Rational design of coaxial MWCNT-COOH@NiCo 2 S 4 hybrid for supercapacitors

A simple one-step hydrothermal route was designed to decorate NiCo 2 S 4 on the surface of carboxylated multiwalled carbon nanotubes (MWCNT-COOHs) to form coaxial MWCNT-COOH@NiCo 2 S 4 hybrid. When employed as supercapacitor electrode material, the MWCNT-COOH@NiCo 2 S 4 electrode shows a large specific capacitance and excellent rate performance. Coupled with activated carbon (AC) negative electrode, the operating voltage of MWCNT-COOH@NiCo 2 S 4 //AC asymmetric supercapacitor (ASC) could be extended to 1.5 V. Moreover, the MWCNT-COOH@NiCo 2 S 4 //AC ASC device achieves a maximum energy density of 33.6 Wh kg −1 at a power density of 375 W kg −1 with good cycle stability (about 83.3% of capacity was retained after 2000 cycles at 3 A g −1 ). In addition, a MWCNT-COOH@NiCo 2 S 4 //AC ASC device can drive a mini-fan. Therefore, the coaxial MWCNT-COOH@NiCo 2 S 4 hybrid is a promising supercapacitor electrode material.