NiFe Layer Research Articles

Three-dimensional self-supporting catalyst with NiFe alloy/oxyhydroxide supported on high-surface cobalt hydroxide nanosheet array for overall water splitting

The development of available dual-function electrocatalysts is of great significance to the effective storage of excess electricity. Here, we obtained a three-dimensional Co(OH)2 nanosheet with high surface area on nickel foam (Co(OH)2/NF) via conventional hydrothermal. NiFe-coated Co(OH)2 nanosheet array (NiFe@Co(OH)2 NSAs/NF) was further constructed by electrodeposition for water splitting. By optimizing and regulating the deposition time, NiFe@Co(OH)2 NSAs/NF with a deposition time of 500 s (NiFe-500@Co(OH)2 NSAs/NF) only needs 98 mV of overpotential and can be stabilized for 100 h for hydrogen evolution at 10 mA cm−2 due to the rich density active components for NiFe alloy/oxyhydroxide layer and interaction with Co(OH)2 nanosheets. Thanks to the excellent 3D nanosheet array structure and the close integration between Co(OH)2 and the upper layer NiFe, NiFe@Co(OH)2 NSAs/NF with a deposition time of 200 s (NiFe-200@Co(OH)2 NSAs/NF) can provide 10 mA cm−2 with only 204 mV and maintain constant catalysis within 100 h. Therefore, the constructed NiFe@Co(OH)2 NSAs/NF (500||200) double-electrode cell for water splitting requires only 1.58 V drive potential and can maintain 24 h durability at 10 mA cm−2. The design of the catalyst opens up new ideas for the large-scale application of transition metals in water splitting.

Permittivity features of multilayer nanoisland systems [FeNi–Al2O3

We study the permittivity (ε) of multilayer nanoisland systems [FeNi–Al2O3]N with different layer thicknesses using spectral ellipsometry. A “metallic” behavior of the permittivity (Re(ε)<0) is found in structures with island FeNi layers, when there is a strong exchange interaction between the layers (dielectric layer thickness d<2 nm). When the exchange interaction in structures is strongly suppressed (Al2O3 layer's thickness d>4 nm), Re(ε)>0, which corresponds to the dielectric behavior of the permittivity. We conclude that the exchange interaction has a significant effect on the permittivity of structures. We also show that the Re(ε) dependences on the FeNi layer thickness for multilayer and single-layer structures are very close when the dielectric layer thickness d>4 nm.

Metal/ SrTiO3 two-dimensional electron gases for spin-to-charge conversion

SrTiO$_3$-based two-dimensional electron gases (2DEGs) can be formed through the deposition of epitaxial oxides like LaAlO$_3$ or of reactive metals such as Al. Such 2DEGs possess a finite Rashba spin-orbit coupling that has recently been harnessed to interconvert charge and spin currents through the direct and inverse Edelstein and spin Hall effects. Here we compare the formation and properties of 2DEGs generated in SrTiO$_3$ by the growth of Al, Ta and Y ultrathin films by magnetron sputtering. By combining in situ and ex situ X-ray photoelectron spectroscopy (XPS) we gain insight into the reduction of the SrTiO$_3$ and the appearance of Ti$^{3+}$ states associated with 2DEG formation, its reoxidation by exposure to the air, and the transformation of the metal into its binary oxides. We extract the carrier densities through magnetotransport and compare them with the XPS data. Finally, working with samples covered by an extra layer of NiFe, we perform spin-pumping ferromagnetic resonance experiments and investigate spin-charge conversion as a function of gate voltage. We identify trends in the data across the different sample systems and discuss them as a function of the carrier density and the transparency of the metal oxide tunnel barrier.

Electron-rich NiFe layered double hydroxides via interface engineering for boosting electrocatalytic oxygen evolution

Modulating the local electronic structures of the active sites represents a promising strategy to improve the activity of electrocatalysts. Here, a facile interface engineering strategy is reported to fabricate electron-rich NiFe layer double hydroxide (LDH) by interfacing with conductive polyaniline (PANI) for significantly improving the OER activity. Experimental and theoretical investigations unveil that the unique electron-rich states of active metal sites in NiFe LDH via the strong interfacial coupling effect can optimize the adsorption free energy of reactive oxygenated intermediates. Remarkably, the electron-rich NiFe LDH electrocatalysts exhibit outstanding OER performance with a low overpotential of 220 mV at a current density of 10 mA cm−2, a small Tafel slope of 44 mV dec−1, and good stability.

