Morphology and crystal-chemical characteristics of cobalt and nickel nanopowders prepared by thermochemical and electrolytic methods

The phase composition and morphology of cobalt and nickel powders and nickel foam have been studied by X-ray diffraction and scanning electron microscopy. The cobalt and nickel powders prepared through solution electrolysis are shown to have a dendritic microstructure. The particle morphology of the nanostructured cobalt and nickel powders and nanostructured nickel foam can be described by a three-level (according to the particle size) model.     

The effect of stacking faults on the electrochemical performance of nickel hydroxide electrodes

The crystal structure of nickel hydroxide comprises of a repetitive stacking of charge neutral layers AbC AbC AbC. A and C denotes the hydroxyl ions which are hexagonally close packed, while b denotes the divalent nickel ions occupying octahedral interstitial sites. The random incorporation of other layers, such as AcB, BaC, CbA, etc., within AbC AbC AbC … stacking sequence can lead to the formation of stacking faults. DIFFaX simulations show that each kind of stacking fault produces a characteristic pattern of non-uniform broadening of the peaks corresponding to the (h 0 ?) reflections in the powder X-ray diffraction (PXRD) pattern of nickel hydroxide. The electrochemical property of each two types of stacking faulted nickel hydroxide is investigated. 2H₂ type of stacking faulted nickel hydroxide delivers better electrochemical activity compared to 3R₂ type stacking faulted nickel hydroxide.     

Magnetic nanofilms of nickel prepared at the liquid-liquid interface

Thin films of metallic nickel with a thickness of the order of 20 nm have been prepared at the organic-aqueous interface at room temperature by the reaction of nickel cupferronate [Ni(C₆H₅N₂O₂)₂] in toluene medium and sodium borohydride (NaBH₄) in aqueous medium. The films were characterized with transmission electron microscopy, scanning electron microscopy and atomic force microscopy. Thicker Ni films could be prepared by carrying out the reaction at the interface at 60 °C. The Ni nanofilms exhibit superparamagnetic behavior.     

α/β互嵌氢氧化镍电极活性材料的结构和电化学性能

采用化学共沉淀法制备了具有α相和β相相互嵌套结构的氢氧化镍.用X-射线衍射(XRD),傅里叶变换红外光谱(FT-IR)和扫描电子显微镜(SEM)分析了样品的微观结构和表面形貌.用循环伏安(CV)、交流阻抗(EIS)和充放电测试表征了样品的电化学性能.结果表明,与纯β相氢氧化镍相比,α/β互嵌结构的氢氧化镍具有更高的电化...     

Synthesis of nanostructured palladium films on porous α-Al2O3 substrates

The lamellar lyotropic liquid crystalline phases of Brij56 nonionic surfactants were used to template the deposition of nanostructured palladium films on α-Al₂O₃ substrates. The reaction between hydrazine hydrate and Pd²⁺ dissolved within the aqueous domains of the liquid crystalline phase generated the nanostructured palladium. The X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission election microscopy (TEM) studies indicated that the resulting films possessed regular arrays of channels with periodicity of 1 nm, which was obviously smaller than that of the templates. The size mismatch might arise from the discharge of nitrogen during the reaction and the relatively low Pd²⁺ concentrations.     

Solvothermal synthesis of nickel nanorods and its magnetic, structural and surface morphological behavior

One-dimensional rod-like nickel nanostructure was fabricated through a simple, efficient and one pot solvothermal approach with hydrazine hydrate and trimethylamine as reducing and morphology directing agents. The phase structure, morphology and magnetic properties of the as-prepared product were extensively characterized by X-ray diffraction, transmission electron microscopy and superconducting quantum interference device magnetometer. X-ray diffraction pattern indicated that the as-synthesized product was nickel with well-crystallized face-centered cubic structure. TEM observation showed that the nickel product consists of rod-like shape with size around 10 nm. Magnetic measurements revealed that the coercive forces of nickel nanorods at 300 K and 4.2 K are 198 Oe and 250 Oe, respectively. Compared with bulk nickel, the nanorods exhibit significant increase in coercive force as a reflection of shape anisotropy. A possible mechanism for the formation of rod-like nanostructure is proposed.     

