FeCo Alloy Research Articles

Ultrafine CoFe Alloy Nanoparticles Confined in Highly Ordered Mesoporous Carbon Films as Catalysts for the Oxygen Evolution Reaction

Ultrafine CoFe Alloy Nanoparticles Confined in Highly Ordered Mesoporous Carbon Films as Catalysts for the Oxygen Evolution Reaction

Diffusion kinetics of borided of low entropy soft magnetic FeCo alloy

Abstract The growth kinetics of boride layers were investigated by boronizing the FeCo low entropy alloy produced by arc melting reverse vacuum system with the pack boriding method at temperatures of 1173 K, 1223 K, 1273 K and for 2, 4, 6 h. FeCo alloy has a single-phase FCC crystal structure and there are linear cracks and homogeneously distributed point voids in its microstructure. The hardness of FeCo alloy is between 170 HV0.05 and 265 HV0.05. The boride layer appearance has a sawtooth appearance, and the layer thickness varies between 62 µm and 172 µm depending on temperature and time. According to the XRD pattern, (CoFe)B and (CoFe)B2 triple phases are present on the boride layer surface. With pack boriding, the hardness of the boride layer increased up to 2262 HV0.05, and the surface hardness of the alloy improved by 8–10 times. The boride layer activation energy of the FeCo alloy boronized with pack boriding was calculated as 89.065 kJ mol−1.

Structurally ordered FeCo@FeCoOx@NC dual-shell nanoparticles synthesized under micro-oxygen conditions: An efficient cocatalyst for BiVO4 photoelectrochemical water oxidation

Electrocatalysts are usually integrated onto light-absorbing semiconductors to form efficient photoelectrochemical water-splitting systems. Transition metal oxide nanoparticles serve as excellent electrocatalysts, but exhibit poor performance as cocatalysts for photoelectrodes. To address this issue, a FeCo@FeCoOx@NC dual-shell nanoparticle (consisting of a FeCo alloy core, an intermediate FeCoOx shell, and an outermost graphitic carbon shell) was prepared under micro-oxygen conditions. The FeCo alloy has the dual functions of rapid hole storage and efficient charge transport, while the FeCoOx layer acts as active sites to accelerate the kinetics of the water oxidation reaction and the graphitic carbon protects the internal structure of the nanoparticles. Under the synergistic effect of FeCo@FeCoOx@NC and NiFeOx cocatalysts, the injection efficiency and separation efficiency of BiVO4 photoanode almost reach 100 %, and the photocurrent density reaches 6.85 mA cm−2 (1.23 VRHE, AM 1.5 G), marking the highest reported value to date.

A Low-Loss High Saturation Fe-Co Alloy for High Power Density Aircraft Electric Motors

A Low-Loss High Saturation Fe-Co Alloy for High Power Density Aircraft Electric Motors

Hierarchical MoO2@MoS2 heterojunction nanosheets anchored with metal-organic framework-derived CoFe alloy as bifunctional catalysts for flexible zinc-air batteries

Crafting a robust, high-performance, non-precious metal-based flexible air electrode is crucial for realizing flexible zinc-air batteries (ZABs). Herein, hierarchical MoO2 and MoS2 heterojunction nanosheets grown on carbon cloth (CC) are prepared through a simple hydrothermal reaction followed by calcination. Afterward, through self-assembly and high-temperature carbonization of zeolitic imidazolate framework-67 (ZIF-67) and Materials of Institute Lavoisier-101 (MIL-101) on the heterojunction nanosheets, a hierarchical structure of nitrogen-doped carbon (NC) encapsulated CoFe alloy nanoparticles (NPs) supported on MoO2@MoS2 heterojunction nanosheets (CC/MoS2@MoO2@CoFe) is obtained. It exhibits remarkable activity and durability for both bifunctional oxygen evolution and reduction reactions (OER/ORR), attributed to the ternary heterojunction formed by NC-coated CoFe alloy NPs uniformly dispersed among the MoO2@MoS2 nanosheets, along with oxygen vacancies at heterogeneous interfaces between MoS2, MoO2, and Co0.72Fe0.28 alloy. As a binder-less self-supporting electrode, the assembled aqueous ZAB demonstrates a maximum power density of 113.6 mW cm–2, surpassing that of Pt/C + RuO2 (75.2 mW cm–2), along with excellent cycling stability. Furthermore, the CC/MoS2@MoO2@CoFe-based flexible ZABs achieve a maximum power density of 54.1 mW cm–2, exhibit good cycling stability for up to 120 cycles, and show outstanding flexibility. This study paves the way for the practical integration of flexible ZABs into wearable electronic devices, heralding a new era of portable power solutions.

