Synthesis Of Low-Dimensional Porous Carbon-based Nanomaterials For Catalyzing Oxygen Reduction

Accelerating the rate of oxygen reduction reaction（ORR）at cathode is the key point to enhance the efficiency of fuel cells.Commercial precious metal catalysts,such as platinum,are high-cost and scarce,which hinders the commercialization of fuel cells.Therefore,it is main objective to develop alternative carbon-based catalysts that are cheap and efficient.In this dissertation,the flake-like Zn-ZIF-L as precursor,carbon nanotubes coated nitrogen-doped porous carbon composites（Fe-L-CNT-x,x presents pyrolysis temperature）were constructed,and iron phthalocyanine-loaded porous graphene was prepared.And then,exploring the relationship between structures of as-prepared catalysts and ORR performance.The main contents are summarized as follows:（1）Fe-ZIF-L with perfect leaf-like morphology as precursor,which has been prepared by the double-solvent method.Next,Fe-ZIF-L was pyrolyzed with dicyanamide under various temperatures to synthesize Fe-L-CNT-x.These derived materials have flake-like morphology,hierarchical pore structures and abundant iron-based active sites（iron nanoparticles,Fe₃C）.Furthermore,electronic conductivity of these catalysts was enhanced by introducing carbon nanotubes.Because of the unique structure and composition,theses catalysts exhibited well electrocatalytic ORR performance.Among them,Fe_7%-L-CNT-900（the concentration of iron is 7%）possesses the desired features for ORR,including moderate heteroatoms doping（N:7.23 atom%,Fe:8.08 atom%）,high degree of graphitization,large specific surface area,and hierarchical porous structures.Fe_7%-L-CNT-900 performs a high electrocatalytic activity for ORR with an onset potential of 1.040 V,half-potentials of 0.88 V.（2）We first synthesized nitrogen-doped porous graphene（GNS）via molten salt method.Comparing with directly carbonized material（NC）,GNS possesses larger specific surface area,from 682.7 m² g^-1 to 1402.4 m² g^-1.Then,iron phthalocyanine（Fe Pc）was immobilized onto the GNS.We have successfully prepared Fe-GNS-y（y presents the mass ratio of Fe Pc and GNS）with different dosage of FePc.Among these samples,Fe-GNS-0.25 demonstrated superb ORR activity than Pt/C in alkaline solution.After 5000 CV cycles,the half-wave potential of Fe-GNS-0.25 exhibited a negative of～12 mV,but that of Pt/C moved negatively～20 mV.These results indicate that Fe-GNS-0.25 has superior stability.