Study On The Preparation Of Two-dimensional MOFs-derived Carbon Materials And Their Catalytic Performance

ZIF(zeolitic imidazolate framework)is a sub-class of MOFs and is a kind of zeolite-like structure formed by coordination of inorganic metal ions and organic imidazolium ester ligands.ZIF-L has the advantages of low cost,high yield,nitrogen self-doping and high carbon and nitrogen content in the structure.It is often used as a precursor to prepare Co-N-C catalyst,which is widely used in the field of electrochemical catalysis.In this paper,we successfully prepared a two-dimensional leaf-like ZIF-L-derived Co-N-C type catalyst.The catalytic properties of the material were tested by designing the precursor material structure.The catalytic active sites were initially explored.The investigation of catalytical mechanism provides a basis for further improving the catalytic performance of ZIF derived materials.1)Bimetallic or trimetallic alloys have good catalytic activity compared to single metal systems,and have unique catalytic activities that are not observed in single-metal systems.We have converted Cu(OH)2 nanowires into two dimensional leaf-like Cu(OH)2 nanomaterials by ultrasound induced self-assembly.Cu(OH)2 was efficiently encapsulated in the ZIF-L-Co structure by fitting the morphology of the leaf Cu(OH)2 and ZIF-L-Co.CuCo alloy nanoparticles encapsulated nitrogen-doped carbonaceous nanomaterials(CuCo@NC)were prepared by high-temperature carbonization of nanocomposites,and exhibited high-efficiency bifunctional electrocatalytic ORR and OER activity and stability in alkaline electrolyte solution.The catalyst was also used to construct a rechargeable zinc-air battery,exhibiting excellent electrocatalytic performance with an energy density of 303.7 mW cm-2 at 20 mA cm-2 and a specific capacity of 751.4 mAh g-1,and good stability.2)After pyrolysis at high temperature,nitrogen content in two-dimensional ZIF-L-Co-derived carbon material is low.To solve this problem,we synthesized leaf-shaped ZIF-L(Zn)@ZIF-L(Co)core-shell composites by epitaxial growth,and combined two different crystal materials into a core-shell material at the molecular level.ZIF-L-Zn have the same topological structure as ZIF-L-Co except for different metal nodes and high nitrogen content after pyrolysis.Co/Zn bimetallic nanoparticles encapsulated nitrogen-doped carbonaceous nanomaterials(ZnCo@NC)were prepared by high temperature calcination.It is a highly efficient ORR electrocatalyst with a peak potential of 981 mV in alkaline electrolyte solution.The half-wave potential value reached 887 mV,and the current remained stable after long-term constant voltage electrolysis of the catalyst,indicating good stability of the catalyst.