Prediction Of Non-layered Two-dimensional Carbides And Investigation Of Their Potentials In Catalytic Field

Serious environmental pollution problem and the shortage of resources urge us to explore new energy sources.Because of its trait of environmental protection and reproducibility,hydrogen energy is regarded as one of the most important new energy sources.There are many ways to produce hydrogen,but how to produce hydrogen on a large scale efficiently and environmentally is a huge challenge.Encourageingly,the electrolytic reaction of water is able to meet the requirements,and more importantly,the raw material for the reaction is water which is abundant on earth.Hydrogenation(HER)is the most important step in the process of electrolysis of water to produce hydrogen,and its reaction efficiency is closely related to the characteristics of the material.Therefore,the development of new and efficient catalytic materials has become a key problem of hydrogen energy utilization.In recent years,non-layered two-dimensional materials have attracted people's attention.The suspended bonds on the surface increase the activity of the materials,so these materials show a high catalytic capacity.Previous research has shown that rock salt structural carbide has high boiling point,high hardness,and good corrosion resistance and oxidation resistance,which are conducive to their good catalytic materials.Therefore,it is of great significance to study two-dimensional carbonides with non-stratified rock salt structure and explore their application in catalysis.Based on the density functional theory,two kinds of non-layered two-dimensional carbide structures,TiC(100)sheet and HfC(100)sheet,were predicted and their catalytic applications were explored in this paper,aiming to find new two-dimensional materials with high catalytic capacity.The main research contents of this article are as follows:(1)The stability of TiC(100)sheet was studied systematically.The research results of cohesive energy,phonon scattering curve and potential energy curve show that the TiC(100)sheet is very stable both in terms of energy and in terms of thermodynamics.(2)The catalytic performance of TiC(100)sheet was systematically studied.The results show that under 1/4 coverage,the bilayer TiC(100)sheet has good catalytic performance(?G_H is 0.13 eV).Further introducing the biaxial tensile strain of about3.25%,?G_H can be reduced to the ideal value(0 eV).The results of studies on the effects of different thicknesses on the catalytic performance of TiC(100)sheet show that under2/4 coverage,four-layered and six-layered TiC(100)sheet have better catalytic performance than bilayer TiC(100)sheet(?G_H are-0.04 and-0.06 eV,respectively).(3)The stability of HfC(100)sheet was studied systematically.The research results of cohesive energy,phonon scattering curve and potential energy curve show that the HfC(100)sheet is very stable both in terms of energy and in terms of thermodynamics.(4)The catalytic performance of HfC(100)sheet was systematically studied.The calculation results of?G_H show that the catalytic performance of the bilayer HfC(100)sheet is not satisfactory.Further introducing a biaxial tensile strain of about 6%,the bilayer HfC(100)sheet exhibits excellent catalytic performance at 1/4 and 2/4 coverage(?G_H are-0.003 and 0.08 eV,respectively).The results of studies on the effect of different thicknesses on the catalytic performance of HfC(100)sheet show that the four-layered and six-layered HfC(100)sheet have good catalytic performance under 2/4coverage(?G_H are-0.04 and-0.07 eV,respectively).