Facile preparation of polybenzoxazine-based carbon microspheres with nitrogen functionalities:effects of mixed solvents on pore structure and supercapacitive performance

In this study,polybenzoxazine(PBZ)-based carbon microspheres were prepared via a facile method using a mixture of formaldehyde(F)and dimethylformamide(DMF)as the solvent.The PBZ microspheres were successfully obtained at the F/DMF weight ratios of 0.4 and 0.6.These microspheres exhibited high nitrogen contents after carbonization.The microstructures of all the samples showed an amorphous phase and a partial graphitic phase.The porous carbon with the F/DMF ratio of 0.4 showed significantly higher specific capacitance(275.1 F·g^-1)than the reference carbon(198.9 F·g^-1)at 0.05 A-g This can be attributed to the synergistic electrical double-layer capacitor and pseudo-capacitor behaviors of the porous carbon with the F/DMF ratio of 0.4.The presence of nitrogen/oxygen functionalities induced pseudo-capacitance in the microspheres,and hence increased their total specific capacitance.After activation with CO2,the specific surface area of the carbon microspheres with the F/DMF ratio of 0.4 increased from 349 to 859 m^2•g^-1 and the specific capacitance increased to 424.7 F·g^-1 This value is approximately two times higher than that of the reference carbon.The results indicated that the F/DMF ratio of 0.4 was suitable for preparing carbon microspheres with good supercapacitive performance.The nitrogen/oxygen functionalities and high specific surface area of the microspheres were responsible for their high capacitance.