NiFe Layer Research Articles

Preparation and corrosion resistance of Ni-Fe layer double hydroxides superhydrophobic film on carbon steel

The nickel-ferric layered double hydroxides (NiFe-LDHs) film which are commonly used as catalysts was fabricated on Q235 steel in-situ via two-step hydrothermal method. And the superhydrophobic NiFe-LDH-PFDTES film was obtained by 1 H, 1 H, 2 H, 2 H-perfluorodecyltriethoxysilane (PFDTES) modification. To a certain extent, the application of NiFe-LDHs has been broadened. The structure and composition of NiFe-LDHs film and NiFe-LDH-PFDTES film were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), and Fourier transform infrared (FT-IR). The wettability of films was analyzed by water contact angle testing. And the corrosion resistance of NiFe-LDHs and NiFe-LDH-PFDTES film in 3.5 wt% NaCl solution were measured by using potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS) techniques. The results show that NiFe-LDHs and NiFe-LDH-PFDTES film were successfully prepared on the surface of Q235 steel. By adjusting the preparation conditions, the NiFe-LDH-PFDTES film with optimal corrosion resistance was prepared in the condition containing the hydrothermal solution concentration is 1 unit and hydrothermal time for 6 h. The hydrophobicity changes little with the hydrothermal parameters, and all reach the state of superhydrophobic, the contact angle is greater than 150°, the sliding angle is less than 1°. For the superhydrophobic film, NiFe-LDHs has excellent synergy with PFDTES, covering of an "air film" on the rough structure of LDHs, blocking the solution from contact with the substrate, thereby providing corrosion resistance. NiFe-LDH-PFDTES film exhibits much better corrosion protective performance than NiFe-LDHs film in 3.5 wt% NaCl solution, the impedance modulus is increased about 4–5 orders of magnitude compared with Q235 steel, and the highest protection efficiency can reach 99.99%.

Odd symmetry planar Hall effect: A method of detecting current-induced in-plane magnetization switching

The robustness of spin–orbit torque (SOT) induced magnetization switching and ease of deposition make type-X devices, where the in-plane easy axis lies perpendicular to the spin polarization, attractive in the field of spintronics. However, universally applicable and straightforward detection of type-X magnetization reversal is still elusive, unlike type-Z switching, which employs DC-based anomalous Hall effect measurement. Here, we demonstrated that the odd planar Hall voltage (O-PHV) signal exhibits an odd symmetry with the application of an external magnetic field which motivates us to develop a reading mechanism for detecting magnetization switching of in-plane magnetized type-X devices. We verified our DC-based reading mechanism in the Pt/Co/NiFe/Pt stack where a thin Co layer is inserted to create dissimilar interfaces about the NiFe layer. Remarkably, the current-induced in-plane fields are found to be significantly large in Pt/Co/NiFe/Pt stack. Furthermore, we employed the O-PHV method to detect the current-induced magnetization switching. The pure DC nature of the writing and reading mechanism of our proposed type-X detection technique through O-PHV makes it the easiest in-plane magnetization detection technique. Moreover, the high repeatability and easy detection of our proposed method will open avenues toward in-plane SOT switching based memory devices and sensors.

Tunable Spin Seebeck Thermopower in Nonlocal Perovskite MAPbBr3‐Based Structure

AbstractRecently organic–inorganic hybrid perovskite (OIHP) has risen suddenly to become a superstar for spintronic applications. Fundamental understanding of its spin properties is of great importance for future advances of its applications in spin‐optoelectronic devices. In this work, the authors pioneer modulation of the spin Seebeck thermopower (SSTP) in a Pt/MAPbBr3/NiFe nonlocal structure via longitudinal spin Seebeck effect measurements. They unravel the effective magnon injection into the perovskite film from the NiFe layer, and the tunability of SSTP in this structure is easily realized through the optimization of morphology and component engineering of the OIHP film. First, upon biasing samples with a magnetic flux density during the preparation process, a high‐quality OIHP film can be obtained, in which the spin scattering can be reduced leading to the SSTP enhancement. Second, by doping Cr into the OIHP lattice, the increased magnetic moment density and the additional in‐plane inverse Rashba–Edelstein effect synergistically improve spin accumulation in the Pt layer and thus tune its SSTP. Unveiling those phenomena is important to understanding magnon transport in the OIHP interlayer, which is instructive for designing magnonic devices based on OIHP film.

