Structural modifications induced by the second discharge process in the Ni(OH)2/NiOOH redox system

Electrochemical behavior and related structural modifications of the nickel hydroxide/oxyhydroxide electrode are investigated as a function of the reduction state achieved on discharge. Reduction proceeds at two successive potential steps, with recovering of the initial structural properties only after the second discharge process. Active material cycled in the positive potential range (vs. Hg/HgO), including only the first discharge step, is non-stoichiometric and characterized by high lattice defect content. Whatever the oxidation state, the presence of Ni³⁺ defects and protonic delocalization are observed. The 2nd discharge process restores O-H covalent bonds and a better defined Ni(II) state, similar to the precursor nickel hydroxide chemically obtained. Electrochemical cycling in the positive potential range is characterized by the retention of the same nanocrystallite dimension and a high fragmented morphology, while the 2nd discharge induces crystallite agglomeration. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Hydrothermal growth and characterization of La(OH)3 nanorods and nanocables with Ni(OH)2 coating

La(OH)₃/Ni(OH)₂ nanocables and La(OH)₃ nanorods were synthesized by the reaction of KOH with La(NO₃)₃ and Ni(NO₃)₂ at 180 °C under a hydrothermal conditions. X-ray diffraction, transmission electron microscopy and thermal analyses indicated that the nanocable consists of La(OH)₃ core and Ni(OH)₂ outer shell. The diameters of the La(OH)₃ nanorods range from 20 to 30 nm and the lengths range from 150 to 1000 nm. The thickness of the Ni(OH)₂ coating ranges from 10 to 20 nm. The formation mechanism of the nanocables is discussed.     

Experimental observation of the 1/3 magnetization plateau in the diamond-chain compound Cu3(CO3)2(OH)2

The magnetic susceptibility, high field magnetization, and specific heat measurements of Cu3(CO3)2(OH)2, which is a model substance for the frustrating diamond spin chain model, have been performed using single crystals. Two broad peaks are observed at around 20 and 5 K in both magnetic susceptibility and specific heat results. The magnetization curve has a clear plateau at one third of the saturation magnetization. The experimental results are examined in terms of theoretical expectations based on exact diagonalization and density matrix renormalization group methods. An origin of magnetic anisotropy is also discussed.     

Ni2(OCH3)2/SiO2催化剂上CO2和CH3OH的吸附和反应性能

采用表面改性和离子交换相结合的方法制备了Ni2 (OCH3 ) 2 /SiO2 负载型双核金属甲氧基配合物催化剂 ,利用红外光谱 (IR)、程序升温脱附 (TPD)、程序升温表面反应 (TPSR)和微反技术考察了催化剂的表面结构以及CO2 和CH3 OH的化学吸附和反应性能 .结果表明 :Ni2 (OCH3 ) 2 /SiO2 中Ni2 + 与载体SiO2 表面O2 -以双齿配位形式键合 ,甲氧基以桥基形式联结双金属离子形成双核物种Ni2 (OCH3 ) 2 ;CO2 在催化剂表面存在甲氧碳酸酯基物种和桥式两种吸附态 ,CH3 OH则只有一种分子吸附态 ;在 10 0～ 2 0 0℃条件下 ,CO2 和CH3 OH在催化剂上的反应产物主要是DMC和H2 O ;根据反应结果 ,讨论了催化反应机理 .     

Magneto-orientational properties of ionically stabilized aqueous dispersions of Ni(OH)2 nanoplatelets

Magnetic and orientational behavior of nickel hydroxide nanoplatelets ionically stabilized in a liquid matrix is studied. Under an applied field the platelets orient their faces normal to its direction. For characterization of the individual behavior of dispersed and non-interacting particles three techniques are used: SAXS, SQUID and magneto-optics. Analysis reveals that nickel hydroxide in a platelet phase is paramagnetic with a pronounced anisotropy of the intrinsic susceptibility, the major component of which (in the direction normal to platelet face) exceeds the minor one by about 25%.     

Humidity sensing properties of Ni(OH)2 nanoparticles synthesized via sonochemical method

This work focuses on humidity sensor based Ni(OH)₂ nanoparticles. The sonochemical method was employed to prepare nanoparticles and impedance analysis was used to characterize sensitivity, response, and recovery time of the prepared sensor. The Ni(OH)₂ sensor was found to have high sensitivity and fast response/recovery time to humidity, and its impedance changed approximately two orders of magnitude from about 2.01 MΩ in dry air 20% RH (relative humidity) to 0.0258 MΩ in 90% RH air. Our results demonstrate the potential application of Ni(OH)₂ nanoparticles for fabricating high performance humidity sensors.     

