optical and electrochemical properties of iron oxide and hydroxide nanofibers synthesized using new template-free hydrothermal method

We report the effect of hydrothermal synthesis conditions on the morphological, optical and electrochemical properties of as-prepared iron oxide (γ-fe2o3) and hydroxide (α-feooh) nanostructures. the physico-chemical identification of these fe-based nanostructures using x-ray diffraction, scanning/transmission electron microscopy, porosity and raman spectroscopy analyses revealed a temperature-depended phase transformation. a maghemite and goethite iron-based nanostructured formation was observed in nanorod and trigonal nanofiber shape-like morphology with mean diameters ranging from 32 to 50 nm. the textural analysis of the nanofibers confirmed mesoporosity with a specific surface area of ~ 129 m2 g−1 (in γ-fe2o3) and 23 m2 g−1 (in α-feooh). the electrochemical performance of the iron oxide and hydroxide nanofiber electrodes with and without the addition of activated carbon (ac) was also investigated. the sample electrodes composed of γ-fe2o3, γ-fe2o3/ac, α-feooh and α-feooh/ac showed remarkable specific capacities of 164 mah g−1, 330 mah g−1, 51 mah g−1 and 69 mah g−1 at 1 a g−1 gravimetric current. the influence of the phase transformation linked to the synthesis temperature, and the inclusion of an electric double-layer ac material into the nanofibers clearly demonstrates an enhancement in their energy-storage capability. furthermore, the fe-based nanofibers exhibited excellent cycling stability with good capacity retention of 73% and 99.8%, respectively, after 2000 cycles at a high 30 a g−1 gravimetric current as well as low resistance obtained by impedance spectroscopy analysis. the implication of the results depicts the potential of adopting these γ-fe2o3 nanorods as suitable material electrodes in electrochemical energy-storage devices.