Hierarchical Fe2O3 nanotube/nickel foam electrodes for electrochemical energy storage

An iron-oxide (Fe2O3) nanotube (NT) array is grown directly as a hierarchical nanoarchitecture on a nickel-foam (NF) surface via a simple and cost-effective immersive process. The morphology and microstructure of Fe2O3 NT arrays are systematically examined by scanning electron, transmission electron, Raman, and X-ray photoelectron spectroscopies. The results reveal that the walls of Fe2O3 NT are composed mainly of agglomerated small alpha-Fe2O3 (hematite) monocrystalline nanoparticles filled with a few ZnO monocrystalline particles. The microstructural influence on the pseudocapacitive performance of the obtained Fe2O3 NT/NF electrodes is also investigated via in-situ X-ray absorption spectroscopy (XAS) and electrochemical measurement. The in-situ XAS results regarding charge storage mechanisms of the Fe2O3 NT/NF electrodes show that a Li+ can reversibly insert/desert into/from the 3D mesoporous textures between the Fe2O3 subunits depending on the applied potential. The electrochemical results indicate that the Fe2O3 NT/NF electrode shows highly reversible features and satisfactory rate abilities. Most significantly, the excellent specific capacitance achieved in Fe2O3 NT/NF nanoelectrodes is as great as 300.1 Fg(-1); energy density 75 W h kg(-1) and power density 4.5 kW kg(-1) are obtained, and the Fe2O3 NT/NF nanoelectrode has acceptable cycling stability after 3000 cycles. (C) 2016 Elsevier Ltd. All rights reserved.