A binder- and carbon-free hydrogen evolution electro-catalyst in alkaline media based on nitrogen-doped Ni(OH)2 nanobelts/3D Ni foam

Journal of Nanoparticle Research - The ground-state magnetic properties of ConPtm binary alloy clusters of size N = n + m ≤?9 are studied systematically as a function of size,...     

Effect of reaction conditions on size and morphology of ultrasonically prepared Ni(OH)(2) powders

Modern electrochemical devices require the morphological control of the active material. In this paper the synthesis of nickel hydroxide, as common active compound of such devices, is presented. The influence of ultrasound in the synthesis of nickel hydroxide from aqueous ammonia complexes is studied showing that ultrasound allows the fabrication of flower-like particles with sizes ranging in between 0.7 and 1.0μm in contrast with the 6-8μm particles obtained in the absence of ultrasound. The influence of gas flow, temperature of the process and surfactants in the ultrasonically prepared powders is discussed in term of shape, size and agglomeration of the particles. Adjusting the experimental condition, spherical or platelet-like particles are obtained with sizes ranging from 1.3μm to 200nm.     

Improved asymmetric electrochemical capacitor using Zn-Co co-doped Ni(OH)2 positive electrode material

The performance of Ni-foam pasted Ni(OH)₂ prepared from co-precipitated Ni(OH)₂ with Zinc (Zn) and Cobalt (Co) as the positive electrode active material of an asymmetric electrochemical capacitor (EC) is studied for the enhancement of the capacitor’s specific energy and power densities. A co-precipitated Ni(OH)₂/activated carbon (AC) composite material and AC were used as a positive and negative electrode material. The AC in the positive electrode is used as an electrolyte reservoir to reduce ionic diffusion resistance regardless of charge/discharge current density. In addition, the simultaneous presence of Zn and Co ions in the Ni(OH)₂ layer improves the efficiency of the active material and reduces the resistance of the unit cell. It was observed that through the effects of the additives in the positive electrode, the asymmetric EC exhibits a high energy density with 35.7 Wh/kg, based on the active material. Furthermore, the energy density decreasing behavior at a high discharge current density was retarded. PACS 81.20.Ev; 73.40.Mr; 66.30.Pa; 66.30.Dn     

Synthesis and Characterization of Nano-sized Zn(OH)2 and Zn(OH)2/PVA Nano-composite

Nano-sized Zn(OH)₂ was synthesized by the co-precipitation method. Further, the structure and properties were tested with FTIR, UV-visible spectroscopy, XRD and TGA as analytical tools. The structural morphology and size of the Zn(OH)₂ synthesized by the co-precipitation method were determined by using FESEM and HRTEM techniques. The effect of the synthesized nano-sized Zn(OH)₂ on the structural and thermal properties of PVA matrix was tested and discussed.     

Preparation,characterization, and electrochemical performances of graphene/Ni(OH)2 hybrid nanomaterials

We report a class of core–shell nanomaterials that can be used as efficient surface-enhancement Raman scattering (SERS) substrates. The core consists of silver nanowires, prepared through a chemical reduction process, that are used to capture 4-mercaptobenzoic acid (4-MBA), a model analyte. The shell was prepared through a modified Stöber method and consists of patchy or full silica coats. The formation of silica coats was monitored via transmission electron microscopy, UV–visible spectroscopy, and phase-analysis light-scattering for measuring effective surface charge. Surprisingly, the patchy silica-coated silver nanowires are better SERS substrate than silver nanowires; nanomolar concentration of 4-MBA can be detected. In addition, “nano-matryoshka” configurations were used to quantitate/explore the effect of the electromagnetic field at the tips of the nanowire (“hot spots”) in the Raman scattering experiment.     

