Synthesis And Application Of Redox Covalent Organic Frame Materials In Supercapacitors

Supercapacitor is a new type of electrochemical energy storage device between battery and traditional capacitor,and its emergence fills the gap of energy and power between the two,and retains the excellent performance of these two energy devices.At present,supercapacitors are widely used in new energy energy storage,transportation and industrial applications,and the key to developing these devices is the discovery of superior electrode and electrolyte materials.In recent years,covalent organic framework（COFs）materials have attracted widespread attention and have been explored as electrode and electrolyte materials for energy storage devices.COFs are a new type of crystalline organic porous polymer linked by covalent bonding,which has the characteristics of adjustable pores,clear structure,high crystallinity,high specific surface area,and functional group modification,which fully meets the conditions and requirements as an electrode material for supercapacitors.However,its inherent shortcomings such as low conductivity and poor accessibility greatly limit its application in electrochemistry and practice.Therefore,it is necessary to discover new COFs materials or find other ways to improve their chemical properties.In this paper,redox active units are introduced into COFs,and experiments show that this process significantly improves its electrochemical performance,bringing many new possibilities to the already vibrant field of electrochemical energy storage materials.1.1,3,5-triformyl triphenol（Tp）was used to react with aniline oligomers of different chain lengths to perform reversible Schiff base reaction to construct two-dimensional covalent organic frameworks（2D COFs）materials with long-cycle and porous redox activity.Four stable 2D COFs（Tp-HZ-COF,Tp-PPD-COF,Tp-DDA-COF and Tp-AT-COF）were successfully synthesized.Among them,the capacitance of Tp-AT-COF is as high as 348.3 F/g at a current density of 0.5 A/g,and the capacitance retention rate is about 70.9%after 5000 cycles.In addition,a TP-AT-COF symmetrical capacitor was developed with a capacitance of 167 F/g at 0.3 A/g and a capacitance retention rate of 70.1%after 4000 cycles.This work developed redox-active 2D COFs with aniline oligomer structures,providing an efficient method for the next generation of advanced high-performance energy storage devices.2.Fourπ-πconjugated 2D COFs of sp²C with redox centers were synthesized by classical Knoevenagel reaction,including COF-Bq-1,COF-Bq-2,COF-Bq-3,and COF-Bq-4.After electrochemical tests,COF-Bq-2 has the best performance,with a capacitance of 60 F/g at 1 A/g,and COF-Bq-1,COF-Bq-2,COF-Bq-3 and COF-Bq-4have excellent cycle stability in 1 M H₂SO₄,and can still reach 84.6,66.1,101.7 and109.2%of the initial capacitance values after 10,000 cycles.In addition,AC//COF-Bq-2 asymmetric assembly was carried out,with a capacitance of 69.4 F/g at a current density of 0.2 A/g,and a capacitance retention rate of 85.34%after 10,000 charge-discharge cycles.This work provides a scalable and simple synthesis method for finding new electrode materials with redox units.3.By adjusting 2D COF（Tp-DADHB-COF）and reduced graphene（r GO）nanosheets with different mass ratios,five composites were synthesized in situ by hydrothermal method,namely COF/r GO-1-1,COF/r GO-2-1,COF/r GO-3-1,COF/r GO-4-1 and COF/r GO-5-1.After electrochemical testing,COF/r GO-3-1 had the best electrochemical performance,with a capacitance of 305.7 F/g at 0.5 A/g in 1 M H₂SO₄ electrolyte,while the capacitance of Tp-DADHB-COF was only 63.2 F/g under the same conditions.After 20,000 cycles at a current density of 20 A/g,the capacitance of COF/r GO-3-1 remains at 93%of the initial value,while the capacitance retention rate of Tp-DADHB-COF is 70%.In order to realize the electrochemical application of high-performance COF/r GO-3-1 electrode materials,they were symmetrically assembled and successfully prepared COF/r GO-3-1symmetrical capacitors.At a current density of 1 A/g,the specific capacitance of the COF/r GO-3-1 symmetrical device is 177.5 F/g.The COF/r GO-3-1 symmetrical device achieves an energy density of 16.6 Wh/kg at a power density of 158.7 W/kg and a capacitance retention rate of 70%after 6000 cycles.The excellent electrochemical performance of COF/r GO-3-1 makes it a superior electrode material for energy storage in supercapacitors.