Study On The Improvement Of The Catalyst Activity Of Functionalized Graphene As Fuel Cell Cathode

As the developments sustainable economic and improvement of human living conditions,it has become a trend that strong demand for clean and sustainable energy.As a clean energy-converting device,proton exchange membrane fuel cells have drawn great attention in recent years due to their high efficiency,high energy density and zero greenhouse gas emissions.In the field of power engineering,fuel cells can be used as a power source for new energy vehicles.Nevertheless,big obstacles are hinding the commercialization of fuel cell.The platinum（Pt）-based catalysts are the common applicated,but with problems of high cost and low stability.Therefore,the development of efficient and economical new catalysts is the main challenge.In this thesis,the first-principles calculation method is used to analyze the catalytic performance of a series of carbon-based non-noble metal-doped catalysts from the perspective of thermodynamics,which provides a theoretical basis for the experimental synthesis of catalytic materials.This article mainly includes the following contents:1.The catalytic activity of cobalt-phosphorus decorated graphene was studied.The ORR electrocatalysis catalyzed by the Co/P doped graphene is investigated by the density functional theory calculations.The binding strength between Co and its coordination is-5.64e V,being much stronger than the Co cohesive energy,which effectively guarantees the stability of Co atomic distribution.According to the adsorption affinity as well as the free energy,the P ligand is easily oxidized by the OH adsorption.Intriguingly,the presence of OH activator significantly boosts the ORR activity of Co/P doped graphene and the corresponding overpotential is reduced from 1.11 V to 0.73 V.Furthermore,the positive influence of P on the ORR activity is highlighted compared with Co C₄ moiety possessed the overpotential of0.92 V.This work provides the deep understanding of OH activation mechanism as well as the new strategy for the design of carbon-based materials as oxygen electrodes.2.The electrocatalytic activity of nitrogen-oxygen doped graphene catalyst was studied.Firstly,different N/O co-doped graphene structures were selected,and the adsorption capacity of the C sites with different N and O positions was analyzed.It is found that N/O doping activiates the adjacent carbon as active site,the overpotiential of the active site is 0.95 V.Benefiting from the influence of O doping on the charge distribution,N/O co-doped graphene possesses stronger adsorption performance and its enhanced ORR catalytic activity.These results support N/O doping graphene as a candidate for ORR.3.The electrocatalytic properties of TM₃（HHTT）₂ on ORR reaction were studied.The results of adsorption studies show that as the atomic number of the transition metal increases,the adsorption energy of the metal center site decreases.The adsorption capacity for oxygen-containing substances decreases in order of Fe,Co and Ni.The analysis of the ORR catalytic activity shows that the determination steps of the ORR rate of Fe and Co are both H₂O formation,Fe"s adsorption capacity for oxygen-containing substances is too strong,OH is difficult to desorb,and Co’s adsorption capacity for oxygen-containing substances is moderate,correspondingly the potentials are 0.58 e V and 0.48 e V,respectively.However,due to the insufficient adsorption capacity of Ni for oxygen-containing substances,the formation of OOH*and the reaction of O*formation is difficult,and the corresponding overpotential is1.10 e V,which is not conducive to the catalysis of ORR reaction.Therefore,due to the influence of the choice of the transition metal center site on the adsorption capacity of oxygen-containing substances,Co₃（HHTT）₂ was selected as an ORR catalyst,indicating the influence of the ligand effect on the catalytic performance,this study provides a theoretical basis for the design and experimental research of new catalysts.