Full spectrum solar hydrogen production by tandems of perovskite solar cells and photothermal enhanced electrocatalysts

Among various methods of hydrogen production, water splitting driven by perovskite solar cell (PSC) is highly desirable due to the abundance of solar energy and low material cost. The key to achieve higher solar-to-hydrogen (STH) conversion efficiency is to reduce the overpotential of water splitting and enhance the solar energy utilization of the system. Herein, we demonstrate a photothermal enhanced oxygen evolution reaction (OER) electrocatalyst by depositing NiFe layer double hydroxide (NiFe LDH) on a three-dimensional carbon nanotubes (CNTs) scaffold. The CNTs can serve double functions, first as a conductive support of the catalyst to effectively transport charge, second as a photon absorber to induce photothermal effect to enhance OER activity. The photothermal enhancement of OER is demonstrated with infrared irradiation, part of the solar spectrum that is normally wasted in a conventional photovoltaic-electrolysis water splitting system. Based on the superior OER activity and photothermal properties, an unbiased water splitting system is constructed by integrating a CNTs@NiFe LDH//Pt/C electrochemical cell (EC) with a semitransparent perovskite solar cell (ST-PSC) mini-module in tandem configuration. The ST-PSC module provides voltage to drive water splitting and transmits infrared light to the rear CNTs@NiFe LDH electrode to induce the photothermal effect. The integrated PSC-EC system improves the STH efficiency from 11.7% to 13.2% with assistance of the photothermal effect and demonstrates a new strategy to harvest the full spectrum of solar irradiation for hydrogen production.

Efficient removal of Cs ion by electrochemical adsorption and desorption reaction using NiFe Prussian blue deposited carbon nanofiber electrode.

Prussian blue (PB) analog (NiFe, CoFe, FeFe, and commercial(cPB)) decorated carbon nanofiber (CNF) electrodes were synthesized by the drop casting method in this study to investigate the interaction between PB and CNF for the electrochemical adsorption (EA) and electrochemical desorption (ED) of Cs ion (Cs+). The adhesion of PB on the electrode and the EA and ED of Cs+ were substantially higher when the CNF electrode was used, compared with the fluorine-doped tin oxide supporting electrode. The use of CNF led to the smooth occurrence of EA and ED of Cs+, where the reported efficiency was: NiFe >FeFe >cPB. The EA and ED of Cs+ on NiFe decorated CNF (C-NiFe) were strongly affected by the loading amount of NiFe. Although the strongest EA capacity was identified when 1mg of NiFe was used, it decreased as the loading amount of NiFe increased. Thus, the EA of Cs+ occurs under the reduction of NiFe with some Fe(III) reduced to Fe(II) of NiFe, thus inducing more adsorption of Cs+. Overall, we confirmed that the C-NiFe electrode with appropriate thickness of NiFe layer is potentially an excellent adsorbent for Cs removal.

Efficient As(V) Removal by Recyclable Composite Nickel–Iron Oxide (NiFe2O4) Derived from NiFe Layered Double Hydroxides In situ Growing on Nickel Foam

Efficient As(V) Removal by Recyclable Composite Nickel–Iron Oxide (NiFe2O4) Derived from NiFe Layered Double Hydroxides In situ Growing on Nickel Foam

The Influence of Loadings and Substrates on the Performance of Nickel‐Based Catalysts for the Oxygen Evolution Reaction

AbstractEfficient and durable catalysts for the oxygen evolution reaction (OER) are of great importance for energy storage and conversion devices. However, an objective evaluation and fair comparison of different catalysts remain challenging due to the different catalyst loadings and substrates for OER measurements. In this work, we investigated NiFe layer double hydroxide and commercial Ni/NiO catalysts with different loadings and substrates of glassy carbon (GC), porous nickel foam (NF), and carbon paper (CP). The activity, cycling stability, and potentiostatic stability of the catalysts are compared with respect to the loading and substrate. Catalyst loading exhibits a volcano trend with OER activity, while it has little impact on stability. The 3D substrates NF and CP significantly improved the OER activity of the catalysts compared to GC, especially at higher loadings. The consistent degradation trend of the catalysts confirms the validity of using NF or CP as substrates for the stability test.

