Controllable Preparation And Regulation Of Uniform Structural Photoanodes For Enhanced Photoelectrochemical Performances

Photoelectrochemical(PEC)technology is one of the most promising ways to solve the problems of clean energy conversion and environmental pollution treatment,which has developed into the research hotspot in the field of energy chemistry and environmental chemistry.For PEC water splitting,the four electron transfer process on the photoanode is the speed-limiting step of the whole PEC system,so the design and preparation of the photoanode is the key issue in this field.The main factors affecting the PEC performance of photoanode are light absorption,charge separation and charge injection.Semiconductor materials which can be used as photoanode have also been greatly developed in recent years,but there are still many defects in single semiconductor material,such as limited light absorption range,easy recombination of photogenic carriers and slow oxidation kinetics.Therefore,how to enhance the light absorption range of photoanode materials,improve the effective separation and high utilization of photogenerated electron-holes,is still a challenge.In view of the above problems,this paper focuses on the controllable preparation and regulation of well-defined structural photoanodes to improve the intrinsic activity,which are further coupled with novel PEC reactions to expand and enhance their performances.Firstly,in terms of structural design and controllable preparation,a series of uniform structural photoanodes with one-dimensional nanorod arrays,two-dimensional nano-square arrays,nanoporous core-shell structure and exposure of active crystal facets were prepared by means of chemical vapor deposition(CVD),electrochemical deposition and hydrothermal synthesis,respectively.In this way,the structural photoanodes can effectively improve the surface/interface environment of the structural photoanodes,to enhance the absorption efficiency,charge separation and charge injection.Secondly,on the basis of structural photoanodes,the design of PEC water splitting coupling related reactions were effectively applied in energy conversion and pollution treatment fields such as urea oxidation,hydrogen production from seawater,tetracycline hydrochloride degradation,etc.,thus broadening the practical application of photoelectrocatalysis in energy chemistry and environmental chemistry.The detailed research contents are as follows:(1)Controllable preparation and photoelectrochemical performances of structural BiVO4 photoanodesTo improve the defects of short charge transfer distance,poor interface charge transport and slow oxidation kinetics for BiVO4,structural design of orderly nanorod arrays with surface/interface engineering including morphology control,hole blocking layer insertion and modification of cocatalyst was carried out.The as-perpared one-dimensional SnO2@BiVO4 core-shell nanorod arrays decorated with cobalt-phosphate cocatalyst(1D SnO2@BiVO4/Co-Pi NRAs)show efficient charge separation and transport properties due to the rational design of conducting core-layer and introduction of the cocatalysts shell.In consequence,the ternary photoanode exhibits promising PEC performance for urea oxidation.Moreover,NiFe-LDH modified F-doped BiVO4 core-shell structural photoanode was also designed and successfully fabricated through surface/interface engineering of element doping and heterojunction construction.The structure of material and PEC properties of the photoanode have been systematically studied,the results show that the maximum photocurrent density of the photoanode at 1.23 V vs.RHE is about 6-fold that of the pristine BiVO4 photoelectrode.Moreover,the obtained F-BiVO4@NiFe-LDH composite photoanode was effectively applied to the PEC degradation of tetracycline hydrochloride and the co-production of hydrogen,with the degradation rate reaching 86%within 2 hours and no attenuation after 4 cycles.Both the two works proposed a new perspective for design and preparation of ordered core-shell heterostructure photoanode,as well as the treatment of organic pollutant wastewater by PEC oxidation and producing high purity hydrogen with cathode simultaneously.(2)Controllable preparation and photoelectrochemical performances of structural BiVO4 photoanode with crystallographic orientationCrystal facets of semiconductor materials play a key role in photocatalysis,because their surface active centers and even their electronic structures depend on specific crystal facets.Different from photocatalytic process of powder materials,photoelectrochemical process requires reasonable exposure to specific crystal facets and good contact between semiconductor materials and conductive substrate.Moreover,the photogenic holes migrated to the surface of the photoanode should be utilized efficiently.Therefore,it is still a challenge to prepare and regulate structural BiVO4 photoanode with crystallographic orientation.Herein,facet engineered BiVO4 photoanode with highly exposed(040)facets parallel to the FTO substrate was prepared by an innovative seed-assisted hydrothermal method.Then the(040)crystal facets were reasonably designed and modified with an efficient cobalt-based atomically two-dimensional nanosheet arrays to further accelerate the surface reaction kinetics.The as-prepared structural BiVO4 composite photoanode with crystallographic orientation presented an impressive 99.47%charge injection efficiency.This work provides a promising approach to fabricate novel photoelectrodes for solar energy conversion,based on facet engineering matched with single-atom cocatalyst strategy.(3)Controllable preparation and photoelectrochemical performances of structural WO3 photoanode with crystallographic orientationHydrogen generation via PEC technology is one of the most ideal strategies for providing sustainable fuel,in particular,from the most abundant seawater resources on the earth surface,to save precious fresh water for production and living.On the basis of the above research,the structural WO3 arrays with crystallographic orientation were designed and prepared,which were further decorated with reasonable distribution of dual-cocatalysts,showing highly efficient and stable PEC H2 generation from natural seawater.The experimental and theoretical results illustrate that photo-generated electrons and holes accumulate directionally on different crystal facets of WO3 to achieve effective spatial separation,owing to the divergent energy levels of each crystal facet.Moreover,the charge utilization is further enhanced by selective modification of Ag nanoparticles and ZnFe-layered double hydroxide on different crystal facets reasonably,getting an average PEC H2 production of 38.18 ?mol h-1 from natural seawater with excellent stability.This work reveals the performance enhancement mechanism of crystallographic oriented WO3 structural photoanodes,and is expected to extend the facet engineering strategy to the design and preparation of other novel semiconductor photoanodes,which also makes a beneficial exploration for the potential applications of PEC hydrogen production from natural seawater.