Preparation Of Nitrogen-Doped Carbon-Based Materials From Schiff-base Polymers And Their Capacitive Performance

Supercapacitor has been widely concerned by researchers because of their merits such as extra-high power density,instant charge/discharge ability,superb durability and wide operating temperature.A major challenge for supercapacitors remains to the achievement of high energy density that is comparable to batteries,while maintaining the high power density and excellent cycle stability.The development of highperformance electrode materials,which determine the performance of supercapacitors,is of great significance to the commercialization of supercapacitors.Among them,carbon materials attract much attention because of their advantages such as non-toxicity,low cost,wide source,great conductivity,large specific surface area,adjustable pore structure,good structural stability,and wide usable temperature range.Large specific surface area endows carbon materials with superior electric double layer capacitance(EDLC).However,the redox reaction hardly occurs and prevents carbon materials from higher specific capacitance.Doping carbon matrix with nitrogen atoms can effectively overcome this defect.This paper is based on the Schiff-base formation reaction to generate dynamic polymer networks.By changing the reaction kinetics,Schiff-base cross-linked polymer networks with different morphologies were constructed through a simple and rapid route,and N-doped hierarchical porous carbon nanoparticles were obtained by temperature-controlled calcination.The influence of specific surface area,pore structure,heteroatom content,especially different morphologies on supercapacitive performance were studied.It has important guiding significance for future highperformance electrodes.The specific research work is summarized as follows:(1)Using 1,3,5-tris(4-aminophenyl)benzene(TAB)and 1,4-phthalaldehyde(TPA)as strating materials,appropriate amount of trifluoromethanesulfonic acid as catalyst,reef coral-like Schiff-base cross-linked polymer(SP)was synthesized quickly and easily through a Schiff-base formation reaction.Then SP was pyrolyzed at different carbonization temperatures to obtain N-doped hierarchical porous carbon materials(HPCN-X).The effect of carbonization temperature on the ordering degree,specific surface area,pore structure and chemical compositions of carbon materials were studied.We further focused on the influence of these factors on the EDLC and faradaic capacitance of electrode materials.The results suggest that high temperature causes the escape of heteroatoms during carbonization,which reduces the surface wettability of carbons thus decreasing effective specific surface area.Lowering the carbonization temperature is beneficial for retaining more heteroatoms,but smaller specific surface area is not conducive to exposure active sites,resulting in reducing effective utilization of heteroatoms.In other words,the excellent supercapacitive performance of HPCN850 is the synergistic effect of the appropriate specific surface area and heteroatom content.(2)Through adjusting the amount and type of catalysts or changing the reactivity of monomers to adjust the reaction rate of Schiff-base formation reaction,a series of Schiff-base cross-linked network polymers(SPs)with different morphologies were synthesized.N-doped hierarchical porous carbon nanoparticles(HPCNs)were obtained after one-step carbonization reaction.The effect of reaction rate on morphology,specific surface area and heteroatom content of electrode materials were studied,and the influence of these factors on EDLC and faradaic capacitance was deeply investigated.The optimal sample(HPCN-3)possesses coral reef-like microstructure,high SSA upto 1003 m2 g-1,and hierarchical porous structure,thus exhibiting excellent electrochemical performance.In 1 M H2SO4 electrolyte,the remarkable specific capacitance of 359.5 F g-1(at 0.5 A g-1),outstanding rate capability and cycle stability are achieved.Additionally,HPCN-3 has the largest normalized EDLC(0.239 F m-2)and faradaic capacitance(10.24 F g-1),which is due to reef coral-like structure endowing HPCN-3 larger external surface area,therefore,improving the effective utilization rate of specific surface area and heteroatoms.