Synthesis Of Nickel-Cobalt Metal Organic Framwork Materials And Their Derivatives And Performance Research Of Supercapacitors

The research and preparation of novel electrochemical active materials are crucial for energy storage.In particular,metal organic frameworks(MOFs)have emerged a promising platform for the development of high-level materials for efficient energy storage systems(ESS).Compared with conventional materials,MOFs provide a variety of unique composition and structural advantages with highly ordered and adjustable metal nodes and organic connectors.In addition,a variety of derivatives can be obtained by using MOFs with appropriate physical and chemical properties.These MOFs based materials are expected to alleviate the issues of conventional electrode materials in ESS.Using Ni2+/Co2+ as the metal source,1,3,5-benzoic acid and 4,4'-bipyridine as organic connectors,Ni-MOF,Ni-MOF@NiO and N-NiCoO were synthesized by solvothermal method and subsequent calcination.Furthermore,the properties of the supercapacitors are studied.The details are as follows:1.We used one-step solvothermal method to prepare the hexagonal Ni-MOF nanocomposites([Ni(HBTC)(4,4'-bipy)](HBTC=1,3,5-benzoic acid,4,4'-bipy=4,4'-bipyridine)by reacting Ni(NO3)2·6H2O with 1,3,5-benzoic acid and 4,4'-bipy in N,N-dimethylformamide.The material shows the excellent supercapacitor performance in 3 M KOH.the specific capacitance of hexagonal Ni-MOF electrode is 977.04 F g'1 at the current density of 0.5 A g-1.After 5000 cycles,the specific capacitance can still keep at 92.34%of the initial value.The basic characteristics of hexagonal Ni-MOF,such as the favorable(001)exposed surface and the cross-linked network structure,are one of the important factors in its electrochemical behavior.2.We use the hexagonal Ni-MOF as the precursor,and heat treat them at different temperatures(350?,450?,550?)to obtain a series of MOFs derived oxides.Specific capacitance value of Ni-MOF@NiO calcined at 350? can reach 1192.71 F g-1,and the decrease is very small after 5000 cycles.The improvement of electrochemical properties can be concluded as:the porous layer frame structure of Ni-MOF material and the uniformly distributed NiO effectively increase the redox active sites and reduce the interface charge transfer resistance as an oxide layer.3.The reaction conditions of the precursor are the same as the above steps:five kinds of MOFs(Co-MOF,Ni-Co-MOF-n,Ni-MOF,n=1,2,4)are prepared by changing the molar ratio of Ni(NO3)2·6H2O and Co(NO3)2·6H2O.Using these five kinds of MOFs as precursors,N-NiCoO composites with different Ni/Co molar ratio are obtained by calcination under air atmosphere.Electrochemical tests show that when the ratio of Ni2+to Co2+is 2,N-NiCoO-2 displays a high capacitance of 945.79 F g-1 at the current density of 1.0 A g-1.After 5000 cycles,the specific capacitance value has only a 6.7%attenuation.The proper ratio of Ni/Co molar ratio and the incorporation of nitrogen are the important reasons for its outstanding electrochemical behavior.