The Preparation And Performance Study On Transition Metal-NC(TM-NC)oxygen Reduction Reaction Electro-catalysts Prepared By Graphene Regulated Electrospinning Technology

Fuel cell vehicles have demonstrated their high cleanliness and high efficiency throughout the world.However,Pt/C catalysts used in fuel cells are expensive,poor cycle stability,and limited resources,all of which hinder the commercialization of fuel cells.At present,transition metal-nitrogen carbon catalysts(TM-NC)are one of the hotspots in the research of developing Pt/C catalyst substitutes,but researcher there have been divergent opinions on the effective active species in TM-NC catalysts.In this study,Fe-NC catalysts with different morphologies were prepared by graphene regulated electrospinning technology,and the activity effect of different Fe and N species in the catalyst on the oxygen reduction reaction(ORR)was explored.The specific results are as follows:1.Layered(>20 layers)structure,sponge nano structure(SNS)and other three-dimensional(3D)fiber network Fe-NC catalysts with multi-pore size distribution were successfully prepared by using graphene regulated electrospinning technology and reported for the first time by the thesis.The catalyst with a 3D interconnected network structure not only facilitates the transfer of electrons in the ORR reaction,but also facilitates the transportation of reactants and products,and will significantly improve the ORR performance of the catalyst.2.The 3D layered structure Fe-NC catalysts with Fe₃C,Fe₃O₄ and Fe_xN as single active species were prepared by heat treatment in N₂,NH₃,air/NH₃ and other atmospheres.Electro-chemical tests show that the Fe-NC catalyst with Fe_xN as the active species shows better ORR performance.3.3D SNS Fe-NC catalysts were prepared by graphene regulated electrospinning technology,the macroscopic morphology of the catalyst was basically the same before and after calcination,show a proportional contraction,with the volume of 5000mm³ and 145mm³respectively.The fiber skeleton is reconstructed during the heat treatment,with the help of the catalysis effects of Fe,graphene is served as a seed to derive carbon nanotubes on the carbon fiber carrier.At the same time,Fe₃C combines with N,forming the Fe₂N component,which is confined in the carbon nanotubes.The specific surface area of the catalyst(487.5m²/g)is approximately double that of the catalyst before reconstitution(282.6m²/g)The 3D SNS Fe-NC catalysts prepared at 700?,800?and 900?all show excellent ORR performance than commercial Pt/C.4.Using XPS fitting analysis technology to explore the influence of M-N_x,pyrrolic-N,pyridinic-N and graphite-N in TM-NC(M=Fe,Co,Ni)catalysts over the ORR activity.The content of different nitrogen species in each catalyst and the corresponding half-wave potential were linearly analyzed.The results show that M-N_x has the highest promotion effect on the ORR performance of TM-NC catalysts.Graphite-N has no effect on the activity,and pyrrolic-N has an inhibitory effect.In summary,this research has reached three conclusions:The macro-morphology of the catalyst will affect the structure and performance of the catalyst;Among Fe-NC catalysts with similar morphology and structure,the active material Fe_xN exhibits higher ORR performance than Fe₃C and Fe₃O₄;M-N_x is the N species with the highest ORR promotion effect on TM-NC catalyst.