Structural and magnetic properties of high magnetization FexCo100-x nanoparticles investigated at the nanoscale: Unveiling the origin of the observed anisotropy

In this work the authors have performed the synthesis of FexCo100-x (0<x<100) alloy nanoparticles (NPs) with different compositions, as well as pure Fe and Co NPs for comparison, by a chemical reduction technique. The subsequent characterization demonstrated excellent quality NPs with the expected bcc cubic (for Fe and FeCo alloys) and hcp hexagonal (for Co NPs) structures showing a room temperature magnetization as high as 235 emu/g for the Fe66Co34 composition alloy. Nevertheless, this soft magnetic character is accompanied by determined values of effective anisotropy as high as 2 MJ/m3. Aiming to deep into the properties of these FeCo alloys as well as to unveil the origin of that observed high anisotropy value, we now present an extensive study at the nanoscale of the synthesized Fe, Co and FexCo100-x alloy nanoparticles by using nuclear techniques as neutron powder diffraction, EXAFS and XANES spectroscopies. Mössbauer spectroscopy revealed that the FeCo alloys are in an A2 disordered solid solution. The obtained results, combined with AFM/MFM images, have demonstrated that despite the cubic bcc structure observed for all FeCo alloys (in excellent concordance with the pure Fe one) the NPs show a "flaky" shape of 50–60 nm size (diameter) but only 3–4 nm thickness, giving rise to a strong shape anisotropy contribution to the observed total effective anisotropy.

FeCo Bimetallic ZIF Derivatives decorated with CoFe-LDH to Promote Bifunctional Oxygen Electrocatalysis Activation.

Reasonably screening the targeted oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) constituents and constructing high-efficiency and stabilized ORR/OER bifunctional electrocatalysts are pivotal for the advancement of rechargeable zinc-air batteries (ZABs). Here, CoFe layered double hydroxide (CoFe-LDH) nanosheets are deposited on nitrogen-doped graphite-carbon polyhedra with FeCo alloy nanoparticles (FeCo/LDH-NGCP). Due to the synergic effect between FeCo-NGCP, CoFe-LDH and FeCo/LDH-NGCP, the electrocatalyst with the abundant and accessible active sites can provide good charge/mass transfer, and thus shows wonderful ORR and OER bifunctional electrocatalytic performance. In ORR tests, FeCo/LDH-NGCP catalyst displays larger half-wave potential (E1/2, 0.89 V vs. 0.85 V), higher limiting current density (JL, 5.91 mA/cm2 vs. 5.14 mA/cm2) and better stability than commercial Pt/C. As for OER, FeCo/LDH-NGCP possesses a smaller overpotential (η) of 299.6 mV at a current density of 10 mA/cm2 and more durable stability than commercial RuO2 (330.6 mV). Furthermore, in ZAB tests, the cycling stability of ZAB-FeCo/LDH-NGCP (over 470 h) outperforms the ZAB-Pt/C+RuO2 (92 h) with commercial electrocatalyst (Pt/C+RuO2). Therefore, the FeCo/LDH-NGCP catalyst offers a new perspective to construct ZABs bifunctional catalysts and their commercial application in ZABs.

