Effectively Improving Capacitive Performance of Three-Dimensional Iron(III) Oxide Nanotube Arrays by Rationally Filling Mesopores with Polypyrrole

Fe₂O₃ is a promising electrode material for electrochemical capacitors, but challenges remain in enhancing its capacitive performance. Herein, we effectively improved the capacitive properties of 3D Fe₂O₃ nanotube arrays by partly filling their mesopores with polypyrrole (PPy) through vapor-phase polymerization. Although the filled PPy was only 9.7 wt %, the resulting hybrid Fe₂O₃/PPy arrays tripled the specific capacitance to 367 F g⁻¹ at 1.0 A g⁻¹, doubled their high rate capability (106 F g⁻¹ at 10 A g⁻¹), and exhibited good cycling stability at high current density. The capacitive performances of the hybrid arrays are among the best for Fe₂O₃-based electrodes. It is believed that the partly filled mesopores not only increase the electronic conductivity and electroactivity of each hybrid nanotube but also avoid blocking the ion-diffusion path. All the features allow the arrays to exhibit synergetic pseudocapacitive properties and to maintain stable and fast electrochemical kinetics. Our findings provide an efficient strategy to boost the electrochemical performances of transition-metal oxide nanomaterials by rationally filling their mesopores with a small amount of a conductive polymer.