Preparation And Electrochemical Properties Of Mofs And Composites

Metal framework（MOF）is a crystalline material with regular structure,which has many advantages such as high specific surface area,high porosity,and easy controllable structure,resulting in great application prospects in energy storage materials.However,MOFs are mainly composed of micropores（<2nm）,with a single channel structure and poor conductivity,which restricts their application in energy storage electrode materials.In view of this,we designed MOFs with multi-level pore structure to improve the shortcomings of MOFs by introducing mesopores and macropores;The conductive materials were introduced to accelerate charge transfer and electron conduction,resulting in improved conductivity of MOFs materials.The MOFs with different compositions and structure were designed and prepared,and the electrochemical properties were investigated The main research content and results are as follows:1)Research on Co-MOF and its derivatives.Using 3D porous graphene as a carrier,3DHG（Three-dimensional holey graphene）/Co-MOF was designed and prepared by in-situ self-assembly method,and its derivative 3DPC（Three-dimensional porous carbon）/Co₃O₄ was further obtained by pyrolysis.The structure,composition and electrochemical properties were studied.The results show that:3DHG/Co-MOF exhibit a typical microporous structure and good conductivity.The specific capacity at a current density of 1 A g^-11 is 154.6 F g^-1.Compared with 3DHG/Co-MOF,the3DPC/Co₃O₄ exhibit an amorphous state,multi-level pores,and rich carbon,which can accelerate charge transfer and ion diffusion;the more active sites provided by Co₃O₄ could facilitates the redox reaction in electrochemistry.Based on these compositional and structural advantages,the 3DPC/Co₃O₄ electrode exhibits excellent electrochemical performance,exhibiting a high specific capacitance of 423 F g^-11 at a current density of 1 A g^-1,the capacitance retention rate is also 85.7%even at 10 A g^-1,showing good rate performance.After 2000 cycles of charge and discharge,the capacitor decayed by about 17%,showing ideal cycle stability.A 3DPC/Co₃O₄//AC asymmetric supercapacitor was prepared by using 3DPC/Co₃O₄ as the positive electrode and activated carbon（AC）as the negative electrode,and the electrochemical performance was studied.The specific capacity was 60.76 F g^-11 at 1A g^-1.It showed a wide potential window of 1.7 V and a maximum energy density of21.1 W h kg^-11 and a power density of 790 W kg^-1.2)Research on Cu-MOF and its composite materials.HKUST-1 was prepared by one-step method and modified with graphene oxide and activated carbon to design and synthesize HKUST-1/GO and HKUST-1/GO/AC composite materials.The structure,composition and electrochemical performance of materials were investigated.The influence of preparation methods and material composition on the structure and performance of materials is clarified.The results show that Cu-MOF and its composites prepared by hydrothermal method show a single microporous structure and a single surface morphology,and the specific capacity is 50.75 F g^-11 at a current density of 1 A g^-1.The Cu-MOFs composite materials prepared by the oscillation method showed a multi-level pore structure by the successful introduction of mesopores and macropores.The mesopore ratio of HKUST-1/GO/AC composites greatly improved and is up to 647.8505 m² g^-1,mesoporous area is 79.69 m² g^-1;The introduction of graphene oxide and activated carbon does not destroy the shape of Cu-MOF crystals,but participate in the nucleation and growth of HKUST-1 crystal,leading to the regular shape of the composite materials,which is beneficial to improve the conductivity of MOFs.Based on the composition and structural advantages,the electrochemical performance of HKUST-1/GO/AC composite material has been greatly improved.When the current density is 1 A g^-1,the specific capacitance values of HKUST-1,HKUST-1/GO and HKUST-1/GO/AC composites are 62.25,111,and208.6 F g^-11 respectively;when the current density increases from 1A g^-11 to 10 A g^-1,the HKUST-1/GO/AC capacitance retention rate is 69%.An asymmetric supercapacitor was prepared by using HKUST-1/GO/AC composite material as the positive electrode and activated carbon as the negative electrode.The specific capacity at 1 A g^-11 current density is 43.125 F g^-1,and the maximum energy density is15.33W h kg^-1,the power density is 799.9 W kg^-1.3)Research on multi-hierarchical Zr-MOF.Zr-MOF containing two ligands of terephthalic acid and 2-aminoterephthalic acid was prepared by solvothermal method.Due to the difference in thermal stability of the two ligands,2-aminoterephthalic acid is removed by pyrolysis at high temperature,causing defects inside Zr-MOF crystal to prepare the multi-hierarchical HP（hierarchically porous）-UIO-66.The structure,composition and electrochemical performance of the material are researched.The results show that the generation of internal defects in the crystal successfully introduces the mesoporous structure into Zr-MOF.The obtained multi-hierarchical HP-UIO-66 material shows a high specific surface area of 769.182 m² g^-1,in which mesoporous area accounts for 38.6%.The introduction of mesoporous could accelerate the transport of electrolyte ions inside active materials,resulting in the enhanced electrochemical performance.When the current density is 1A g^-1,the HP-UIO-66 obtains a specific capacitance of 492.7 F g^-1.When the current density increases from 1A g^-11 to 10 A g^-1,the specific capacity is 362.5 F g^-1.The capacity retention rate is 73.6%,showing good rate performance.An asymmetric supercapacitor was assembled by using HP-UIO-66 as the positive electrode and activated carbon as the negative electrode.The operating voltage range of the device is 1.6 V.When the current density is 1,2,3,5 and 10 A g^-1,the specific capacitance values are 53.75,46.25,42.19,35.94 and 28.19 F g^-1,the maximum energy density of the device is 19.11Wh kg^-1,and the corresponding power density is 828.92 W kg^-1.