Preparation And Photoelectrochemical Water Oxidation Performance Of Bismuth Vanadate-based Photoanodes

Converting solar energy into hydrogen energy through semiconductor photoelectrochemical water splitting can effectively address the shortage of fossil fuels and environmental pollution issues.In recent years,monoclinic BiVO₄ has attracted considerable attention as a photoanode material because it can achieve a maximum photocurrent density of⁷.6 mA/cm² in theory?corresponding to a solar-to-hydrogen conversion efficiency of 9.3%under AM 1.5G illumination?.However,the poor charge separation and transfer properties,as well as the sluggish water oxidation kinetics severely limit its photocatalytic efficiency during the photoelectrochemical water oxidation of BiVO₄.In this paper,the water oxidation performance of BiVO₄ film photoanode was improved by means of doping,cocatalyst coupling and crystal facet engineering,the mechanism was also analyzed and demonstrated.The main research contents and results are as follows:?1?Using In³⁺as a dopant to substitute partial sites of Bi³⁺for the modification of surface states on BiVO₄ film photoanode,thus enhancing the photoelectrochemical water oxidation activity.The experimental results showed that the photocurrent density of the 7%In³⁺doped BiVO₄ photoanode was 1.56 mA/cm² at 1.23 V vs.RHE,which is twice that of undoped BiVO₄photoanode under the same conditions.Density functional theory calculations indicated that the surface energy of BiVO₄ is decreased after In³⁺doping,which reduces the amount of exposed unsaturated Bi atoms and broken Bi-O bonds on BiVO₄ surface,thus inhibited the surface charge recombination.Therefore,the enhanced water oxidation activity on the In³⁺doped BiVO₄ photoanode can be attributed to In³⁺-doping passivated the surface states of BiVO₄.?2?Using p-type CuCoO₂ with high spin Co³⁺_?Oh?as the co-catalyst to synergistically improve the surface charge separation and transfer efficiencies as well as the reaction kinetics for water oxidation of BiVO₄ film photoanode.The results showed that comparing to the BiVO₄photoanode?1.23 mA/cm²,1.23 V vs.RHE?,the CuCoO₂-coupled BiVO₄ photoanode exhibited a higher photocurrent density of 3.32 mA/cm² at 1.23 V vs.RHE;And its stability was also significantly enhanced,about 79%water oxidation activity is retained after 5 hours.The enhanced water oxidation activity and stability of CuCoO₂/BiVO₄ photoanode can be attributed to the synergistic effect of CuCoO₂-electrocatalysis and BiVO₄-photocatalysis in thermodynamics and kinetics.?3?BiVO₄ polyhedral films with exposed{121},{132},{211}and{251}high index facets were prepared by using a Bi₂O₃ template-induced method,and the surface charge separation,transfer properties and water oxidation kinetics of BiVO₄ were investigated.The results showed that,the multi high index facets BiVO₄-A film photoanode has a higher photocurrent density?1.21 mA/cm²,1.23 V vs.RHE?and a more negative water oxidation onset potential?0.52 V vs.RHE?compared with the normal BiVO₄-B film photoanode.Theoretical calculations indicated that the adsorption of H₂O molecules on BiVO₄{121}and{132}high index facets is energetically favorable for subsequent dissociation and oxidation relative to that on{010}and{110}low index facets.