First-principles Study Of The Design And Application Of Two-dimensional Boron-carbon Based Functional Materials

Recent years,the research on structural engineering of two-dimensional(2D)materials has been widely explored,aiming to obtain specific functional materials.The combination of 2D carbon-based materials with electron-deficient boron shows different structural characteristics and electronic properties,which is beneficial to the functional application of the original system.Therefore,it is of great significance to explore 2D boron-carbon-based functional materials with large specific surface area,high structural stability and unique electronic properties by means of structural engineering.The main work and innovations of this thesis are as follows:First,four dynamically and energetically stable 2D boron-carbon-based materials,B₄C₉,BC₆,BC₂₀ and BC₂₀-II,are designed by a bottom-up synthesis with different boron-carbon-based precursors.The band structure and density of states studies show that B₄C₉and BC₆ have semi-metallic properties,while BC₂₀ and BC₂₀-II exhibit metallicity,because the electron-deficient of boron leads to a shift in the Fermi level.In addition,it is proved that BC₂₀ has the best energy stability,and maintains structural integrity at high temperature,by energy comparison and molecular dynamics simulation.Then,the performance of BC₂₀ as anode for potassium ion battery was investigated.The most stable adsorption site of K ions on the surface of BC₂₀ is above the center of the boron-carbon hexagonal ring,and its adsorption energy is lower than that of pristine graphene,indicating that the doping of boron atoms is beneficial to enhance the adsorption of potassium ions on graphene.The study of the electronic structure shows that the boron dopants result in an empty state above the BC₂₀ Fermi level,which is favorable for the filling of K valence electrons.The result of kinetic performance study shows that K ions have a lower migration barrier(0.19 e V),indicating the high charge and discharge rate.Through the potassiation process,it is determined that the maximum load of K ions on BC₂₀ is 16 without causing surface deformation and potassium clusters.The corresponding open circuit voltage is only 0.29 V,and the theoretical capacity is as high as 854 m Ah/g.All the results demonstrate that BC₂₀ is a promising anode material for potassium-ion batteries.Finally,the performance of BC₂₀ as a catalyst for CO₂ electroreduction is studied.The adsorption of gas on BC₂₀ showed that CO₂ has a large adsorption energy,which enhances the catalytic efficiency;while the adsorption performance of HCOOH is poor,which is conducive to the rapid desorption as the final catalytic production.Study on the reaction mechanism of electroreduction of CO₂ shows that BC₂₀ can catalyze the reduction of CO2 to HCOOH at-0.73 V.The potential side reaction is hydrogen evolution reaction,which is endothermic and cannot proceed spontaneously,indicating that the BC₂₀ monolayer has good catalytic activity and catalytic selectivity.In conclusion,a novel 2D boron-carbon-based functional material BC₂₀ is proposed by bottom-up synthesis strategy.According to the study of the stability,electronic structure,chemisorption performance,kinetic performance,and catalytic performance,BC₂₀ shows great application prospects in anode materials of potassium-ion battery and carbon dioxide electrocatalysis.