Synthesis Of BiVO₄-based Photoelectrodes And Photoelectrocatalytic Water Splitting Performance

Hydrogen energy is considered to be an ideal energy,because of its renewable,environmentally friendly,high energy density,and large-scale preparation.Photoelectrocatalytic water splitting for hydrogen production is in line with the concept of green chemistry and sustainable development,and has received widespread attention.At present,the application of photoelectrocatalytic water splitting technology in practical production still faces some difficulties,the most prominent is the catalytic ability of photoelectrode materials.Bismuth vanadate?BiVO₄?as a hot spot material for photoelectrocatalytic water splitting has the characteristics of visible light absorption,suitable valence band position,and low cost and easy availability.However,poor photo-induced carrier transportation and slow kinetics for oxygen evolution of BiVO₄ makes the photoelectric conversion efficiency far from the theoretical value.In this thesis,BiVO₄ was modified by element doping,surface modification and composite structure to improve the photoelectrocatalytic water splitting efficiency of BiVO₄.The main research contents of this thesis are as follows:?1?Preparation of phosphorus-doped BiVO₄ photoanode and its photoelectrocatalytic water splitting properties.Phosphorus doped BiVO₄?P-BiVO₄?photoanodes were prepared by dip-coating method.XPS analysis showed that phosphorus doping makes BiVO₄ have more abundant oxygen vacancies than pure BiVO₄.EIS and Mott-Schottky results show that P-BiVO₄ has less interfacial resistance and higher carrier concentration.The photocurrent density of the 2%P-BiVO₄ photoanode was as high as 0.28 mA·cm^-2 at1.23 V?vs RHE?in 0.5 M Na₂SO₄electrolyte,which is 2.8 times that of pure BiVO₄ photocurrent.?2?Preparation of Co₃O₄ modified BiVO₄ photoanode and its Photoelectrocatalytic water splitting properties.Since the zeta potential of Co-MOF and BiVO₄ is different,Co-MOF is adsorbed onto the surface of BiVO₄ photoelectrode,and the Co₃O₄ film-modified BiVO₄ photoelectrode is obtained after high temperature treatment.Combined with XRD,SEM and XPS analysis,Co₃O₄was successfully loaded on the surface of BiVO₄.Co₃O₄ acts as a cocatalyst to increase the oxidation power of BiVO₄.Compared with pure BiVO₄,the electron injection efficiency of9Co₃O₄/BiVO₄ photoelectrode is significantly improved,indicating Co₃O₄ acts as a cocatalyst to increase the oxidation hydrodynamics of BiVO₄.Under the simulated sunlight irradiation and1.23 V?vs RHE?bias,the optimal 9Co₃O₄/BiVO₄ photoelectrode has a photocurrent density of2.35 mA·cm^-2,which is 2.9 times than that of pure BiVO₄(0.81 mA·cm^-2).?3?Preparation of MCo₂O₄/BiVO₄?M=Mn,Zn?composite structure and its photoelectrocatalytic water splitting properties.The porous structure of BiVO₄ electrode was synthesized by electrochemical deposition and heat treatment,and then the co-catalystMCo₂O₄?M=Mn,Zn?was spin-coated to obtain MCo₂O₄/BiVO₄?M=Mn,Zn?composite photoelectrode.SEM images showed that the particles of MCo₂O₄?M=Mn,Zn?were uniformly distributed on the surface of porous BiVO₄.The DRS image shows thatMCo₂O₄?M=Mn,Zn?broadens the absorption range of visible light of BiVO₄electrode.The charge injection efficiency of the sample was studied by using Na₂SO₃ as a hole trapping agent.The high charge injection efficiency of MCo₂O₄/BiVO₄ indicates that the combination of BiVO₄ and MCo₂O₄ can enhance the oxidizing water capacity.Under simulated sunlight irradiation?AM 1.5G?and 1.23 V?vs RHE?bias,the optimal photocurrent of BiVO₄loaded with ZnCo₂O₄ and MnCo₂O₄ reached 2.15 mA·cm^-2 and 2.79 mA·cm^-2,which are 2.6times and 3.4 times of pure BiVO₄(0.81 mA cm^-2),respectively.