Preparation And Photoelectrochemical Properties Of BiVO₄ Photoanodes

Energy crises and environmental pollution are major problems facing humanity.Developing renewable clean energy is the key to solving energy and environmental problems.As a clean energy source,hydrogen energy is considered as the most potential renewable energy.At present,solar energy can be used to generate hydrogen through photocatalytic water decomposition and photoelectrochemical water splitting.Compared with photocatalytic decomposition of water,photoelectric catalysis is a more efficient way to obtain hydrogen.Semiconductor photoelectrode materials play an important role in photoelectrochemical water splitting.Among them,BiVO₄ is widely used in photoelectrocatalysis because of its stable chemical properties and narrow band gap.However,BiVO₄ still has problems such as slow charge transportation and photogenerated electron-hole pair recombination.In order to promote the transportation and separation of photogenerated charges,a ternary composite g-C₃N₄/Ag/BiVO₄ and Ni-doped BiVO₄ photoanodes were constructed and the photoelectrocatalysis behaviors of the materials were studied.The results are as follows:?1?BiVO₄ photoanode materials with porous structure were prepared by spin-coating and calcination.Based on the characterization of the morphology,phase and optical properties of BiVO₄ photoanode,the photocurrent density of BiVO₄photoanodes prepared under different conditions was measured by LSV.The effects of PVA content in precursor solution,number of spin coatings and calcination temperature on the photoelectrochemical properties of BiVO₄ photoanode were investigated.The results show that the content of PVA in the precursor solution and the number of spin coatings affect the morphology and optical absorption intensity of BiVO₄ photoanodes,and the calcination temperatures affect the crystallinity of BiVO₄ photoanodes,thus affecting their photoelectrochemical properties.When the content of PVA is 0.6 g,the number of spin coatings is three layers and the calcination temperature is 500?,the photocurrent density of BiVO₄ photoanode is the highest.The photocurrent density of BiVO₄ photoanode can reach 0.46 mA?cm^-22 when the applied bias voltage is 1.0 V?vs.Ag/AgCl?.?2?g-C₃N₄/Ag/BiVO₄ photoanodes were prepared by the impregnation method.The phase,morphology and optical properties were characterized by XRD,SEM,TEM,XPS and UV-vis.The results show that Ag nanoparticles and g-C₃N₄nanosheets are uniformly coated on the surface of BiVO₄.The photocurrent density of g-C₃N₄/Ag/BiVO₄ photoanode can reach 1.85 mA?cm^-2under an applied bias voltage of 1 V?vs.Ag/AgCl?,about 4 times that of BiVO₄ photoanode(0.43 mA?cm^-2).Mott-Schottky and electrochemical impedance spectroscopy?EIS?measurements show that the composite material can increase the carrier density of BiVO₄photoanodeandpromotethecarriertransportandseparationatthe semiconductor/electrolyte interface.Compared with BiVO₄ photoanode,the IPCE of g-C₃N₄/Ag/BiVO₄ photoanode increases from 14.0%to 28%.?3?Ni-doped BiVO₄ photoanodes were prepared by hydrothermal method,and the influence of Ni doping on the photoelectrochemical properties of BiVO₄photoanode was explored.The UV-visible diffuse reflectance spectrum shows that the band gap of BiVO₄ photoanode decreases after Ni doping,which is more beneficial to light absorption.The photoelectrochemical properties of BiVO₄ photoanodes and Ni-BiVO₄ photoanodes were evaluated by LSV,EIS,Mott-schottky,IPCE,etc.The results show that the photocurrent density of 0.5%Ni-doped BiVO₄ photoanode could reach 1.01 mA?cm^-2?1V vs.Ag/AgCl?,which is about 1.57 times that of the undoped BiVO₄ photoanode.After Ni doping,the lifetime of electrons increases from7.4 ms to 13.1 ms and the IPCE of Ni doped BiVO₄ photoanode increased from14.0%to 20%.These results show that Ni doping can increase the carrier concentration,promote the carrier transport and the photoelectrc conversion efficiency of BiVO₄ photoanode,thereby improving the photoelectrochemical performance.