CoNi Layers Research Articles

Wood-derived freestanding integrated electrode with robust interface-coupling effect boosted bifunctionality for rechargeable zinc-air batteries

Fabricating non-noble metal-based carbon air electrodes with highly efficient bifunctionality is big challenge owing to the sluggish kinetics of oxygen reduction/evolution reaction (ORR/OER). The efficient cathode catalyst is urgently needed to further improve the performance of rechargeable zinc-air batteries. Herein, an activation-doping assisted interface modification strategy is demonstrated based on freestanding integrated carbon composite (CoNiLDH@NPC) composed of wood-based N and P doped active carbon (NPC) and CoNi layer double hydroxides (CoNiLDH). In the light of its large specific surface area and unique defective structure, CoNiLDH@NPC with strong interface-coupling effect in 2D-3D micro-nanostructure exhibits outstanding bifunctionality. Such carbon composites show half-wave potential of 0.85 V for ORR, overpotential of 320 mV with current density of 10 mA cm-2 for OER, and ultra-low gap of 0.70 V. Furthermore, highly-ordered open channels of wood provide enormous space to form abundant triple-phase boundary for accelerating the catalytic process. Consequently, Zinc-air batteries using CoNiLDH@NPC show high power density (aqueous: 263 mW cm-2, quasi-solid-state: 65.8 mW cm-2) and long-term stability (aqueous: 500 h, quasi-solid-state: 120 h). This integrated protocol opens a new avenue for the rational design of efficient freestanding air electrode from biomass resources.

Controllable formation of amorphous structure to improve the oxygen evolution reaction performance of a CoNi LDH.

The morphology design of layered double hydroxides (LDHs) is an important way to determine the catalytic performance of LDH materials. A novel structure of CoNi LDH sheets with amorphous structure on the edge was prepared by electrooxidation. It was characterized by XRD, SEM, TEM and XPS. It was found that during the electrooxidation, some of the Co2+ ions were oxidized to Co3+ to form amorphous CoOOH intermediates, which promoted the OER performance. The electrochemical test results show that CoNi LDH treated by electrooxidation for 6 hours has an ultra-low overpotential of 206 mV at a current density of 10 mA cm-2, and can work stably under alkaline conditions for more than 10 hours. This work suggests that introducing an amorphous structure on LDH through electrooxidation produces abundant active sites, which is an easy and efficient method to improve the OER performance of CoNi LDHs.

Facile Assembly of Hybrid Micro-Supercapacitors for a Sunlight-Powered Energy Storage System.

Herein, hybrid micro-supercapacitors (MSCs), consisting of positive CoNi layer double hydroxides (LDHs) decorated on carbon nanotubes (CoNi LDHs@CNTs) and negative CNT electrodes, were assembled by facile drop-coated and electrodeposition methods. The as-fabricated MSCs were optimized in view of electrochemical performance, and the CoNi LDHs-2@CNTs//CNT MSC exhibited a favorable performance and was thus chosen to be the candidate for MSC device package. The packaged CoNi LDHs-2@CNTs//CNT MSC demonstrated a large areal capacitance of 11.0 mF·cm-2 at a current density of 0.08 mA·cm-2, a good rate performance (56% areal capacitance retained at a higher current density of 0.4 mA·cm-2), and a favorable cycling stability and reversibility (92% of the original areal capacitance was retained after 5000 cycles). Furthermore, the MSC device recorded an energy density of 1.5 μWh·cm-2 at a power density of 42.5 μW·cm-2 and was successfully applied for the storage of energy supplied by solar cells to operate a red light-emitting diode. All these findings demonstrated the promising practical energy storage application of the as-fabricated hybrid MSC devices in the construction of sunlight-powered energy storage systems.

Perpendicularly magnetized epitaxial Co/Ni multilayers grown on Ru(0001) layers by alternate monoatomic layer deposition

The hcp stacked Bh-ordered CoNi film was a candidate material to simultaneously have large uniaxial magnetic anisotropy energy (Ku) and a low Gilbert damping constant, which were previously predicted by a first-principles calculation. In this paper, we investigated the film growth condition to form the hcp stacked CoNi layers. [Co(1 ML)/Ni(1 ML)]N multilayers were epitaxially grown on Al2O3(11-20)/Ru(0001) underlayers by molecular beam epitaxy using an alternate monoatomic layer deposition technique with changing growth temperature (Ts) and repetition number (N). As the results of structural characterizations by x-ray diffraction measurements, it was found that the fcc- and hcp-CoNi phases were mixed in the samples, and the volume fraction of the fcc phase was larger than that of the hcp phase. However, the formation of the hcp-CoNi phase was promoted near the interface with the Ru layer having the hcp structure. The low growth temperature and the small N increased the volume fraction of the hcp phase. The Ku value of 5.1 Merg/cm3 was achieved for the [Co(1 ML)/Ni(1 ML)]20 multilayer grown at room temperature. In addition, a perpendicularly magnetized film was realized even for the thin sample with N = 5 (2 nm). This means that the Co/Ni multilayers are a thin ferromagnetic material suitable for application to spintronic devices.

