Hollow Nanobarrels of α-Fe2O3 on Reduced Graphene Oxide as High-Performance Anode for Lithium-Ion Batteries

Design and synthesis of yolk-shell Fe2O3/N-doped carbon nanospindles with rich oxygen vacancies for robust lithium storage

Ferric oxide (Fe₂O₃) is an attractive anode material for lithium-ion batteries (LIBs) with a high theoretical capacity of 1005 mA h g^-1. However, its practical application is greatly restrained by the rapid capacity fading caused by the large volume expansion upon lithiation. To address this issue, we have designed and synthesized a unique yolk-shell Fe₂O₃/N-doped carbon hybrid structure (YS-Fe₂O₃@NC) with rich oxygen vacancies for robust lithium storage. The obtained results show that YS-Fe₂O₃@NC delivers a high reversible capacity of 578 mA h g^-1 after 300 cycles at a current density of 5 A g^-1, about 11 times that (53.7 mA h g^-1) of pristine Fe₂O₃. Furthermore, a high specific capacity of 300.5 mA h g^-1 even at 10 A g^-1 is achieved. The high reversible capacities, excellent rate capability and cycle stability of YS-Fe₂O₃@NC might be attributed to the elaborate yolk-shell nanoarchitecture. Moreover, electron percolation and a local built-in electric field induced by oxygen vacancies in the Fe₂O₃ matrix could also enhance the kinetics of Li⁺ insertion/deinsertion.

Magnetic Vortex States in Toroidal Iron Oxide Nanoparticles: Combining Micromagnetics with Tomography

Iron oxide nanorings have great promise for biomedical applications because of their magnetic vortex state, which endows them with a low remanent magnetization while retaining a large saturation magnetization. Here we use micromagnetic simulations to predict the exact shapes that can sustain magnetic vortices, using a toroidal model geometry with variable diameter, ring thickness, and ring eccentricity. Our model phase diagram is then compared with simulations of experimental geometries obtained by electron tomography. High axial eccentricity and low ring thickness are found to be key factors for forming vortex states and avoiding net-magnetized metastable states. We also find that while defects from a perfect toroidal geometry increase the stray field associated with the vortex state, they can also make the vortex state more energetically accessible. These results constitute an important step toward optimizing the magnetic behavior of toroidal iron oxide nanoparticles.

Micro/Nanoengineered α-Fe2 O3 Nanoaggregate Conformably Enclosed by Ultrathin N-Doped Carbon Shell for Ultrastable Lithium Storage and Insight into Phase Evolution Mechanism

The Fe-based transition metal oxides are promising anode candidates for lithium storage considering their high specific capacity, low cost, and environmental compatibility. However, the poor electron/ion conductivity and significant volume stress limit their cycle and rate performances. Furthermore, the phenomena of capacity rise and sudden decay for α-Fe₂ O₃ have appeared in most reports. Here, a uniform micro/nano α-Fe₂ O₃ nanoaggregate conformably enclosed in an ultrathin N-doped carbon network (denoted as M/N-α-Fe₂ O₃ @NC) is designed. The M/N porous balls combine the merits of secondary nanoparticles to shorten the Li⁺ transportation pathways as well as alleviating volume expansion, and primary microballs to stabilize the electrode/electrolyte interface. Furthermore, the ultrathin carbon shell favors fast electron transfer and protects the electrode from electrolyte corrosion. Therefore, the M/N-α-Fe₂ O₃ @NC electrode delivers an excellent reversible capacity of 901 mA h g^-1 with capacity retention up to 94.0 % after 200 cycles at 0.2 A g^-1 . Notably, the capacity rise does not happen during cycling. Moreover, the lithium storage mechanism is elucidated by ex situ XRD and HRTEM experiments. It is verified that the reversible phase transformation of α↔γ occurs during the first cycle, whereas only the α-Fe₂ O₃ phase is reversibly transformed during subsequent cycles. This study offers a simple and scalable strategy for the practical application of high-performance Fe₂ O₃ electrodes.

