Study On Phenanthroquinone-based Conjugated Microporous Polymers And Their Supercapacitors

Supercapacitors are a new type of green energy storage device.The energy storage mechanism of supercapacitors comes from electric double layer capacitors and pseudocapacitors.The supercapacitors exhibit the characteristics of fast charging and discharging,high power density,long service life,and green safety.At present,one of the focus of research on supercapacitors is to develop new electrode materials that have both electric double layer capacitance and pseudocapacitance energy storage mechanism.The key is to improve the specific surface area and redox activity of the material.Conjugated microporous polymers,on the other hand,have micropores,high specific surface area,and the designability of molecular structure,which enables redox-active functional groups to be introduced into the molecular framework.Therefore,conjugated microporous polymers have great application potential in the field of supercapacitors.In this research,we choose tris-(4-aminophenyl)amine(TA),2,7-dibromo-9,10-phenanthrenequinone(2,7-DPA)and 3,6-dibromo-9,10-phenanthrenequinone(3,6-DPQ)as building units and two phenanthrenequinone-based conjugated microporous polymers were synthesized by the Buchwald-Hartwig coupling reaction,namely PQCMP-27 and PQCMP-36,with a specific surface area of 60 m~2 g^-1,showing strong redox activity.Among them,the supercapacitors constructed by PQCMP-36 can reach 567 F g^-1 under the three-electrode system,1 M H₂SO₄ and at a current density of 1A g^-1.At a current density of 2 A g^-1,after 6000 cycles of charging and discharging,70%of the initial capacitance and nearly 100%coulomb efficiency of the supercapacitors can still be maintained.In order to further improve the rate performance and cycle stability of PQCMP-36,the third building unit 3,5-dibromophenylboronic acid(BA)was introduced when synthesizing PQCMP-36,and the redox of PQCMP-36 was optimized by changing its ratio.Thus,phenylboronic acid modified PQCMP-36 was obtained.When the introduction amount of BA was 20%,the supercapacitors constructed by the modified polymer in the three-electrode system,1 M H₂SO₄ and at a current density of 1 A g^-1 had a specific capacitance of up to 810 F g^-1.After 6000 cycles of charge and discharge,the initial capacitance of the supercapacitors can still maintain 84%,and the Coulomb efficiency is close to 100%.In addition,in order to realize the potential of polymers for energy storage applications in flexible capacitors,PQCMP-36 was further grafted onto the surface of benzene bromide modified carbon nanotube fibers(Br@CNF)through Buchwald-Hartwig coupling to obtain a core-shell structure PQCNF.Under the three-electrode system,in 1 M H₂SO₄ and at a current density of 1A g^-1,the area specific capacitance of PQCNF is as high as 552 m F cm^-2.Further assembly of PQCNF and PVA/H₃SO₄ gel electrolyte to obtain symmetrical fibrous supercapacitor PQCNF@SCs,which show excellent flexibility and bending resistance.Under the current density of 0.25 m A cm^-2,the area specific capacitance of PQCNF@SCs can reach 224 m F cm^-2,and the power density can reach0.25 m W cm^-2.The research of this subject provides new insights for the design and preparation of conjugated microporous polymers and their applications in the field of supercapacitors.At the same time,the prepared fibrous supercapacitors provides a broadening of the applications of conjugated microporous polymers in the field of flexible energy storage.