A General Model for the Ductility of Intermetallics Applied to Fe-Co Alloys

The mechanical properties, specifically ductility, of high performing soft magnets such as Fe-Co alloys are a limiting factor to their broader use in a number of systems. The understanding of the mechanical robustness in these materials is currently insufficient to be able to support the growing interest in applications such as magnetic shielding or electric motors. Fe-Co alloys provide the highest commercially available magnetic saturation and high magnetic permeability but have very poor ductility. The addition of vanadium to these alloys has allowed for significant commercialization and some ductility improvements, but the fundamental reasons for the observed improvements are not well understood. In most published work on mechanical properties in these alloys, the precise chemistry of the alloys investigated, often a critical aspect of intermetallics, is not reported or controlled and thermal history is unclear. This work creates a ductility model that is sensitive to changes in chemistry and can predict relative strain to failure as well as brittle fracture mode for intermetallics and is applied to Fe-Co alloys. Through the application of density functional theory (DFT), this model identifies defect stabilities, anti-phase boundary (APB) energies, the energy necessary to cross-slip, and cleavage energies and combines them through energetic competition to determine a relative failure strain. The model correctly predicts ductility improvements with the addition of vanadium as well as the transition from intergranular to transgranular cleavage, though more precise experiments are necessary to appropriately validate the various improvements observed.

Bamboo-like nitrogen-doped carbon nanotubes directly grown from commercial carbon black for encapsulating FeCo nanoparticles as efficient oxygen reduction electrocatalysts

Efficient methods for preparing carbon nanotube (CNT)-confined metal catalysts are of great significance for electrocatalysis. Hence, in this study, Fe and Co promoters were added to the precursors of commercial carbon black and melamine to form N-doped CNTs confined bimetallic catalysts (FeCo@N-CNTs) via in situ pyrolysis. The FeCo@N-CNT catalysts exhibited a bamboo-like morphology with FeCo alloy nanoparticles encapsulated in the CNTs and high activity toward the oxygen reduction reaction, with a half-wave potential of 0.864 mV, higher than that of commercial Pt/C (0.827 mV) in alkaline solutions. The catalytic performance is attributable to the synergistic effects between the FeCo alloy and N-doped CNT structure. Moreover, the confinement of the FeCo nanoparticles inside the CNTs imparted the prepared catalysts with resistance to methanol poisoning and long-term stability. This versatile method of synthesizing CNTs directly from carbon black provides a new strategy for preparing high-performance non-precious-metal-based N-doped CNT catalysts for practical fuel cell applications.

Core-shell cobalt-iron@N-doped carbon: A high-performance cathode material for lithium-sulfur batteries.

Lithium-sulfur batteries hold great promise as energy storage systems, but the shuttle effect of lithium polysulfides (LiPS) and large volume variation limit their capacity and cycle life. We have developed CoFe alloy wrapped in N-doped porous carbon spheres (e-CF@NC) with a core-shell structure through simple copolymerization and pyrolysis. The nitrogen-doped porous carbon shell provides electron and ion transport channels and more active sites for electrolyte ion adsorption. The high chemically stable carbon can limit the segregation of polysulfides, further improving the battery cycling stability. Besides, the inside CoFe alloy particles catalyze the conversion between LiPS and Li2S, speeding up reaction kinetics and reducing solvation of active sites. Consequently, lithium-sulfur batteries with e-CF@NC-2 as the cathode display a high initial specific capacity of 1146 mA h g-1 at 0.1 C, excellent rate performance (891 mA h g-1 at 1 C, 741 mA h g-1 at 2 C), and satisfied cycle stability (average capacity decay rate of 0.033% per cycle at 1 C for 300 cycles), demonstrating significant application potential.

A(CoFe)(S2)2/CoFe heterostructure constructed in S, N co-doped carbon nanotubes as an efficient oxygen electrocatalyst for zinc-air battery

