Research On Controllable Construction Based On Bimetallic MOFs And Its Application In Supercapacitors

With the increase of fossil fuel consumption and the increasingly serious environmental pollution,there is an pressing need to exploit efficient,renewable,stable and clean for energy conversion and storage equipment.Supercapacitors are an important emerging energy storage device with the advantages of high power density,long cycle life,environmental friendliness,and fast charging and discharging.They are widely employed in electronic communications,transportation,military industry,aerospace and other fields.As an important part of supercapacitors,the performance of electrode materials(specific surface area,electrochemical activity,conductivity and stability)directly affects the performance of supercapacitors(capacitance,energy density,rate performance and cycle stability),and decides on its commercial application.Therefore,the design and develop of advanced electrode materials with excellent performance is the key to the evolution of supercapacitors.As a porous material,metal-organic framework material has the advantages of high specific surface area,adjustable pore size,redox active sites,etc.,which is a potential supercapacitor electrode material.However,most MOFs have low capacitance,which largely hinders their applications.By partially replacing the central metal ions to form bimetallic MOFs,their electrochemical performance is better than that of monometallic MOFs.This is attributed to the synergistic effect of the enhancement in electrical conductivity,the spread in specific surface area and the increase in pores,which is increasing the contact area between the electrode and the electrolyte and shortening the ion transport path.Meawhile,the synergistic effect of the enhanced oxidation state of the bimetallic component in the electrode and the central metal ion can effectively promote the conductivity of MOFs.With the development of flexible electronic components and wearable electronic devices,high-performance flexible supercapacitors have received extensive attention in recent years.The introduction of flexible polymer materials into MOFs electrode materials not only enhances the conductivity of MOFs,but also gives the electrode materials flexibility.This thesis focuses on designing and synthesizing bimetallic MOFs electrode materials with excellent properties and assembling them into supercapacitor devices to study their electrochemical performance;further introducing flexible polymer materials to explore the performance of flexible supercapacitor devices.The following work has been specifically carried out:1.Using 3,3′,5,5′-terphenyltetracarboxylic acid as ligand,a series of(Ni Co-MOF)bimetallic MOFs with different molar ratios of cobalt and nickel were synthesized by hydrothermal method and directly employed as a capacitor active electrode material and prepared into a supercapacitor device,and explored the influence of different metal ratios on electrochemical performance.Meanwhile,the materials with the highest capacitance value were made into a supercapacitor device.The electrochemical test results exhibited that when the current density was 0.5 A/g and the ratio of Ni:Co was 7:1,the specific capacitance of Ni:Co-MOF is the highest,which was 529.655 F/g.The electrochemical performance test results of the assembled symmetrical supercapacitor device Ni Co-MOF//SC showed that when the current density was 0.5 A/g,its specific capacitance value was 67.28 F/g.When the power density was 400.75 W/kg,the corresponding maximum energy density was 23.92Wh/kg.This work shows that the synergistic effect of bimetals can effectively promote the conductivity of MOFs,which provides a positive guiding significance for the application of MOFs in the field of electrochemical energy storage.2.Bt hot pressing technology,the CC/Ni_x-ZIF-8 flexible electrode materials with different nickel-zinc ratios were synthesized on a flexible carbon cloth substrate.And then flexible polypyrrole-polyethyleneglycol(PPy-PEG)was introduced by electropolymerization deposition method,a flexible CC/MOF/PPy-z composite electrode material was prepared.The electrochemical performance test showed that when the Ni content was 0.8 mmol,the current density of electropolymerized PPy-PEG was 0.8 m A/cm~2,and the electropolymerization was2400 s,the prepared electrode material had the best electrochemical performance;and when the current density was At 1 m A/cm~2,the measured area specific capacitance value of CC/MOF/PPy-2400 s was 296.63 m F/cm~2.On this basis,the CC/MOF/PPy-2400 s composite electrode material was assembled into a CC/MOF/PPy-2400 s//SC symmetrical flexible supercapacitor device.When the current density of the device was 1 m A/cm~2,the area specific capacitance was 33.75 m F/cm~2;when the power density was 400.00 W/cm~2,the corresponding maximum energy density was 3 Wh/cm~2.At the same time,through the flexibility test,it was found that the capacitance value of the electrode material is basically not lost after multiple bending and folding,indicating that the device had excellent flexibility.This work indicates that electropolymerization and deposition of PPy-PEG polymer on MOFs electrode materials can be employed as an energy storage material for flexible devices,which is attritued to the cross-linked network structure between polyol and polypyrrole through hydrogen bonding and electrostatic interaction,enhanceing the mechanical strength and flexibility of the material,and improving the conductivity of materials.