Study On The Mechanism Of Functionalized Graphene Electrocatalytic Oxygen Reduction Reaction

Fuel cell is the main and effective power generation device in modern society.It can directly convert chemical energy into electrical energy.It has the advantages of high efficiency,cleanliness,and low noise.It has been widely used in real life.In the oxygen reduction reaction(ORR),platinum and its alloys are the most widely used catalysts,but their high cost,low reserves,and poor stability are not conducive to the commercial development of fuel cells.Therefore,scientists are committed to finding efficient and inexpensive non-metallic catalysts to reduce or replace the use of platinum and its platinum-based alloy catalysts.Graphene has a large specific surface area,a high Young's modulus,good electrical conductivity,high charge mobility,and it can be used as an electrocatalytic carrier.However,graphene has disadvantages such as overhigh chemical stability,non-hydrophilicity,weak interaction with other media,poor solubility in organic solvents,and strong van der Waals force between layers,which tends to cause aggregation and other disadvantages.So requires modification of graphene.Therefore,the graphene needs to be modified,and the modified graphene is widely used in various fields,and its mechanism of action is also proposed and revealed one after another.In this dissertation,based on the first-principles method of density functional theory,the catalysis of S-N double-doped graphene and surface functionalized graphene in the oxygen reduction reaction and the catalytic activity of nitrogen-doped graphene are related to the factors.The main contents are as follows:First,the ORR mechanism of S-N double-doped graphene was studied using the B3LYP/6-31G** method.The S and N atom doping models at different positions were constructed.The charge,spin density and adsorption of OOH groups were obtained.The catalytic active sites can be evaluated.In order to predict its catalytic performance,electronic structures,reaction free energy,and transition state energy barriers for different pathways were calculated.Then,the effects of different potentials on the ORR were discussed,providing theoretical guidance for the experimental operation.This article also focuses on the introduction of nitrogen atoms that can achieve the ORR from the two-electron path to the four-electron path.Secondly,this paper studies the ORR activity and mechanism of surface graphene oxide(-OH,-COOH,C=O)in acidic and alkaline environments.Then we calculated the energy change during electron transfer under different condition and pointed out the suitable reaction route based on the change of free energy.Finally,the effects of differentpotentials on the ORR were discussed,providing theoretical guidance for the experimental operation.The results show that the graphene oxide can promote the ORR of the four-electron transfer,which depends on the special electronic structure of the graphene surface containing oxygen functional groups.Finally,under the framework of density functional theory,the catalytic active sites of N-doped graphene carbon materials as non-metal catalysts for oxygen reduction reactions were studied.In this paper,periodic and aperiodic(cluster)methods were used to study the adsorption sites of OOH.The electronic properties and topological structure of different size models are discussed.The results of the study indicate that the catalytic activity of carbon materials is closely related to the type,position and size of nitrogen doping.Therefore,when we choose to model the simulation of carbon nanomaterials,we should carefully choose a reasonable model based on the actual situation,to avoid improper construction results in unreasonable results.