Self-templated transformation of Co-ZIF-L into hierarchical porous CoS2/Co-Ni LDHs with improved electrochemical activities

CoS2/Co-Ni layered double hydroxides (LDHs) with a rational tailored pore structure are developed by partial sulfurization of Co-ZIF-L and subsequent Ni2+ etching for the transformation of zeolitic imidazolate frameworks (ZIFs) to layered double hydroxides. The as-synthesized CoS2/Co-Ni LDHs maintain the leaf-like structure and have rich hierarchical pores. More importantly, CoS2 nanoparticles are uniformly embedded among Co-Ni LDH layers, facilitating mass diffusion and favorably exposing more active sites. Benefiting from these desirable compositional and structural features, a remarkable specific capacitance (capacity) of 1784 F/g (223 mAh/g) at 1 A/g is delivered by CoS2/Co-Ni LDHs. Furthermore, the as-assembled CoS2/Co-Ni LDH//activated carbon as the asymmetric supercapacitor device also exhibits a high energy density of 125 Wh/kg at a power density of 800 W/kg and a superb capacitance retention of 98 % after 5000 cycles, outperforming many Co-Ni LDH based electrode materials reported in the literature.

Enhanced activity and stability of Co-Ni-P-B catalyst for the hydrogen evolution reaction via predeposition of Co-Ni on a Cu substrate

In this work, the effect of a predeposited Co-Ni layer on the catalytic activity and long-term durability of the quaternary Co-Ni-P-B catalyst for the hydrogen evolution reaction (HER) is investigated. To study the effect of predeposition of the Co-Ni layer for the Co-Ni-P-B catalyst, both Co-Ni-P-B/Co-Ni/Cu and Co-Ni-P-B/Cu catalysts are prepared. The current density for HER of the Co-Ni-P-B/Co-Ni/Cu catalyst at −0.5 VRHE is 36.1% higher than that of Co-Ni-P-B/Cu in 0.5 M H2SO4 solution at 18 °C. This is because the porous morphology of the Co-Ni-P-B/Co-Ni/Cu catalyst leads to a 10.6% larger electrochemical surface area and higher atomic ratio for both the P and B contents, which act as a proton acceptor and a supplier of electrons to the d orbital of the transition metals, respectively, compared to Co-Ni-P-B/Cu on the catalytic surface. Furthermore, the Co-Ni-P-B/Co-Ni/Cu catalyst retains 94.5% of the catalytic activity during durability test of 1 h owing to its higher adhesion strength between the substrate and catalyst and rougher morphology, whereas the Co-Ni-P-B/Cu catalyst shows a retention of only 64.4%.

Room temperature perpendicular exchange bias in CoNi/(Co,Ni)O multilayers with perpendicular magnetic anisotropy directly induced by FM/AFM interface

Abstract We have investigated the room temperature perpendicular exchange bias (PEB) at the ferromagnetic CoNi/antiferromagnetic (Co,Ni)O interfaces. CoNi/(Co,Ni)O multilayers with sharp interfaces have been sputter-deposited on glass substrates. It is found such multilayers show strong PMA and room temperature PEB. The PMA is considered originate from the interfacial anisotropy due to the facts that the CoNi layers are of poor crystallinity and it is difficult to obtain strain-induced anisotropy. The room temperature PEB indicates the well-balanced Neel temperature and anisotropy energy of the antiferromagnetic (Co,Ni)O mixed oxide layer.

Low-field magnetization process and complex permeability of FeCoBSiTa wires coated with hard magnetic CoNi layer

Biphase wires consisting of a soft magnetic amorphous nucleus surrounded by a hard magnetic CoNi layer of variable thickness were obtained by means of rotating water-quenching method and subsequent electroplating technique. Magnetization processes for all the biphase wires were resolved in terms of reversible bulging of magnetic domains and spin rotation by means of complex permeability measurements within the frequency range of 10 Hz–13 MHz. Results are interpreted in terms of CoNi layer effect on the magnetic anisotropy of the soft core.