New polyethylene nanocomposites prepared by in-situ polymerization method using nickel a-diimine catalyst supported on organo-modified ZnAl layered double hydroxide

New nanocomposites based on polyethylene (PE) and organo-modified ZnAl layered double hydroxide (O-ZnAl-LDH) were prepared by an in-situ polymerization method. The late-transition-metal catalyst, bis(4,4′-methylene-bis-(2,6-diisopropylimino))acenaphthene nickel dibromide complex, was firstly supported on the O-ZnAl-LDH layers and subsequently initiated the polymerization of ethylene. Different from commonly used solution or melt intercalation method, such strategy could induce easily the nanosclae dispersion of the O-ZnAl-LDH layers in the PE matrix, as confirmed by the analyses from X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. From the curves of thermogravimetric analysis (TGA), it was found that the decomposition temperature of the nanocomposite with 12.9 wt% O-ZnAl-LDH could be 60.5 °C higher than that of pure PE when 30% weight loss was selected as a measuring point, showing an improved thermal oxidation stability. From the melt rheological tests, it was found that the resultant PE nanocomposites had obvious increases in the storage modulus and complex viscosity when compared with pure PE, showing an enhanced viscoelastic response.     

Preparation of nanostructured nickel aluminate spinel powder from spent NiO/Al2O3 catalyst by mechano-chemical synthesis

In this paper, the possibility of mechano-chemical synthesis, as a single step process for preparation of nanostructured nickel aluminate spinel powder from NiO/Al₂O₃ spent catalyst was investigated. Powder samples were characterized in terms of composition, morphology, structure, particle size and surface area using complementary techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential thermal analysis (DTA) and volumetric adsorption of nitrogen. It was found that formation of spinel was possible after 60 h of milling with no heat treatment. Additionally, influence of mechanical activation on the heat treatment temperature was discussed. It was observed that heat treatment of 15 h milled sample at 1100 °C is enough to produce nickel aluminate spinel. A product of direct mechanical milling showed higher value of surface area (42.3 m²/g) and smaller crystallite size (12 nm) as compared to the heat treated product.     

A low temperature composite-hydroxide approach to NiO nanocrystals

Nanocrystalline NiO has been successfully synthesized via a low temperature molten composite hydroxide route using nickel chloride hydrate as nickel source. The as-obtained oxide nanocrystals were characterized by X-ray powder diffraction and transmission electronic microscopy. It is found that the ratio of reagent to molten solvent has a great influence on the quality of the products. The effect of temperature and time was also investigated. The present route may have a good prospect to prepare many functional nanomaterials.     

Structure and electrochemical performance of nickel hydroxide synthesized by rapid quench method

Nickel hydroxide with amorphous structure has been synthesized successfully by chemical precipitation method combined with rapid quench technique. The microstructure and morphology of the prepared samples were analyzed by XRD, Raman spectra, IR spectra, and SEM. The electrochemical performance of the sample was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests. The discharge capacity of the amorphous nickel hydroxide is 330.0 mAh g⁻¹ at 0.2C, much higher than that of the theoretical capacity of β-nickel hydroxide (289.0 mAh g⁻¹). Moreover, the amorphous nickel hydroxide exhibits higher electrochemical reaction reversibility, lower electrochemical impedance, and better cyclic stability compared with β-nickel hydroxide.     

