Nickel Hydroxide Samples Research Articles

Evaluation of the effects of oxygen evolution on the capacity and cycle life of nickel hydroxide electrode materials

The effect of charge–discharge cycling on the capacity of surface-adhered nickel hydroxide (Ni(OH) 2) micro-particles is investigated in aqueous KOH by cyclic voltammetry, and compared with that for pasted nickel hydroxide electrodes. Cyclic voltammetry on adhered Ni(OH) 2 micro-particles enables rapid screening of four types of commercially available, battery-grade, nickel hydroxide samples and allows the separation of the oxidation process from the oxygen evolution reaction. With large pasted electrodes, due to their high uncompensated resistance ( R u), these processes are poorly resolved. Pasted β-nickel hydroxide electrodes with a specific capacity of between 190 and 210 mAh g −1 are charged and discharged at constant currents greater than 15 C (18 mA cm −2). With no voltage limit in the charging profile, excess oxygen evolution occurs and capacity fading is observed within the first 50 cycles. Loss of capacity is attributed to the degradation of the electrode due to excess oxygen evolution at switching potentials greater than 0.55 V versus Hg/HgO (1 M KOH). X-ray diffraction (XRD) measurements confirm the formation of γ-NiOOH in these electrodes. Limiting the cell voltage to 1.5 V, and thereby minimizing oxygen evolution, results in no observed capacity loss within 100 cycles, and only β-Ni(OH) 2 can be detected by XRD phase analysis.

Classification of stacking faults and their stepwise elimination during the disorder → order transformation of nickel hydroxide

Nickel hydroxide samples obtained by strong alkali precipitation are replete with stacking faults. The local structures of the stacking faults resemble the stacking patterns of different polytypic modifications that are theoretically possible among the layered hydroxides. This resemblance becomes a basis for the classification of stacking faults into different types. Each type of stacking fault produces a characteristic non-uniform broadening of peaks in the X-ray powder diffraction pattern of nickel hydroxide. DIFFaX simulations aid the classification and quantification of stacking faults. Hydrothermal treatment of a poorly ordered nickel hydroxide slurry at different temperatures (338-473 K) and different durations (5-48 h) shows that the stacking faults are removed in a stepwise manner. The as-precipitated sample has 17-20% stacking faults of the 3R(2) variety, which evolve into the 2H(2) type at 413 K. The 2H(2) stacking faults persist up to 443 K. The stacking faults are completely removed only at 473 K. At this temperature an ordered beta-Ni(OH)(2) phase is observed.

고등학교 화학 교과서의 ‘용액’ 단원에 대한 입자 수준의 컴퓨터 보조 수업자료 개발 및 적용 효과 분석

Alpha Nickel hydroxide samples have been synthesized by electrodeposition on platinum and nickel substrates at current densities of 1, 5, 6, 7 and 10 mAcm？2 at a controlled temperature of 30.00 oC from Ni(NO3)2 bath. Platinum substrate shows a tendency to incorporate less nitrate ions with increase in current density thus producing less hydroxy-deficient nickel hydroxide layers. On the whole the interlayer distance (d003) is found to be inversely proportional to the amount of nitrate ions incorporated in-between the lattice. For the first time we have observed a decrease in lattice spacing with increase in concentration of intercalant (anions) and the reason for lattice contraction is attributed to the columbic attractive forces exerted by the oppositely charged nitrate ion and positively charged slabs. The Infrared spectra of the samples with expanded interlayers show two types of OH vibrations corresponding to hydrogen bonded and non-hydrogen bonded OH groups whereas the contracted interlayers show only hydrogen-boded OH groups. Although the faradaic efficiency is found to increase with increase in applied current there is a local minimum at 6.0 mAcm？2 current density on both platinum and nickel substrates. In this manuscript, GC-MS data is provided which clearly demonstrates the electrodeposited nickel hydroxide sample to consist of huge amount of carbonate ions although the electrolyte solution in nickel nitrate.

New insights on the microstructural characterisation of nickel hydroxides and correlation with electrochemical properties

Two sets of laboratory-prepared and industrial nickel hydroxide samples were studied and their microstructure characterized by performing Rietveld refinements with a spherical harmonic-implemented algorithm using both neutron and X-ray powder diffraction data. The results indicate that the anisotropic line broadening present in their patterns is mainly related to the anisotropy in size, as β-Ni(OH)2 exhibits a platelet shape. Indeed, the determined crystallite sizes are fully consistent with mean particle diameters measured by TEM. The relative degree of stacking faults was estimated from the extent of shifts in reflections 10l where l ≠ 0 and found to be larger for samples with smaller particle/crystallite sizes. This approach, involving independent assessment of the crystallite size and the relative amount of stacking faults, allowed us to confirm that samples with small crystallite size are those exhibiting significant amounts of stacking faults. The results of the electrochemical tests on both sets of samples indicate that the particle/crystallite size is the primary factor determining the electrochemical yield and that the gradual appearance of stacking faults with decreasing size creates a synergic effect in the increase of capacity. Thus, there exists a threshold size of approximately 350 A in diameter and 100 A in thickness below which the degree of faulting is clearly correlated to the electrochemical capacity values achieved.