Preparation of CoNi high surface area porous foams by substrate controlled electrodeposition

We demonstrate that nanofabrication of 3D dendritic CoNi alloy foams with an open porous structure can be achieved by electrodeposition onto a single-crystalline Cu(111) substrate at ambient conditions. The very low wettability of this substrate caused by its low surface energy allows tailoring the CoNi deposit morphology. This is concluded from a comparison of polycrystalline Cu substrates with single-crystalline ones of different orientations. The advantages of the present CoNi alloy foams are low internal stresses and good mechanical stability on the substrate. In a second step, by comparing the catalytic properties of the achieved foam with those of CoNi layers obtained on polycrystalline Cu substrates, it is shown that the morphology of the CoNi layers has a decisive influence on the kinetics of the surface redox reaction. The higher reaction rate makes the open foam suitable as catalyst for oxygen evolution in electrolysers. The reversibility of the redox process provides great potential for the achieved porous layers to be used as positive material in alkaline batteries.

Multipeak ferromagnetic resonance behaviour tailored by magnetoelastic coupling in FeSiB/CoNi layered microwires

The aim of this work is to report on the influence of the presence of a magnetically hard layer with large thickness on the ferromagnetic resonance (FMR) behaviour of soft/hard biphase microwires. Such microwires consist of a FeSiB soft nucleus, an intermediate glass layer and a CoNi hard outer shell, and are prepared by the combined quenching and drawing technique with electrochemical deposition. The unusual FMR response observed for this biphase system is characterized by the presence of a multipeak absorption spectrum that depends on the static field and on the thickness of the hard phase by means of magnetoelastic coupling. For a thick enough CoNi layer, the internal stresses induced in the nucleus during the electroplating process are very strong, giving rise to three electromagnetic absorptions: one at a low frequency related to the CoNi shell and two at higher frequencies corresponding to the FeSiB nucleus which are ascribed to two well-defined magnetization regions with different magnetic anisotropies.

Electrodeposition of CoNiFe Alloys on n-Type Silicon

Co, CoNi and CoFeNi layers were formed on n-type silicon by electrodeposition method from sulfate solutions. The obtained films were characterized by Cyclic Voltammetry (CV), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometry (EDS). The results show that the morphology and the stoechiometry of CoNi and CoNiFe deposits depend on several parameters (bath composition, applied potential…). The addition of sodium acetate as complexion agent in the bath leads to the formation of highly compacted and smooth films with a good adherence to the substrate.

Circular Magnetoelastic Anisotropy Induced in the Nucleus of an FeSiB-CoNi Soft-Hard Bi-Phase Microwire

Multilayer amorphous microwires have been prepared coating a precursor FeSiB amorphous nucleus with a crystalline CoNi outer layer. The FeSiB as-cast amorphous wire is characterised by an unique bistable behavior where magnetization reverses from one remanent state to another through a single large Barkhausen event at a field value known as switching field, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sw</sub> . In multilayer microwires, the presence of a second magnetic phase, a magnetically harder CoNi layer, substantially modifies the values of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sw</sub> via two coupling mechanisms: magnetoelastic and magnetostatic interactions between the two phases. In this paper, a systematic study on the effects of the geometrical characteristic of the outer phase on the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sw</sub> behavior is presented. M-H analysis and fluctuation studies by induction technique were performed on a family of samples having different CoNi thicknesses.

Multilayer systems magnetostatically coupled: Magnetization profile and local volume domain structure

Micrometric trilayer ribbons have been prepared consisting of a melt-spun Co-base ultrasoft amorphous nucleus surrounded by two electroplated magnetically harder polycrystalline CoNi layers. A detailed study of the magnetostatic coupling between the two magnetic phases has been performed by analyzing the local low-field hysteresis loops of the soft phase under the remanent stray field of the harder layers. Due to the magnetostatic character of the interaction, the dimensions and configuration of the hard phase play a very important role in the bias field distribution modifying the susceptibility and the fractional volume of different magnetization regions inside the soft nucleus. A reversal magnetization model is proposed to understand the complex magnetostatic interaction in such composite trilayer ribbons. An important achievement of this work is the derived understanding of magnetic structure of the system along ribbon axis, by means of a local displaceable pick-up coil employed during the hysteresis loop measurements.

