Constructing Ultrahigh-Capacity Zinc–Nickel–Cobalt Oxide@Ni(OH)2 Core–Shell Nanowire Arrays for High-Performance Coaxial Fiber-Shaped Asymmetric Supercapacitors

Abstract

Increased efforts have recently been devoted to developing high-energy-density flexible supercapacitors for their practical applications in portable and wearable electronics. Although high operating voltages have been achieved in fiber-shaped asymmetric supercapacitors (FASCs), low specific capacitance still restricts the further enhancement of their energy density. This article specifies a facile and cost-effective method to directly grow three-dimensionally well-aligned zinc-nickel-cobalt oxide (ZNCO)@Ni(OH)2 nanowire arrays (NWAs) on a carbon nanotube fiber (CNTF) with an ultrahigh specific capacitance of 2847.5 F/cm3 (10.678 F/cm2) at a current density of 1 mA/cm2, These levels are approximately five times higher than those of ZNCO NWAs/CNTF electrodes (2.10 F/cm2) and four times higher than Ni(OH)2/CNTF electrodes (2.55 F/cm2). Benefiting from their unique features, we successfully fabricated a prototype coaxial FASC (CFASC) with a maximum operating voltage of 1.6 V, which was assembled by adopting ZNCO@Ni(OH)2 NWAs/CNTF as the core electrode and a thin layer of carbon coated vanadium nitride (VN@C) NWAs on a carbon nanotube strip (CNTS) as the outer electrode with KOH poly(vinyl alcohol) (PVA) as the gel electrolyte. A high specific capacitance of 94.67 F/cm3 (573.75 mF/cm2) and an exceptional energy density of 33.66 mWh/cm3 (204.02 μWh/cm2) were achieved for our CFASC device, which represent the highest levels of fiber-shaped supercapacitors to date. More importantly, the fiber-shaped ZnO-based photodetector is powered by the integrated CFASC, and it demonstrates excellent sensitivity in detecting UV light. Thus, this work paves the way to the construction of ultrahigh-capacity electrode materials for next-generation wearable energy-storage devices.