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

Abstract 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).