Three-dimensional carbon nanotubes/iron oxyhydroxide shell/core hybrid as a binder-free electrode for the flexible supercapacitor

Carbon nanotubes/iron oxyhydroxide (CNTs/FeOOH) three-dimensional hybrid with shell/core nanostructure is designed as a binder-free electrode for the flexible supercapacitor (SC) application. The coiled and dense CNT forest is preferentially fabricated on flexible carbon fiber cloth (CC) by chemical vapor deposition (CVD) and employed as a highly conductive carrier for electrodeposition growth of FeOOH. The average diameter and length of the single CNT are 30–60 nm and 2–3 μm. The shell/core structured CNTs/FeOOH three-dimensional hybrid maintains the consistent interconnecting network morphology, contributing to overcoming the problem of poor conductivity of FeOOH and the transmission of electron channels and the diffusion of electrolyte ions. The CNTs/FeOOH hybrid exhibits a high mass-specific capacitance of 824 F g−1 (or 0.59 F cm−2) in 1 M Na2SO4 electrolyte at 0.5 mA cm−2. By increasing the FeOOH deposition weight, the enhanced area-specific capacitance of 0.892 F cm−2 (or 564 F g−1) is obtained at 0.5 mA cm−2, and the enhanced capacitance retention can reach 96% after 3000 charge/discharge cycles. Besides, a flexible SC is fabricated using the CNTs/FeOOH hybrid electrode and carboxymethyl cellulose (CMC)/Na2SO4 gel electrolyte. The SC displays an energy density as high as 13.33 Wh kg−1 at a power density of 1000 W kg−1. The SC device shows large bending deformation, and these SC devices pack can drive a red diode to work. These results provide such a shell/core structured CNTs/FeOOH three-dimensional hybrid that can be used as potential and low-cost electrode material for flexible SC.