Exploring anode materials with an excellent electrochemical performance is of great significance for supercapacitor applications. In this work, a N-doped-carbon-nanofiber (NCNF)-supported Fe₃C/Fe₂O₃ nanoparticle (NCFCO) composite was synthesized via the facile carbonizing and subsequent annealing of electrospinning nanofibers containing an Fe source. In the hybrid structure, the porous carbon nanofibers used as a substrate could provide fast electron and ion transport for the Faradic reactions of Fe₃C/Fe₂O₃ during charge–discharge cycling. The as-obtained NCFCO yields a high specific capacitance of 590.1 F g⁻¹ at 2 A g⁻¹, superior to that of NCNF-supported Fe₃C nanoparticles (NCFC, 261.7 F g⁻¹), and NCNFs/Fe₂O₃ (NCFO, 398.3 F g⁻¹). The asymmetric supercapacitor, which was assembled using the NCFCO anode and activated carbon cathode, delivered a large energy density of 14.2 Wh kg⁻¹ at 800 W kg⁻¹. Additionally, it demonstrated an impressive capacitance retention of 96.7%, even after 10,000 cycles. The superior electrochemical performance can be ascribed to the synergistic contributions of NCNF and Fe₃C/Fe₂O₃.

The conversion of low-cost, sustainable biomass into high-value porous carbon as an electrode material for supercapacitors has attracted considerable recent attention. Almost all efforts are focused on developing advanced carbon electrode materials without conducting large-scale experiments. Utilizing cotton pulp board as the prototype, we demonstrate that honeycomb-like porous carbon could be completely and repeatedly obtained by a one-step activation method. The preparation method is facile and industrially feasible, and could be used for the scalable production of multiple heteroatom-doped honeycomb-like porous carbon (MHDHPC) with excellent reproducibility and high yield. MHDHPC exhibits ultrahigh gravimetric capacitance and volumetric capacitance due to its high surface area, ultrahigh microporosity, relatively high density and surface heteroatom-rich nature. A MHDHPC//MHDHPC based symmetric supercapacitor can deliver a superior volumetric energy density of 13.1 Wh L⁻¹ in 6 M KOH. These exciting results provide a sustainable, scalable and low-cost method to prepare MHDHPC for high volumetric-performance supercapacitors.