Synthesis And Electrochemical Properties Of Metal-Organic Frameworks Based On 4-(pyridine-4-yl) Phthalic Acid Ligand

Metal-organic complexes?MOCs?are a class of new organic-inorganic hybrid materials constructed of organic ligands and metal ions.They have potential applications in fluorescence,gas adsorption,catalysis,electrocatalysis,electrochemistry,supercapacitors,etc.The application of MOCs in electrochemistry has attracted extensive attention from researchers.In this paper,under solvothermal conditions,based on the nitrogen-containing aromatic carboxylic acid ligand 4-?pyridin-4-yl?phthalic acid?H₂PYPA?and transition metal ions self-assembled synthesis of 11 novel MOCs,They conducted X-ray single crystal diffraction,X-ray powder diffraction,elemental analysis,infrared and thermogravimetric structural characterization.At the same time,they focused on the properties of MOCs as electrode materials.The main contents are as follows:1.Based on H₂PYPA ligands and Ni?II?,Co?II?,Mn?II?metal salts,three novel complexes 1-3 were constructed.The structure shows that 1 and 2 are isomorphic 2D layered structures.Then,the 3D supramolecular structure was further formed by hydrogen bonding.3also belongs to the 2D layered structure.In addition,under solvothermal conditions,based on H₂PYPA and five imidazole ligands 1,4-bis?benzimidazole-?benzene?bibb?,1,7-bis?1-imidazolyl?fluoro?1,7-bif?,1,4-diimidazole benzene?bib?,4,4-diimidazole biphenyl?bibp?and 1,4-bis?1-benzimidazolyl?benzene?bimb?and transition metal ion self-assembly synthesis 7 novel complexes were found.The structure shows that 4-7 is isomorphic,with the same crystal system,space group and topological type?fsc?,all of which are porous MOCs with 3D porous structure.8 is a 2D layered structure with holes.9 and 10 are 3D isomorphic and the topology type is sqc 69.Finally,a MOC was synthesized with 1,7-Bis?imidazol-1-ylmethyl?benzene?1,7-bif?and Ni?II?ions under solvothermal conditions.The structure shows that the topology type of 11 is 2D porose network structure of sql.2.Electrochemical tests show that electrode based on the complex 1 exhibits high electrochemical performance,and its specific capacitance can reach 597.8 F g^-11 when the current density is 0.5 A g^-1,with good rate performance and good cyclic stability,after charge and discharge 2000 times,the capacitance remains 94.62%.In addition,the 1//AC asymmetric supercapacitor has a higher energy density of 45.3 Wh kg^-11 and a power density of 882.5 W kg^-1.These results indicate that the 1-based electrode has potential application prospects in terms of supercapacitors.The complex 2 based electrode and the complex 3based electrode were tested by the three-electrode system to calculate capacitances of 122 F g^-11 and 152 F g^-1,respectively.The maximum capacitance of the complex 4-10 based electrode is 52.0,360.8,320.8,172,72.0,320.5 and 151.8 F g^-1,and the maximum capacitance of the complex 9 electrode assembled into an asymmetric supercapacitor is 37.9 F g^-1,the energy density is 20.1 Wh kg^-11 and the power density is 1445.9 W kg^-1,which can still maintain 85.6%after 5000 cycles.Through electrochemical characterization of the electrode of the complex 11,the specific capacitance is 319.0 F g^-11 at the current density of 0.5 A g^-1.After 1000 cycles of charge and discharge,the capacitance remains 96.78%.It shows that the complex 11 electrode has good electrochemical performance.3.The results show that the capacitance behavior of the electrodes is generated by the Faraday oxidation-reduction reaction of metal ions and controlled by diffusion.The porous nature of the electrode material is conducive to electrolyte ions entering the gaps of the electrode material to store charge,promote effective charge transport and rapid electrolyte penetration,and furthermore,the low resistance also accelerates the electron transfer rate.