Studies Of ZIFs-based Catalysts With Improved Performance For Oxygen Reduction Reaction

Proton exchange membrane fuel cells（PEMFCs）have been widely used in many fields such as automobiles,drones and mobile portable due heir cleanliness,high efficiency,low noise,low operating temperature.The high cost and poor durability are the two fatal problems hinder their application in industry.Among them,platinum-based catalyst accounts for about half of the cost of PEMFC.Catalysts with low cost and high performance are crucial for the commercialization of PEMFCs.Catalysts composed various carbon materials and Fe N-Z₈,as well as Fe N-Z₈@Z₆₇catalysts using Z₈@Z₆₇ core-shell structure material as support,were prepared in this dissertation.The effects of carbon material and content,iron precursor and content,as well as post-treatment on the oxygen reduction reaction performance and structure of the catalyst were studied systematicly.The main research results are as follows:Composite catalysts were prepared using various carbon material and Fe N-Z₈ precursor.The Fe N-Z₈/r GO-10:1 composite catalyst,with the mass ratio of Fe N-Z₈ to GO in the precursor was 10:1 and GO was introduced by ball milling,has the best ORR activity.The moderate amount of GO can effectively prevent the collapse of Fe N-Z₈structure during high-temperature heat treatment,resulting in a higher specific surface area and smaller particle size of the composite catalyst.In addition,the existence of lamellar structure r GO in the composite catalyst can increases the degree of graphitization of the catalyst and the mass transfer capacity.These are the possible reasons for the improvement of 3wt%Fe Ac-Fe N-Z₈/r GO-10:1.The 3 wt%Fe Ac-Fe N-Z₈/r GO-10:1 composite catalyst,prepared by the re-doped of 3 wt%Fe from Fe Ac into the Fe N-Z₈/GO-10:1 composite catalyst,has poor ORR activity compared to Fe N-Z₈/r GO-10:1 composite catalyst.Compared to Fe N-Z₈/r GO-10:1 composite catalyst,3 wt%Fe Ac-Fe N-Z₈/r GO-10:1-Acid-NH₃ composite catalyst,obtained by acid leaching and heat treatment in NH₃,has comparable initial activity,as well as obvious improved stability with the unchanged limit current density and 40 m V decrease of onset potential.The removable of unstable iron and Fe₃C with smaller size after acid leaching,as well as the more stable active sites obtained during the pyrolysis in NH₃ are the main reasons for 3 wt%Fe Ac-Fe N-Z₈/r GO-10:1-Acid-NH₃ with excellent stability.Z₈@Z₆₇ Nanomaterials with core-shell structure were successfully synthesized by seed-mediated method.The Fe N-Z₈@Z₆₇ catalyst,prepared with 1,10-phenanthroline and Fe SO₄·7H₂O was obtained by carbonization in Ar at 900℃a catalyst precursor containing 0.3 wt%Fe,show best ORR activity due to the synergistic effect between Co₃C and Fe₃C species in the catalyst.