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

3D porous graphitic biomass carbon as advanced supercapacitor electrode materials synthesized by a low-cost and effective one-step method. In this work, we established a one-step strategy to synthesize three-dimensional porous graphitic biomass carbon (PGBC) from bamboo char (BC), and studied its electrochemical performance as electrode materials for supercapacitors. Using potassium ferrate (K 2 FeO 4 ) to fulfil the synchronous carbonization and graphitization of bamboo carbon, this method is less time-demanding, highly efficient and pollution-free, when compared with a conventional two-step strategy. The as-prepared PGBC sample possessed a porous structure with a large specific surface area (1732 m 2 g −1 ) and abundant micropores, as well as a high graphitization degree demonstrated by XRD and Raman. Further electrochemical measurements revealed that the PGBC electrode exhibited a high specific capacitance of 222.0 F g −1 at 0.5 A g −1 , and the solid-state symmetric supercapacitor in an aqueous electrolyte (KOH/PVA) presented considerable synergetic energy–power output properties with an energy density of 6.68 W h kg −1 at a power density of 100.2 W kg −1 , and 3.33 W h kg −1 at 10 kW kg −1 . Moreover, the coin-type symmetric supercapacitor in an ionic liquid electrolyte (EMIM TFSI) delivered a higher energy density of 20.6 W h kg −1 at a power density of 12 kW kg −1 . This approach holds great promise to achieve low-cost, green and industrial-grade production of renewable biomass-derived carbon materials for advanced energy storage applications in the future.

BHNC synthesized by carbonizing a bamboo-based industrial by-product possesses excellent energy-power synergetic outputting properties among the best ever reported for carbon-based supercapacitors in the Ragone chart. Bio-inspired beehive-like hierarchical nanoporous carbon (BHNC) with a high specific surface area of 1472 m 2 g −1 and a good electronic conductivity of 4.5 S cm −1 is synthesized by carbonizing the industrial waste of bamboo-based by-product. The BHNC sample exhibits remarkable electrochemical performances as a supercapacitor electrode material, such as a high specific capacitance of 301 F g −1 at 0.1 A g −1 , still maintaining a value of 192 F g −1 at 100 A g −1 , negligible capacitance loss after 20 000 cycles at 1 A g −1 , and a high power density of 26 000 W kg −1 at an energy density of 6.1 W h kg −1 based on active electrode materials in an aqueous electrolyte system. Moreover, an enhanced power density of 42 000 W kg −1 at a high energy density of 43.3 W h kg −1 is obtained in an ionic liquid electrolyte system, which places the BHNC-based supercapacitors in the Ragone chart among the best energy–power synergetic outputting properties ever reported for carbon-based supercapacitors.

Mesoporous carbon hollow spheres (MCHS) have wide applications, including catalysis, absorption, and energy storage/conversion. Herein, we report a one-pot, surfactant-free synthesis of MCHS using three molecules: resorcinol, formaldehyde, and tetrapropyl orthosilicate. The co-condensation process between the in situ generated silica primary particles and the polymer oligomers is regulated, leading to monodispersed MCHS with adjustable pore sizes from micropores to 13.9 nm. The resultant MCHS shows excellent performance for electrochemical double-layer capacitors with high capacitance (310 F g(-1) at 1 A g(-1)), excellent rate capability (157 F g(-1) at 50 A g(-1)), and outstanding cycling stability (98.6% capacity retention after 10 000 cycles at 10 A g(-1)). Our one-pot synthesis strategy is versatile and can be extended to fabricate metal oxide@mesoporous carbon yolk-shell structures in the absence of surfactant, paving the way toward designed synthesis of nanostructured mesoporous carbon composites for various applications.