Template-Free, Self-Doped Approach to Porous Carbon Spheres with High N/O Contents for High-Performance Supercapacitors

A template-free and self-doping approach is developed for fabricating N,O-enriched porous carbon spheres (PCSs) via direct carbonization/activation of melamine-glyoxal polymer. The interconnected spherical morphology of PCSs generates stacking porosities as ion reservoirs for rapid ion diffusion and affords conductive networks to shorten the transport lengths for electron transfer. Besides, PCSs exhibit a large surface area (1302 m² g^–1), ample ultramicropores (0.54 nm), and developed supermicro- and mesopores. This unique pore architecture provides optimized ion-accessible pore size to enhance double layer capacitance, and serves as ion-highways for rapid diffusion of electrolyte ions. Furthermore, high N/O elements (7.97/10.16 wt %) incorporated into PCSs improve surface wettability and supply additional pseudocapacitance. Therefore, the resultant PCS electrodes exhibit superior electrochemical performances, such as a high specific capacitance up to 344 F g^–1 at 1.0 A g^–1, remarkable rate capability, and long-term stability in a three-electrode. Notably, the PCS-based supercapacitor exhibits an impressive energy density of 33.37 Wh kg^–1 and power density of 9000 W kg^–1 in Na₂SO₄ electrolyte. This result provides a simple and efficient fabrication of PCSs for high-performance supercapacitors.