High-Performance Pseudocapacitor Electrodes Based\non α‑Fe₂O₃/MnO₂ Core–Shell\nNanowire Heterostructure Arrays

Abstract

A simple wet chemical technique has\nbeen employed to fabricate\nMnO₂ nanolayer-coated α-Fe₂O₃/MnO₂ core–shell nanowire heterostructure arrays\nto prepare unique pseudocapacitor electrodes. The coating of MnO₂ on α-Fe₂O₃ nanowires is triggered\nby the reduction of KMnO₄ solutions by the metallic (Au)\nfilm on which the polycrystalline α-Fe₂O₃ nanowires have been grown electrochemically. This metallic film\nalso acts as the current collector by making direct contact with the\narrays of the 1D nanoheterostructures. The as-prepared α-Fe₂O₃/MnO₂ nanoheterostructures are found\nto exhibit excellent specific capacitance, high energy density, high\npower density, and long-term cyclic stability as compared with the\nbare α-Fe₂O₃ nanowire electrodes. The\nunique geometry of the 1D nanoheterostructures with high effective\nsurface area to allow faster redox reaction kinetics, the incorporation\nof two highly redox active materials in the same structure, and the\nporous surface structures of the heterostructure to allow facile electrolyte\ndiffusion help in the superior electrochemical performance of the\nα-Fe₂O₃/MnO₂ nanoheterostructures.\nThe maximum specific capacitance of 838 F g^–1 (based\non pristine MnO₂) has been achieved by cyclic voltammetry\nat a scan rate of 2 mV s^–1 in 1 M KOH aqueous solution.\nThe hybrid α-Fe₂O₃/MnO₂ nanocomposite\nelectrodes also exhibit good rate capability with excellent specific\nenergy density of 17 Wh kg^–1 and specific power\ndensity of 30.6 kW kg^–1 at a current density of\n50 A g^–1 and good long-term cycling stability (only\n1.5% loss of its initial specific capacitance after 1000 cycles).\nThese studies indicate that the α-Fe₂O₃/MnO₂ nanoheterostructure architecture is very promising\nfor next-generation high-performance pseudocapacitors.