The Design Of Porous Electrode Materials Derived From Metal-organic Frameworks And Their Application In Electrochemical Energy Storage

With the rapid economic development,the energy crisis and the intensification of environmental pollution are urgently required to find clean alternative energy sources,and their associated energy storage so as transformation technologies.Porous carbon,porous oxide and its composite materials are widely used in supercapacitors and lithium-ion battery electrode materials.Self-assembly method,nano-casting method and template method are used to prepare porous materials,in which the template method is divided into soft template and hard template method.Using MOFs as precursor to synthetise porous functional materials is belong to a hard template method.Compared with the traditional method,it is a simple method with low cost,controllability and other advantages.The method is also an effective method for the preparation of special nanostructured electrode materials.It can effectively improve the electrochemical energy storage performance by regulating and designing the microstructure of the electrode material.Therefore,the purpose of this paper is to develop a method using MOFs as precursors to control the design of MOFs,porous carbon,porous oxide and its composite electrode materials,such as ion doping or carbonization,in order to further improve the materials' electrochemical energy storage performance.The main research contents are as follows:The ZnO/carbon mesocrystals with hierarchical porous cubic architecture were synthesized from metal organic frameworks(Zn-MOF-5)by pyrolysis of high-quality MOF-5 crystal materials at different annealing temperature in the present of nitrogen atmosphere.The ZnO/carbon composites had a maxium specific surface area(2214.9 m2 g-1)and abundant mesoporous struture(3.5 nm).The composites were evaluated as the electrode materials for supercapacitor in 1 M KCl aqueous solutions.The influences of annealing temperature,morphology,pore distruction on specific capacity and cycle life were investigated.It was found that the ZnO/carbon comopistes with higher mesopore volumes and external surface area exhibits enhancing higher rate preformance and better cycle stability.The maximum specific capacitance was found to be 206.3 F g-1at 10 mV s-1 and the stable cycling properties measurement showed the sample kept 96.5%after 1000 cycles at a 4 A g-1 current density.NiFe-MIL88B-x(0<x<2.5)micro-nanorods with different Ni doping amounts were prepared by one-step solvothermal method.With the increase of Ni/Fe ratio,the pore structure changes from dense opposing to opening phase,indicating that Ni2+ replace some of the Fe3+ in the framework of MOFs increases the lattice constant.While adding Ni ions effectively reduce the size of the particles.Electrochemical studies have shown that the FeNi-MIL88B specific capacitance increases from 62 F/g to 230 F/g(10 mV/s)as the amount of nickel ion doping increases.The lithium test results have shown that FeNi-MIL88B-0.5 is more than Fe-MIL88B(370 mAh/g)at 100 mAh/g.In order to study the capacitance properties of porous materials based on MOFs precursor,MIL88B(Fe)and MIL88B(FeNi)samples were carbonizaed at different temperature to prepare metal oxide/carbon composites.XRD results showed that Fe2O3/C and NiFe2O4/C composites were obtained by carbonization at 600? and Fe/Fe3O4/C and FeNi/NiFe2O4/C composites at 900?.The results of electrochemical analysis showed that the carbonized sample had excellent specific capacitance and capacitance retention ratio compared with the precursor.The specific capacitance of FeNi/NiFe2O4/C composites reached 163.5 F/g(10 mV/s),and the capacitance retention was 87.15%with the sweep speed increased from 10 mV/s to 100 mV/s.The excellent performance of composites was due to the uniform particle size and nano-size of the electrode material,which ensured the full contact of the electrolyte solution and the electrode material,shortens the diffusion distance of the ions.(Co,Mn,Ni)-MOFs and their bimetallic dopant solid solutions were prepared by solvothermal method.The electrochemical properties of the electrode materials doped with MOFs were studied systematically.The electrochemical performance of[Ni3(HCOO)6]was higher than that of[Co3(HCOO)6](318.8 F/g)and[Mn3(HCOO)6](180.5 F/g)at 10 mV/s.For CoNi-MOFs the specific capacitance of CoxNi1-x(HCOO)6 was better than that of MOFs of monomeric formic acid ligands,wherein the specific capacitance of[Co1,5Ni1.5(HCOO)6]is 888.8 F/g(10 mV/s).The primary discharge capacity of[Co1.5Ni1.5(HCOO)6](1515 mAh/g)was better than[Co3(HCOO)6](1181 mAh/g)[Ni3(HCOO)6](1020 mAh/g)at a current density of 100 mA/g.