Tailored functional group vitalization on mesoporous carbon nanofibers for ultrafast electrochemical capacitors

Electric double layer capacitors (EDLCs) are attracting attention as rational energy storage platforms owing to their rapid and reversible charge adsorption/desorption at the electrode interface. Despite these advantages, EDLCs still face challenges in improving their ultrafast-rate capability for realizing its tailored applicability. In this study, tailored functional group vitalization was introduced on carbon nanofibers (CNFs) using chemical interactions between poly(methyl methacrylate-co-methacrylic acid), thiourea, and phosphorus red during thermal activation of electrospun polymer fibers. The tailored functional group vitalization effects include a simultaneous introduction of sulfur and phosphorus co-incorporated heterostructures from surface to interior of the CNFs (SPD-PCNF). In the surface region, sulfur and phosphorus containing functional groups are developed, which promotes electrolyte wettability and fast ionic diffusion kinetics at the CNFs/electrolyte interface. In the interior region, sulfur (2.4 at%) and phosphorus (2.0 at%) atoms are co-doped inside the carbon lattice, which improves electrical conductivity. In both the surface and interior region, accelerated specific mesopore area (1318.9 m²/g) and proportion are developed throughout the CNFs, which accommodates increased amounts and favorable ionic transport routes for charge adsorption/desorption. With these synergistic effects on charge transfer kinetics, SPD-PCNF electrode exhibited ultrafast-rate capability (112.8 F/g at 20 A/g and 14.0 Wh/kg at 36,000 W/kg).