Transition metal alloys can exhibit synergistic intermetallic effects to obtain high activities for oxygen reduction/evolution reactions (ORR/OER). However, due to the insufficient stability of active sites in alkaline electrolytes, conventional alloy catalysts still do not meet practical needs. Herein, by using polypyrrole tubes and cobalt-iron (CoFe) Prussian blue analogs as precursors, CoFe sulfides is in-situ formed on CoFe alloys to construct (CoFe)(S2)2/CoFe heterostructure in sulfur (S) and nitrogen (N) co-doped carbon nanotubes (CoFe@NCNTs-nS) via a low-temperature sulfidation strategy. The as-marked CoFe@NCNTs-12.5S exhibits a comparable ORR activity (half-wave potential of 0.901 V) to Pt/C (0.903 V) and a superior OER activity (overpotential of 272 mV at 10 mA cm−2) to RuO2 (299 mV). CoFe@NCNTs-12.5S also exhibits ultralow charge transfer resistances (ORR-6.36 Ω and OER-0.21 Ω) and an excellent potential difference of 0.617 V. The sulfidation-induced (CoFe)(S2)2/CoFe heterojunctions can accelerate interfacial charge transfer process. Tubular structure not only disperses the (CoFe)(S2)2/CoFe heterostructure, but also reduces the corrosion of active-sites to enhance catalysis stability. Zinc-air battery with CoFe@NCNTs-12.5S achieves a high specific capacity (718.1 mAh g−1), maintaining a voltage gap of 0.957 V after 400 h. This work reveals the potential of interface engineering for boosting ORR/OER activities of alloys via in-situ heterogenization.

FeCo Alloy Nanoparticles Supported on N-doped Mesoporous Carbon Spheres for Hydrogen Evolution and Reduction of Organic Dyes

FeCo Alloy Nanoparticles Supported on N-doped Mesoporous Carbon Spheres for Hydrogen Evolution and Reduction of Organic Dyes

Silk Fibroin Film Decorated with Ultralow FeCo Content by Sputtering Deposition Results in a Flexible and Robust Biomaterial for Magnetic Actuation.

Magnetically responsive soft biomaterials are at the forefront of bioengineering and biorobotics. We have created a magnetic hybrid material by coupling silk fibroin─i.e., a natural biopolymer with an optimal combination of biocompatibility and mechanical robustness─with the FeCo alloy, the ferromagnetic material with the highest saturation magnetization. The material is in the form of a 6 μm-thick silk fibroin film, coated with a FeCo layer (nominal thickness: 10 nm) grown by magnetron sputtering deposition. The sputtering deposition technique is versatile and eco-friendly and proves effective for growing the magnetic layer on the biopolymer substrate, also allowing one to select the area to be decorated. The hybrid material is biocompatible, lightweight, flexible, robust, and water-resistant. Electrical, structural, mechanical, and magnetic characterization of the material, both as-prepared and after being soaked in water, have provided information on the adhesion between the silk fibroin substrate and the FeCo layer and on the state of internal mechanical stresses. The hybrid film exhibits a high magnetic bending response under a magnetic field gradient, thanks to an ultralow fraction of the FeCo component (less than 0.1 vol %, i.e., well below 1 wt %). This reduces the risk of adverse health effects and makes the material suitable for bioactuation applications.

Alloy Reconstruction in Pyrolytic Bowknot-like Heteronuclear CoFe Clusters for Electrocatalytic Application.

The construction of doped molecular clusters is an intriguing way to perform bimetallic doping for electrocatalysts. However, efficiently harnessing the benefits of a doping strategy and alloy engineering to create a nanostructure for electrocatalytic application at the molecular level has consistently posed a challenge. Here we propose an in situ reconstruction strategy aimed at producing an alloy nanostructure through a pyrolysis process, originating from bowknot-like heterometallic clusters. The Schiff base, denoted as ligand L1 (o-vanillin ethylenediamine), was introduced as a precursor to coordinate Fe and Co metals, thereby yielding a heteronuclear metal cluster [(FeCo)(L1)2O]CH3CN. Subsequently, a comprehensive investigation of the in situ reconstruction process [(FeCo)(L1)2O](CH3CN) → [(FeCo)(L1)2O] → [M-O-M/M-O] [CH3+/CH3O+/H2C═N/C2H5+/C4H4+] → [FeCo/Fe3O4/Fe2O3/Co3O4][carbon layer] led to the formation of MOx/CoFe@NC-700 during the pyrolysis. This process reveals that the metals Fe and Co in the clusters undergo partly in situ evolution into FeCo alloys, resulting in the successful preparation of MOx/CoFe@NC (M = Fe, Co) nanomaterials that leverage the advantages of both doping strategies and alloy engineering. The synergistic interaction between alloy particles and metal oxides establishes active sites that contribute to the excellent oxygen evolution (OER) and hydrogen evolution (HER) catalytic behaviors. Notably, these materials exhibit outstanding OER and HER properties under alkaline conditions, with overpotentials of 191 and 88 mV for OER and HER, respectively, at 10 mA cm-2. Investigation of the in situ conversion of Schiff base bimetal clusters into alloy materials through pyrolysis offers a novel strategy for advancing electrocatalytic applications.