Layer thickness dependence of CPP giant magnetoresistance in individualCoNi∕Cumultilayer nanowires grown by electrodeposition

Giant magnetoresistance (GMR) effect of $\mathrm{Co}\mathrm{Ni}∕\mathrm{Cu}$ nanowires grown by electrodeposition using an array of parallel through holes in anodized alumina membranes was studied in the current-perpendicular-to-plane (CPP) geometry as a function of the CoNi and Cu layer thicknesses. The CPP-GMR measurements were carried out by making a point contact with individual nanowires using a metallic plunger tip. In the range of the CoNi layer thickness ${t}_{\mathrm{Co}\mathrm{Ni}}=2--510\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and that of the Cu layer thickness ${t}_{\mathrm{Cu}}=4.2--42\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, the maximum value of CPP-GMR change observed in the $\mathrm{Co}\mathrm{Ni}∕\mathrm{Cu}$ nanowires was 23% at room temperature. The variation of the CPP-GMR with ${t}_{\mathrm{Co}\mathrm{Ni}}$ at fixed ${t}_{\mathrm{Cu}}$ and that with ${t}_{\mathrm{Cu}}$ at fixed ${t}_{\mathrm{Co}\mathrm{Ni}}$ is discussed in terms of the series-resistor model and the Valet-Fert model for CPP-GMR. The effects of various factors such as superparamagnetism in very thin CoNi layers and dipole-dipole interactions between CoNi layers on the CPP-GMR of $\mathrm{Co}\mathrm{Ni}∕\mathrm{Cu}$ nanowires are also discussed.

Field Angle and Thickness Dependence of Coercivity in Electrodeposited CoNi–Cu Multilayer Nanowires

Variation in the coercivity of CoNi-Cu multilayer nanowires grown by electrodeposition using a hole pattern of alumina templates has been systematically studied as a function of the CoNi layer thickness and the angle between an applied magnetic field and the nanowire axis. We have found that the magnetization reversal for the nanowires with thin disk-shaped CoNi layers is in the coherent rotation mode, while that for the nanowires with long rod-shaped CoNi layers can be interpreted by a combination of the coherent rotation and curling modes. With decreasing CoNi layer thickness t(CoNi) from 6.8plusmn0.8 to 1.7plusmn0.2 nm, the coercivity rapidly decreases from 305 to 10 Oe, indicating that for t(CoNi)<1.7plusmn0.2 nm, the CoNi layers of the nanowires become superparamagnetic at room temperature. The room temperature superparamagnetism is further confirmed by magnetization measurements at low temperatures using a superconducting quantum interference device. The estimated blocking temperatures for t(CoNi)=1.7plusmn0.2 and 1.0plusmn0.1 nm are 181 and 136 K, respectively

Magnetic layer thickness dependence of magnetization reversal in electrodeposited CoNi/Cu multilayer nanowires

The magnetization reversal of electrodeposited CoNi/Cu multilayer nanowires patterned in an array using a hole template has been investigated. The reversal mode is found to depend on the CoNi layer thickness t(CoNi); with increasing t(CoNi) a transition occurs from coherent rotation to a combination of coherent and incoherent rotation at around t(CoNi)=51 nm. The reversal mode has been identified using the magnetic hysteresis loops measured at room temperature for CoNi/Cu nanowires placed at various angles between the directions of the nanowire axis and external fields using a vibrating sample magnetometer. The nanowire samples have a diameter of ∼250 nm and constant Cu layer thickness of 4.2 nm with various t(CoNi) ranging from 6.8 nm to 7.5 μm. With increasing t(CoNi), the magnetic easy axis moves from the direction perpendicular to nanowires to that parallel to the nanowires at around t(CoNi)=51 nm, indicating a change in the magnetization reversal mode. The reversal mode for the nanowires with thin disk-shaped CoNi layers ( t(CoNi)=6.8, 12 and 17 nm) is of a coherent rotation type, while that for long rod-shaped CoNi layers ( t(CoNi)=150 nm, 1.0, 2.5 and 7.5 μm) can be consistently explained by a combination of coherent rotation and a curling mode. The effects of dipole–dipole interactions between nanowires and between adjacent magnetic layers in each nanowire on the reversal process have been discussed.

