Construction Of BiVO₄ Composite Photoanode And Its Photoelectrochemical Water Splitting

The excessive exploitation and use of fossil fuels have brought resource depletion and air pollution to the earth.Photoelectrochemical（PEC）water splitting can reduce fossil pollution and produce clean energy hydrogen,which has attracted wide attention worldwide.In order to produce hydrogen by means of PEC water splitting driven by solar,the development of stable,efficient and low-cost photoelectrode materials is the key.Bismuth vanadate（BiVO₄）,as an oxide semiconductor,has a suitable band gap of 2.5 eV and a high theoretical photocurrent density of 7.5 mA/cm²（AM 1.5 G,100 mW/cm²）,making it a promising photoelectrode material in the field of photoelectrochemical hydrogen generation.However,the serious recombination of photogenerated carriers,slow carrier migration rate and slow oxidation kinetics of the electrode extremely restricted its photoelectrochemical（PEC）performance,which make it difficult to reach the theoretical photocurrent intensity.In this paper,the photochemical properties and the stability of of BiVO₄ were improved by the construction of heterojunction and deposition of Co-Pi co-catalyst.The relevant research carried out in this paper is as follows:（1）BiVO₄ nanofilms were prepared on FTO by metal-organic decomposition（MOD）.Red Bimetal electrode film（BiOI）was deposited on the conductive glass by electrodeposition.Afterwards VO（acac）₂ solution was dropped uniformly on BiOI film,and then chemical-thermal process was used to convert Bimetal film to yellow BiVO₄ by annealing.n-BiVO₄/p-CuBi₂O₄ thin film photoanode was successfully prepared by electrochemical deposition of p-type CuBi₂O₄ on BiVO₄ thin film under constant voltage condition,which was used for Photoelectrochemical（PEC）water splitting.By controlling the addition amount of CuBi₂O₄,the best performance of the photoelectrode was achieved.The results show that n-BiVO₄/p-CuBi₂O₄ heterojunction photoanode has excellent PEC water oxidation performance when the mass fraction of CuBi₂O₄ is 10%,the photocurrent density reached 3.15 mA/cm²at 1.23 V vs.RHE,which was 3.6 times that of bare BiVO₄.When p-CuBi₂O₄ was loaded,the recombination rate of electron and hole decreased significantly under the action of the built-in electric field,which promoted the charge transfer to the electrode surface and improved the water oxidation rate of BiVO₄-based electrode.（2）After the addition of cobalt phosphate（Co-Pi）cocatalyst,the photocurrent density reached 5.52 mA/cm²at 1.23 V vs.RHE,which was 6.3 times that of bare BiVO₄.The morphology,structure,optical and photoelectrochemical properties of BiVO₄/CuBi₂O₄/Co-Pi film electrodes were characterized by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,ultraviolet-visible（UV-Vis）spectroscopy,and electrochemical impedance spectroscopy（EIS）,and photoelectric chemical properties of BiVO₄/CuBi₂O₄/Co-Pi film electrodes were tested.Under the action of built-in electric field and band bending,BiVO₄/CuBi₂O₄/Co-Pi composite electrode material shows good light absorption characteristics,low carrier interfacial transfer resistance,excellent photoelectric chemical properties and stability.As a hole receiving layer,cobalt phosphate（Co-Pi）cocatalyst layer can effectively collect holes,promote the separation and migration of carriers,and accelerate the water oxidation reaction on the electrode surface.BiVO₄/CuBi₂O₄/Co-Pi photoanode showed excellent photocatalytic activity of water oxidation,and the photoelectric corrosion degree of the photoanode decreased in the reaction.The addition of Co-Pi significantly improved the photochemical stability of BiVO₄ material.