A one-step fabrication method of flexible magnetostrictive fiber ribbon based on Fe50Co50 alloy and its characteristics study

Magnetostrictive materials are widely used in sensors, actuators and micro-nano electronics because of their excellent performance. However, traditional rigid magnetostrictive materials are difficult to adapt to the flexible and deformable structure of flexible electronic devices. In order to solve the deformation, sensing and control problems in the field of flexible electronics, a one-step new method of is proposed to deposit Fe50Co50 fiber ribbons with reciprocated and loop structures on flexible substrate. Helmholtz coil is designed to test the magnetostrictive positive effect ability of Fe50Co50 ribbon, and its magnetostrictive strain curve is analyzed. Furthermore, frequency domain characteristics of Fe50Co50 ribbon are tested, and the influence of externally driving magnetic field on elastic layer materials and resonance output characteristics is analyzed. The experimental results show that Fe50Co50 ribbon exhibits good low-frequency magnetic field characteristics. And free end displacement of Fe50Co50 ribbon based on loop structure, under 12 mT alternating magnetic field and 134 mT bias magnetic field, reaches a peak-to-peak value of 870 μm for first-order resonance, and 320 μm for second-order resonance. This verifies that Fe50Co50 ribbon possesses the expected properties that magnetostrictive materials should have, and innovatively breaks through the technical bottleneck of manufacturing flexible micro-nano magnetostrictive energy exchange components.

Comparative study in magnetic properties of FeCo alloy nanowires and a first-order reversal curve analysis

FeCo alloy nanowires have potential applications in data storage, magnetic sensors and spintronic devices. In this paper, FeCo alloy nanowires with varying diameters were fabricated within an anodic aluminum oxide (AAO) template using electrodeposition method at a constant potential. Characterization of the morphology and structure revealed that the polycrystalline body-center-cubic(bcc) FeCo alloy nanowires were obtained. The influence of diameter of FeCo alloy nanowires on magnetic interaction, domain state and magnetic mechanism was investigated through a first-order reversal curve (FORC) analysis. The findings showed that with an increase in the diameter of FeCo alloy nanowires from 20 nm to 60 nm and 100 nm, the interaction force between the FeCo alloy nanowires increased, the domain state of FeCo alloy nanowires changed from Single Domain (SD) to Multi-Domain (MD), the magnetic reversal mode changed from coherent reversal mode to curling reversal mode.

Constructing heterointerfaces to enhance electron transfer of CoFe/CoFe2O4 mediated electro-Fenton process for bisphenol A degradation: Mechanistic insights and performance evaluation

The inefficient electron transfer and Fe(III)/Fe(II) cycle remain significant obstacles in the electro-fenton process. Herein, a nitrogen-doped graphite felt (NGF)-supported CoFe/CoFe2O4 heterostructure is synthesized that achieves highly efficient interfacial electron transfer and stable Co/Fe redox cycle. Theoretical calculations demonstrate that the CoFe/CoFe2O4 heterointerfaces induce local charge redistribution benefiting from the electronic communication between electron acceptor (CoFe2O4) and electron donor (CoFe). Analysis of the Fermi level indicates that the introduction of CoFe alloy enhances the electron density of the catalyst. The CoFe/CoFe2O4@NGF cathode can remove bisphenol A (BPA) completely in 90 min, and the pseudo-first-order kinetic constant (0.0625 min−1) is 23 times higher than the GF system. Notably, the CoFe/CoFe2O4@NGF electrode maintains excellent catalytic capability and stability within a broad pH range (3–11). The construction of the CoFe/CoFe2O4 heterostructure reduces the adsorption energy of oxygen, which ultimately increases the yield of reactive oxygen species (ROS). Quenching experiments revealed that hydroxyl radical (·OH) played a dominant role in the degradation of BPA, and significantly reduced the biotoxicity of intermediate products. This work offers a dependable approach for developing bimetallic catalysts with high catalytic activity.