Superparamagnetic behavior in ultrathin CoNi layers of electrodeposited CoNi∕Cu multilayer nanowires

We present evidence that in a very thin regime the magnetic layers become discrete islands and superparamagnetic in multilayered CoNi(1–17nm)∕Cu(4.2nm) nanowires grown by pulsed electrodeposition using a hole pattern of anodized alumina templates. Magnetic hysteresis loops measured at room temperature using a vibrating sample magnetometer show that superparamagnetism appears at t(CoNi)&amp;lt;1.7nm, due to a volumetric reduction of the CoNi layers that may result in discontinuity of the layer or formation of islands. The magnetic hysteresis loops for the superparamagnetic nanowires can be represented by the Langevin function. The temperature dependence of coercivity data obtained for the superparamagnetic nanowires using a superconducting quantum interference device indicates that the magnetization reversal can be consistently explained by the Stoner-Walfarth model for coherent rotation. The volumetric reduction accounted for the observed superparamagnetism is probably due to an electrochemical exchange reaction between CoNi and Cu species at the interface during each Cu deposition cycle. The exchange reaction may cause partial dissolution of the CoNi layers at the interface which is eventually stabilized by cementation with Cu. The effects of the nucleation and growth process on the formation of superparamagnetic islands are also discussed.

Coercivity and magnetization reversal mechanism in ferromagnet/antiferromagnet bilayers: Correlation with microstructure of ferromagnetic layers

Exchange biasing in ${\mathrm{Co}}_{20}{\mathrm{Ni}}_{80}∕\mathrm{Fe}\mathrm{Mn}$ and ${\mathrm{Co}}_{80}{\mathrm{Cr}}_{20}∕\mathrm{Fe}\mathrm{Mn}$ bilayers has been investigated, where the CoCr layers are of granular structure and the CoNi layers are in the form of a single phase. In the above two series of bilayers, the exchange field is proportional to $1∕{t}_{\mathrm{FM}}$ (${t}_{\mathrm{FM}}$ denotes ferromagnetic layer thickness). For $\mathrm{Co}\mathrm{Ni}∕\mathrm{Fe}\mathrm{Mn}$ bilayers, the coercivity and the uniaxial anisotropic field decrease with increasing ${t}_{\mathrm{FM}}$ with a linear scale of $1∕{t}_{\mathrm{FM}}$. Since they are equal to each other, the magnetization reversal process can be described by magnetization coherent rotation and the coercivity enhancement can be explained in terms of a uniaxial anisotropy model. For $\mathrm{Co}\mathrm{Cr}∕\mathrm{Fe}\mathrm{Mn}$ bilayers, however, the coercivity displays unusual behaviors. First, in comparison with that of single CoCr layer films, the coercivity is reduced instead of enhanced. Secondly, it increases with increasing ${t}_{\mathrm{FM}}$. Finally, the coercivity of the bilayers is not equal to the uniaxial anisotropic field. A noncoherent rotation process is proposed to occur during the magnetization reversal process. The different characteristics of the coercivity and magnetization reversal mechanisms in the two series of bilayers result from the different microstructures in the CoNi and CoCr layers. The present work might be helpful to clarify the mechanism for the coercivity enhancement in ferromagnet/antiferromagnet bilayers.

Ferromagnetic resonance linewidth in CoNi/FeMn bilayers

Out-of-plane ferromagnetic resonance (FMR) spectra of sputtered Co40Ni60/FeMn bilayers with various CoNi layer thicknesses were measured and analyzed by the Landau–Lifshitz–Gilbert equation. With increasing CoNi layer thickness, the effective demagnetizing field increases and the Lande g factor decreases. At the same time, the peak-to-peak linewidth ΔHpp in the parallel and perpendicular configurations decreases. The angular dependence of the FMR linewidth can be described very well by the intrinsic Gilbert damping effect and the magnetic inhomogeneity. The Gilbert damping G factor is inversely proportional to the CoNi layer thickness and proportional to (g-2)2 with the variation of the CoNi layer thickness.

Role of domain and interface spin structure on exchange bias in CoNi/Gd/CoNi trilayers

In this study, dc remanence measurements were performed on a sputter deposited CoNi(top)/Gd/CoNi trilayers. The remanence state of the CoNi(top)/Gd bilayer, which is the hard layer, determines the exchange bias field strength. If the sample is cooled from room temperature at the remanence state corresponding to the hard layer coercive field, the exchange bias becomes zero. Domains form in the hard layer at this remanence state. The angular dependence of the coercive field does not indicate magnetization reversal by domain wall motion. The bottom soft CoNi layer exchange couples to each domain in the hard layer at the interface. This causes the exchange bias field to become zero on the average. If the trilayer is cooled at its full remanence state, the formation of Hb anisotropy is observed in the angular dependence of coercivity.