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‒1. 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 m2∙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.