BiVO₄ Photoanode Prepared By Metal-organic Decomposition And Its Photoelectrochemical Water Splitting Performance

Photoelectrochemical（PEC）water splitting is an effective method to convert solar energy into hydrogen energy,which has great potential to solve the energy crisis and environmental problems,so it has received much attention in recent decades.Among the numerous photoanode materials,BiVO₄has the advantages of suitable band gap,environmental friendliness and low fabrication cost,which make it become a potential photoanode material.The metal-organic decomposition method（MOD）is one of the most popular methods for preparing BiVO₄photoanodes due to its simple process,suitable for large-area preparation,and high compatibility with modification technology.However,the BiVO₄photoanode prepared by MOD method has the problem of poor reproducibility.The reproducibility problem of thin film preparation not only affects the manufacturability of BiVO₄photoanode,but also affects the accuracy and credibility of the research results.Improving the PEC performance of BiVO₄photoanode by improving the preparation method is another important subject.Although the PEC performance of BiVO₄photoanode can be improved by modification technology,the unmodified BiVO₄photoanode determines the upper limit of its performance after modification.In addition,the understanding of the nature of BiVO₄is still insufficient.Surface states play a crucial role in PEC devices.However,up to now,few studies have reported the effect of the electron occupancy rate of surface states on the surface hole transfer efficiency in solar water splitting.Therefore,this paper focuses on improving the reproducibility of BiVO₄photoanode prepared by MOD method,improving the PEC performance of unmodified BiVO₄photoanode,and exploring the effect of BiVO₄photoanode surface state on PEC performance.The main results are as follows:1.Improve the reproducibility of BiVO₄photoanode prepared by MOD method by using dimethyl sulfoxide（DMSO）as the solvent of the precursor solution.The instability of the precursor solution is the main reason for the poor reproducibility of the BiVO₄photoanode prepared by MOD method.Using DMSO as the solvent of the precursor solution can effectively enhance the stability of the precursor solution,thereby improving the reproducibility of BiVO₄photoanode.The dispersion coefficient（standard deviation/average value）of the BiVO₄photoanode prepared with DMSO（D-BiVO₄）is 0.12.For comparison,the dispersion coefficient of the BiVO₄photoanode prepared with methanol（M-BiVO₄）is0.23.In addition,using DMSO as solvent can also effectively improve the PEC performance of BiVO₄photoanode.At 1.23 V vs.RHE,the photocurrent density of D-BiVO₄reached to1.15 m A cm^-2（AM 1.5 G,+1.23 V vs.RHE）,which is 4.1 times higher than that of M-BiVO₄photoanodes.Using DMSO as solvent can reduce the charge recombination in the bulk of BiVO₄photoanode,thereby improving the charge transport ability of the electrode.2.On the basis of using DMSO as the solvent of the precursor solution,the UV-US treatment of the precursor solution can effectively improve the PEC water splitting performance of the BiVO₄photoanode.The photocurrent density of BiVO₄photoanode prepared by using the precursor solution with UV-US treatment reaches to 1.76 m A cm^-2（AM1.5 G,+1.23 V vs.RHE）,which is 12.3 times of the BiVO₄photoanode prepared by the precursor solution without treatment.Research and analysis shown that the UV-US treatment can not only increase the porosity of the film,but also increase the concentration of oxygen vacancies in the BiVO₄photoanode.Combining the porous structure and the strategy of increasing oxygen vacancies,the PEC performance of the BiVO₄photoanode has been significantly improved.3.Explore the effect of surface states of BiVO₄photoanode on surface hole transfer efficiency.In this study,we measured the surface hole efficiency of the BiVO₄photoanode under front-and back-illumination,and analyzed the electron occupancy rate of surface states by the capacitance values of surface states fitted by photoelectrochemical impedance spectroscopy（PEIS）.Compared with back-illumination,under front-illumination,the surface hole transfer efficiency is higher and the electron occupancy rate of surface states is lower.These results show that the electron occupancy rate of the surface state is an important factor affecting the surface hole transfer efficiency.The decrease of the electron occupancy rate of the surface state can reduce the trapping probability of the surface state for holes,thereby reducing the recombination probability of carriers on the surface and enhancing the surface hole transfer efficiency.