Theoretical Study On The Application Of Two-dimensional Heterostructure Based On MXene In Electrocatalytic Hydrogen Evolution Reaction

For a long time,the use of electrochemical water splitting to produce hydrogen has been considered an important technology that will not cause serious environmental pollution.Through the electrocatalytic hydrogen evolution reaction（HER）,water can be converted into hydrogen with high combustion value,which becomes an ideal clean energy that can replace fossil fuels.At present,in the selection of electrocatalytic hydrogen evolution reaction catalyst,noble metal-based catalysts are still the most effective HER catalysts,especially platinum,which is currently the most advanced HER catalyst.However,the limited resources and high cost of noble metal-based catalysts hinder their development and application,so there is an urgent need to develop non-precious metal HER catalysts with high efficiency and low cost.Recently,two-dimensional（2D）ultrathin nanomaterials have gradually become a research hotspot due to their unique layered structure and excellent electrochemical performance.Based on this,material scientists designed and synthesized a series of two-dimensional materials with excellent electrocatalytic properties,such as graphene,transition metal dichalcogenides（TMDs）,graphitic carbon nitride（g-C₃N₄）and 2D transition metal carbon（nitride）compounds（MXene）,etc.The electrochemical properties were studied in depth.However,compared with Pt catalysts,2D materials still have a large room for improvement in HER catalytic activity,which is mainly attributed to their higher hydrogen adsorption free energy.Therefore,how to improve the HER activity of two-dimensional materials has become the bottleneck factor for whether such materials can enter the stage of large-scale application.Recent studies have demonstrated that heterostructures composed of 2D materials such as MXene exhibit superior catalytic performance over similar catalysts in electrochemical water splitting.However,the enhancement mechanism of such heterostructures composed of two-dimensional materials in electrocatalytic performance is still unclear and needs to be further explored.In order to solve the above problems,we explored the effects of different functional groups,doping rates,and heterostructure types on the HER performance of 2D material heterostructures through theoretical simulations,and conducted an in-depth analysis of their intrinsic causes.This provides a good theoretical support for the design and optimization of novel HER catalysts.The main research contents are as follows:Firstly,based on the first-principles density functional theory,we studied the geometric and electronic properties of the heterostructure composed of MXene（Ti₂CO₂,V₂CO₂,Sc₂CO₂）and NDG,which further investigated the effects of mxene type,N doping rate and H coverage on HER activity.The results show that there is obvious electron transfer between the interfaces of heterostructures.In the process of forming heterostructure,the addition of MXene changed the electronic structure of NDG surface,which in turn enhanced the adsorption of H on NDG surface and effectively improved the HER activity.Among the heterostructures composed of different types of MXene and NDG with different doping rates,Sc₂CO₂/NDG exhibited the best catalytic activity.These research results are of great significance for the design and improvement of high activity electrocatalysts in the future.Secondly,on the basis of the above work,the effect of the types of functional groups on the geometric and electronic properties of the heterostructure and its HER performance was studied after the heterostructures formed by MXene with three functional groups of-O,-F and-OH and graphene with different N doping rates.The results show that the magnitude and direction of electron transfer under different functional groups are different due to the difference of the work function in the two-dimensional materials.In addition,the types of functional group will also have a certain influence on the electronic properties and HER activity of the heterostructures.Among them,the O functional group has the greatest impact on the heterostructures.The heterostructure in which the O functional group is located shows better catalytic activity.Finally,we investigated the geometrical and electronic properties of twelve heterostructures built with different MXenes（Sc₂CO₂～W₂CO₂）and B-doped graphene,as well as their H adsorption properties.The results show that the type of MXene has a certain influence on the HER performance of the heterostructure.During the formation of the heterostructure,there is a certain electron transfer between the heterostructure interfaces due to the difference of the constituent unit work function,which in turn affects the heterostructure.Among all heterostructures,Y₂CO₂/BDG has the largest binding energy and better HER performance.Subsequently,with the different types of MXenes,their effects on the adsorption of H to BDG are also different.Comparing all the heterostructures,the Y₂CO₂/BDG heterostructure is closest to the H adsorption energy of Pt,indicating that Y₂CO₂/BDG is a relatively potential HER catalyst.