Designation Of BiVO₄-based Composite Photoanodes For Photoelectrochemical Water Oxidation

III Photoelectrochemical?PEC?water splitting has been regarded as a promising route to replace the traditional hydrogen production methods,such as steam reforming of fossil energy and electrolysis of water.Moreover,the rate-limiting step of water splitting belongs to oxygen evolution reaction.Therefore,constructing a high-efficiency photoanode and exploring how it works play an important role in PEC water splitting field.BiVO₄,a typical study object for photoelectrocatalysis,possesses suitable bandgap and sufficiently positive valence band.However,its main drawbacks including poor electron mobility,short hole diffusion length and sluggish reaction kinetics hinder the actual photocurrent density and solar to hydrogen?STH?efficiency far away from the theoretical values.To solve the problems,we focus on researching the impacts for BiVO₄ of doping?heterojunction and co-catalyst.The main contents are as follows:1.We firstly assemble a CoPi/NiMoO₄/BiVO₄ composite photoanode using hydrothermal method for loading NiMoO₄ and photo-assisted electrodeposition method for depositing Co Pi.The as-prepared photoanode exhibits excellent PEC performance,for example,the photocurrent density reaches 5.3 m A cm^-2 and the photo utilization efficiency achieves up to 1.18%.On the basis of physical characterizations and electrochemical measurements,we attribute to the reasons as follows: 1)The fully coated NiMoO₄ layer makes unexpected synergistic effects with BiVO₄ on account of the heterojunction formation,which facilitates the electrons and holes separated quite effectively.Additionally,the solar light absorption ability is improved and surface charge transfer efficiency??trans?is enhanced due to the excellent absorption capacity and electrical conductivity of NiMoO₄.2)The modification of co-catalyst Co Pi can capture the photo-generated holes that reach the surface of electrode for water oxidation reaction,which further enhance the photo utilization efficiency to 1.18%.2.Mo⁶⁺ is doped into the lattice of BiVO₄ by a spin-coating and calcination method firstly,and then the p-type semiconductor Ag VO₃ is loaded on it through a successive ionic layer adsorption and reaction?SILAR?process.Consequently,the as-obtained photoelectrode owns outstanding PEC catalysis activity compared to the bare BiVO₄.In detail,it boosts the photocurrent density by 7 folds at 1.23 V vs.RHE,and moves the onset potential negatively by 387 m V.With detailed physical and electrochemical characterization,we contributed the excellent PEC performance to appropriate Mo doping that enhances the carrier density and electron mobility of BiVO₄ as well as the more exposed?040?facet for retarding recombination and increasing active sites.It is worth mentioning that the simple SILAR process grows Ag VO₃ nanoparticels homogeneously with uniform diameter of 3-5 nm,and abundant oxygen vacancy emerged on the surface,which are beneficial for exporting photo-generated holes and increasing active sites for water oxidation reaction.