Lithium-induced amorphization of Ni–Fe layered-double-hydroxide for highly efficient oxygen evolution

Engineering structure is a promising pathway to adjust the physicochemical properties of materials to optimize the performance for various applications. Herein, we designed a highly efficient NiFe layered-double-hydroxide (NiFe LDH) nanosheets arrays catalyst for superior oxygen evolution reaction electrocatalysis by lithium-induced amorphization. Electrochemical lithium tuning of layered NiFe LDH crystal makes for the formation of amorphous NiFe intermediate with abundant active sites. It exhibits excellent electrocatalytic activity towards the oxygen evolution reaction with an overpotential of 259 mV at 50 mA cm−2, a Tafel slope of 56 mV dec−1 and prominent long-term stability, better than the RuO2 as benchmark catalysts. Experimental studies show that the electrochemical tuning contributes to the enhancement of NiFe LDH intrinsic activity due to crystallinity loss, morphology changes and formation of grain boundaries. This work enlightens a unique strategy to effectively design the advanced electrocatalysts by regulating the structure of material.

Molecular Understanding of the Impact of Saline Contaminants and Alkaline pH on NiFe Layered Double Hydroxide Oxygen Evolution Catalysts

Molecular Understanding of the Impact of Saline Contaminants and Alkaline pH on NiFe Layered Double Hydroxide Oxygen Evolution Catalysts

Promoting Bifunctional Water Splitting by Modification of the Electronic Structure at the Interface of NiFe Layered Double Hydroxide and Ag.

Electrochemical water splitting is a promising method for the renewable production of high-purity hydrogen via the hydrogen evolution reaction (HER). Ni-Fe layered double hydroxides (Ni-Fe LDHs) are highly efficient materials for mediating the oxygen evolution reaction (OER), a half-reaction for water splitting at the anode, but LDHs typically display poor HER performance. Here, we report the preparation of self-organized Ag@NiFe layered double hydroxide core-shell electrodes on Ni foam (Ag@NiFe/NF) prepared by galvanic etching for mediating both the HER and OER (bifunctional water-splitting electrocatalysis). This synthetic strategy allowed for the preparation of organized hierarchical architectures which displayed improved the electrochemical performance by tuning the electronic structure of the catalyst and increasing the surface area utilization. X-ray photoelectron spectroscopy (XPS) and theoretical calculations revealed that electron transfer from the Ni-Fe LDH to Ag influenced the adsorption of the reaction intermediates leading to enhanced catalytic activity. The Ag@NiFe/NF electrode displayed overpotentials as low as 180 and 80 mV for oxygen and hydrogen evolution, respectively, at a current density of 10 mA cm-2, and improvements in the specific activity by ∼5× and ∼1.5× for the oxygen and hydrogen evolution reaction, respectively, compared to benchmark NiFe hydroxide materials. Additionally, an integrated water-splitting electrolyzer electrode can be driven by an AA battery.

High catalytic performance of core-shell structure ZnCo2O4@NiFe LDH for oxygen evolution reaction

It is of great significance to develop efficient and cheap electrocatalysts for oxygen evolution reaction (OER) to promote the further development of water splitting. An effective method is to prepare ideal catalysts by integrating different components, which can increase the number of active sites and generate the synergistic effect among different components. Based on this idea, the NiFe LDH (NiFe Layered Double Hydroxide) nanosheets are anchored on ZnCo2O4 nanowires to form a core-shell structure ZnCo2O4@NiFe LDH. Thanks to the synergistic effect between ZnCo2O4 and NiFe LDH, the ZnCo2O4@NiFe LDH shows excellent catalytic performance for OER. It only needs a low overpotential of 249 mV to achieve the current density of 10 mA cm−2 with a low Tafel slope of 96.7 mV dec-1. Furthermore, after 20 h of stability test, the catalytic performance of the ZnCo2O4@NiFe LDH shows no obvious attenuation. Therefore, this work provides a promising strategy for the future development of OER systems.

