A cost-effective high-performance asymmetric supercapacitor (ASC) with a functionalized carbon nanotube (FCNT) film and Fe2O3@C nanocomposite grown on carbon paper is fabricated in aqueous KOH electrolyte. The Fe2O3@C nanoparticles are prepared through a facile coprecipitation and carbonization method. By virtue of their unique three-dimensional nanostructure for excellent electrical conductivity and easy access to electrolyte, the established novel aqueous ASC device possesses a wide working potential window from 0 to 1.5 V and presents superb electrochemical properties with excellent rate performance and a high energy density of 21.21 Wh kg–1. A synergistic effect of capacitive and faradaic charge-storage mechanisms may be responsible for the superior performance. This research may herald the advent of ASC device potential application for electrical vehicles, smart power grids, and intermittent renewable energy sources.

Carbon materials have been used as negative electrodes for supercapacitor applications; nevertheless, owing to the low capacitance, they have limited ability to enhance the supercapacitor electrochemical properties.

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