Preparation And Photoelectrochemical Performance Of ZnO Homojunction And TiO₂/ZnO Heterojunction

With the utilization of fossil energy,energy crisis and environmental pollution have become two major problems for human to solve.Photocatalytic water splitting technology can convert solar energy into hydrogen energy,which is a promising renewable energy technology.In order to improve the efficiency of charge separation of photocatalyst,one of the most effective methods is to build composite junction.Based on metal defect and oxygen defect control,n-ZnO/p-ZnO and n-TiO₂/p-ZnO film electrodes were prepared,and the effect of internal electric field of p-n on the catalytic activity of film electrodes was investigated.Firstly,the n-ZnO/p-ZnO homojunction were prepared by in-situ solvothermal growth of metal deficient ZnO in n-ZnO.EPR and M-S curves show that metal vacancies and oxygen vacancies can regulate the p-type and n-type conductivity of ZnO.PEC tests show that p-n homojunction can reduce the charge transfer resistance,promoting the separation and transmission of photogenerated carriers,enhancing its photocatalytic activity.When the solvothermal time is 36 h,n-ZnO/p-ZnO electrode has the highest photoelectrocatalytic activity（1.56 mA/cm²,1.23 V vs.RHE）and stability.In addition,the piezoelectric effect can generate piezoelectric electric field on surface of ZnO,strengthening the reverse migration of photogenerated carriers and improving the photoelectrocatalytic performance.Then,n-TiO₂/p-ZnO heterojunction nanoarrays were prepared by loading p-ZnO quantum dots（3-5nm）on the surface of TiO₂ through solvothermal method.The characterization results show that the introduction of p-ZnO QDs can not only improve the absorption capacity of TiO₂,but also form a strong internal electric field at the p-n junction interface,which promote the transfer of photogenerated electrons and holes,and improves the efficiency of carrier separation.When the amount of zinc acetate was 10 mg,n-TiO₂/p-ZnO showed the highest photocatalytic activity（1.70 mA/cm²,1.23 V vs.RHE）and good stability.Besides,Ni OOH was modified on the surface of catalyst by electro-deposition,thus enhancing the transfer of photogenerated carriers and improving the reactivity of the catalyst.