Nanoarchitectured Nitrogen-Doped Graphene/Carbon Nanotube as High Performance Electrodes for Solid State Supercapacitors, Capacitive Deionization, Li-Ion Battery, and Metal-Free Bifunctional Electrocatalysis

A three-dimensional nanostructured nitrogen-doped graphene/carbon nanotube composite has been synthesized via a thermal annealing process, using the high surface attachment properties of uric acid (solid nitrogen precursor) with graphene oxide and oxidized multiwalled carbon nanotube. In the synthesis procedures, the attachment of uric acid to graphene oxide surfaces and the oxidized multiwalled carbon nanotubes via hydrogen bonding and electrostatic forces in the solution leads to a lamellar nanostructure during thermal annealing by the proper insertion of carbon nanotubes in graphene layers with nitrogen doping. The resultant composite has good atomic percentage of N (11.2 at. %) and shows superior electrochemical energy storage and conversion properties compared with nitrogen-doped graphene only and physically mixed nitrogen-doped graphene and nitrogen-doped carbon nanotube samples. The composite exhibits high gravimetric and volumetric capacitance (324 F g-1 at a current density of 1 A g-1) as electrode in solid-state supercapacitors, superior capacitive deionization (440 F g-1 at a current density of 1 A g-1) in 1 M sodium chloride solution, and as high-performance anode in lithium-ion batteries (1150 mAh g-1 at 0.1 A g-1) with long-term cycling stability. In addition, the composite demonstrates efficient metal-free bifunctional electrocatalysis toward the oxygen reduction and evolution reactions, comparable with the commercial electrocatalysts.