Magnonic band structure in CoFeB/Ta/NiFe meander-shaped magnetic bilayers

In this work, we investigate the spin-wave propagation in three-dimensional nanoscale CoFeB/Ta/NiFe meander structures fabricated on a structured SiO2/Si substrate. The magnonic band structure has been experimentally determined by wavevector-resolved Brillouin light scattering spectroscopy and a set of stationary modes interposed by two dispersive modes of Bloch type have been identified. The results could be understood by micromagnetic and finite element simulations of the mode distributions in both real space and the frequency domain. The dispersive modes periodically oscillate in frequency over the Brillouin zones and correspond to modes, whose spatial distributions extend over the entire sample and are either localized exclusively in the CoFeB layer or the entire CoFeB/Ta/NiFe magnetic bilayer, with in-phase precession of the dynamic magnetization in the two layers. Low-frequency stationary modes are concentrated in horizontal segments of the topmost NiFe layer with sizeable amplitudes in the vertical CoFeB and NiFe segments and out-of-phase precession. The findings are compared with those of single-layer CoFeB meander structures with the same geometry parameters, which reveals the influence of the dipolar coupling between the two ferromagnetic layers on the magnonic band structure.

Investigation of Cu/NiFe composite wires by SAMR method

Composite Cu/NiFe wires with two different compositions of electrolytic NiFe layers were investigated by the small angle magnetization rotation (SAMR) method. From the measurements the induced anisotropy and the saturation magnetostriction constants were determined. The measurements were compared with the theoretical model based on the quasistatic approximation. The experimental results well agreed with the theory.

Anchoring Active Sites by Pt2FeNi Alloy Nanoparticles on NiFe Layered Double Hydroxides for Efficient Electrocatalytic Oxygen Evolution Reaction

Strategy of anchoring alloy nanoparticles made up of the efficient catalytic element (e.g., Ni, Fe) on dodecyl sulfate (DS‐)‐intercalated NiFe layered double hydroxides (DS‐‐NiFe LDH) obtained by a convenient one‐step hydrothermal coprecipitation method for essentially enhancing oxygen evolution reaction (OER) performance was proposed. The results of structural characterization indicate Pt2FeNi alloy nanoparticles evenly distribute on the surface of DS‐‐NiFe LDH. The sizes of the Pt2FeNi nanoparticles, closely related to their OER performance, could be well‐controlled by adjusting the amount of H2PtCl6 addition. The composite structure of as‐prepared product was stable during processes of synthesis, exfoliation, self‐assembly, and subsequent electrocatalytic OER. Rigorous electrochemical test proving the contributing catalytic active sites was located at the interface between Pt2FeNi and DS‐‐NiFe LDH, and the Ni and Fe were the major active elements while O atoms are adsorption sites. The formation of Pt2FeNi nanoparticles could greatly prompt the reduction of Tafel slope. The best‐performing Pt2FeNi/DS‐‐NiFe LDH with a Pt content of 0.98 wt% achieved low overpotential of 204 mV at 10 mA cm−2 and 262 mV at 50 mA cm−2. This work provides a convenient and effective strategy to create additional active sites for enhancing OER performance of NiFe LDH and make contribution to its wide application.

Planar Hall Voltage Properties of Ta/NiFe/Ta/NiFe/Ta Multilayer for Biosensor Applications

Recently, magnetic nanoparticles and planar Hall resistance (PHR) devices used in biomolecule diagnosis and biological applications have attracted considerable attention as biosensors. The voltage properties of a planar Hall device with a Ta/NiFe/Ta/NiFe/Ta multilayer that was prepared in a cross-shaped pattern at a width of 0.5 mm using a shadow mask, were investigated. The sensitive planar Hall voltage (SPHV) obtained from the planar Hall voltage (PHV) curves of a Ta(5 nm)/NiFe(6 nm)/Ta(t = 2-8 nm)/NiFe(6 nm)/Ta(5 nm) multilayered sample was a few mV/Oe in the fine magnetic field region of the external magnetic field of ± 1.0 Oe. In particular, the thickness of Ta(t = 8 nm), the PHR ratio, magnetic sensitivity, and SPHV improved significantly by as much as 36.4 %, 28 %/Oe, and 1.6 mV/Oe, respectively. These results can be used in the development of a PHR biosensor with a high sensitivity for the detection of nanoparticle-antibody binding, even in a simple structure formed only out of a ferromagnetic NiFe layer.

