High-energy asymmetric electrochemical capacitors based on oxides functionalized hollow carbon fibers electrodes

Asymmetric supercapacitors (ASC) using traditional porous carbon as negative electrode usually suffer from low energy density. Herein, we report a high-performance negative electrode by growing columnar Fe2O3 nanorods vertically on activated hollow yet conductive carbon fiber (aCF), featuring bundled nanorods with a diameter of 50-70 nm and a length of 200-300 nm. The porous nature originated from the unique assembly of these Fe2O3 nanorods results in large electrochemically active surface area, yielding a high specific capacitance of 988 F g(-1) in 2.0 M KOH electrolyte. An asymmetric capacitor with aCF-Fe2O3 as negative electrode and nickel-cobalt double hydroxide (NiCo-DH) grown on aCF as positive electrode showed an extended working voltage window up to 1.6 V in aqueous KOH, thus delivering a maximum energy density of 83.7 Wh kg(-1) at the power density of 392.3 W kg(-1). Interestingly, the ASC exhibits remarkable cycling stability with 94.6% capacitance retention even after 10000 cycles of charge-discharge. These performances are far superior to most of previous ASCs with respect to energy density, rate capability or cycling stability. It has been demonstrated that two ASCs connected in series are able to power various electronic devices, including a red light-emitting diode indicator, toy car, a fun and an electronic timer.