Controllable construction of mesoporous hollow carbon spheres rich in micropores from waterborne benzoxazine and their application in supercapacitors

Mesoporous hollow carbon spheres (MHCSs) with mesoporous channels and nanocages structure have unique advantages in energy storage. However, this structure alone does not significantly enhance the electrochemical double layer capacitance (EDLC). Additionally, the current hydrophobic nature of polymer precursors with high char yield impedes effective binding with templates due to polarity differences. Moreover, the use of toxic organic solvents presents obstacles to further development. So, it remains a challenge to prepare MHCSs rich in micropores using polar polymers with high char yield in green solvent. In this work, we prepared MHCSs rich in micropores (MMHCSs) using waterborne benzoxazine as a carbon sources and dendritic/fibrous nano-silica as a sacrificial hard template using water as the solvent and combined with freeze-drying, curing, carbonization and an activation step. The optimal MMHCSs (MMHCSs306–1–7000.5 h) has a large specific surface area (1057 m2 g−1), and has a maximum specific capacitance value near 221.45 F g−1 at 0.5 A g−1 in a three-electrode system, the specific capacitance still reaches 156.66 F g−1 at a high current density (20 A g−1) due to the full utilization of micropores in the presence of mesoporous-shell and hollow-core. When assembled into a symmetrical supercapacitor, the energy density reaches 5.91 Wh kg−1 when the power density is 137.5 W kg−1. The study provides an eco-friendly method for preparing MMHCSs, and the unique structure has potential application in supercapacitors.