Biogenic Hematite from Bacteria: Facile Synthesis of Secondary Nanoclusters for Lithium Storage Capacity

Ferrihydrite, or iron(III) (oxyhydr)oxide (Fe(OH)₃), a representative scavenger of environmentally relevant toxic elements, has been repurposed as a low-cost and scalable precursor of well-developed hematite (α-Fe₂O₃) secondary nanoclusters with a hierarchically structured morphology for lithium-ion anode materials. Here, we report that the bacteria Clostridium sp. C8, isolated from a methane-gas-producing consortium, can synthesize self-assembled secondary hematite nanoclusters (∼150 nm) composed of small nanoparticles (∼15 nm) through the molecular structural rearrangement of amorphous ferrihydrite under mild conditions. The biogenic hematite particles, wrapped with graphene oxide reduced in situ by the reducing bacteria Shewanella sp. HN-41 via one-pot synthesis, deliver an excellent reversible capacity of ∼1000 mA h g^-1 after 100 cycles at a current density of 1 A g^-1. Furthermore, the heat-treated hematite/rGO exhibits a capacity of 820 mA h g^-1 at a high current density of 5 A g^-1 and a reversible capacity of up to 1635 mA h g^-1 at a current density of 100 mA g^-1. This study provides an easy, eco-efficient, and scalable microbiological synthetic route to produce hierarchical hematite/rGO secondary nanoclusters with potential as high-performance Li-ion anode materials.

Three-dimensional porous microspheres comprising hollow Fe2O3 nanorods/CNT building blocks with superior electrochemical performance for lithium ion batteries

It is highly desirable to develop anode materials with rational architectures for lithium ion batteries to achieve high-performance electrochemical properties. In this study, three-dimensional porous composite microspheres comprising hollow Fe2O3 nanorods/carbon nanotube (CNT) building blocks are successfully constructed by direct deposition and further thermal transformation of beta-FeOOH nanorods on CNT porous microspheres. The CNT porous microsphere, which is prepared by a spray pyrolysis, provides ample sites for the direct growth of beta-FeOOH nanorods. During the further oxidation process, the beta-FeOOH nanorods are transformed into hollow Fe2O3 nanorods as a result of dehydroxylation and lattice shrinkage, resulting in the formation of hollow Fe2O3 nanorods/CNT porous microspheres. Such a hierarchical structure of composite microspheres not only facilitates electrolyte accessibility but also offers conductive networks for electrons during electrochemical reactions. Accordingly, the electrodes exhibit a high discharge capacity of 1307 mA h g-1 after 300 cycles at a current density of 1 A g-1; this is associated with an excellent capacity retention of 84%, which is calculated from the initial cycle. In addition, the composite delivers a discharge capacity of 703 mA h g-1 at a current density of 15 A g-1.

Hierarchical Fe2O3@C@MnO2@C Multishell Nanocomposites for High Performance Lithium Ion Batteries and Catalysts

The Fe₂O₃@C@MnO₂@C (FCMC) nanocomposites containing spindle-like Fe₂O₃ as a core and MnO₂ nanoflakes as a sandwiched shell and double carbon layers have been successfully prepared by a facile method. As anode materials of lithium ion batteries (LIBs), the cycling stability, rate performance, and conductivity of the prepared FCMC nanocomposites are far beyond those of the carbon-free Fe₂O₃@MnO₂ (FM) nanocomposites. The hierarchical structure with double layers of carbon effectively enhances the ion conductivity and electrochemical performance of transitional metal oxides, indicating that carbon in FCMC played an important role during lithium ion storage. The initial discharge/charge capacity of the FCMC electrode reaches as high as 1240.2/1215.9 mAh g^-1, and the discharge capacity is over 1000 mAh g^-1 at 500 mA g^-1 after 50 cycles. Additionally, the unique hierarchical structural characteristic with double layers of green carbon with a high degree of graphitization makes FCMC an excellent catalyst in removing methylene blue (MB) dye from solution with H₂O₂ under a slight heating with the degradation time as short as 10 min. Our work presents a new perspective on carbon modified multilayer core-shell oxide structure, which can be applied to many fields such as energy storage and catalyst.

Encapsulated Vanadium-Based Hybrids in Amorphous N-Doped Carbon Matrix as Anode Materials for Lithium-Ion Batteries

Recently, researchers have made significant advancement in employing transition metal compound hybrids as anode material for lithium-ion batteries and developing simple preparation of these hybrids. To this end, this study reports a facile and scalable method for fabricating a vanadium oxide-nitride composite encapsulated in amorphous carbon matrix by simply mixing ammonium metavanadate and melamine as anode materials for lithium-ion batteries. By tuning the annealing temperature of the mixture, different hybrids of vanadium oxide-nitride compounds are synthesized. The electrode material prepared at 700 °C, i.e., VM-700, exhibits excellent cyclic stability retaining 92% of its reversible capacity after 200 cycles at a current density of 0.5 A g^-1 and attractive rate performance (220 mAh g^-1 ) under the current density of up to 2 A g^-1 . The outstanding electrochemical properties can be attributed to the synergistic effect from heterojunction form by the vanadium compound hybrids, the improved ability of the excellent conductive carbon for electron transfer, and restraining the expansion and aggregation of vanadium oxide-nitride in cycling. These interesting findings will provide a reference for the preparation of transition metal oxide and nitride composites as well.

