Modification Of Bismuth Vanadate-Based Photoelectrode And Study On Photoelectrochemical Water Splitting Performance

The environmental problems caused by the burning of fossil fuels promote the preparation technology of green energy hydrogen to obtain considerable development.Photoelectrochemical（PEC）water splitting for hydrogen production is one of the most promising strategy.In the whole water splitting system,the design of photoelectrode is the key to improve the conversion of light energy into hydrogen energy.The narrow band gap and reasonable band edge position of BiVO₄ make it have great potential in photoelectrochemical water splitting.However,the serious electron hole recombination and slow water oxidation kinetics of BiVO₄ make the photocurrent density less than the theoretical value.In order to solve the above problems,construction of the heterostructure,loading of co-catalyst and doping of elements are adopted to optimize the charge transfer at the bulk and interface,so as to improve the photocurrent density and hydrogen production efficiency of BiVO₄.In this project,three different schemes are used to optimize the photoelectrochemical properties of BiVO₄,as follows:（1）The poly-dopamine（PDA）rich in functional groups was grown on BiVO₄ by the solution method,and then the thin-layer PDA was used as the functional support for the confined growth co-catalyst of Co-Pi（Co₃（PO₄）₂）to finally synthesize Co-Pi/PDA/BiVO₄ photoelectrode.PDA/BiVO₄ heterojunction can accelerate the separation efficiency of electron hole pairs.The function group confined bond growth of Co-Pi can reduce the aggregation of Co-Pi,facilitate the dispersion and size control of Co-Pi,significantly increase the catalytic activity sites at the interface,and thus accelerate the kinetics of water oxidation reaction at the photoelectrode.Compared with BiVO₄,the photocurrent density of Co-Pi/PDA/BiVO₄ is 7 times that of BiVO₄.At the same time,the charge injection efficiency and photoelectric conversion efficiency are also significantly improved.（2）Ag-Pi/BiVO₄ photoelectrode was synthesized by successive ionic layer adsorption reaction（SILAR）at room temperature.The preparation of Ag-Pi/BiVO₄ was proved by XRD,XPS and TEM.Ag-Pi/BiVO₄ heterojunction can accelerate charge transfer and improve the efficiency of electron hole pair separation.BiVO₄ with three-dimensional structure provides a larger specific surface area,which can provide more attachment sites for Ag-Pi nanoparticles,thus speeding up the water oxidation process.Therefore,the charge injection efficiency of Ag-Pi/BiVO₄ is significantly increased.Meanwhile,the onset potential has negatively shifted,which greatly improves the photocurrent density.（3）BiVO₄-Ni/Co₃O₄ photoelectrode was synthesized by hydrothermal method and high temperature annealing method,and its morphology and properties were characterized.Ni doping can improve the conductivity of the photoelectrode and facilitate the charge transfer.At the same time,Ni/Co₃O₄ as a co-catalyst for oxygen evolution can significantly accelerate the slow kinetics of water oxidation and avoid large-scale charge accumulation at the interface.The photoelectrochemical impedance spectrum,charge injection efficiency and separation efficiency of BiVO₄-Ni/Co₃O₄prove the great improvement of charge transfer capability,meanwhile,the photocurrent density and the photoelectric conversion efficiency of the photoelectrode are excellent.