Kinetics of Ni2Si growth from pure Ni and Ni(V) films on (111) and (100) Si

The kinetics of Ni₂Si growth from pure Ni and from Ni_0.93V_0.07 films on (111) and (100) silicon has been studied by the combination of He⁺ backscattering, x-ray diffraction, Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) techniques. The activation energies are 1.5 and 1.0 eV for pure Ni and Ni(V) films, respectively while the pre-exponential factors in Ni(V) are 4–5 orders of magnitude smaller than in the pure Ni case. The variations in the measured rates are related to the different grain size of the growing suicide layers. The vanadium is rejected from the silicide layer and piles up at the metalsilicide interface.     

Hydrothermal Synthesis at High Pressure and Temperature of the Mg 7.5 Ni 6 H 3 (AsO 4 ) 8 (OH) 6 and Mg 8 Ni 4 H 6 (PO 4 ) 8 (OH) 6 Compounds

The Mg 7.5 Ni 6 H 3 (AsO 4 ) 8 (OH) 6 and Mg 8 Ni 4 H 6 (PO 4 ) 8 (OH) 6 compounds have been synthesized by using hydrothermal techniques at high pressure and temperature. The crystal structure of the arsenate phase has been refined with the Rietveld method. The compounds are isostructural. The structure consists of a three-dimensional framework in which the presence of triangular and hexagonal channels is observed. Reflectance diffuse measurements confirm the hexacoordination of the Ni(II) ions in both compounds. The magnetic behaviour indicates the presence of antiferromagnetic interactions between the Ni(II) ions placed in the double chains.     

喷嘴-平板直流电晕放电中的OH(A2S+→X2P, 0-0)光谱研究

 为更深入地认识电晕放电低温等离子体中自由基的生成机理，以发射光谱测量为基础并结合背景气体淬灭率影响，研究了常压下喷嘴-平板电晕自由基簇射过程中放电参数、背景气体、电极气成分等因素对OH(A²S⁺→X²p, 0-0)发光的影响。结果表明：在放电参数影响中，放电电压及放电电流都会影响OH生成量，OH发光随功率增加而大大增强；在加湿氮气直流电晕放电中有明显的OH(A²S⁺→X²p, 0-0)光谱存在，但加湿空气条件下OH生成较少；载气增湿后OH生成量明显增多，而Ar和O­2的存在分别增强和减弱了OH(A²S⁺→X²p, 0-0)发光，可能的原因是这两种物质影响了放电和OH(A²S⁺)的淬灭。     

Barriers to internal rotation and tunnelling splittings of the torsional states in the HO(CH2)OH,DO(CH2)OH and DO(CH2)OD molecules

Torsional states caused by vibrations of hydroxyl groups in the methanediol molecule and its two deuterated analogues – DO(CH₂)OH and DO(CH₂)OD were analysed at MP2/cc-pVTZ and CCSD(T)/cc-pVQZ levels of theory. In the first case, 2D PES and 2D surfaces of kinematic coefficients were calculated with geometry optimisation for all other geometric parameters, and in the second case, only the energy of optimised configurations at the MP2/cc-pVTZ level of theory was determined. Then 2D PES was recounted to the complete basis set (CBS) limit by extrapolating the results of calculations at the MP2/cc-pVTZ and MP2/cc-pVQZ levels of theory The calculated values were then averaged over four equivalent points on the coordinate plane. Hamiltonian matrices were constructed using DVR and Fourier methods. After their subsequent diagonalization, the energies of the stationary torsional states were computed. Their classification by C_2V(M) and C_S(M) molecular symmetry groups has been performed. The splitting values due to the tunnelling of the thirty most deeply located torsional states in the three studied molecules were also determined. The torsional states, internal rotation barriers, and tunnelling frequencies in the molecules of methanediol and hydrogen trioxide were compared.     

Resistometric and X-ray investigation of (Ni2Cu)1−x Sn x alloys

Resistometric measurements have revealed the approximate position of the solvus line in the isopleth phase diagram of (Ni₂Cu)_1–x Sn _x alloys for Sn content between 0 and 14 at.% and temperatures between 600 and 900°C. The data were analyzed on the ground of a model which takes into account their dynamic character. Within the two-phase region they indicate the existence of two different phase-states of the system. Control X-ray measurements have shown that in the high temperature region above approx. 700°C the second phase is of theDO ₃ structure. Our results are in variance with published data.These measurements were kindly supported by the Czech Grant Agency under Contract Nr. 106/93/513. The help of Mrs. A. Svobodová during the preparation and evaluation of X-ray measurements is gratefully acknowledged.