Carbon Nanotube/Reduced Graphene Oxide/Aramid Nanofiber Structural Supercapacitors

Reduced graphene oxide/aramid nanofiber (rGO/ANF) supercapacitor electrodes have a good combination of energy storage and mechanical properties, but ion transport remains an issue toward achieving higher energy densities at high current because of the tightly packed electrode structure. Herein, carbon nanotubes (CNTs) are introduced to prevent rGO flake stacking to improve the rate capability of the rGO/ANF structural supercapacitor. The effect of CNTs on the rGO/ANF composite electrode's mechanical and electrochemical properties is investigated by varying the composition. The addition of 20 wt % CNTs led to an increase in Young's modulus up to 10.3 ± 1.8 GPa, while a maximum in ultimate strain and strength of 1.3 ± 0.14% and 55 ± 6.8 MPa, respectively, was found at a loading of 2.5 wt % CNTs. At low specific currents, the electrodes performed similarly (160–170 F g–1), but at high specific currents (5 A g–1), the addition of 20 wt % CNTs led to a significantly higher capacitance (76 F g–1) as compared to that of rGO/ANF electrodes without CNTs (26 F g–1). In addition, the energy density also improved significantly at high power from 1.4 to 5.1 W h L–1 with the addition of CNTs. The improvement in mechanical properties is attributed to the introduction of additional hydrogen-bonding and π–π interactions from the carboxylic acid-functionalized CNTs. The increase in capacitance at higher discharge rates is due to improved ion transport from the CNTs. Finally, in situ electrochemomechanical testing examines how capacitance varies with strain in these structural electrodes for the first time.