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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]

• 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]