Starch-enabled electrospinning and aqueous activation for ultrahigh surface area, heteroatom-doped carbon nanofibers for high-performance supercapacitors.

Starch-based carbon nanofibers hold great promise for sustainable supercapacitor electrodes due to the natural abundance and renewability of starch. However, transforming starch into carbon nanofibers remains challenging because of its poor thermal stability, which often leads to structural collapse during thermal treatment. Herein, we propose a ternary polymer strategy (starch/PAN/PMMA) to overcome this limitation, enabling successful electrospinning while preserving structural integrity. Notably, starch serves a dual function as a renewable carbon source and, more importantly, an enabler for a green aqueous activation process. The fibrous network takes up the aqueous KOH/thiourea solution mainly through capillary action, while the hydroxyl groups of starch provide additional water affinity at the molecular level. This allows uniform impregnation of the precursor fibers and achieves simultaneous chemical activation and in-situ N/S doping in a single step, without organic solvents or complex pre-drying. The resulting hierarchically porous carbon nanofibers exhibit an ultrahigh specific surface area of 1952.30 m2/g and deliver a specific capacitance of 517.5 F/g at 0.5 A/g, an energy density of 23.25 Wh/kg, and 97.58% capacitance retention after 10,000 cycles at 5-10 A/g. This work unlocks the potential of starch for high-performance energy storage through a safer, more sustainable aqueous activation route.