Preparatiom And Photoelectrochemistry Properties Of In Situ Modified TTiO₂/BiVO₄ Heterojunction Thin Films

In photoelectrocatalytic(PEC)water splitting into hydrogen system,TiO₂/BiVO₄ heterostructure photoanode formed by recombination of TiO₂and BiVO4,with the advantages of increasing the lifetime of carriers and accelerating the separation of photogenerated electron-hole pairs,and is simple in preparation and low in cost,which are widely studied and applied.However,the relative conduction and valence band positions of BiVO₄ and TiO₂ were unfavorable.In common cases,the conduction band potential Vs NHE for TiO₂ is negative,while it is positive for BiVO₄.As a result,the electrons were hindered to transfer from BiVO₄ to TiO₂ in thermodynamics.And the weak adsorption capacity of BiVO₄ on its surface,photogenerated electron-hole pairs easily recombined still exist.Photoelectrocatalytic efficiency of the mass-based photoanode.Therefore,to solve the TiO₂/BiVO₄ heterostructure photoanode limit factors and improve the photoelectrode photocatalytic efficiency has important research and application value.In this paper,in-situ doping modified TiO₂/BiVO₄heterostructure photoanode materials were designed and prepared,which successfully solved the above problems and improved the photocurrent density and light conversion efficiency of the heterojunction photoelectrode.The main contents are as follows:(1)Hydrothermal method was used to prepare ZnO nanorods as the supporting framework for TiO₂ growth.Then the TiO₂ sol doped in situ was spin-coated on the ZnO nanorod support framework.After removal of the ZnO nanorods,Ta:TiO₂nanotubes with high network structure was formed.The Ta:TiO₂nanotubes were then prepared by spin coating BiVO₄ on Ta:TiO₂ nanotubes to prepare a Ta:TiO₂/BiVO₄ photoanode.The prepared Ta:TiO₂/BiVO₄ photoanode has more excellent charge transport properties and photoelectrocatalytic performance than the undoped TiO₂/BiVO₄photoanode.The feasibility of facile method described above has been investigated.With different photoelectrochemical and structural characterization techniques,we identify the effect of Ta on the energy band adjustment of anatase TiO₂,confirming the Type II alignment with BiVO₄.The Ta:TiO₂/BiVO₄heterostructures exhibited high photocurrent densities of 1.77 m A/cm2 at 1.23 V vs RHE bias and more than 3-fold increase in photocurrent density compared to TiO₂/BiVO₄(0.58 m A/cm2).The maximum photocatalytic efficiency of Ta:TiO₂/BiVO₄ photoanode was0.24%,and the applied bias was 0.95V(vs.RHE).Under the same conditions,the photoconversion efficiency was improved by 3.5 times compared with TiO₂/BiVO₄ photoanode.The novel facile method proposed here can greatly improve the performance of BiVO₄ for solar water oxidation,making the large-scale preparation possible.(2)ZnO nanorods were prepared by hydrothermal method as the support skeleton for TiO₂ growth,and then the Ta:TiO₂ sol was spin-coated on the ZnO nanorod support framework.After the ZnO nanorods were removed,highly networked TiO₂ nanotubes were obtained,Mo-BiVO₄/Ta:TiO₂ photoanode was prepared on TiO₂ nanotubes by in-situ Mo-doped BiVO4 spin-on coating.The prepared Mo-BiVO₄/Ta:TiO₂photoanode has more excellent charge transport properties and photoelectrocatalytic properties than the undoped Ta:TiO₂/BiVO₄photoanode.The experimental results show that the absorption band edge of the heterojunction electrode after Mo doped is about 510nm,The photocurrent density of Ta:TiO₂/BiVO₄ photoanode was 0.64m A/cm²at1.23V vs.RHE.the optimized Mo-BiVO₄/Ta:TiO₂ photoanode was markedly improved with a photocurrent density of 2.58 m A/cm²at 1.23V vs.RHE,which increased by 2.5 times than that of Ta:TiO₂/BiVO₄ photoanode.The maximum light conversion efficiency of Mo-BiVO₄/Ta:TiO₂photoanode was 0.44%and the bias voltage was 0.95V(vs.RHE).Under the same conditions,the light conversion efficiency increased by 83%than that of Ta:TiO₂/BiVO₄ photoanode.The stability test showed that the Mo-BiVO₄/Ta:TiO₂ photoanode has the ability to work stably for a long time and has the value of further research and application.