In-situ Fabrication Of CdS-based Heterojunction And Research On Its Photocatalytic Hydrogen Production

As a cheap and green solar energy conversion technology,photocatalytic hydrogen production technology has proposed an ideal research direction to solve the world’s energy problems and achieve the goal of"double carbon"in China.Therefore,it has also been widely concerned by more and more researchers.However,with the deepening of research,the scientific and technological problems restricting the further development of photocatalytic hydrogen production technology have gradually surfaced,such as low solar spectrum utilization rate,low quantum efficiency,low surface reaction efficiency,etc.Taking the typical Cd S hydrogen production photocatalyst as an example,this paper intends to solve the above problems through a variety of heterostructure construction methods.Moreover,the reaction mechanism is practiced and proved by the experimental methods of XRD,SEM,TEM,XPS,DRS,hydrogen production test,photoelectrochemical test,etc.Meanwhile,we proposed and verified a novel composite photocatalyst preparation scheme.The main research contents and results are as follows:（1）The surface modification of Cd S photocatalyst by metal Cd can improve the surface carrier transfer efficiency and surface reaction efficiency of Cd S photocatalyst.In this stage of work,we creatively prepared Cd S/Cd₂SO₄（OH）₂ composites by one-step hydrothermal method instead of depositing metal Cd on Cd S surface by photochemical deposition method.The experimental results show that Cd₂SO₄（OH）₂can not only form type-II heterojunction with Cd S,capture photogenerated electrons in Cd S and improve the separation efficiency of photogenerated carriers,but also be reduced in situ by photogenerated electrons to metal Cd as electron capture trap and hydrogen production active center,and improves the surface carrier transfer efficiency and surface reaction efficiency of photocatalyst.As a result,compared with the hydrogen evolution efficiency（HER）of pure Cd S photocatalyst under UV,visible and simulated sunlight,the HER of Cd S/Cd₂SO₄（OH）₂ composite is increased by 40.1%,147.4%,50%and the HER of in-situ formed Cd S/Cd composite is increased by 89.9%,320.7%,117.9%respectively.Meanwhile,this study not only simplifies the experimental steps of the prepared Cd S/Cd composites,but also avoids the loss of Cd S activity in the process of photochemical deposition.（2）The introduction of narrow gap Ag₂S material improves the internal carrier transfer efficiency and solar energy absorption range of Cd S/Cd₂SO₄（OH）₂photocatalyst.In this stage of work,we selectively deposited Ag₂S on the surface of Cd S by in-situ ion exchange method.As expected,Ag₂S successfully extended the light absorption range of Cd S/Cd₂SO₄（OH）₂ system to the NIR,which makes the Ag₂S/Cd S/Cd₂SO₄（OH）₂ system show infrared photocatalytic activity.Meanwhile,Ag₂S can form a dense type-II heterojunction with Cd S,further promote the directional flow of carriers in Cd S,and it will not affect the in-situ reduction of Cd₂SO₄（OH）₂ to metal Cd in the photocatalytic process.As a result,due to means of potential difference,photogenerated electrons and holes in the Ag₂S/Cd S/Cd system will be directionally transferred to Cd metal and Ag₂S respectively,which not only makes the carrier space separate and greatly limits the carrier recombination,but also provides different redox reaction sites on the surface of Cd S and greatly improves the surface reaction efficiency.Ultimately,the Ag₂S/Cd S/Cd composite achieves excellent full-spectrum photocatalytic hydrogen production activity,and its light-to-hydrogen conversion efficiency（STH）is one order of magnitude higher than that of pure Cd S photocatalysts.