Reduced graphene oxide carbon nanotube hybrid fibers with narrowly distributed mesopores for flexible supercapacitors with high volumetric capacitances and satisfactory durability

Although graphene fiber supercapacitor is promising as an efficient, flexible and lightweight power source for wearable smart electronic devices, it has a limitation of low volumetric capacitance caused by its loose porous structure and unsatisfactory wettability with electrolytes. Herein, continuous hybrid fibers consisting of reduced graphene oxide (RGO) and carbon nanotubes (CNTs) are fabricated as highly capacitive electrodes by wet-spinning of non-liquid-crystal dispersion of graphene oxide and CNTs with the assistance of a capillary orientation apparatus followed by moderate chemical reduction. The addition of the aligned CNTs benefits the construction of a compact structure with narrowly distributed mesopores in the hybrid fibers, enhances tensile strength of the fibers, and improves internal electrical conduction of the fiber electrode, while the presence of RGO provides pseudocapacitance derived from its residual oxygen-containing groups. Consequently, the hybrid fiber supercapacitor with a polyvinyl alcohol/H2SO4 electrolyte delivers not only high volumetric capacitance of 354.9 F cm(-3) and high energy density of 12.3 mW h cm(-3) at a current density of 0.1 A cm(-3), but also exhibits long cycling stability of 94% after 10,000 cycles and satisfactory bending durability. A stable foldable supercapacitor with origami-based structure is well constructed with high prospects in miniaturized flexible and stretchable devices. (C) 2019 Elsevier Ltd. All rights reserved.