Plasmonic Enhancement in Water Splitting Performance for NiFe Layered Double Hydroxide-N10 TC MXene Heterojunction.

MXene-based material has attracted wide attention due to its tunable band gap, high conductivity and impressive optical and plasmonic properties. Herein, a hetero-nanostructured water splitting system was developed based on N-doped Ti3 C2 (N10 TC) MXene and NiFe layered double hydroxide (LDH) nanosheets. The oxygen evolution reaction performance of the NiFe-LDH significantly enhanced to approximately 8.8-fold after incorporation of N10 TC. Meanwhile, the Tafel slope was only 58.1 mV dec-1 with light irradiation, which is lower than pure NiFe-LDH nanosheets (76.9 mV dec-1 ). All results manifested the vital role of the N10 TC MXene induced plasmonic hot carriers via electrophoto-excitation in enhancing the full water splitting performance of the as-prepared system. This work is expected to provide a platform for designing various plasmonic MXenes-based heterogeneous structures for highly efficient catalytic applications.

Inversion of angular-dependent planar magnetoresistance in epitaxial Pt/γ′-Fe4N bilayers

The conversion between charge and spin through spin–orbit coupling (SOC) is critical in heavy nonmagnetic metal/ferromagnetic metal systems. Here, both the single γ′-Fe4N films and the epitaxial Pt/γ′-Fe4N bilayers were fabricated by facing-target sputtering. In the Pt(3 nm)/γ′-Fe4N(tFe4N ≤ 6 nm) bilayers, the anisotropy magnetoresistance (AMR) exhibits an “M” shape, which is opposite to that of the single γ′-Fe4N film with a “W” shape. Meanwhile, the planar Hall resistivity (PHR) reversal also appears. The inversion of AMR and PHR after capping a 3-nm-thick Pt layer on the γ′-Fe4N layer is mainly determined by the interfacial effect, in which the magnetic-proximity-effect induced the interface Pt local moments and the inverse-spin-Hall-effect caused the reflected spin-current to charge-current conversion. Our work helps to understand the interfacial SOC effects and has potential application in the field of magnetic sensors.

Spin injection into vanadium dioxide films from a typical ferromagnetic metal, across the metal–insulator transition of the vanadium dioxide films

A vanadium dioxide VO2 film shows metal-insulator transition (MIT) induced by changing environmental temperature. We report the temperature dependence of electromotive force properties generated in VO2/Ni80Fe20 bilayer junctions under the ferromagnetic resonance (FMR) of the Ni80Fe20 layer. An electromotive force generated in a VO2/Ni80Fe20 bilayer junction under the FMR showed a small change across the MIT temperature of the VO2 film, while the VO2 film resistance drastically changed. This behavior was not only explained with the temperature dependence of the electromotive force property generated in the Ni80Fe20 film itself under the FMR, but also with the generated electromotive forces due to the inverse spin-Hall effect (ISHE) in the VO2 film under the FMR of the Ni80Fe20 film. That is, we successfully demonstrated the spin injection from a Ni80Fe20 film into a VO2 film across the MIT temperature of the VO2 film.

Exchange coupling and natural ferromagnetic resonance phenomena in Fe40Co37Zr11N12/ZrN/Ni80Fe20 film systems with in-plane uniaxial anisotropy

Ferromagnetic Fe40Co37Zr11N12/ZrN/Ni80Fe20 film systems with a uniaxial anisotropy in the film plane were synthesised by reactive magnetron sputtering and by post annealing in a static magnetic field. Investigation on the energy exchange interaction between the ferromagnetic layers without and with an interface layer were carried out. This exchange impacts the static magnetisation properties as well as the natural resonance frequency behaviour and its damping features caused by spin current generated damping and/or anti-damping effects. As static polarisation loops are slightly but distinguishably different dependent on the interface thickness, the films definitely exhibit a distinct variation in their frequency spectra. By means of the interface layer with different thickness, various dynamic behavioural patterns could be observed. This can be assumed because the observed ferromagnetic resonance dual lines show remarkable changes in their full width at half maxima (FWHM) at frequencies of around 600 MHz attributed to the Ni80Fe20 layers and 2.3 GHz attributed to the Fe40Co37Zr11N12 layers if interface layer are applied.

