Metal-organic Frameworks/Polypyrrole Composite Electrode For Supercapacitor

Metal-organic frameworks?MOFs?are a class of long-ranged and well-alligned porous crystalline materials.Because of outstanding porosity value,high specific surface area and easily adjustable structure,MOFs play an indispensable role in diverse field.Meanwhile,through using MOFs'own structure characteritics,MOFs can act as a host molecule to load gust molecule.Composite materials derived from MOFs usually involve some specifical perfermances which are superior to single material.For example,polyoxometallate?POMs?can embeded in MOFs and formed composite material?MOFs@POMs?which used in energy storage field.It is apparent that pure MOFs as the supercapacitor electrode material is not practicable because of its insulator-like characteristic which restricts the electron transfer.In light of such limitations,in recent years,various functional or conductive materials have been mixed/intercalated with MOFs to improve their potential for such applications?e.g.,rechargeable batteries,optoelectronics,and supercapacitors?.Lately,many of these composite materials have been recognized as next-generation electrodes for the development of efficient supercapacitors.Besides,some special traits include structure and synergistic effects make these composite materials show tremendous potential in energy storgy aspect.Trying to achieve high specific capacitance and cycling stability,three MOFs-based supercapacitor composite positive electrodes have been designed and synthesized.Firstly,MOFs have zeolite structure were obtained via stirred at room temperature.After polypyrrole?PPy?modified MOFs,composite electrode MOF/PPy was successfully sunthesized.Seondly,two kinds of composite material MOFs@POMs arised in Teflon-lined autoclave when POMs crystals embened in MOFs canals.During electrochemical deposition,PPy was covered in the MOFs@POMs surface.The novel composite electrode was denoted MOFs@POMs/PPy.A variety of physical characterization methods were used to test the composite electrode materials in detail.Electrochemical methods were used to characterize the cyclic voltammetry?CV?and galvanostatic charge–discharge?GCD?measurements.At last,the synergistic effect of all kinds of consitituent on the composite electrode was investigated.1.ZIF-67 was synthesized under room temperature using Co ions and 2-methylimidazole?Hmim?.In this step,the electrode was named CC/ZIF-67.To largely embody the advantage of ZIF–67 in supercapacitor,electrochemical deposition was used to obtain PPy in our work.In this composite electrode,PPy grows up rely on the morphology surface of ZIF–67 and forms a"Carbon-to-MOFs-to-PPy"conducting network.Consequently,the electrode was named CC/ZIF-67/PPy.CC/ZIF-67/PPy was the first work to intergrate ZIF-67 and PPy toghter via electrochemical deposition.Finally,the composite electrode material CC/ZIF-67/PPy got a great electrochemical performance than CC/ZIF-67.As a result,in 6 M KOH solution,CC/ZIF–67/PPy composite electrode shows excellent capacitance of 284.3 F g^-1(180.7 mF cm^-2).Moreover,ultrahigh long-life cycling stability of 100.7%after 40000 cycles was obtained and this value is the best one with reported MOFs–based supercapacitor electrode.The remarkable capacitance retention is even better than some double electric layer capacitor material,such as graphene,activated carbons and so on.2.NENU-5 and MIL-100@PMo12 were synthesized under high temperature in Teflon-lined autoclave using Cu ions,Fe ions and trimesic aid?BTC?.In this step,NENU-5was chose to be the testing object because of it's better electrochemical performance than MIL-100@PMo12 and this electrode was named CC/NENU-5.Secondly,the CC/NENU-5was acted as work electrode during the electrodeposition process.PPy looks like a conducting network and covers on the surface of NENU-5.Consequently,the electrode was named CC/NENU-5/PPy.CC/NENU-5/PPy was the first work to intergrate MOFs@POMs and PPy toghter via electrochemical deposition.At last,the composite electrode material CC/NENU-5/PPy got a great electrochemical performance than CC/NENU-5 and CC/Cu-MOF/PPy?CC/HKUST-1?.As a result,in 1 M H₂SO₄ solution,CC/NENU-5/PPy composite electrode shows ultrahigh capacitance of 508.6F g^-1(2753.45 mF cm^-2).The sepecific capacitance?areal capacitance?value is the best one with reported POMs-based center supercapacitor electrode.Moreover,high long-life cycling stability of 80.7%after 8000 cycles was obtained.This considerable lifetime is better than most electrode materials which act POMs as reaction center.