Microstructural analysis of nickel hydroxide: Anisotropic size versus stacking faults

Two different approaches for studying sample’s contributions to diffraction-line broadening are analyzed by applying them to several nickel hydroxide samples. Both are based in the refinement of powder diffraction data but differ in the microstructural model used. The first one consists in the refinement of the powder diffraction pattern using theFAULTSprogram, a modification ofDIFFaX, which assigns peak broadening mainly to the presence of stacking faults and treats finite size effects by convolution with a Voigt function. The second method makes use of the programFULLPROF, which allows the use of linear combinations of spherical harmonics to model peak broadening coming from anisotropic size effects. The complementary use of transmission electron microscopy has allowed us to evaluate the best approach for the Ni(OH)2case. In addition, peak shifts, corresponding to reflections 10l(l≠0) were observed in defective nickel hydroxide samples that can be directly correlated with the degree of faulting.

Synthesis of nickel hydroxide: Effect of precipitation conditions on phase selectivity and structural disorder

The synthesis of nickel hydroxide by precipitation from a suitable solution containing dissolved Ni 2+ ions is described. A large matrix of precipitation conditions is explored to generate a wide range of nickel hydroxide samples. While most precipitation reactions result in the formation of β-nickel hydroxide, the samples differ from one another in the degree of structural disorder as reflected by the differences in their powder X-ray diffraction (PXRD) patterns. A correlation of the long-range structure as deduced from diffraction studies with the short-range structure as deduced from infrared (IR) spectral studies is performed. The aim is to control the synthesis conditions to obtain materials with ‘tailor-made’ structural disorders.

Nickel hydroxide ageing time influence on its solubility in water acidified with sulphuric acid

Nickel hydroxide samples freshly settled as well as stored over 1 month, 2 months and 6.5 years were examined for their solubility rate in diluted H 2SO 4 solutions of pH 1.9 and 2.8 as a function of time. Samples with a longer ageing history dissolved less readily than freshly settled ones. It was determined that the resistance to dissolving rose with sample ageing time and the solubility of the 6.5 years stored sample was particularly low. X-ray examination evidenced that during storage the crystallinity of Ni(OH) 2 subsequently rose. The parallelity of both time-dependent phenomena allows the conclusion that with nickel hydroxide ageing the transformation of disordered nickel hydroxide species into crystalline Ni(OH) 2 (without phase changes) is responsible for increasing nickel hydroxide resistance to dissolving in acidic solutions. Such decrease of nickel hydroxide solubility with ageing in case of waste nickel hydroxide, is worth to notice in a view of environment protection against pollution with electroplating waste.

Effect of preparation parameters on electrolytic behaviour of turbostratic nickel hydroxide

Turbostratic nickel hydroxide samples were prepared by neutralising nickel sulphate solution with urea. Initial nickel concentration and urea to nickel ratio were the two parameters changed for studying their effect on physico-chemical and electrolytic properties of nickel hydroxide. Depending on the preparation conditions the electrolytically active component of nickel hydroxide varied between 63 and 91% with respect to the theoretical value of 456 mAh/g Ni. The variation in discharge capacity has been explained in terms of degree of hydration, intercalated anions and nature of phases present under various experimental conditions. The turbostratic nickel hydroxide obtained from a dilute solution (0.085 M), having a poorly crystalline nature and fine particles of nearly spherical nature with <5 μm diameter, exhibited a maximum discharge capacity of 415 mAh/g Ni.

Morphology and electrochemical performance of nano-scale nickel hydroxide prepared by supersonic coordination–precipitation method

Nano-phase nickel hydroxide samples were prepared by a method combining supersonic and coordination–precipitation methods. The samples exhibit β-phase Ni(OH)2 through X-ray diffraction analysis. It is shown that the grain size with the irregular grain shape is about 40 nm and ranges from 20 to 50 nm through transmission electron microscopy. Clustering phenomena were observed. The positive electrode discharge test made of a mixture of micrometer sized spherical Ni(OH)2 and nano-phase Ni(OH)2 was carried out. The results showed that the capacity of the electrode can be increased by about 14% when the nano-phase Ni(OH)2 doped concentration is 8 wt%. X-ray photoelectron spectroscopy analysis indicates that nano-phase Ni(OH)2 can increase the transformation between Ni3+ and Ni2+ in the charge–discharge cycle when the nano-phase Ni(OH)2 is doped, and as a result the utilization of active material on the positive electrode is improved.

