Highly controllable growth of carbon nanotube-functionalized graphene*

The development of graphene with as-grown nanostructures to enhance its electrical and electrochemical properties is vital for various applications, yet remains a challenge. We employ nanoparticles as a catalyst and use ultra-low concentrations of carbon sources for the controlled synthesis of extended carbon nanotubes on the graphene surface via chemical vapor deposition (CVD). Contrary to previously reported non-transparent graphene and carbon nanotube hybrids, the nanotubes synthesized in our study can achieve a height as low as ~100 nm, leading to highly transparent carbon nanotube-functionalized graphene. Based on results from Kelvin probe force microscopy and conductive atomic force microscopy, the graphene substrate and the carbon nanotubes are covalently bonded. Transport and electrochemical measurements reveal that the as-grown carbon nanotube–functionalized graphene has electrical conductivity comparable to bare CVD graphene, with its electrochemical activity being enhanced fivefold.