Electrochemical Quartz Crystal Microbalance Study on the Electrodeposition of Fe, Co and Fe-Co Alloys

Cobalt-iron alloys are interesting soft magnetic materials which are used for example in magnetic sensors and transducers. They can be obtained by different techniques such as PVD, magnetron sputtering, or casting. One easy and not very expensive way to produce these alloys is the electrochemical deposition technique, which was also chosen in this study.This contribution will describe the electrodeposition of Co, Fe and Fe-Co alloys (Fe70Co30) from an aqueous sulphate-based electrolyte containing boric acid as a buffer and sodium citrate and citric acid besides the metal sulphates. Potentiostatic step experiments and cyclic voltammetry were performed in parallel to electrochemical quartz crystal microbalance. Thus, we could identify the potential at which the deposition of the metals sets in, the mass of the deposited species as well as the current efficiency. We could also extract the partial current due to hydrogen evolution reaction and the partial current due to individual metal or their alloys from the total current density. The morphology and structure of the deposited films were investigated by means of SEM and XRD, respectively. The grain size of the deposits was calculated from the XRD data using Scherrer equation. Addition of citric acid to the electrolyte results in the smaller grain size of the deposited Fe-Co films.

The effect of vanadium on the magnetic and mechanical properties of B2 FeCo alloy: a DFT approach

FeCo alloys play an important role in soft magnetic materials with a wide range of technological applications due to their high saturation magnetization and Curie temperature. However, these alloys have low ductility at room temperature. The ductility can be improved by the ternary addition of elements such as V. A density functional theory supercell approach was used to generate B2 Fe50Co50-xVx (0 &lt; x &lt; 50) structures and the properties were evaluated at different atomic percentage compositions to determine the ductility at room temperature. The structures were fully optimized to obtain better equilibrium ground-state properties such as lattice parameters and thermodynamic properties for both binary and ternary systems. The stability of Fe50Co50-xVx was evaluated from the heats of formation, elastic properties, and phonon dispersion curves. Furthermore, magnetic strength was evaluated from magnetic moments. It was found that all structures are thermodynamically stable due to the negative heats of formation. The calculated Pugh's ratio and Poisson's ratio confirm that alloying with V effectively improved the ductility. It was also found that Fe50Co50-xVx showed a positive shear modulus for the entire concentration range investigated, in agreement with phonon dispersion curves. The ternary addition of V to the FeCo system resulted in reduced magnetic strength due to a decrease in magnetic moments. These findings reveal that B2 FeCo-V alloys can be used as components and actuators for the automotive industry.

Preparation and Microwave-Absorbing Properties of FeCo Alloys by Condensation Reflux Method.

Five groups of FeCo alloy samples with different atomic ratios of Fe/Co (3:7, 4:6, 5:5, 6:4, 7:3) were prepared using the condensation reflux method. The results indicate that varying the atomic ratios of Fe/Co has a significant impact on the microstructure, electromagnetic parameters, and microwave absorption properties of FeCo alloys. As the Fe atom content increases, the morphology of the FeCo alloys transitions from irregular flower-shaped to uniformly spherical and eventually to lamellar. The attenuation of electromagnetic waves in the five groups of alloys is primarily due to magnetic loss. Among them, Fe6Co4 exhibits the best absorption performance, with a minimum reflection loss (RL) value of -35.56 dB at a frequency of 10.40 GHz when the matching thickness is 7.90 mm. Additionally, at a matching thickness of 5.11 mm, the maximum effective absorption bandwidth (EAB) reached 2.56 GHz (15.44-18 GHz).