Novel peanut-like α-Fe2O3 superstructures: Oriented aggregation and Ostwald ripening in a one-pot solvothermal process

Superstructured α-Fe2O3 nanorods as novel binder-free anodes for high-performing fiber-shaped Ni/Fe battery

Fiber-shaped energy storage devices areindispensableparts of wearable and portable electronics. Aqueous rechargeable Ni/Fe battery is a very appropriate energy storage device due to their good safety without organic electrolytes, high ionic conductivity, and low cost. Unfortunately, the low energy density, poor power density and cycling performance hinder its further practical applications. In this study, in order to obtain high performance negative iron-based material, we first synthesized α-iron oxide (α-Fe₂O₃) nanorods (NRs) with superstructures on the surface of highly conductive carbon nanotube fibers (CNTFs), then electrically conductive polypyrrole (PPy) was coated to enhance the electron, ion diffusion and cycle stability. Theas-prepared α-Fe₂O₃@PPy NRs/CNTF electrode shows a high specific capacity of 0.62 Ah cm^-3 at the current density of 1 A cm^-3. Furthermore, the Ni/Fe battery that was assembled by the above negative electrode shows a maximum volumetric energy density of 15.47 mWh cm^-3 with 228.2 mW cm^-3 at a current density of 1 A cm^-3. The cycling durability and mechanical flexibility of the Ni/Fe battery were tested, which show good prospect for practical application. In summary, these merits make it possible for our Ni/Fe battery to have practical applications in next generation flexible energy storage devices.

Shape-controlled iron oxide nanocrystals: synthesis, magnetic properties and energy conversion applications

Iron oxide nanocrystals (IONCs) with various geometric morphologies show excellent physical and chemical properties and have received extensive attention in recent years.

Novel red blood cell shaped α-Fe2O3 microstructures and FeO(OH) nanorods as high capacity supercapacitors

Novel red blood cell shaped α-Fe₂O₃ microstructures were first synthesized through a hydrothermal method by using NH₄Cl as a structure-directing agent.

Novel nanostructured hematite–spongin composite developed using an extreme biomimetic approach

The characteristic mineral-free fibrous skeletons (made of structural protein-spongin) of H. communis (Demospongiae: Porifera) was used as a structural template in hydrothermal synthesis of hematite (α-Fe₂O₃) nanoparticles.

Hollow cocoon-like hematite mesoparticles of nanoparticle aggregates: structural evolution and superior performances in lithium ion batteries

We report the facile, fast, and template-free preparation of hollow α-Fe2O3 with unique cocoon-like structure by a one-pot hydrothermal method without any surfactants in a short reaction time of 3 h only. In contrast, typical hydrothermal methods to prepare inorganic hollow structures require 24 h or a few days. Templates and/or surfactants are typically used. The hollow α-Fe2O3 nanococoon was thoroughly characterized by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Ex situ analysis of a series of samples prepared at different reaction times clearly revealed the structural evolution and possible formation mechanism. Superior electrochemical performance in terms of cyclability, specific capacity, and high rate was achieved, which could be attributed to its unique hollow cocoon-like structure. Structural stability was revealed by analyzing the samples after 120 charge-discharge cycles. The unusual structural stability of the hollow α-Fe2O3 nanococoons after 120 cycles, which is rarely observed for transition metal oxides of particle aggregates, will guarantee further research investigation. Experimental evidence further demonstrated that hollow nanococoons exceed solid nanococoons in reversible lithium-ion storage.

The influence of precursors on phase evolution of nano iron oxides/oxyhydroxides: optical and magnetic properties

The present investigation describes the evolution of nanoiron oxide/oxyhydroxide phases synthesized under identical conditions of precipitation using different starting reagents.

Electrospun hollow cage-like α-Fe2O3 microspheres: synthesis, formation mechanism, and morphology-preserved conversion to Fe nanostructures

Novel 3D hollow cage-like α-Fe₂O₃ and Fe microspheres were fabricated by electrospinning followed by an annealing process for the first time.

Hydrothermal evolution, optical and electrochemical properties of hierarchical porous hematite nanoarchitectures

Hollow or porous hematite (α-Fe2O3) nanoarchitectures have emerged as promising crystals in the advanced materials research. In this contribution, hierarchical mesoporous α-Fe2O3 nanoarchitectures with a pod-like shape were synthesized via a room-temperature coprecipitation of FeCl3 and NaOH solutions, followed by a mild hydrothermal treatment (120°C to 210°C, 12.0 h). A formation mechanism based on the hydrothermal evolution was proposed. β-FeOOH fibrils were assembled by the reaction-limited aggregation first, subsequent and in situ conversion led to compact pod-like α-Fe2O3 nanoarchitectures, and finally high-temperature, long-time hydrothermal treatment caused loose pod-like α-Fe2O3 nanoarchitectures via the Ostwald ripening. The as-synthesized α-Fe2O3 nanoarchitectures exhibit good absorbance within visible regions and also exhibit an improved performance for Li-ion storage with good rate performance, which can be attributed to the porous nature of Fe2O3 nanoarchitectures. This provides a facile, environmentally benign, and low-cost synthesis strategy for α-Fe2O3 crystal growth, indicating the as-prepared α-Fe2O3 nanoarchitectures as potential advanced functional materials for energy storage, gas sensors, photoelectrochemical water splitting, and water treatment.