Synthesis Of Porous Carbon Materials Derived From Porous Aromatic Frameworks For Supercapacitors

Due to the increase in energy consumption,research on energy storage technology has become a hot topic in academia.So far,scientists have made significant efforts to explore alternative sustainable energy sources as well as advanced energy conversion and storage systems.Supercapacitors have received widespread attention due to their low cost,long cycle life,and excellent safety.The electrode materials are the the most critical component for supercapacitors.Porous carbon materials has shown great potentials in supercapacitor electrodes owing to their high electrical conductivity,excellent chemical stability,and non-toxicity to the environment.In the past decades,porous aromatic frameworks?PAFs?materials have developed rapidly and have wide applications in the fields of gas adsorption,separation,storage,catalysis,etc..The unique structure and characteristics,including high specific surface area,adjustable pore structure,and controllable chemical composition,make them the best candidates as precursors for porous carbon materials.In this article,we studies the design and synthesis of noval porous aromatic frameworks as well as explores the effect of its structure on the electrochemical performance for supercapacitors,mainly including the follows:Firstly,a porous aromatic framework?PAF?material?LNU-18?with two kinds of nitrogen atoms(N_triazine and N_amine)was prepared via a Suzuki coupling reaction.After carbonization at 700,800,and 900?,respectively,there is no obvious change for morphology compared with their precursor accompanied by an enlargement in the surface area.Evaluated in an alkali environment?6 M KOH?,LNU-18-800 as the electrode material reached a maximum specific capacitance of 269 F/g at a current density of 0.5 A/g.To reveal their mechanism,PAF-48 with a similar theoretical structure as LNU-18 but whole carbon skeleton was carbonized and its capacitance?54 F/g?is ca.four times lower than LNU-18-800.The above results prove that it is an effective means by doping different kinds nitrogen atoms in the polymer skeleton to significantly improve the electrochemical performance of the material after carbonization.Secondly,we prepared an alkyl chain?C8?appended porous aromatic framework?LNU-16?,whose pore space were occupied by the octyl groups with a kinetic diameter of 7–8?.After the carbonization process,the alkyl chains serving as the self-sacrificial template directed the formation of micropore,which provides the extra-space for the thermal-driven skeletal deformation to form the ultramicropore?<0.7 nm?.This modulated ultramicroporous structure provided a favorable path for electrolyte penetration and transportation.The porous carbon material derived from LNU-16 revealed superior electrochemical performance including the high specific capacitance,good rate capability,and long-term stability in 6 M KOH electrolyte.The specific capacitance of LNU-16-800 can achieve at 294 F/g,twice larger than that of conventional activated carbon electrodes?120 F/g?.Consequently,the synthesis of ultramicroporous carbon via self-sacrificial template route opens up a promising gate to adjust porous structure for high-performance application in supercapacitors.Finally,we synthesized a series of porous aromatic frameworks?LNU-34,LNU-35,LNU-36,and LNU-37?,which were constructed by making the different monomers self-polymerize or co-polymerize with cyanuric chloride via Friedel-Crafts reaction.And then the porous carbon materials C-LNU-34,C-LNU-35,C-LNU-36and C-LNU-37 were prepared by carbonized directly at 900?,after that,these carbons are used in supercapacitor electrodes.The results show that C-LNU-35,which contained nitrogen atoms and rich?-conjugated structure,has the best electrochemical performance.And the specific capacitance of C-LNU-35 can reach366 F/g at 0.5 A/g.The excellent performance of C-LNU-35 can be mainly attributed to that the N-doped can change the wettability of the electrode and the rich?-conjugated structure can also provide a large number of active sites to facilitate ion transport,thus enhancing the electrochemical performance.