First-Principles Study On Electronic Structure And Photocatalytic Activity Of Two-Dimensional ZrS₂/XSe（X=In,Zn） Heterostructures

Photocatalytic water decomposition technology provides a broad prospect for the use of solar energy and water resources to solve the current energy crisis.Hydrogen energy has the characteristics of high efficiency,cleanliness and a wide range of sources,so it is the best choice to realize the sustainable development of human society.Among the many methods of hydrogen production,the use of abundant water resources and sunlight in nature to produce hydrogen by photolysis is a very ideal method.However,when a single semiconductor material is used as a photocatalyst,it usually has some defects such as narrow light absorption range and high recombination rate of photogenerated carriers,which makes its hydrogen production efficiency on the low side.The construction of van der Waals heterostructure is an effective way to improve the efficiency of photocatalyst for hydrogen production.Inthis thesis,the electronic structure and photocatalytic properties of ZrS₂/InSe and ZrS₂/ZnSe heterojunctions are constructed and discussed based on the first principle.Firstly,the electronic and optical properties of ZrS₂/InSe van der Waals heterostructures are studied systematically based on density functional theory（DFT）.The most stable geometric structure is obtained by calculating the binding energy of the ZrS₂/InSe heterostructure model,and its thermodynamic stability is verified by molecular dynamics simulation.The calculated results show that the ZrS₂/InSe heterostructure has Type-Ⅱ type energy band arrangement,and the staggered band structure is beneficial to the separation of photogenerated carriers,which provides indispensable conditions for the application of heterostructure in the field of photolysis.At the same time,the migration path of photogenerated electrons and holes in ZrS₂/InSe heterostructures accords with the direct Z-scheme charge transfer mechanism,which has a suitable band edge position for hydrogen and oxygen evolution reactions,and the Z-scheme mechanism can retain the stronger redox ability of heterostructure materials.Inaddition,the ZrS₂/InSe heterostructure has better optical absorption coefficient than the two monolayer materials.The optical properties of the heterostructure can be regulated by applying biaxial strain,so as to improve the photocatalytic properties of the heterostructure.The 21.31%conversion efficiency of solar energy for hydrogen production means that ZrS₂/InSe heterostructure has great potential in the field of photocatalytic decomposition of water to hydrogen.Inorder to find suitable monolayer materials and ZrS₂ to construct more excellent heterostructure photocatalysts,monolayer ZnSe was vertically stacked on top of monolayer ZrS₂ to build ZrS₂/ZnSe heterostructure.The electrical and optical properties and charge transfer mechanism of two-dimensional ZrS₂/ZnSe heterostructure were studied.The results show that ZrS₂/ZnSe heterostructure is an indirect band gap semiconductor with Type-Ⅱ band arrangement.The built-in electric field from ZnSe to ZrS₂ accelerates the reorganization of photogenerated electrons in ZrS₂ and photogenerated holes in ZnSe,resulting in the accumulation of photoexcited electrons and holes in the conduction band（CB）of the ZnSe layer and the valence band（VB）of the ZrS₂ layer,respectively.The results show that the ZrS₂/ZnSe heterostructure is a direct Z-scheme photolysis mechanism.Inaddition,the band edge position of ZrS₂/ZnSe heterostructure jumps over the redox potential of water decomposition,and its optical absorption coefficient is significantly higher than that of monolayer materials in ultraviolet and visible light region.Inaddition,the high conversion efficiency of 23.26%indicates that ZrS₂/ZnSe heterostructure has important application prospects in the field of photolysis water.