A scalable nano-engineering method to synthesize 3D-graphene-carbon nanotube hybrid fibers for supercapacitor applications

In this work, we describe a simple approach for the synthesis of three-dimensional graphene (3D-G) - carbon nanotube (CNT) hybrid fibers via Chemical Vapor Deposition (CVD). The obtained hybrid fiber was employed as a free-standing current collector in an electrochemical supercapacitor thus avoiding any conductive additives or metals. The amount of graphene synthesized on the CNT fiber and its properties have been easily tuned by different processing parameters, as described in the paper below. The fabricated fibers revealed a reasonable mechanical strength of 220.4 MPa and high electrical conductivity up to 649 Scm−1. They also showed excellent electrochemical properties and capacitance that was important for their energy storage application. Interconnected PANI nanorods were grown on these fibers by oxidation polymerization, and the resulted fibrous hybrid structures were used as electrodes to make supercapacitors. The created devices employed an ionic liquid gel electrolyte (PVDF-EMIMBF4) which had a voltage window of 3.2 V, thus increasing significantly the energy densities of the supercapacitors. The tested devices achieved a gravimetric energy density of 12.93 Wh/kg and a power density of 1350.25 W/kg at a current density of 1 A/g. They also demonstrated an areal energy density of 14.54 μWh/cm2 and a power density of 1.37 mW/cm2 at a current density of 1 mA/cm2.