| Energy crisis and environmental pollution are important issues that need to be solved for the sustainable development of modern society.Solar energy is vastly abundant and renewable energy resource in the planet,which is regarded as one of the most promising ways to produce hydrogen to address energy challenges.WO3 is an n-type metal oxide semiconductor with an optical band gap of 2.5-2.8 e V,which absorbs about 12%of the solar spectrum.Moreover,it has a lot of attractive advantages,such as medium hole diffusion length??150 nm?,good electron mobility(?12 cm2 V-1 s-1),good corrosion resistance in acidic electrolytes,and earth-abundant.However,severe bulk carrier recombination,poor stability,as well as sluggish surface oxidation kinetics are major drawbacks of WO3 photoanodes in solution with p H>4.Therefore,modification of the WO3photoanode is a necessary strategy to improve its photocatalytic performance.In view of the above shortcomings of WO3 photoanode,the effects of photoelectrocatalytic water splitting performance on different substrates,nanostructures and heterojunction materials were systematically studied and the structure-activity relationship of the WO3 photoanode was gradually enhanced.The specific research contents are as follows:?1?Construction of WO3-based photoanode composites based on FTO substrates:WO3nanoplate arrays was prepared via hydrothermal method.Then,the WO3 nanoplate array was wrapped with Bi VO4 by a drop coating method to construct a WO3/Bi VO4 type II heterojunction.In order to further improve the PEC performance,the WO3/Bi VO4 composite nanoplate array deposits a Zn O passivation layer with a certain oxygen vacancy by an atomic layer deposition?ALD?process at low temperature.The results show that the designed WO3/Bi VO4/Zn O photoanode exhibits a higher photocurrent density(?2.96 m A cm-2,1.23VRHE),a lower initial potential(?300 m VRHE),and a higher IPCE value?72.8%at 380 nm?and better stability?attenuation only about 9%after 6 h of reaction?,benefiting from the constructed type II heterojunction and the introduced oxygen-deficient Zn O passivation layer.?2?Synthesis of WO3 self-supported photoanode:hydrothermal reaction in aqua regia solution was performed at different temperatures,using a metal tungsten sheet as a raw material.The metal tungsten is used as the substrate,and the tungsten source is provided by the self-corrosion of the tungsten sheet in the aqua regia solution.After the hydrothermal reaction,the WO3·H2O nanostructure is grown on the tungsten sheet,and the self-supported WO3photoanode is obtained by calcination in the air.The effects on its microscopic nanostructures were investigated by changing the temperature and time of the hydrothermal reaction.The results show that the in-situ preparation of a self-supported WO3 photoanode consists of an inner layer of nanoparticles,an intermediate layer having a gradually increasing size,and an outer layer of an array of nanosheets,forming a spatially distributed homojunction.At the same time,the distributed homojunction leads to the formation of a gradient oxygen vacancy distribution from the inner layer to the outer layer,thereby generating a spatially distributed built-in electric field in the photoanode,which greatly improves the separation efficiency of the carrier.The prepared WO3 photoanode exhibited a photocurrent density of up to 1.81 m A cm-2in a neutral electrolyte solution at 1.23 VRHE under AM 1.5G irradiation.?3?Synthesis of multilayer WO3 self-supported photoanode:Based on the synthesis of self-supported WO3 photoanode,the WO3.H2O lamellar structure prepared by hydrothermal reaction,and it can be retained after calcination by coupling foaming technology.Due to the large specific surface area and the shortened carrier diffusion pathway,the separation and transfer efficiency of the photo-generated carriers of the obtained photoanode are significantly improved,reaching 87%and 79%at 1.23 VRHE,respectively.?4?Synthesis of Au nanoparticle-modified WO3 self-supported photoanode:The loading of noble metal Au nanoparticles was carried out on the multilayer WO3 photoanode.In this work,certain amounts of Au particles were deposited on the surface of the multilayer WO3photoanode and between the layers by magnetron sputtering.The results show that the absorption of the multilayer WO3 photoanode in the visible region is enhanced after the Au particles loaded.The Au nanoparticles attached to WO3 act as sensitizers,absorb resonance photons,generate thermal electrons from surface plasmon resonance?SPR?excitation,and inject hot electrons into the conduction band of WO3 layer nanostructures.Theoretical calculations also show that the electron injection of Au into the conduction band of WO3produces a built-in electric field directed from Au to O,thereby reducing the recombination rate of photogenerated carriers.The photocurrent is increased by about 20%compared to the non-modification photoanode. |
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