Porous Graphene-Carbon Nanotube Scaffolds for Fiber Supercapacitors

Fiber nanomaterials can become fundamental devices that can be woven into smart textiles, for example, miniaturized fiber-based supercapacitors (FSCs). They can be utilized for portable, wearable electronics and energy storage devices, which are highly prospective areas of research in the future. Herein, we developed porous carbon nanotube-graphene hybrid fibers (CNT-GFs) for all-solid-state symmetric FSCs, which were assembled through wet-spinning followed by a hydrothermal activation process using environmentally benign chemicals (i.e., H₂O₂ and NH₄OH in deionized water). The barriers that limited effective ion accessibility in GFs were overcome by the intercalation of CNTs in the GFs which enhanced their electrical conductivity and mechanical properties as well. The all-solid-state symmetric FSCs of a precisely controlled activated hybrid fiber (a-CNT-GF) electrode exhibited an enhanced volumetric capacitance of 60.75 F cm^-3 compared with those of a pristine CNT-GF electrode (19.80 F cm^-3). They also showed a volumetric energy density (4.83 mWh cm^-3) roughly 3 times higher than that of untreated CNT-GFs (1.50 mWh cm^-3). The excellent mechanical flexibility and structural stability of a miniaturized a-CNT-GF are highlighted by the demonstration of negligible differences in capacitance upon bending and twisting. The mechanism of developing porous, large-scale, low-cost electrodes using an environmentally benign activation method presented in this work provides a promising route for designing a new generation of wearable, portable miniaturized energy storage devices.