Preparation Of Multi-doped Carbon Nanocomposites Based On ZIF-67 And Their Performances For Oxygen Reduction Reduction

With the rapid development of society,the energy crisis and environmental problems have become increasingly serious.As a green energy technology,fuel cells can directly convert chemical energy into electrical energy,which has the advantages of high efficiency,high power density and no pollution to the environment.However,the slow oxygen reduction reaction（ORR）greatly limits the commercial application of fuel cells.So far,the main electrocatalysts are still Pt-based catalysts,but its high price,scarce raw materials,poor long-term work stability and methanol tolerance ability have seriously hampered the commercialization of fuel cells.Therefore,there is an urgent need to explore excellent ORR catalysts.In recent years,the carbon-based electrocatalysts derived from metal-organic frameworks（MOFs）have attracted great attention.These catalysts have excellent catalytic activity and characteristics（e.g.,large surface area,large pore volume,uniform pore distribution,and tunable chemical structure and so on）.In this thesis,we have designed and synthesized three new electrocatalysts by using cobalt-based zeolitic imidazole framework（ZIF-67）as the precursor,and studied their electrocatalytic properties for the ORR.The main original results were as follows:（1）The ZIF-67 was used as the precursor,and its surface was functionalized with PEDOT.Then,a novel Co,S and N multi-doped carbon catalyst was obtained by the pyrolysis and acid etching processes.The morphology,size and structure of the prepared samples were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）.The effects of pyrolysis temperature,PEODT amount and etching on sample size,morphology and ORR performance were systematically investigated.The results show that the pyrolysis temperature,PEODT amount and acid etching play a key role in the electrochemical performance enhancement of the catalyst.（2）A novel Fe,Co,S and N co-doped porous carbon composite catalyst was designed and synthesized by using ZIF-67 and sulfonated iron phthalocyanine as the precursors.The composition,morphology and surface structure of the prepared catalysts were characterized by SEM,TEM,XRD and XPS techniques.At the same time,the effects of different precursor ratios and pyrolysis temperatures on the structure and electrochemical performance of as-prepared catalysts were investigated.The results show that the prepared catalyst has high electrocatalytic activity and stability for the ORR,the half-wave potential reaches 0.856 V vs.RHE,and the limiting current density reaches 6.32 mA cm^-2.（3）The ZIF-67 was first grown in situ on the surface of MWCNT support.Then,a new type of Co,N-doped carbon composite catalyst was obtained by the pyrolysis.The prepared catalysts were physically characterized by SEM,TEM,XRD and XPS techniques.The effects of ligand content and heat treatment temperature on the structure and electrochemical performance of as-prepared catalyst materials were systematically investigated.The results show that the prepared catalyst had good ORR activity(Half-wave potential:0.8461 V_RHE;Limiting current density:5.6mA cm^-2),methanol tolerance ability and durability,and its ORR activity did not decrease significantly after 2000 CV cycles.