Research On Electrodes Materials For Metal Organic Framework Based Hybrid Supercapacitors

Metal organic framework（MOF）is composed of metal ions and organic ligands through coordination bonds.It has the characteristics of high specific surface area,periodic pore structure,and multi-component active sites,and has great application potential in the field of catalysis and energy storage.In this study,the research and development of electrode materials for hybrid supercapacitors were carried out based on MOF and its derivatives.Supercapacitors display the advantages of high power density,high charge-discharge rate and high cycle life.However,compared with batteries,the lower energy density of supercapacitors has been a crucial factor that restricts their further development.The structural characteristics of MOF and its derivatives provide abundant possibilities for the development of high-performance supercapacitor electrode materials.Considering the high power and high energy potential of metal hydroxide nanostructure and pristine MOF,this work took MOF and its derived layered hydroxides as the object to conduct in-depth research.The main research contents and results are as follows:（1）ZIF-67 is used as a precursor to synthesisα/β-phase Co（OH）₂ with different nanosheets morphologies by adjusting the p H of the reaction,and the effects of with/without interlayer ions on the structure during the derivative formation process are investigated.The topological transition process and mechanism of 3D structure ZIF-67（?）2D layered structure Co（OH）₂ are revealed.（2）The electrochemical performance of cobalt hydroxides with different crystal phases,compositions and morphological structures are studied for electrodes materials of hybrid supercapacitors.Stable large interlayer spacing and interlayer crystal water together maintain the structural stability of the electrode material during the intercalation process of electrolyte ions,which also enhance its specific capacitance and specific power.The layeredα-Co（OH）₂-A displays a higher specific capacity of 87.1m Ah g^-1 at 1 A g^-1,rate capability of 77%capacity retention at 20 A g^-1and cycle stability of over 100%capacity retention over 200,000 charge-discharge cycles at 4 A g^-1,which exceeds most previously reported supercapacitors electrode materials.In addition,this work demonstrates that the charging ofα-Co（OH）₂ is processed by OH^-intercalation the interlayer and reacting with internal H⁺to form H₂O.（3）A series of citrate-intercalated Ni-Co LDHs electrode materials are synthesized by hydrolyzing ZIF-67 by solution method.The effect mechanism and electrochemical performance of different composition and structure of Ni-Co-LDHs are studied.The electrode of high Ni content shows high specific capacity.Simultaneously,the electrode of high Co content displays high rate capability and cycling stability,and citrate ions strongly support the layered structure as pillars.The Ni-Co-LDH-C-4:1 electrode displays high specific capacity of 254.9 m Ah g^-1(1835 F g^-1)at 1 A g^-1.The Ni-Co-LDH-C-1:4 electrode exhibits specific capacity of 134.7 m Ah g^-1(970 F g^-1)at 1A g^-1,over 100%capacity retention after 10,000 charge-discharge cycles,which is higher than most reported nickel-cobalt layered double hydroxides in the literature.Hybrid supercapacitor is constructed with Ni-Co-LDH-C-1:4 and commercial active carbon（AC）as the positive and negative electrode materials,respectively.The Ni-Co-LDH-C-1:4//AC delivers an energy density of 28.3 Wh kg^-1 at the power density of 373.5 W kg^-1.（4）A pristine MOF material Ni₃（Ni₃·HATD）₂ based on hexaazatriphenylene is synthesized by multi-step method,which exhibits abundantπ-πstacking of interlayer,π-d conjugation in-plane,N and Ni active sites,and offers an efficient transport pathway for the charge storage.The Ni₃（Ni₃·HATD）₂ electrode displays a high specific capacity of 373.3 m Ah g^-1(2688 F g^-1)at 1 A g^-1.Compared with the specific capacitance of MOF electrode materials in the literature,Ni₃（Ni₃·HATD）₂ increases by about 2-3 times.The hybrid supercapacitor of Ni₃（Ni₃·HATD）₂//AC delivers a high energy density of57.9 Wh kg^-1 at the power density of 400 W kg^-1.In this work,high-performance MOF electrode materials are designed and synthesized,which provided a new method and possibility for the subsequent development of MOF-based high-performance electrode materials.