Parity-controlled spin-wave excitations in synthetic antiferromagnets

We report in this study the current-induced-torque excitation of acoustic and optical modes in Ta/NiFe/Ru/NiFe/Ta synthetic antiferromagnet stacks grown on SiO2/Si substrates. The two Ta layers serve as spin torque sources with the opposite polarizations in both spin currents and Oersted fields acting on their adjacent NiFe layers. This can create the odd symmetry of spatial spin torque distribution across the growth direction, allowing us to observe different spin-wave excitation efficiency from synthetic antiferromagnets excited by homogeneous torques. We analyze the torque symmetry by the in-plane angular dependence of symmetric and anti-symmetric line shape amplitudes for their resonance and confirm the parallel (perpendicular) pumping nature for the acoustic (optical) modes in our devices, which is in stark contrast to the modes excited by spatially homogeneous torques. We also present our macrospin model for this particular spin-torque excitation geometry, which excellently supports our experimental observation. Our results offer capability of controlling spin-wave excitations by local spin-torque sources, and we can explore further spin-wave control schemes based on this concept.

Electrocatalytic oxygen evolution surpassing benchmark RuO2 using stable, noble metal free vanadium doped hematite co-modified by NiFe Layered Double Hydroxide

Exploring a low-cost, efficient and stable electrocatalyst to replace noble metal-based catalysts for oxygen evolution reaction (OER) is highly demanding for practical applications. Herein, we have proposed vanadium doping and co-modification of α- Fe2O3 utilizing NiFe LDH for noble metal free electrocatalytic oxygen evolution reaction (OER), which exceeds the performance of benchmark RuO2 under similar experimental conditions. Vanadium doping enhances the carrier density, whereas NiFe LDH contributes to the surface active sites for promoting water oxidation kinetics. A five-fold enhancement in electrochemically active surface area (ECSA) for α- Fe2O3:V-NiFe LDH (2.5 mF/cm2) compared to α- Fe2O3 (0.5 mF/cm2) is observed with a turnover frequency (TOF) of 7.6/s (α- Fe2O3:V-NiFe LDH). α- Fe2O3:V-NiFe LDH exhibited an impressive overpotential of 190 mV @ 10 mA/cm2 with corresponding Tafel slopes of 42 mV/dec. The electrocatalyst, α- Fe2O3:V-NiFe LDH also exhibited excellent durability for over 1000 cycles and continuous chronoamperometric responses for over 12 h at 25 mA/cm2, current density with an average Faradaic yield of 93%. Detailed electrochemical studies with long-term stability indicate the potential of as-synthesized composite α- Fe2O3:V-NiFe LDH for utilization as a heterogeneous catalyst for efficient oxygen evolution reaction.

Hierarchical S Andwich Nife Layered Double Hydroxide/Reduced Graphene Oxide For Superb Energy Density Asymmetric Supercapacitors

Hierarchical S Andwich Nife Layered Double Hydroxide/Reduced Graphene Oxide For Superb Energy Density Asymmetric Supercapacitors

Boosting the electrocatalytic performance of NiFe layered double hydroxides for the oxygen evolution reaction by exposing the highly active edge plane (012).

The intrinsic activity of NiFe layer double hydroxides (LDHs) for the oxygen evolution reaction (OER) suffers from its predominantly exposed (003) basal plane, which is thought to have poor activity. Herein, we construct a hierarchal structure of NiFe LDH nanosheet-arrays-on-microplates (NiFe NSAs-MPs) to elevate the electrocatalytic activity of NiFe LDHs for the OER by exposing a high-activity plane, such as the (012) edge plane. It is surprising that the NiFe NSAs-MPs show activity of 100 mA cm−2 at an overpotential (η) of 250 mV, which is five times higher than that of (003) plane-dominated NiFe LDH microsheet arrays (NiFe MSAs) at the same η, representing the excellent electrocatalytic activity for the OER in alkaline media. Besides, we analyzed the OER activities of the (003) basal plane and the (012) and (110) edge planes of NiFe LDHs by density functional theory with on-site Coulomb interactions (DFT+U), and the calculation results indicated that the (012) edge plane exhibits the best catalytic performance among the various crystal planes because of the oxygen coordination of the Fe site, which is responsible for the high catalytic activity of NiFe NSAs-MPs.