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Summary: The development of efficient methods to achieve a porous activated carbon nanostructures electrode for high‐performance electrochemical double‐layer capacitor (EDLC) is urgently needed at present. In this study, biomass‐based porous hollow carbon nanofiber/nanosheet with suitable micro/mesopores was successfully prepared using a low‐cost simple approach through chemical activation at direct pyrolysis. Biomass‐based porous carbon was performed in two different chemical activation of KOH and ZnCl2. The effects of the different KOH/ZnCl2 concentrations at high‐temperature pyrolysis on the morphological structure and porosity were investigated. The synthesized activated carbon possesses micro/mesopores hollow nanofiber/nanosheet, which enhanced specific surface area from 15.163 m2 g−1 to ultrahigh specific surface area of 1041.900 m2 g−1. These behaviors exhibit a high specific capacitance of 213 F g−1 in a two‐electrode system with excellent energy and power density of 29.6 Wh kg−1 and 106.6 W kg−1 at 1 M H2SO4 aqueous electrolyte. These results provided accurate information about a feasible approach to synthesize biomass‐based porous hollow carbon nanofiber/nanosheet to boost high‐performance energy storage devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Self-O-doped Alpinia galanga stem-based carbon nanofiber succesfully synthesis. • The hierarchical porous carbon exhibit high specific surface area of 1065.58 m2/g. • The porous carbon was performed in solid-free binder form. • In 2-electrode system, supercapacitor possessed specific capacitance of 226F g−1. In this study, activated carbon with hierarchical pores and a nanofiber structure doped with oxygen was prepared using a pure biomass-based sustainable strategy involving integrated chemical impregnation and pyrolysis. Alpinia galangal stem was chosen as it functions as fast conductive network with abundant electrochemical active sites for high-grade electrode materials. The optimal precursor exhibited self-doping of oxygen ranging from 6.15 to 15.69 % with 1065.58 m2/g, which contributed to the redox reaction of the electrode material. When tested in a 2-electrode system, the porous carbon nanofibers showed a high specific capacitance of 226F g−1 at 1 A g−1 in 1 M H 2 SO 4 electrolyte, producing an energy density of 9.3483 Wh kg−1 with a coulombic efficiency of 89.01 %. The results showed that oxygen-doped hierarchical porous carbon nanofibers produced from Alpinia galangal stem biomass and designed to be solid-free of binders are highly promising as high-quality electrode materials that can improve sustainable supercapacitor performance. [ABSTRACT FROM AUTHOR]

The rapid development of consumer electronics, electric vehicles, and smart meters demands high-performance energy storage devices. By now, supercapacitors are expected to become one of the most promising energy devices for future energy technology. In this work, NiO nanoparticles supported on activated carbon nanofibers (NiO/ACNFs) have been synthesized by atomic layer deposition technique, which is directly used as self-supporting binder-free electrodes for supercapacitors. Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman results show that NiO nanoparticles (3.1 nm) are uniformly coated on ACNFs. The NiO/ACNFs-600 electrodes demonstrate a specific capacitance of 870 F·g−1 (1 A·g−1) and good rate capability (remain 67% at 10 A·g−1). The asymmetric supercapacitor devices with NiO/ACNFs-600//ACNFs electrodes yield a fairly high energy density of 39.85 Wh·kg−1 at 2000 W·kg−1 and excellent capacitance retention of 87% after 10,000 cycles. The excellent electrochemical capacitance performance for NiO/ACNFs is attributed to the high conductivity and large specific surface area of ACNFs, high capacity, small size, and even dispersion of NiO as well as the synergistic effect between them. These results demonstrate that NiO/ACNFs can serve as excellent electrode materials for high-performance asymmetric supercapacitors. [Display omitted] • NiO is dispersed evenly on lignin-derived ACNFs by ALD for the first time. • The oxygen-containing functional groups of ACNFs provide the active site for the anchoring of NiO. • Combined advantages of porous ACNFs and highly dispersed NiO nanoparticles. • NiO/ACNFs-600 electrode exhibits excellent specific capacitance of 870 F·g−1 (1 A·g−1). • NiO/ACNFs-600//ACNFs device yields outstanding energy density of 39.85 Wh·kg−1 at 2000 W·kg−1. [ABSTRACT FROM AUTHOR]