Highly Efficient High-Pressure Homogenization Approach for Scalable Production of High-Quality Graphene Sheets and Sandwich-Structured α-Fe2O3/Graphene Hybrids for High-Performance Lithium-Ion Batteries

A highly efficient and continuous high-pressure homogenization (HPH) approach is developed for scalable production of graphene sheets and sandwich-structured α-Fe₂O₃/graphene hybrids by liquid-phase exfoliation of stage-1 FeCl₃-based graphite intercalation compounds (GICs). The enlarged interlayer spacing of FeCl₃-GICs facilitates their efficient exfoliation to produce high-quality graphene sheets. Moreover, sandwich-structured α-Fe₂O₃/few-layer graphene (FLG) hybrids are readily fabricated by thermally annealing the FeCl₃ intercalated FLG sheets. As an anode material of Li-ion battery, α-Fe₂O₃/FLG hybrid shows a satisfactory long-term cycling performance with an excellent specific capacity of 1100.5 mA h g^-1 after 350 cycles at 200 mA g^-1. A high reversible capacity of 658.5 mA h g^-1 is achieved after 200 cycles at 1 A g^-1 and maintained without notable decay. The satisfactory cycling stability and the outstanding capability of α-Fe₂O₃/FLG hybrid are attributed to its unique sandwiched structure consisting of highly conducting FLG sheets and covalently anchored α-Fe₂O₃ particles. Therefore, the highly efficient and scalable preparation of high-quality graphene sheets along with the excellent electrochemical properties of α-Fe₂O₃/FLG hybrids makes the HPH approach promising for producing high-performance graphene-based energy storage materials.

A corn-inspired structure design for an iron oxide fiber/reduced graphene oxide composite as a high-performance anode material for Li-ion batteries

A porous iron oxide fiber/reduced graphene oxide composite with a corn-inspired structure design as a high-performance anode material for li-ion batteries.

Microwave assisted fabrication of a nanostructured reduced graphene oxide (rGO)/Fe2O3 composite as a promising next generation energy storage material

A supercapacitor electrode material, rGO–Fe₂O₃ composite, prepared by a facile microwave assisted in situ technique, delivers a high specific capacitance of 577.5 F g⁻¹ at a current density of 2 A g⁻¹ with a long cycle life and high rate performance.

Rational Design of α-Fe2O3/Reduced Graphene Oxide Composites: Rapid Detection and Effective Removal of Organic Pollutants

α-Fe2O3/reduced graphene oxide (α-Fe2O3/rGO) composites are rationally designed and prepared to integrate organic pollutants detection and their photocatalytic degradation. Specifically, the composites are used as the substrate for surface-enhanced Raman scattering (SERS) to detect rhodamine 6G (R6G). Repeatable strong SERS signals could be obtained with R6G concentration as low as 10(-5) M. In addition, the substrate exhibits self-cleaning properties under solar irradiation. Compared with pure α-Fe2O3 and α-Fe2O3/rGO mechanical mixtures, the α-Fe2O3/rGO composites show much higher photocatalytic activity and much greater Raman enhancement factor. After 10 cycling measurements, the photodegradation rate of R6G could be maintained at 90.5%, indicating high stability of the photocatalyst. This study suggests that the α-Fe2O3/rGO composites would serve both as recyclable SERS substrate and as excellent visible light photocatalyst.

Cross-linked porous α-Fe2O3 nanorods as high performance anode materials for lithium ion batteries

Novel cross-linked porous α-Fe₂O₃ nanorods are synthesized via a hydrothermal-calcination method. They display outstanding lithium storage performance.

Graphene oxide: strategies for synthesis, reduction and frontier applications

In this review article, we describe a general introduction to GO, its synthesis, reduction and some selected frontier applications. Its low cost and potential for mass production make GO a promising building block for functional hybrid materials.