Synthesis And Characterization Of Low-platinum Iron-nitrogen Co-doped Holey Graphene Catalysts For Oxygen Reduction Reaction

Proton exchange membrane fuel cells(proton exchange membrane fuel cell,PEMFC)are highly efficient power generation devices that directly convert chemical energy into electrical energy.However,the high cost of platinum-carbon catalysts used for the oxygen reduction reaction(ORR)has limited their commercialization.To reduce the cost of PEMFCs,it is necessary to reduce the amount of platinum used without compromising the catalytic performance.One way to do this is to increase the atomic utilization of platinum by optimizing the chemical composition,crystal structure,and surface morphology of the catalyst.Another way is to optimize the properties of the catalyst carrier.The properties of the carrier have a significant impact on the activity and stability of the catalyst.In this thesis,a series of doped graphene supports by doping different heteroatoms into graphene oxide were synthesized.The effects of porous structure,type and content of heteroatom doping,and synthesis method on the ORR activity were investigated.Then platinum nanoparticles were loaded on the supports to explore the effects of reducing agent,support,and loading amount on the ORR performance of the catalyst.Finally,the catalyst properties were characterized using physical characterization methods such as X-ray diffraction(XRD),Xray photoelectron spectroscopy(XPS),Raman spectroscopy,and highresolution transmission electron microscopy(HR-TEM).the effect of catalyst structure on the ORR performance were explored by combining theoretical calculations.Our results show that the ORR activity of the catalysts can be significantly improved by optimizing the chemical composition,crystal structure,surface morphology,and properties of the catalyst carrier.The best catalyst we found had a high ORR activity,good stability,and low platinum loading.Our work provides a new strategy for the design and synthesis of high-performance ORR catalysts for PEMFCs.The main research contents of this thesis are as follows:Initially,iron-nitrogen co-doped holey graphene(Fe,N-HG)supports were synthesized through a one-pot method at 40°C using graphene oxide as the precursor.Urea and melamine were employed as nitrogen sources,iron(II)sulfate heptahydrate provided iron,and hydrogen peroxide acted as the pore-forming agent.The Fe,N-HG support exhibited the highest oxygen reduction catalytic activity.Heteroatom doping modified the electronic structure of graphene,while the pore size distribution on the surface of holey graphene was controlled by varying the hydrogen peroxide amount,thereby tailoring surface properties and oxygen reduction performance.Subsequently,platinum nanoparticles were deposited on the surface of the heteroatom-doped holey graphene supports using a liquid-phase reduction approach.The impacts of the platinum reduction method,support material,and platinum content on the oxygen reduction activity of the platinum-loaded heteroatom-doped holey graphene catalysts were investigated.Optimization yielded platinum-loaded iron-nitrogen codoped holey graphene(Pt/Fe,N-HG)synthesized by depositing 10%platinum nanoparticles on Fe,N-HG using ethylene glycol reduction.This catalyst displayed enhanced oxygen reduction catalytic activity compared to commercial 20% platinum on carbon(Pt/C).Finally,physical characterization combined with theoretical calculations was employed to analyze the oxygen reduction promotion mechanism of Pt/Fe,N-HG.The results demonstrated that iron-nitrogen doping modified the electronic and geometric structure of the support,enabling the uniform dispersion of small platinum nanoparticles on the support surface.Additionally,platinum atoms coordinated with iron and nitrogen atoms exhibited higher activity and stability for the oxygen reduction reaction.