Chemical Vapor Deposition of Carbon Nanocoils Three-Dimensionally in Carbon Fiber Cloth for All-Carbon Supercapacitors.

An Au/K bicatalyst-assisted chemical vapor deposition process using CH to grow high-density carbon nanocoils (CNCs) uniformly on the fibers in carbon fiber cloth substrates three-dimensionally was developed. An as-deposited substrate (2.5 × 1.0 cm) showed a high electrochemical active surface area (16.53 cm), suggesting its potential usefulness as the electrode in electrochemical devices. The unique one-dimensional (1D) helical structure of the CNCs shortened the diffusion pathways of the ions in the electrolyte and generated efficient electron conduction routes so that the observed serial resistance was low (3.7 Ω). By employing two-electrode systems, a liquid-state supercapacitor (SC) in HSO (1.0 M) and a solid-state SC with a polypropylene (PP) separator immersed in HSO (1.0 M)/polyvinylalcohol were assembled and investigated by using CNC-based electrodes. Both devices exhibited approximate rectangular shape profiles in the cyclic voltammetry measurements at various scan rates. The observations indicated their electric double-layer capacitive behaviors. From their galvanostatic charge/discharge curves, the specific capacitances of the liquid SC and the solid SC were measured to be approximately 137 and 163 F/g, respectively. In addition, the solid-state CNC-based SC possessed excellent energy density (15.3 W h/kg) and power density (510 W/kg). The light weight solid SC (0.1965 g, 2.5 × 1.0 cm) was bendable up to 150° with most of the properties retained.