Controllable Synthesis Of Cobalt/Nickel-4-Pyridinecarboxylic Acid Framework Materials And Their Derivatives And Performance Research Of Supercapacitor

Electric energy storage devices are new energy storage devices that are currently addressing problems related to the rapid depletion of fossil fuel resources and the everincreasing greenhouse effect.Supercapacitors(SCs)are of great interest because of their higher power density and charge/discharge cycle stability than batteries.Metal organic frameworks(MOFs)have attracted extensive interest from chemists and materials scientists because of their well-defined structures and potential applications.MOFs are potential electrode materials for SCs due to their unique structure and rich chemical-physical properties:1)The high porosity of MOFs can effectively accommodate electrolyte solutions;2)The metal-rich centers of MOFs can be used as redox active sites.In addition,derivatives based on MOFs,such as hydroxides,phosphides,sulfides,etc.,are becoming new electrode materials for SCs due to their unique composition and structure as well as good electrochemical activity and stability:1)MOFs derivatives retain the porous structure and high specific surface area of MOFs precursors;2)MOFs derivatives have higher electrical conductivity and specific capacity.In this paper,we designed and synthesized a series of cobalt/nickel-4-pyridinecarboxylic acid framework materials and used them as the basis for the controlled synthesis of nickel hydroxide microspheres and NiCoP nanoparticles/phosphate/carbon-based composites by hydroxide and phosphorization treatments,respectively,which were used as electrode materials for SCs and their electrochemical performance were systematically investigated.1.A series of MOFs with spindle structures(labeled as Ni-MOF,Co/Ni-MOF-1:1,Co/NiMOF-1:5,Co/Ni-MOF-1:15 and Co-MOF,respectively)were synthesized by a solvothermal method by using nickel nitrate hexahydrate and cobalt nitrate hexahydrate in different molar ratios as metal precursors and 4-pyridinecarboxylic acid as organic ligands.Electrochemical tests showed that Co/Ni-MOF-l:15 has the highest specific capacitance(359 F g-1 at 0.5 A g1),the best rate performance(81.5%retention at 5 A g-1)and cycling stability(81%retention after 5000 cycles),due to the synergistic effect between the bimetals with the best Co/Ni ratio that effectively improves electrochemical performance of MOFs.2.Microspherical Ni-MOF-1 was synthesized using nickel nitrate hexahydrate,4pyridinecarboxylic acid and terephthalic acid as precursors.A series of nickel hydroxide with microsphere morphology(labeled as Ni(OH)2-1h,Ni(OH)2-6h and Ni(OH)2-12h,respectively)were synthesized by immersing them in 1 M KOH solution according to their structural characteristics.Electrochemical tests showed that Ni(OH)2-6h,obtained at 6 h,had the highest specific capacitance(512 F g-1 at 0.5 A g-1)and good cycling stability(74%retention after 5000 cycles).The excellent specific capacitance performance of Ni(OH)2-6h is attributed to its large specific surface area and porosity,which facilitate the diffusion of electrolyte and ion transport.3.A series of NiCoP nanoparticles/phosphate/carbon-based composites(NiCoP/POx/CT)were synthesized by controlling the phosphorization temperature using the bimetallic Co/Ni-MOF-1:1 as the precursor for the phosphorization reaction.Electrochemical tests showed that the NiCoP/POx/C-300 obtained at 300℃ had the highest specific capacitance(637 F g-1 at 0.5 A g-1)and good rate performance(82.7%retention at 5 A g-1).The reason for the excellent performance of NiCoP/POx/C-300 is the synergistic effect between Ni and Co in NiCoP nanoparticles,which can improve the adsorption capacity of OH-and contribute to the improvement of electrochemical performance.