Theoretical Study On Oxidation-reduction Reaction Of Substrate-Controlled Graphene

In recent years,with the rapid development of science and technology,the level of computers has also been rapidly improved,which makes the first-principles method based on the density functional theory widely used in many fields.Scientific researchers usually use the density functional theory to understand the electronic structure and basic properties of materials from the microscopic scale view,and use this research method to design some new functional materials.With the gradual unveiling of many unique properties and excellent properties of nanomaterials,their applications have begun to attract widespread attention.The study of surface catalytic activity of low-dimensional functional materials is of great significance for understanding the catalytic reaction mechanism and designing novel composite catalysts.The application of first-principles calculations to understand the basic catalytic properties of low-dimensional material surfaces at the atomic level is an important means for us to search for suitable catalysts.In this paper,we studied the catalytic activity and reaction mechanism of the redox reaction of graphene,pyridinic N-doped graphene,and substrate-controlled graphene surface from the viewpoint of computational simulation.In the first chapter,we mainly introduced the basic framework of density functional theory and the software packages used in this paper.Density functional theory is usually based on quantum mechanics.It is considered that the ground state properties of a multi-particle system are a function of electron density of the ground state.Therefore,based on the electron density of the ground state of the system,the properties of the system are obtained by solving the ground state particle density function.This density function is mainly established by the Kohn-Sham equation,which converts multi-particle systems with complex interactions into effective particles without interacting systems.The ground state charge density function is solved by exchange-correlation functional and self-consistent iterative calculations.At this point,we will figure outthe corresponding system energy,which is called the energy of the ground state.In the calculation and application of the density functional theory,the related software packages also play a auxiliary role,providing an effective tool for the theoretical simulation calculation.In the second chapter,we mainly introduced the mechanism of redox reaction.In recent years,the transfer mechanism of two-electron and four-electron step wasthe most discussed mechanism of redox reaction.However,it was found that the four-electron step presented more reliability in numerous studies and comparisons.Many scientific researchers have found that each step in the four-electron step transfer mechanism has a proton and an electron transfer.According to the reaction mechanism of four-electron step in the process of redox reaction,werespectivelygot the stable structures of the initial state,intermediate state and final state by DFT calculation.The binding energy of each state is obtained by self-consistent iterative method,and the Gibbs free energy of each reaction step is obtained according to the relevant equation.The catalytic activity of various catalysts was analyzed by means of adsorption energy,Gibbs free energy and electron structure.In the third chapter,we mainly studied the electrocatalytic activity of pure graphene and pyridinic N-doped graphene in oxygen reduction reaction(ORR).First,pure graphene was used as the catalytic surface,and the surface catalytic process of redox reaction was calculated.Pyridinic N was then doped into graphene,and the effect of nitrogen doping on the electrocatalytic activity in the oxygen reduction reaction(ORR)was investigated.It was found that when pyridinic N-doped graphene was used as an ORR catalyst in the reaction,although the work function of the entire system was reduced,and the adsorption energy of each intermediate state was relatively smallerthan pure graphene,the overall catalytic effect was influenced bythe acidity and basicity of the reaction solution.Under acidic conditions,the effect of pure graphene and pyridinic N-doped graphene as an ORR catalyst was not obvious.In the fourth chapter,we mainly combined our theoretical work with experiments,developing a novel organometallic complex(N-heterocyclic carbene(NHC)-cobalt complex)with NHC as a nitrogen-containing precursor and N-doped carbon nanosheets coated with Co nanoparticles,which may bea highly active ORR catalyst.Experimental and theoretical calculations have demonstratedthat encapsulation of Co nanoparticles in N-doped carbon nanosheets can faciliatethe protonation of O2 during ORR,thereby promoting the catalytic activity of ORR.These results provide new prospects for the rational design and bottom-up synthesis of ORR heteroatom-doped carbon materials.In the last chapter,we used density functional theory(DFT)to calculate the electrocatalytic activity of different substrate-loaded graphene as an electrocatalyst for oxygen reduction(ORR).Although many scientific researchers have previously designed a series of substrate-loaded graphene catalysts(such as Fe and Ni,etc.)and have also demonstrated an increase in their ORR catalytic activity,up tonow,graphemes loaded by anionic compounds are rarely studied.The anionic compounds not only have the advantages of stable structure and good safety performance,but also ion channels,which can facilitate the diffusion and transmission of electron ions,and are considered to be more ideal cathode materials for lithium ion batteries.In this chapter,we mainly used the anion compounds Y5i3 and Ca2N as examples to load pure graphene,respectively,to study the influence of substrates of graphene on the catalytic activity of redox reactions.The calculated results showed that both Y5Si3 and Ca2N can transfer electrons to the surface of graphene,which reduces the local work function system,faciliates the protonation of O2,reduces the ORR reaction barrier,and promotes the ORR activity.