Synthesis Of Novel MOFs Materials And Their Application As Electrode Materials Of Supercapacitor

Electrochemical capacitor,also known as supercapacitor,represents an important class of energy storage device because of its high power density.Porous carbon materials,such as activated carbon,are commercial supercapacitor materials that operate by storing charge on electrochemical double layers?EDLs?.This is in contrast to the storage of charge by redox reactions as exemplified by metal oxide pseudocapacitors.Carbon-based materials operate at a very high charge/discharge rate with a long life cycle but have low capacitance,while metal oxide materials have high capacitance but their redox reactions lead to low life cycle.Metal-organic frameworks?MOFs?contain metal centers,in which the metal and organic constituents can be varied to promie their high capacitance and long cycle life.Therefore metal-organic frameworks material has become an important candidate as supercapacitor matrial.MOFs materials store energy through reversible Faraday reactions,charge transfer between the electrolyte and the active material.MOFs have more regular structure,higher specific surface area,rela tively concentrated pore size distribution,and more diverse functions compared with conventional supercapacitor materials as well as good conductivity.In addition,carbon materials achieved by directly carbonizing MOFs also exhibit good electrochemical performance.In this thesis,several kinds of novel MOFs materials were synthesized by simple methods and used as electrode materials,and their electrochemical properties were studied.The main contents and results are as follows:1.A novel ZIF-CH₃-Co material was at first synthesized by simple stirring at room temperature,and then resulting nanoporous cobalt-rich carbons were obtained by direct carbonization of this Co-ZIF material.When used as electrode materials for supercapacitors,this ZIF material and resulting nanoporous carbons showed good electrochemical performances.The ZIF possessed the highest specific capacitance of160.30 Fg^-1at 0.5 Ag^-1as well as an excellent rate capability with a capacitance rention of 73.72%at 10 Ag^-1and a good cycling stability with 100.00%of its initials specific capacitance after 8000 cycles.In addition,the obtained nanoporous carbons displayed ideal capacitor behaviors and were promising electroactive materials for supercapacitors at low current density.The nanoporous carbon prepared at 650?possessed a high specific capacitance of 393.00 Fg^-1at 0.5 Ag^-1and a wide potential application range of-1.0⁰.33 V.2.By using r GO,CNT respectively and 1,3,5-benzenetricarboxylicacid,nickel nitrate as raw mateials,two novel r GO/MOF-Ni and CNT/MOF-Ni composites were synthesized by a simple hydrothermal process.Addition of graphene and carbon nanotubes effectively improved the conductivity of the resulting composites.For comparison,r GO-COOH-Ni material was also synthesized by directly coordination of the carboxyl-functionalized graphene oxide r GO-COOH with Ni.It was found that the two MOF-Ni based composites had better electrochemical properties than rGO-COOH/Ni.And comparied with rGO/MOF-Ni,CNT/MOF-Ni possessed higher SC,better rate performance as well as longer cyclic life for its particular structure.Specific capacitance of CNT/MOF-Ni reached 955.20 Fg^-1and 569.75 Fg^-1at the current densities of 1.0 Ag^-1and 10 Ag^-1with a capacitance retention of 59.60%.When it was continually charged and discharged for 9000 cycles 80.00%of the initial specific capacitance was retained.3.A new type of cobalt based MOF material MOF-P was prepared by using piperazine containing N-heterocyclic as the monomer and its electrochemical performance as supercapacitor electrode material was studied.The results showed that the MOF material exhibited very excellent electrochemical properties.At the current density of 3.0 Ag^-1MOF-P exhibited the highest specific capacitance of 1236.80 Fg^-1and when the current density was increased to 5(15 Ag^-1),10 times(30 Ag^-1),and even 16.67 times(50 Ag^-1),82.60%,74.70%and 67.60%of specific capacitance was retained observed,respectively.It is noteworthy that 80.00%of the initial specific capacitance value was still retained after 6000 cycles at a high current density of 30 Ag-¹.4.A novel zinc based ZIF material ZIF-SH was synthesized with imidazole and2-mercapto-6-methylbenzimidazole as the monomers and used as an electrode material for supercapacitors.High specific capacitance,excellent rate performance and relatively good cyclic stability indicated it was a promising electrode material.The ZIF-SH electrode exhibited the highist specific capacitance of 258.73 Fg^-1at the current density of 0.3 Ag^-1and when the current density was increaed to 3 Ag^-1?10times?,the capacitance retention rate was 71.75%.In addition,when it was cycled3000 times at the currnt density of 5 Ag^-1,55.56%of the initial specific capacitance was retained.