Synthesis Of Biemetallic MOFs And Graphene Oxide Hybrid MOFs And Study On Performance Of Supercapacitors

Metal-organic frame materials(MOFs),a kind of inorganic and organic porous crystalline materials with periodic network structure,large specific surface area and high porosity,are widely used in the preparation of electrode materials for supercapacitors.It has been reported that the electrochemical properties of MOFs are closely related to their morphology,redox center,porous structure and microstructure.Transition metal MOFs,which rely on the rapid redox reaction of metal ion centers to store electric energy,have relatively large specific capacitance and working voltage,and become the star materials for the preparation of supercapacitor(SCs)electrodes.However,the stability and conductivity of most MOFs are poor,which limits their development in supercapacitors.Based on the theory of hard and soft acid-base and topological frame design principle,metal cations with low redox potential were introduced into typical reported single metal SBU in a controlled way to construct alloy-like heterometallic organic frame materials.The introduction of heterogeneous metals may not only increase the complexity of secondary building unit(SBUs),but also lead to frame structural defects,such as vacancy or aperture classification,and even affect the covalent bond function.We call this characteristic"heterogeneity."This heterogeneity increases the robustness of the MOFs frame structure to a certain extent,thus increasing the thermal and water stability of the biemetallic MOFs,and improving their electrochemical performance as electrode materials.In addition,the combination of MOFs with graphene oxide(GO)is another way to improve their electrochemical performance.GO is a two-dimensional layered structure.The oxygen-containing functional groups on both sides of the structure can attract metal ions and increase the dispersion force within the framework,affecting the crystallization of MOFs,leading to the growth of MOFs,and then regulating the structure,morphology and crystal size of MOFs.At the same time,the space between the layered GO and the 3D MOFs can store the electrolyte ions well.In addition,MOFs are a typical pseudocapacitive material,while GO is double-layer electrode material.The composite material can combine the advantages of the two materials and exhibit better electrochemical performance than their respective materials.This paper provides an effective strategy for the construction of high-performance MOFs electrode materials.The specific research contents and results of this paper are as follows:1.In order to design heterometallic MOFs electrode materials with good stability and high specific capacitance,firstly,a typical tri-core cluster[M₃(O/OH)(O₂C)₆]was selected.It presented a highly symmetric tri-prism,showing good compatibility with different metals such as Fe,Co,Ni,Cr,Al,Ga,In,etc.Therefore,with the Fe-MOF(MOF-1)as the template,and with the aim of using the low oxidation state transition metals(Mn,Ni,Co)with similar metal ion radius,the alloying properties of MOF-2?4 are designed to improve their specific capacitance and stability as electrode materials.Electrochemical tests were performed under the same conditions.The results show that the specific capacitance of MOF-1 is 226.0 F g^-1,and the specific capacitance of MOF-2?4 is 412.0,492.6 and 533.7 F g^-1,respectively.The asymmetric supercapacitor MOF-4//AC,reduced the specific capacitance by 25%after 5000cycles of charge and discharge.At 750.6 W kg^-1,the output energy density was 17.9 Wh kg^-1.2.A series of single transition metal M-MOF and graphene oxide(GO)composites M-MOF@GO(M=Zn,Co,Ni)were synthesized by self-assembly under hydrothermal conditions.By means of powder XRD,XPS,SEM and other characterization methods,it was proved that GO and MOFs composite was successful,and its electrochemical properties were explored.The experimental results show that the specific capacitance of the composite MOF@GO is higher than that of the corresponding original MOF.The specific capacitance of Ni-MOF@1.5GO is 694.6 F g^-1(0.5 A g^-1).Asymmetric supercapacitor Ni-MOF@1.5GO//AC has a power density of 753.3 W kg^-1,an energy density of 15.4 Wh kg^-1,and a capacitance retention rate of 75%for 3000 cycles,showing a long cycle life.