Use of NiFe Layered Double Hydroxide as Electrocatalyst in Oxygen Evolution Reaction: Catalytic Mechanisms, Electrode Design, and Durability

Use of NiFe Layered Double Hydroxide as Electrocatalyst in Oxygen Evolution Reaction: Catalytic Mechanisms, Electrode Design, and Durability

Field-driven Modulation of Spin Hall Magnetoresistance in Nanoscale-layered Pt/IrMn₃/NiFe Heterostructures

Spin Hall magnetoresistance (SMR) emerges from both spin Hall effect (SHE) and inverse spin Hall effect (ISHE), which is usually investigated in a nonmagnetic heavy metal (NM) in contact with a ferromagnet (FM). Depending on the orientation of FM magnetization and spin polarization of NM layer, the transmission or reflection of the spin current at the FM\NM interface could occur. SMR was investigated in 1.5 nm NiFe\3.0 nm IrMn₃\3.0 nm Pt magnetic heterostructures. IrMn₃ thin film grown on ferromagnetic NiFe layer exhibits the glassy magnetic behavior and displays spin reorientation transition in the magnetic field-temperature space. Below the Néel temperature of IrMn₃, the angle dependence of MR measurement in the xy and xz plane showed a normal positive SMR. However, a sign change in SMR was observed in the magnetic field applied in the yz plane. The switching from negative to positive SMR occurs at the field above a critical value of 6 kG. Our results provide a potential advantage for the source of spin flow in the signal in multilayer heterostructures and highlight the importance of magnetic structure (Néel vector) in AF, which opens the possible way to manipulate the spin current transportation and AF memory devices.

Tailoring anomalous Hall effect by spin–orbit coupling in epitaxial Au/Fe4N bilayers

Anomalous Hall effect (AHE) is one of the most fascinating topics in condensed matter physics related to spin–orbit coupling (SOC). In this paper, we report on the AHE of high-quality epitaxial Au/Fe4N bilayer films, which were grown by a plasma-assisted molecular beam epitaxy system. A scaling involving multiple competing scattering mechanisms and a shunting model were adopted to analyze the AHE in detail. Compared with Fe4N single layers and Cu/Fe4N bilayers, the AHE of Au/Fe4N bilayers is dramatically modified by strong SOC of the Au layer. Analysis has shown that aside from extra scatterings from Au atoms that diffused from an Au layer to a Fe4N layer, both spin Hall effect of Au and magnetic proximity effect near the Au/Fe4N interface contribute to the modification of the AHE. Variation of coercivity with the change of current, which could be attributed to spin–orbit torque, implies that the measured AHE is a combination of the AHE of Fe4N and strong SOC of Au.

Electronic structure regulation of nickel-iron layered double hydroxides by tuning ternary component for overall water splitting

NiFe layer double hydroxide (LDH) preserves high electrocatalytic activities for oxygen evolution reaction (OER); however, the catalytic performance on hydrogen evolution reaction (HER) is still suffering from poor catalytic activities. In this work, zinc (Zn)-doped NiFe LDH was synthesized as an excellent bifunctional electrocatalysts in alkaline electrolyte. For OER performance, the NiFeZn LDH achieves a Tafel slope of 35.2 mV/dec, which is much lower than that of commercial IrO2 catalysts (124.3 mV/dec). Expected, NiFeZn LDH also remains enhanced HER activity with an overpotential of 236 mV at 50 mA/cm2, superior to most of reported transition metal LDHs. The density functional theory results demonstrated that the Zn dopants could effectively manipulate the electronic structure of NiFeZn LDH, which is responsible to the enhanced active sites for HER.

