Preparation Of Hollow Ternary Metal-Organic Framework And Their Electrochemical Properties

In the process of industrialization in our country,exploitation of traditional mineral resources has led to environmental pollution and depletion of mineral resources.Supercapacitors（SCs）have the advantages of high power density,rapid charge and discharge,and high cycle stability,which play an important role in the application of energy storage devices.Metal-organic frameworks（MOFs）have been playing an important role in electrochemical applications due to their characteristics of high porosity,large surface area,adjustable pore structure and abundant natural redox active sites.Among them,MOFs with hollow structure have more advantages due to their unique cavity structure,which can effectively shorten the ion transport path and provide abundant chemical active sites.Therefore,in this paper,solvothermal preparation of a unique hollow microspheroidal nickel-cobalt organic framework（Ni Co-MOF）was carried out to explore the effects of different influencing factors on its morphology,structure and electrochemical performance through reasonable structural design of the material,the optimal proportion of metal ions and reaction temperature.Furthermore,manganese ion with strong coordination ability was introduced into Ni Co Mn-MOF on the basis of nickel-cobalt organic framework,and the solvothermal preparation of nickel-cobalt-manganese ternary organic framework（Ni Co Mn-MOF）was conducted in one step,which effectively improved the cyclic stability of Ni Co-MOF.By changing the ratio of metal ions and the content of polyvinylpyrrolidone（PVP）in the system,the influence of different conditions on the structural characteristics of the material morphology was explored,and the electrochemical performance was further analyzed.In this paper,a Ni Co-MOF with hollow spherical structure was constructed by solvothermal reaction using nickel nitrate hexahydrate and cobalt nitrate hexahydrate as metal ion centers,homophthalic acid as a ligand,and polyvinylpyrrolidone as a dispersant,whose unique hollow structure can facilitate the diffusion and movement of electrolyte ions and provide a large number of redox active sites,effectively improving the specific electric capacity of the material.specific electric capacity.By varying the molar ratio of Ni Co ions and the solvothermal reaction temperature,the constructed Ni Co-MOF exhibited the best electrochemical performance when the Ni Co molar ratio was 3:1 and the reaction temperature was 150℃.It exhibits a specific capacitance of 909F g^-1 at a current density of 1 A g^-1.At 10 A g^-1,it still maintains a specific capacitance of55.3%.The constructed Ni Co-MOF//AC is capable of providing an energy density of28.9 Wh kg^-1 at a power density of 799.9 W kg^-1.The hollow spherical Ni Co Mn-MOF with a more stable structure is formed by introducing manganese ions on the basis of Ni Co-MOF.Its unique hollow spherical structure can help regulate the stress problems caused by volume expansion during rapid charging and discharging,and thus improve its cycling stability.In addition,the synergistic effect of Ni Co Mn ions possessing multiple valence states can provide excellent redox reactions.The Ni₃Co₁Mn_0.5-MOF prepared with Mn²⁺addition of 0.1875mmol and PVP addition of 1 g can exhibit a high specific capacitance of 1430 F g^-1 at 1A g^-1.The assembled Ni Co Mn-MOF//AC exhibited a specific capacitance of 189.7 F g^-1at a current density of 1 A g^-1,provided a high energy density of 66.75 Wh kg^-1 at a power density of 791.65 W kg^-1,and achieved a capacitance retention rate of 88.52%even after10,000 cycles at 10 A g^-1.and exhibits a high Coulomb efficiency of 99.57%.