to its advantages such as universality and harmlessness,and therefore efficient conversion of solar energy to chemical energy（e.g.,hydrogen）is an ideal way to meet long-term energy needs.Solar photovoltaic chemistry（PEC）hydrogen production by hydrolysis has attracted a lot of attention from researchers.Metal oxide semiconductors are considered to be excellent candidates for photoelectrodes in PEC hydrolysis systems due to their own advantages of high stability,low cost,and non-toxicity,however,their drawbacks such as poor electronic conductivity and slow water oxidation kinetics limit their practical applications in PEC hydrolysis.In this thesis,BiVO₄andα-Fe₂O₃semiconductor photoanodes were prepared based on fluorine-doped Sn O₂conducting glass（FTO）by an efficient and low-cost method,and the PEC performance of single BiVO₄andα-Fe₂O₃semiconductor materials were improved by introducing narrow bandgap semiconductors Bi₂S₃and ZnFe₂O₄to construct type II heterojunctions,respectively,and further improved by modifying redox graphene（r GO）and cobalt phosphate（Co-Pi）co-catalysts synergistically with the heterojunction to enhance the photoanode PEC performance.The details of the study are as follows:（1）BiVO₄ nanoparticles were homogeneously grown on FTO substrates by electrodeposition,and the type-II heterojunction BiVO₄/Bi₂S₃was constructed by introducing the narrow band gap semiconductor Bi₂S₃using a facile hydrothermal method considering its energy band structure,and then the r GO was modified on the surface of the photoanode using spin coating and thermal reduction methods.The results show that the photocurrent density of the BiVO₄/Bi₂S₃/r GO photoanode at 1.23 V vs RHE(2.40 m A·cm^-2)is 3.4 times higher than that of the bare BiVO₄photoanode(0.70 m A·cm^-2),and the onset potential is negatively shifted by 140 m V compared with that of BiVO₄.The highest efficiency of IPCE and ABPE reaches 39.68%and 0.24%,respectively,while the charge transfer resistance R_ctdecreases to 163Ω.This is attributed to the construction of the heterojunction and its synergistic effect with r GO,which extends the light absorption of the photoanode,promotes the effective separation of carriers,and improves the PEC performance of BiVO₄.（2）The hole diffusion length ofα-Fe₂O₃is only 2-4 nm,and for its high electron-hole complexation rate,α-Fe₂O₃/ZnFe₂O₄type II heterojunction was prepared by introducing ternary bimetallic oxide ZnFe₂O₄using the successive ion layer adsorption（SILAR）method,and further depositing Co-Pi groups to provide more hole acceptors and catalytic for the photoanode sites to accelerate water oxidation.The results show that theα-Fe₂O₃/ZnFe₂O₄/Co-Pi photoanode has the best PEC performance,and the photocurrent density can reach 2.05 m A·cm^-2,which is 2.5 times higher than that of the bareα-Fe₂O₃photoanode(0.60m A·cm^-2),with a negative cathodic shift of 221 m V in the starting potential and IPCE and ABPE efficiencies were improved to 1.7 and 4.6times that of the bareα-Fe₂O₃photoanode,respectively,indicating that the construction of heterojunctions and the deposition of Co-Pi groups can effectively reduce the complexation rate of electron-hole pairs,provide more active sites for water oxidation,and improve the PEC performance ofα-Fe₂O₃.