Synthesis And Energy Storage Properties Of Transition Metal Nanomaterials Derived From Metal-organic Frameworks

As the most important component of supercapacitors,electrode materials play a decisive role in the electrochemical performance of supercapacitors.The rational design and construction of the structure and composition of the active material and optimization of the synthesis process in the preparation process can effectively improve the conductivity,specific surface area and active site of the active material.Transition metal compounds derived from metal-organic frameworks(MOFs)have many advantages such as high theoretical capacity,large specific surface area,controllable morphology and simple synthesis process.However,most MOFs-derived transition metal compound materials are prone to agglomeration in the practical application,and exhibit poor cycle stability after a certain number of cycles,which seriously inhibits the performance of supercapacitors.In this paper,starting from the construction of unique nanomaterial structure,through reasonable and ingenious structural design,a series of Zn,Ni,Co based transition metal compound nanoelectrode materials derived from metal organic framework(MOFs)with unique structural characteristics and excellent electrochemical performance were synthesized,and effectively solve the problem of easy agglomeration of MOFs themselves.The main research contents of this paper are as follows:1?Using the highly conductive 2D nanosheet material MXene as the substrate,the Co-based metal organic framework nanomaterial ZIF-67 is grown in situ on the surface of MXene through the electrostatic interaction between the positive and negative charges.After the subsequent etching of Ni(NO₃)₂·6H₂O solution and the final selenization treatment,the honeycomb-like MXene@Co Se₂/Ni₃Se₄ nanosheet composite material was successfully prepared.The special design of constructing another sheet Co Se₂/Ni₃Se₄ on the 2D MXene nanosheet in situ makes the composite material have a large specific surface area,high conductivity and excellent electrochemical performance.When the current density is 1 A g^-1,it can reach a specific capacitance of 1019 C g^-1.After 5000cycles of constant current charge and discharge,the specific capacitance can still maintain 80%of the initial value,showing excellent cycle stability.The asymmetric supercapacitor assembled by MXene@Co Se₂/Ni₃Se₄ and activated carbon electrode has a power density of 757 W kg^-1 and an energy density of up to 90 Wh kg^-1,indicating that MXene@Co Se₂/Ni₃Se₄ can be used as high-performance supercapacitor electrode material.2?Using ZIF-67 as metal precursor and sacrifice template,a kind of Co₃S₄@Ni Co₂S₄ hollow nanocage composite with dual core-shell structure is constructed by ion exchange strategy and curing treatment.The large hollow structure in the composite can effectively accommodate electrolyte ions and shorten the transport distance between the ions and the active material.The electrochemical kinetic behavior of MOFs-derived transition metal sulphides as electrode materials for supercapacitors is systematically studied.The results show that the capacitance contribution mainly comes from the surface capacitance control,which provides a basis for the realization of high energy density supercapacitors.When the power density is 750 W kg^-1,the energy density can reach 58 Wh kg^-1.3?Taking advantage of the excellent conductivity of 3D nickel foam and using it as the reaction substrate.First of all,through a simple hydrothermal reaction,a kind of Zn Ni Co ternary metal mixture nanowire array is uniform Ly grown on the surface of nickel foam skeleton.Then,through the diffusion of ions in the solution,Co²⁺is coordinated with organic ligand in dimethylimidazole solution.As the reaction time increases,ZIF-67nanospheres are grown in situ on the surface of the Zn Ni Co nanowire array.The Zn Ni Co P@Co P nanowire arrays with specific structure is obtained by low temperature phosphating treatment.Under the best experimental conditions,the Zn Ni Co P@Co P nanowire array exhibits excellent specific capacitance(1483 C g^-1,1 A g^-1)and rate performance(77%capacitance retention,from 1 to 10 A g^-1.This work effectively solves the agglomeration problem of MOFs and provides a new method for designing high-performance supercapacitor electrode materials.