Preparation Of BiVO₄ Photoanodes With Oxygen Defect And Ni²⁺ Doping For Photoelectrochemical Applications

Over the past few decades,in order to achieve rapid and efficient economic development,the over-exploitation and usage of petroluem and other energy sources has not only made the energy shortage become a major problem affecting today's social development,but also the products of combustion have seriously polluted the global environment.The application of solar energy to photoelectrochemical?PEC?water splitting is a popular way to store sustainable energy while reducing human dependence on fossil fuels.The construction of oxygen defects or metal ion doping on the catalyst surface are two effective ways of photoelectrocatalysis and modification.In this paper,the oxygen deficient BiVO4 was synthesized by cyclic electrodeposition and its mechanism was explored.The photoelectric efficiency of the catalyst was further improved by introducing Ni²⁺doping.Firstly,the oxygen defect multi-layer BiVO4 thin films were synthesized by multi-cycle electrodeposition followed by annealing at high temperature.Multi-layer BiVO4 films have monoclinic scheelite structure,and the morphology is changed from densely compact film to sponge-like network,and then bulk structure with the increase of electro-deposited layers.X-ray photoelectron spectra indicates the presence of abundant oxygen vacancies and V⁴⁺species in multi-layer BiVO4,especially for 3-layer one.For visible-light PEC performance,3-layer BiVO4 shows the highest photocurrent among the samples,is up to 5.80 mA/cm² in sulfite oxidation and 1.79 mA/cm² in water splitting at 1.23 V versus a reverse hydrogen electrode?RHE?under 1 sun irradiation?100 mW/cm²?,with very high IPCE achieved nearly83%and 25%?at 420 nm?,respectively.The extremely high PEC performance of3-layer BiVO4 is attributed to its morphology of sponge-like network and the modulated band structure by the oxygen vacancies and V⁴⁺species.Moreover,the multi-layer BiVO4 also shows very high photostability.This work provides a multi-layer-construction method for highly visible-light-active PEC anodes for practical applications.On the basis of previous work,Ni²⁺doped BiVO4 is introduced in one step by means of electrodeposition and re-annealing.By introducing Ni²⁺doping,the morphology of BiVO4 is gradually linked by particles that are far apart from each other and are not linked to each other,and thus the transfer of electrons in the material is enhanced.XPS spectra shows that the material contains a certain amount of oxygen defects,Ni²⁺ions are used as shallow donors to enhance the separation of photo-generated electrons and holes.In visible PEC reaction,the photocurrent density of 5%Ni²⁺doped BiVO4 is 2 times over than pure BiVO4,and the doped material has good photostability.Under a simulated sunlight,when the illumination intensity is100 mW/cm²,the photocurrent of pure BiVO4 is 1.25 mA/cm²,and the photocurrent of 5%Ni²⁺doped BiVO₄ is 2.7 mA/cm².