Spin transport properties in a naphthyl diamine derivative film investigated by the spin pumping

We report the spin transport properties in a thin film of a naphthyl diamine derivative: N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)-2,2′-dimethylbenzidine (α-NPD). In a palladium (Pd)/α-NPD/Ni80Fe20 tri-layer structure sample, a pure spin current is generated in the α-NPD layer with the spin pumping driven by ferromagnetic resonance (FMR). The generated spin current is absorbed into the Pd layer, and converted into a charge current with the inverse spin-Hall effect (ISHE) in Pd. An electromotive force due to the ISHE in the Pd layer is observed under the FMR of the Ni80Fe20 layer, which is clear evidence for the spin transport in an α-NPD film. The spin diffusion length in an α-NPD film is estimated to be about 62 nm at room temperature, which is long enough as a spin transport material for spintronic devices.

Hydrogen desorption characteristics of Mg hydride films with Ni and Ni-based alloy catalyst layers deposited by magnetron sputtering

We investigated the effects of nickel and nickel-based alloys as catalysts to reduce the hydrogen desorption temperatures of magnesium hydride films deposited by magnetron sputtering. We measured the hydrogen desorption spectra of magnesium hydride films with nickel and Ni-Co, Ni-Fe, Ni-Ti, and Ni-Cu alloy catalytic layers by thermal desorption spectroscopy. The chemical composition of the magnesium hydride films was MgH1.7 as determined by elastic recoil detection analysis and X-ray diffraction. MgH1.7 film with a nickel layer (Ni/MgH1.7) showed onset and termination temperatures of hydrogen desorption were 100°C and 178°C, respectively. The onset temperatures of Ni-Co/MgH1.7, Ni-Fe/MgH1.7, and Ni-Ti/MgH1.7 were higher than that of Ni/MgH1.7, which was almost the same as that of Ni-Cu/MgH1.7. To lower the hydrogen desorption temperature, we prepared a multilayer film [Ni/MgH1.7]5 by depositing MgH1.7 and nickel layers alternately five times, but this did not decrease the onset temperature of the multilayer film. On the basis of the experimental results, we discussed a possible mechanism underlying hydrogen desorption from magnesium hydride films with catalytic layers.

Giant response to spin-orbit torques in heavy-metal/ferromagnetic bilayers associated with magnetic reversal

Using bilayer films of $\ensuremath{\beta}$-Ta (5 nm)/${\mathrm{Ni}}_{0.8}{\mathrm{Fe}}_{0.2}$ (2 nm), we fabricate elliptical structures which exhibit uniaxial magnetic anisotropy, resulting in single magnetic domain behavior. We study induced spin-orbit torques (SOTs) in these devices with first- and second-order harmonic Hall measurements for current flowing along the long axis of the ellipses and external magnetic field applied in the film plane. We observe a giant response to the SOTs associated with magnetization reversal of the NiFe layer, and we correlate it quantitatively with a $d{\ensuremath{\varphi}}_{m}/d{\ensuremath{\varphi}}_{H}$ term, where ${\ensuremath{\varphi}}_{m}$ and ${\ensuremath{\varphi}}_{H}$ are the in-plane angles of the magnetization and the magnetic field, respectively. We discuss theoretical and applicative implications of this intriguing behavior.

NiFe Layered Double Hydroxide Electrocatalyst Prepared via an Electrochemical Deposition Method for the Oxygen Evolution Reaction

Herein, we aimed to obtain NiFe layered double hydroxide (LDH) with a controlled phase and surface morphology as a highly active and stable oxygen evolution catalyst via the electrochemical deposition method, which was thermodynamically stable for the oxygen evolution reaction (OER) in an alkaline medium. The NiFe-LDH sample was analyzed by sophisticated instruments and tested as an electrocatalyst on Toray carbon (TC). The NiFe-LDH electrocatalyst showed an excellent performance with lower overpotential of 0.27 V at 35 mA cm−2 and higher density of 125 mA cm−2 for OER in the 1 M KOH electrolyte solution. Moreover, the prepared catalyst exhibited unpredictable long-time stability for 700 h. From our knowledge, NiFe-LDH is a robust highly stable electrocatalyst compared to the recent reports.

