Study On The Fabrication Of Zinc Oxide Photoanode And Their Photoelectrochemical Properties

Due to the excessive consumption of traditional fossil energy and the increasingly serious environmental pollution,it will be the focus of future research to find appropriate ways to solve the problems of environmental pollution and energy shortage.In recent years,photoelectric chemistry（PEC）decomposition of water to produce hydrogen technology has attracted people’s attention in the production and application of sustainable energy.Converting solar energy into clean hydrogen energy has become an effective way to solve the energy dilemma.The key to this method is the development of high-performance optical electrode materials.Zn O high exciton binding energy,high stability,good optical properties such as high reaction activity and rich raw material storage,make it become the ideal material to solve the problem of energy and environment is one of the,however due to the wide bandgap（3.37 e V）leads to low efficiency of light energy absorption and the serious composite carrier hindered its further application.In this paper,Zn O photoanodes were modified by surface modification,supported catalyst and surface polarization methods,and the photochemical properties of Zn O photoanodes were improved effectively.The specific research contents are as follows:（1）BFO/Zn O composite photoanode with core-shell structure was prepared by loading bismuth ferrite onto Zn O photoanode by spin-coating method.By optimizing the experimental conditions,the photocurrent density of the composite photoanode reaches 0.93m A/cm² at the bias voltage of 1.23 V（vs.RHE）,which is 1.41 times that of the Zn O photoanode.The charge injection efficiency and charge separation efficiency of the composite photoanode are significantly improved by the internal electric field on the surface.The increase of photocurrent density is due to the driving force provided by the built-in electric field of the ferroelectric material bismuth ferrate,which improves the charge separation efficiency of the composite photoanode.More carriers are involved in the redox reaction of water decomposition,which improves the PEC performance of the composite photoanode.（2）Narrow band gap nitrogen-doped carbon nitride（NCN）was prepared on the basis of g-C₃N₄.Then carbon quantum dots（CQD_S）solution was prepared by one-step ultrasonic alkali-assisted method.With Zn O nanorods as the substrate,g-C₃N₄,NCN and CQD_S were loaded on Zn O by spin-coating and impregnation methods,and different composite photoanodes were prepared.Namely,Zn O/g-C₃N₄,Zn O/NCN and Zn O/NCN/CQDs.The photocurrent density of Zn O/NCN/CQDs photoanode reaches 1.20 m A/cm² at the bias voltage of 1.23 V（vs.RHE）is 1.82 times that of Zn O photoanode,while the ABPE value of Zn O/NCN/CQDs composite photoanode reaches 0.258%,which is 2.10 times that of Zn O photoanode.Loading narrow band gap NCN can improve the light absorption range of Zn O photoanodes,and photosensitized CQDs can improve the electron transport capacity and light absorption capacity of Zn O photoanodes.Therefore,under the cooperative modification of NCN and CQDs,the PEC performance of Zn O/NCN/CQDs composite photoanodes is greatly improved.（3）The surface polarization of Zn O photoanode was investigated by solvothermal method.The Zn O photoanode was placed in a mixed solution of glycerol and ethanol and polarized by solvothermal method.The obtained photoanode was named Gly-Zn O.In the case of no supported catalyst and doping,the PEC performance of Zn O photoanode was greatly improved.The photocurrent density of Gly-Zn O photoanode increases from 0.66m A/cm² to 1.01 m A/cm²（1.23 V vs.RHE）is 1.53 times that of Zn O photoanode,and the charge injection efficiency and charge separation efficiency of Gly-Zn O photoanode are improved.The improvement of PEC performance after polarization is attributed to the fact that a large number of hydroxyl groups with electric dipoles form an electric field on the Zn O surface and increase the band edge,thus forming a homojunction in the Zn O interior.At the same time,the surface electric field drives the separation and transport of photogenerated electron hole pairs and accelerates the kinetics of water oxidation reaction of zinc oxide photoanode.