Synthesis of Fe/N Co-doped Porous Carbon Spheres Derived from Corncob for Supercapacitors with High Performances

Corncob, as a sustainable biomass waste, is mainly composed of hemicellulose. Herein, on the basis of natural corncob as substrates, Fe/N co-doped porous carbon spheres were designed via a consecutive FeCl3-mediated hydrothermal reaction and mild KHCO3 activation route for supercapacitor electrode materials. Owing to the low hydrolysis temperature of hemicellulose and hydrolysis promotion of Fe3+, the corncob-derived hydrochar exhibited special carbon sphere morphology. Interestingly, the carbon sphere morphology was well-preserved upon the melamine-mediated KHCO3 activation. As a result of the short ion diffusion distance, unique packing architecture, and developed micro–mesoporous structure of the carbon spheres, optimized CCAC-Fe-M-50% manifested superior ion transfer kinetics and rate performances (87% up to 20 A g–1). Meanwhile, the electrochemical investigation of CCAC-Fe-M-50% in a three-electrode setup illustrated high capacitance (338 F g–1 at 1 A g–1). In a two-electrode setup, the CCAC-Fe-M-50%||CCAC-Fe-M-50% device revealed supreme cyclability (102.7% retention after 5000 cycles) and extremely low Rct (0.59 Ω) and Rs (4.54 Ω). These superior properties were attributed to the large SBET (2305.7 m2 g–1), the multiple redox possibilities (Fe3+, Fe2+, and N functional groups), and the carbon sphere morphology with a micro–mesoporous structure, which enhanced ion physisorption, pseudocapacitance, and electrolyte/ion diffusion, respectively. Besides, the fabricated CCAC-Fe-M-50%||CCAC-Fe-M-50% device in a neutral electrolyte demonstrated a superb energy density (ED) of 18.60 Wh kg–1 at the power density (PD) of 455 W kg–1. The currently presented strategy with superior results might lead to the novel development of biomass-based ultraperformance electrode materials for supercapacitors and other high-tech applications.