Carbon-nanotube@graphene core-shell nanostructures as active material in flexible symmetrical supercapacitors

A carbon nanomaterial with core-shell structure was constructed from a composite of graphene and carbon nanotubes (CNT@G). A unique technology called polymer-assisted metal-catalyzed chemical vapor deposition (CVD) was used to first disperse a gold catalyst precursor, via the assistance of polyvinyl alcohol, on the CNT surface and then facilitate graphene growth by reducing the gold nanoparticles during CVD. A CNT@G/Ni electrode was then prepared from the CNT@G core-shell nanocomposite without using polymer bonding or annealing. The as-fabricated CNT@G/Ni electrode with mass loading of 3 mg cm(-2) exhibited a high specific capacitance of 620.3 F g(-1) at a scanning rate of 1 mV s(-1) in the three-electrode configuration. When the mass loading of the electrode reached 5 mg cm(-2), the areal capacitance was 781.2 mF cm(-2) at a scanning rate of 1 mV s(-1). Symmetric supercapacitors were constructed using these CNT@G/Ni electrodes and a gel electrolyte consisting of carboxymethyl cellulose and potassium hydroxide. The devices offered advantages of flexibility, high operating voltage (1.8 V), high specific capacitance (268.7 mF cm(-2)), and high cycling performance (120.4% capacity retention after 10000 cycles).