Preparation And Properties Of Nitrogen-Doped Mesoporous Carbon Materials Based On Melamine Resin

Porous carbon materials have important properties such as high specific surface area and pore volume,unique morphology,tunable pore structure,excellent thermal,chemical and mechanical stability,and have been widely used in energy conversion and storage.The electrochemical properties of mesoporous carbon materials can also be improved by introducing nitrogen elements to modify the physical and chemical properties of the carbon matrix.Many challenges remain for the synthesis of mesoporous carbon materials with desired structures and functions for target applications.In this thesis,monodisperse mesoporous carbon nanospheres with tunable size and structure were prepared by soft-templating method using mimic resin（MF）oligomers as carbon and nitrogen precursors,amphiphilic triblock copolymer as mesoscopic structure template,and1,3,5-trimethylbenzene（TMB）as auxiliary.The size tuning of monodisperse mesoporous MF polymer nanospheres was controlled by adding HCl to adjust the p H of the reaction,and then different nitrogen-doped mesoporous carbon microspheres with different mesoporous sizes（N-MCs-n,where n is the diameter of the carbon sphere,nm）were obtained.The morphology,mesostructure and microstructure were analyzed by XRD,SEM,TEM,N₂ adsorption and desorption and XPS,and the effects of different surfactants,melamine-to-formaldehyde ratio and HCl dosage on the morphology of monodisperse mesoporous MF polymer nanospheres and mesoporous carbon microspheres were investigated.The results showed that the best mesoporous carbon microspheres were prepared by surfactant F127,melamine-to-formaldehyde ratio of 1:1,HCl to melamine ratio of 0.2～0.45,and the specific surface area of the prepared monodisperse nitrogen-doped mesoporous carbon microspheres was 315 cm² g^-1,the pore volume was 1.03 cm³ g^-1,and the nitrogen content was 25.5%.The nitrogen-doped mesoporous carbon microspheres were chemically activated by KOH and characterized by XRD,SEM,TEM,N₂ adsorption and desorption,and XPS.The activated N-MCs-50 was selected for cyclic voltammetry,constant current charge-discharge and electrochemical impedance spectroscopy tests.The results showed that in the three-electrode system,the specific capacitance in aqueous 2 M KOH electrolyte solution was 196.0 F g^-1 at a current density of 0.2 A g^-1;the capacitance was maintained at 129.37 F g^-1（capacitance retention of 65.8%）at a high current density of 10 A g^-1,and the capacitance retention was90.2%for 5000 cycles.In the two-electrode system,the specific capacitance of N-MCs-50 is44.37 F g^-1 with a multiplicative performance of 0.1 to 10 A g^-1 and a capacitance retention rate of 74.3%.The synthesized nitrogen-doped mesoporous carbon microspheres exhibit excellent supercapacitor performance and good electrochemical stability.