Microwave-assisted synthesis of nickel nanoparticles

Nickel nanoparticles with uniform, monomorphic self-assembled flower-like microstructure were synthesized by reduction of nickel chloride with hydrazine hydrate in the presence of polyvinylpyrrolidone (PVP) in ethylene glycol under microwave irradiation. An appropriate amount of Na₂CO₃ was necessary for the formation of monomorphic and uniform Ni nanoflowers. Small amount of NaOH and a higher concentration of hydrazine were beneficial to the formation of Ni nanoflowers with a smaller diameter and a narrower distribution. The transmission electron microscopy (TEM) and X-ray diffraction measurements manifested that the as-synthesized Ni nanoflower was the assembles self-organized by hundreds of smaller primary nanoparticles with an average dimension of about 6.3 nm.     

Large-scale and shape-controlled synthesis and characterization of nanorod-like nickel powders under microwave radiation

The nanorod-like nickel powders were fabricated via hydrothermal liquid phase reduction route under microwave irradiation with hydrazine hydrate as a reducing agent as well as polyvinyl alcohol as a dispersant and/or structure directing agent. The morphology and structure of as-prepared products could be easily tuned by adjusting process parameters such as pH value and microwave irradiation time. The resulting materials were characterized by X-ray diffraction (XRD), scanning electron microscope, transmission electron microscopy and selected-area electron diffraction (SAED). The results demonstrated that pure nickel powders with face-centered cubic (fcc) structure were prepared at relatively mild condition and no characteristic peaks of nickel oxide in the XRD pattern were found. The phenomenon of lattice expansion for Ni powders was explained in details according to the XRD theory. As-prepared Ni sample was of obvious shape anisotropy with length diameter ratio of 5. Magnetic measurements shown that the magnetic properties of nanorod-like (fcc) Ni powders were quite different from those of hexagonal closed-packed (hcp) Ni nanoparticles. Furthermore, it had more strong ferromagnetic properties than that of Ni powders both bulk and nanoparticles.     

Synthesis and magnetic properties of shuriken-like nickel nanoparticles

Shuriken-like nickel nanoparticles were successfully synthesized by a thermal decomposition method at 200 °C with Nickel(II) acetylacetonate (Ni(acac)₂) as the precursor and oleylamine (OAm) as the solvent and reductant, respectively. The phase structures, morphologies and sizes, and magnetic properties of the as-synthesized nickel products were characterized in detail by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer (VSM). Some key reaction parameters, such as the reaction time, reaction temperature and surfactants, have important influence on the morphology of the final products. XRD pattern indicated that the products are well-crystallized face-centered cubic (fcc) nickel phase. SEM images demonstrated that the nickel nanoparticles are shuriken-like morphology with average size around 150 nm. The mechanism of shuriken-like Ni nanoparticles (NPs) is proposed. The magnetic hysteresis loops of shuriken-like and spherical nickel products illustrated the ferromagnetic nature at 300 K, indicating its potential applications in magnetic storage.     

Preparation and electrochemical performance of nano-scale nickel hydroxide with different shapes

Platelet-like, flake-like, and needle-like nano-scale β-Ni(OH)₂ particles were prepared by coordination homogeneous precipitation method in this paper. X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared absorption spectra (IR) were used to characterize the microstructure and morphology of the products. The nano-scale Ni(OH)₂ composite electrodes were prepared by mixing 10 wt.% samples with spherical Ni(OH)₂ to carry out charge-discharge test. The results show that the nano-scale Ni(OH)₂ composite electrodes have higher discharge specific capacity, and the nickel hydroxide nanoneedles show a better adulteration performance than the others.     

Ni 2p X-ray photoelectron spectroscopy study of nanostructured nickel oxide

Herein the detailed analysis of the Ni 2p X-ray photoelectron spectra of nanostructured nickel oxide samples with three different average crystallite sizes is reported. The observed main line broadening and the increase in the relative intensity of the ∼1.5 eV satellite structure are discussed taking into account the large surface to volume ratio, high concentration of Ni²⁺ vacancies and enhancement in the Ni 3d-O 2p hybridization. The influence of these factors on the possible local and non-local screening mechanisms accompanying the photoemission of Ni 2p core level electron is analyzed on the basis of the Ni₇O₃₆ cluster calculations.     