Heterogeneous layered multiple transition metal composite electrocatalysts with controlled composition for hydrogen production

The exploration of highly efficient and low-cost bifunctional electrocatalyst is essential for overall water splitting, especially for industrial application under alkaline conditions. Herein, we propose a controllable structural engineering strategy of constructing heterogeneous layered electrocatalyst with wetting surface for hydrogen evolution reaction and oxygen evolution reaction. Heterogeneous layered NiFe LDH (layered double hydroxide)/CoFeP/NF (Ni foam) with superhydrophilic surfaces is successfully fabricated by successive electrodeposition, phosphorization and solvothermal method. The NiFe LDH/CoFeP/NF for hydrogen evolution achieves a low overpotential of 198 mV at 50 mA cm−2 in 1.0 M KOH. An overpotential of 269 mV is required at 50 mA cm−2 for oxygen evolution. Meanwhile, the practical utilization of NiFe LDH/CoFeP/NF as bifunctional electrocatalysts for overall water splitting yields 1.73 V at 50 mA cm−2 in the two-electrode cell. Moreover, NiFe LDH/CoFeP/NF can retain over 50 h without an obvious degradation at 10 mA cm−2. The satisfactory operating stability and high activity of NiFe LDH/CoFeP/NF in alkaline solution can be attributed to the heterogeneous layered structure and excellent hydrophilic surface. The study provides a strategy to engineering heterogeneous layered structures with wetting surface for excellent electrocatalytic activities toward overall water splitting.

Promoting Surface Reconstruction of NiFe Layered Double Hydroxide for Enhanced Oxygen Evolution

AbstractA dynamic surface reconstruction of oxide electrocatalysts in alkaline media is widely observed especially for layered double hydroxide (LDH), but little is known about how to promote the reconstruction toward desired surfaces for improved oxygen evolution reaction (OER). Here, surface reconstruction of NiFe LDH nanosheets is successfully induced to a higher degree via in situ sulfur doping than that by natural electrochemical activation. Theoretical calculations, operando Raman, and various ex situ characterizations reveal the S anion‐induced effect can lower the energy barrier and facilitate the phase transformation into highly active S‐doped oxyhydroxides. The generated S‐NixFeyOOH can optimize the intermediate adsorption and facilitate the OER kinetics. The reconstructed S‐oxyhydroxides catalyst presents superior OER activity and long‐term durability compared to undoped ones. This work provides a structure–composition–activity relationship during the in situ surface restructuring of NiFe LDH pre‐catalysts.

The Effect of Obliquely Sputtered Cu Underlayers with Different Thicknesses on the Magnetic Properties of 50 nm Ni80Fe20 Thin Films

The magnetic properties of 50 nm Ni80Fe20 deposited on Cu underlayers with different thicknesses by obliquely sputtering were studied. It was found that the in-plane uniaxial magnetic anisotropy (IPUMA) of the Ni80Fe20 film can be induced by the obliquely sputtered Cu underlayer deposited under the NiFe layer. The IPUMA field of NiFe film varies between 20 Oe and 40 Oe when the thickness of Cu underlayer varies from 5 nm to 50 nm. The permeability spectrum results show that the damping factor increases with increasing Cu underlayer thickness. This indicates that changing the thickness of the Cu underlayer of obliquely sputtering is an effective method to adjust the damping factor in the dynamic magnetization process of Ni80Fe20 thin films.

Magnetic Properties of GaAs/NiFe Coaxial Core-Shell Structures.

Uniform nanogranular NiFe layers with Ni contents of 65%, 80%, and 100% have been electroplated in the potentiostatic deposition mode on both planar substrates and arrays of nanowires prepared by the anodization of GaAs substrates. The fabricated planar and coaxial core-shell ferromagnetic structures have been investigated by means of scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). To determine the perspectives for applications, a comparative analysis of magnetic properties, in terms of the saturation and remanence moment, the squareness ratio, and the coercivity, was performed for structures with different Ni contents.

NiFe Layered Double Hydroxide Nanosheets Anchored on Cobalt Nanocrystal Matrixes as Electrocatalysts for Oxygen Evolution

NiFe Layered Double Hydroxide Nanosheets Anchored on Cobalt Nanocrystal Matrixes as Electrocatalysts for Oxygen Evolution