Metal Organic Frameworks Derived Carbon Supported Pt-based Cataltsts For Oxygen Reduction Reaction

H₂ is regarded as“the ultimate enengy of the 21^st century”because of its resource-rich,zero pollution and high energy density.Hydrogen energy can be used effectively by developing proton exchange membrane fuel cells（PEMFCs）.However,the commercialization of PEMFC is mainly hampered by the sluggish oxygen reduction reaction（ORR）,which heavily depends on expensive Pt-based catalysts.This thesis mainly introduces the development status of the PEMFC and outlines the recent progress in the development of catalysts for oxygen reduction reaction,meanwhile mechanisms of ehancing acticity and stability are included.The dissertation mainly studies composite Pt-based catalysts with low-loading of Pt,high activity and stability,and then reveals mechanisms of improvement for ORR.Firstly,the Co-N-C support was prepared by stirring at room temperature,and then Pt/Co-N-C composite catalysts with two active sites were prepared by microwave-assisted ethylene glycol（EG）process.The effects of heating method,p H of solution and microwave heating time have been systematically studied.It is concluded that the optimal conditions:microwave heating,p H=12,microwave heating for 100 s.The mass activity of Pt/Co-N-C was 2.8 times higher than that of the commercial Pt/C.The stability tested in the N₂ and O₂ saturated 0.1 M HCl O₄electrolyte of Pt/Co-N-C was better than the commercial Pt/C.During the catalytic process,the synergistic effect between Pt and Co-N₄ significantly promoted the reaction kinetic of the ORR.Through comparing Pt-based catalysts on different supports,proving that the electronic structure of Pt was regulated by Co-N-C supports,turning down the center of d-band for Pt and then changing the adsorption energy between Pt and the reaction intermediate of oxygen for enhanced ORR activity.Besides,the interaction between Pt and Co-N-C supports could make Pt dispersed uniformly and anchored firmly on the Co-N-C supports,which greatly improved the stability of catalysts.In order to improve the activity and stability of catalysts for ORR further,PtCo alloys were constructed.The as-prepared 10%Pt/Co-N-C catalysts were annealed at high temperature.The effects of heating atmosphere,heating temperature and heating time for PtCo/Co-N-C have been systematically researched,and determined the best optimum process that was heated at 700℃in H₂/Ar lasting for 0.5 h.The half-wave potential of catalysts was 0.921 V,which was 60 m V higher than the commercial Pt/C.The mass activity of PtCo/Co-N-C ottained 0.700 A mg _Pt^-1,exceeding the standard of DOE.The stability of PtCo/Co-N-C was improved obviously comparing with 10%Pt/Co-N-C,achieving negligible the half-wave potential loss after 5,000 cycles of an accelerated durability test in O₂ and losing 16 m V after 30,000 potential cycling in O₂.Thus,the activity and stability were enhanced significantly by alloying.A part of Co that reduced from Co-N-C diffused into Pt nanocrystals and then formed PtCo/Co-N-C.The electronic structure of Pt was regulated distinctly.The compressive strain effect and ligand effect turned down the center of d-band for Pt.The adsorption energy between Pt and the reaction intermediate of oxygen was reduced.Meanwhile,the synergistic effect and the interaction between PtCo nanoparticles and Co-N-C promoted the enhanced activity and stability further.