Novel Carbon-based Electrocatalysts Derived From MOFs And Structure-activity Study

The burning of non renewable fossil fuels has led to serious climate and environmental problems,the sustainable development of human society urgently needs more efficient energy conversion and storage systems.The research and development of zinc air battery plays an important role in solving the energy problem.Although Pt-group noble-metal-based catalysts have excellent electrocatalytic activity,their application in the above electrochemical devices is greatly limited by their low reserves and stability.Therefore,it is urgent to develop high-performance non-noble-metal electrocatalysts.Recently,transition metals-based catalysts derived from metal organic frameworks（MOFs）have become a research hotspot because of their high porosity,large specific surface area and multiple active centers.Doping non-noble Fe and Ni in MOFs has stronger corrosion resistance and higher catalytic activity.In this dissertation,novel transition metals and nitrogen co-doped porous carbon materials were successfully synthesized and used as electrocatalysts for oxygen electrode reactions.The morphology and structure of the as-prepared materials were analyzed by scanning electron microscope（SEM）,transition electron microscope（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and Raman spectroscopy techniques.The electrocatalytic performances of the as-synthesized catalysts were studied by cyclic voltammetry（CV）,linear scanning voltammetry（LSV）,chronovoltammetric current-time（i-t）method and accelerated durability test（ADT）,etc.The results obtained are summarized as follows:1.Novel Fe-N-C-T（where T represents the pyrolysis temperature）materials were successfully prepared by pyrolysis of iron acetylacetonate@ZIF-9 at different temperatures.The optimized Fe-N-C-900 catalyst has the good catalytic activity for oxygen reduction reaction（ORR）in alkaline solution,with an onset potential of 0.96V vs.RHE,a half wave potential of 0.84 V vs.RHE,the limit current density of 5.5m A cm^-2.The fabricated zinc-air battery with Fe-N-C-900 as the air cathode displayed better battery performance than the commercial Pt/C catalyst.2.A novel Fe-N-C material was designed and prepared by the pyrolysis of the tetra（4-pyridine-oxyl）ferrophthalocyanine@ZIF-8 co-assembly at 1000℃.The reaction time used for the synthesis of the tetra（4-pyridine-oxyl）ferrophthalocyanine@ZIF-8 co-assembly plays crucial role in improving activity of the resultant catalysts toward ORR.The optimized Fe-N-C-18 h catalyst showed remarkable electrocatalytic activity for ORR in alkaline solution,with a distinctly positive onset potential of 0.99 V vs.RHE and a large limit current density of 8.0 m A cm^-2 at 1600 rpm.The assembled Fe-N-C-based zinc air battery has better performance than Pt/C-based battery.3.In order to realize bifunctional oxygen electrocatalytic performance of the catalyst,dual metals（Fe and Ni）-coordinated tetra（4-pyridine-oxyl）phthalocyanine were introduced during the synthesis of ZIF-8 and the subsequent pyrolysis of the dual metals-coordinated tetra（4-pyridine-oxyl）phthalocyanine@ZIF-8 led to a novel bifunctional Fe/Ni-N-C catalyst.Thanks to the strong electronic interaction between Fe and Ni,the formation of highly-active Fe/Ni-N_x sites exhibited outstanding bifunctional activity for both oxygen reduction（ORR）and evolution（OER）reactions,with a positive onset potential of 0.98 V vs.RHE,a positive half-wave potential of0.83 V vs.RHE and a large limiting current density of 6.2 m A cm^-2 for ORR,and with a low overpotential of 250 m V at 10 m A cm^-2 for OER.The rechargeable zinc air battery assembled with Fe/Ni-N-C as air electrode is better than Pt/C+Ru O₂ catalyst.