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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]

Flexible electrode materials play an important role in flexible portable energy storage devices. Carbon-based nanofiber has attracted numerous attentions due to its advantages on flexibility, safety, and reliability. Herein, we reported a novel and simple method to fabricate nitrogen-boron co-doped hollow porous carbon nanofiber (HPCNF) membranes as flexible supercapacitor electrodes. The higher specific surface area (413.98 m2/g) of HPCNF and the co-doping of N and B resulted in a high specific capacitance of 200.2 F/g (0.1 A/g). After 3000 cycles, NB-HPCNF still maintained high capacitance retention (104.81%). This study provides a new idea for electrochemical energy storage, which is beneficial to the deeper development of portable flexible devices. [Display omitted] • A novel and simple method was used to fabricate nitrogen-boron co-doped hollow porous carbon nanofiber membranes. • The well-developed hollow channels facilitated fast and efficient charge transport in carbon nanofibers. • A solid-state symmetric supercapacitor has good electrochemical properties and good mechanical stability. [ABSTRACT FROM AUTHOR]

Construction of hierarchically porous carbon electrode materials is considered as an efficient strategy for improving the performance of supercapacitors. Nevertheless, how to precisely control the pore structure for preferable improvement the capacitance performance and fabricate in a cost-efficient way is still a scientific challenge. In this paper, an industrial by-product of coal tar pitch is used as precursor to prepare interconnected hierarchically porous carbons, with another domestic waste of eggshell as a pore-forming template and an inner-activator, combined with KOH in-situ activation. The as-prepared porous carbons exhibit large specific surface area (S BET , 1398–2103 cm2 g−1), well-developed interconnected hierarchically architecture, and excellent electrochemical performance. Among them, the optimal TS-PCE-4 based symmetric supercapacitor possesses a high capacitance of 238 F g−1 at 0.5 A g−1 with an excellent rate capability, exhibits long cycle stability with capacitance retention of 95.85 % after 10,000 cycles, and delivers energy densities of 8.27–5.47 Wh kg−1 at power density in the range of 125–4925 W kg−1 in 6 M KOH aqueous electrolyte. This work offers a facile and low-cost route to construct interconnected hierarchically porous carbons for energy storage devices. [Display omitted] • An industrial by-product of coal tar pitch was used to fabricate the hierarchically porous carbons via a facile route. • The domestic waste of eggshell was served as a pore-forming template and an inner-activator. • The carbons show large specific surface area and well-developed interconnected hierarchically porous architecture. • The optimum sample displays outstanding supercapacitor performance. [ABSTRACT FROM AUTHOR]

One-dimensional hierarchical porous carbon nanofibers (CNFs) embedded with Co 3 O 4 nanoparticles in a hollow channel (PPMCo) are fabricated by coaxial electrospinning followed by thermal treatment. The degree to which the CNF surface is exposed to Co 3 O 4 nanoparticles was controlled by the cobalt(II) acetate concentration. The well-controlled structure of PPMCo with porous structure, heteroatoms, and amorphous Co 3 O 4 nanoparticles provided fast ion transport and large reaction surface area, resulting in effective ion migration to the active site and a high rate capacity of the electrode. Benefitting from the unique structure, the PPMCo supercapacitor electrodes displays a high specific capacitance of 188 Fg−1 at 1 mAcm−2, rate capability of 82% when the current density is increased from 1 to 20 mAcm−2, and cycling stability of 93% for 10,000 cycles. The good capacitive performance of the PPMCo electrode is attributed to the synergistic effect of the hierarchical porosity, electroactive material of Co 3 O 4 , high effective surface area, and polar effects by heteroatoms. [Display omitted] • Hierarchical porous CNF embedded with Co3O4 was prepared by coaxial electrospinning. • The degree of CNF exposed to Co3O4 was controlled by the Co(OAc)2 concentration. • The hollow core of the core part provides a fast electron transport channel. • Amorphous Co3O4 helps transport ions by reducing the charge transfer resistance. • The heteroatom functional groups on the carbon surface enhance the pseudocapacitance. [ABSTRACT FROM AUTHOR]

• Micro-electrode arrays were fabricated on a graphite substrate using lithography and carbonization. • Conductive fibers produced via electrospinning and carbonization were decorated with RuO 2 particles. • The 3D micro-electrodes were used in fabrication of all - carbon symmetric supercapacitors. • The specific capacitance reached 219.2 F g−1 at a current density of 1 A g−1 in 1 M H 2 SO 4 electrolyte. [Display omitted] This study employed a carbon microelectromechanical system (C-MEMS) in fabricating a 3D micro-electrode array of conductive carbon cylinders directly on the surface of a graphite substrate. The capacitance of the array was further enhanced by decorating it with a composite material comprising highly-porous carbon nanofibers (CF) and electroactive RuO 2 nanoparticles to function as an active electrode. In galvanostatic charge-discharge tests, the specific capacitance of an electrode decorated with RuO 2 30 wt%/CF was 219.2 F g−1 at a current density of 0.5 A g−1, which is 2.27 times higher than that of the pristine CF electrode. When the current density was increased from 0.5 A g−1 to 3 A g−1, the capacitance retention of the RuO 2 30 wt%/CF electrode was 54.8%. A symmetric supercapacitor based on the RuO 2 30 wt%/CF composite electrode exhibited an impressive energy density of 74.2 Wh kg−1 with power density of 4333 W kg−1. It also demonstrated good capacitance retention of 80.2% following 3000 consecutive charge/discharge cycles at a current density of 2 A g−1. [ABSTRACT FROM AUTHOR]