Design,Synthesis And Electrocatalytic Properties Of Zeolitic Imidazolate Frameworks-based Composites

The composite materials based on Metal-Organic Frameworks?MOFs?precursors generally exhibit large specific surface area,high porosity and adjustable regular pores.The dissertation has selected the composites of one kind of MOFs,namely Zeolitic Imidazolate Frameworks?ZIFs?as precursors for pyrolysis at high temperature.The electrocatalytic performance of the resultant materials was investigated,and the synergistic catalytic effects of different components were explored to establish the structure-activity relationship between the composites and the catalytic properties,high-performance electrocatalysts for water spliiting will be developed.The main research contents of this dissertation are as follows:1.The introduction of carbon nanotubes?CNTs?and phosphomolybdic acid?POMs?during the synthesis of ZIF-67 generated POM@ZIF-67/CNTs,in which ZIF-67-encapsulated phosphomolybdic acid?POMs?precursors were connected by carbon nanotubes?CNTs?,subsequent pyrolysis under specific atmosphere gave rise to CNTs-loaded molybdenum-doped cobaltosic oxide composites?Mo-Co₃O₄/CNTs?.The structure,morphology,metal content,specific surface area and pore size distribution of the target materials as well as the oxygen evolution reaction?OER?catalytic performance in alkaline medium were investigated.The results have shown that the catalytic performance of Mo-Co₃O₄/CNTs is superior to those of Co₃O₄ and Co₃O₄/CNTs,and Mo-Co₃O₄/CNTs also possesses outstanding long-term stability.Mo doping and CNTs introduction have a significant synergistic effect on the improvement of electrocatalytic performance of Mo-Co₃O₄/CNTs.2.The sandwich-structure composite?ZIF-8/MnO₂?was obtained through the growth of ZIF-8 nanoparticles on the surface of manganese dioxide nanosheets.After carbonization under argon atmosphere and subsequent acidic washing,highly graphitized carbon nanoflakes?GCF?were obtained.The high-temperature pyrosis of GCF and dicyandiamide mixture under Ar atmosphere gave rise to highly graphitized nitrogen-doped carbon nanoflakes?NCF?.The structure,morphology,elemental valence state,chemical environment,specific surface area and pore size distribution of the target materials as well as the oxygen reduction reaction?ORR?catalytic performance were investigated.The results have shown that NCF has a positive initial potential and half-wave potential as well as a larger ultimate diffusion current density when compared to amorphous carbon from ZIF-8 carbonization,GCF and commercial Pt/C.NCF also exhibits excellent resistance to methanol poisoning and long-term stability when compared to Pt/C catalyst.After NCF was supported on a carbon fiber paper(1 mg cm^-2)as a positive electrode material,and a zinc plate was used as a negative electrode material,and a 6 M KOH aqueous solution containing 0.2 M zinc acetate was used as an electrolyte to assemble a zinc-air battery.The measurements of the electrochemical workstation and battery test system have shown that its open circuit voltage,power density,discharge voltage and stability are suprerior to zinc-air batteries assembled by commercial Pt/C as a cathode material under the same conditions.