Preparation And Photoelectrochemical Properties Of Heterojunction Based On ZnO Photoanode

With the rapid development of human society,energy and environmental issues have become increasingly prominent,and establishment of a clean energy system becomes an inevitable trend.Hydrogen,as a renewable clean energy with high energy density,will play an important role.Since Fujishima and Honda first adopted the semiconductor TiO₂photocatalytic decomposition of water to produce hydrogen in 1972,photoelectrochemical（PEC）water splitting has attracted attention due to its clean,low power consumption and sustainable characteristics.Constructing a semiconductor heterojunction not only can use the solar spectrum in a wider range,but also facilitate the separation of electrons and holes.Therefore,in this study,we used ZnO nanorods（ZnO NRA）as the photoanode to improve its PEC performance by construstingstructure of the heterojunctionand adjust the morphology.The main research work is listed as follows:1.The built-in electric field existed in the p-n junction is benefit for the separation of electrons and holes,therefor p-n junction is often used for PEC research.However,interface defects can cause the recombination of electrons and holes,limiting the further improvement of PEC performance.In this study,we first prepared n-type ZnO NRA by hydrothermal method,and then deposited Al on the surface of ZnO NRA by thermal evaporation.Al was then spontaneously oxidized to Al₂O₃,and finally the p-type was deposited by electrochemical deposition.Cu₂O was deposited on the surface of ZnO NRA-Al₂O₃.PEC performance test results indicate that,compared with ZnO,the PEC performance improvement of ZnO NRA/Cu₂O p-n junction is not obvious due to the existence of interface defects.However,when a thin layer of Al₂O₃is inserted at the interface,the defects at the interface are greatly reduced,effectively inhibiting the recombination of electrons in the conduction band of ZnO NRA with holes in the valence band of Cu₂O,and finally PEC performance is greatly improved.2.sensitizing ZnO NRA photoanode with CdS quantum dots can increase the specific surface area of the ZnO NRA photoanode,thereby greatly increasing the CdS loading amount and promoting the generation of more photogenerated electrons and holes.In this study,ZnO NRA was first prepared by hydrothermal method,and then sulfided with thioacetamide to obtain the ZnO NRA/Zn S hollow pipe array structure.Finally,the CdS quantum dots were modified on the surface of the ZnO NRA/Zn S hollow pipe array by the water bath method to prepare the ZnO NRA/Zn S/CdS photoanode.The PEC performance test results show that,compared with ZnO NRA,ZnO NRA/Zn S,ZnO NRA/CdS and ZnO NRA/CdS/Zn S,the PEC performance of ZnO NRA/Zn S/CdS is the best.3.The NiO is a p-type semiconductor with a narrow band gap.A layer of NiO modified on the surface of ZnO NRA-CdS can effectively promote hole transport and improve the PEC stability of CdS.In this study,ZnO NRA was first prepared by hydrothermal synthesis,then CdS quantum dots were modified on the surface of ZnO NRA,and finally NiO_x nanoparticles were modified on the surface of ZnO NRA-CdS by chemical bath deposition to obtain ZnO NRA-CdS-NiO_x.The PEC performance test results show that when the applied voltage is 1.5 V（vs.Ag/Ag Cl）,compared with ZnO NRA-CdS and ZnO NRA,ZnO NRA-CdS-NiO_x has the largest photocurrent density and the best PEC stability.