Synthesis of hexagonal close-packed nanocrystalline nickel by a thermal reduction process

Hexagonal close-packed nickel has been synthesized through reduction of nickel chloride by KBH₄ in ethylenediamine at 300 °C. X-ray powder diffraction and selected-area electron diffraction showed that the as-prepared samples were nickel with a hexagonal close-packed structure. Transmission electron microscopy indicated that the products were nanoclusters, which consist of nickel nanoparticles. The magnetic coercivity of the hcp nanocrystalline nickel is as high as 94.3 Oe.     

Structural and electrochemical properties of nanostructured nickel silicides by reduction and silicification of high-surface-area nickel oxide

Nanostructured nickel silicides have been prepared by reduction and silicification of high-surface-area nickel oxide (145 m² g^?1) produced via precipitation. The prepared materials were characterized by nitrogen adsorption, X-ray diffraction, thermal analysis, FT-IR spectroscopy, scanning electron microscopy, transmission electron microscopy, magnetic and electrochemical measurements. The nickel silicide formation involves the following sequence: NiO (cubic) → Ni (cubic) → Ni₂Si (orthorhombic) → NiSi (orthorhombic) → NiSi₂ (cubic), with particles growing from 13.7 to 21.3 nm. The nickel silicides are ferromagnetic at room temperature, and their saturation magnetization values change drastically with the increase of Si content. Nickel silicides have remarkably low electrical resistivity and noble metal-like properties because of a constriction of the Ni d band and an increase of the electronic density of states. The results suggest that such silicides are promising candidates as inexpensive yet functional materials for applications in electrochemistry as well as catalysis.     

Submicrometer-sized hollow nickel spheres synthesized by autocatalytic reduction

A facile method to fabricate submicrometer-sized hollow nickel spheres by autocatalyzing the redox reaction around a sacrificial colloidal particle surface is presented in this paper. The size distribution of these spheres can be controlled by regulating the concentration of the alkali solution. The hollow nickel particles were characterized by field emission scanning electron microscopy, transmission electron microscopy and X-ray powder diffraction. The hollow spheres produced by this process may have potential applications in many fields, including chemistry, biotechnology and materials science.     

Effect of the titanium ion concentration on electrodeposition of nanostructured TiNi films

Electrodeposition of nanostructured titanium–nickel films was performed and the effect of the concentration of the titanium source on the film characteristics was investigated. Scanning electron microscopy indicated circular crystallites on the surface of the electrodeposited titanium–nickel film with a fairly uniform size distribution. XRD studies showed that the electrodeposited TiNi films contained TiNi with a preferred crystallographic orientation of [002]. Surface analysis using X-ray photoelectron spectroscopy (XPS) revealed that the electrodeposited titanium–nickel film contained elemental titanium and nickel, hydroxide of nickel, and oxides of titanium and nickel. As the titanium ion concentration was increased, the titanium content in the film was increased while the deposition rate and crystallite size of the film were decreased. A blue-shift in the UV/Vis peak was also observed with increasing titanium ion concentration.     

Effect of finite size on the magnetization behavior of nanostructured nickel oxide

Nanostructured nickel oxide samples having different average particle sizes are synthesized through a wet chemical route. Room temperature magnetic hysteresis of the samples are recorded using a vibrating sample magnetometer. The magnetic properties of the samples are found to be markedly different from those of single crystalline nickel oxide. The sample with an average particle size of 2-3 nm showed superparamagnetism with magnetization curves defined by the Langevin function. Anomalously large uncompensated magnetic moment associated with this sample is attributed to the multisublattice magnetic structure. Interestingly, samples with larger average particle sizes of 13 and 18 nm exhibited superantiferromagnetism with the magnetization curves varying linearly with applied field and susceptibility values larger than that of bulk nickel oxide. The results highlight the importance of surface atoms and surface driven spin rearrangements in determining the magnetic properties of nanostructured nickel oxide.