Effect of precipitating agents on the physicochemical and electrolytic characteristics of nickel hydroxide

Nickel hydroxide samples were prepared from nickel sulphate solution using three different precipitating agents, namely urea, sodium hydroxide and ammonia under identical preparation conditions. Depending on the nature of precipitating agent, Ni content of the precipitates varied between 44.5% and 53.6%. From the XRD patterns, it was observed that urea produces poorly crystalline nickel hydroxide with only a few broad peaks corresponding to α-form. The presence of this phase was confirmed from the FTIR spectrum. β-Nickel hydroxide was obtained using sodium hydroxide or ammonia as the precipitating agent. The initial discharge potentials of 420, 436 and 441 mV with discharge capacities of 415, 374 and 335 mA h/g of nickel were obtained from the products obtained using urea, sodium hydroxide and ammonia, respectively. The study showed that the product obtained by using urea is of best quality with respect to its electrolytic property. However, this product was lowest in percentage of nickel (44.5%) and exhibited maximum weight loss (37.9%) at 800 °C, which is found to be due to a combination of water of hydration and intercalation of anions. The study on the effect of precipitation parameters such as initial nickel salt concentration and ageing time (urea as the precipitating agent) showed that the discharge capacity decreases with the increase in initial nickel concentration or on ageing the samples at ambient temperature. The nickel content during these variations was ∼42%.

Nickel immobilization in ceramic matrix admixed with waste nickel hydroxide

WAXS examinations performed with nickel hydroxide samples heated to various temperatures showed that freshly settled wet nickel hydroxide sample contains some amount of crystalline β-Ni(OH) 2 structure and its share increased when sample was dried during 3 weeks at ambient temperature. However, the share significantly decreased when the sample was dried at 110 °C and more so at 250 °C. Crystalline phase traces of Ni(OH) 2 disappeared after sample burning at 980 °C and instead the distinct presence of crystalline NiO was determined. The above samples were examined for solubility in stoichiometric amount of sulphuric acid diluted with water to pH 1.9 and 2.8. Solubility was determined by measuring nickel ion concentration in leachate by the AAS method. The dissolving rate was found to decrease with the rise of temperature to which the nickel hydroxide samples were heated. The solubility of Ni(OH) 2 sample burnt at 980 °C was undetectable during 90 h solubility-testing time likely due to its transformation into sparingly soluble crystalline NiO. The latter is considered to be the reason for effective immobilization of waste nickel hydroxide in ceramic prepared by blending with clay and sintering at 980 °C.

X-ray diffraction and micro-Raman spectroscopy analysis of new nickel hydroxide obtained by electrodialysis

Industrial nickel hydroxide samples produced by electrodialysis have been characterized both by X-ray diffraction (XRD) and by micro-Raman spectroscopy. A comparison with some commercial products of β-type Ni(OH) 2 is made. Aged in KOH solution, these nickel hydroxides are transformed to the β-Ni(OH) 2 phase and undergo Ostwald ripening, leading to crystallite sizes ranging between 260 and 380 Å with a reduction in defects. The anisotropic broadening of the XRD peaks in the β-Ni(OH) 2 pattern is interpreted in terms of crystalline lattice micro-strains and crystallite size. For the first time, Rietveld refinement has been performed on industrial Ni(OH) 2. The results indicate that the micro-strain effects increase the peak width according to the sequence of families ( hk0)→(00 l)→( h0 l). This study shows that the presence of proton vacancies leads to a lower degree of distortion in the crystalline lattice than does the presence of stacking faults or the adsorption of inorganic species at the border of the crystallites. A very high concentration of point defects inducing strong distortions in the crystal lattice is correlated with the presence of high energy Ni–O bond vibrations in the Raman spectra, with a frequency shift towards unusually high values.

The Structure of Ni ( OH ) 2: From the Ideal Material to the Electrochemically Active One

A structural model is proposed to explain the abnormal broadening of the (10ℓ) and (20ℓ) lines in the X‐ray diffraction pattern of nickel hydroxide. This model, based on a hypothesis of the presence of stacking faults, allows us to rationalize the empirically established relationship between the presence of such peculiarities in X‐ray diffraction patterns and the good electrochemical behavior of the material. Two types of stacking faults, i.e., growth and deformation faults, corresponding to the existence within the hexagonal oxygen packing of one or two face‐centered cubic oxygen sequences, respectively, have been identified. The simulation, with the DIFFaX program, of the X‐ray diffraction patterns of nickel hydroxide samples has allowed us to determine in a general way the nature and the amount of stacking faults. It is shown that the stability of protons in tetrahedral sites depends on whether they are in the vicinity of a stacking fault or not, and this explains the improvement of both the chargeability of the material and its electronic conductivity in the presence of defects. It is shown as well that stacking faults in the electrochemically active material lead to a more facile transition to the γ phase during overcharge in concentrated electrolyte. © 1999 The Electrochemical Society. All rights reserved.

Electrochemical and Raman Studies of Beta‐Type Nickel Hydroxides Ni1 − xCox ( OH ) 2 Electrode Materials

A large variety of pure and cobalt‐substituted nickel hydroxides of well‐controlled chemical composition, particle size, and morphology have been prepared and characterized by x‐ray, transmission electron microscopy, electrochemical, and Raman spectrometry studies. The hydroxide particle size and its Co‐substituted content were found to govern the Ni‐electrode capacity. Once these parameters were controlled, β‐nickel hydroxide specimens able to reversibly exchange more than one electron per metal atom (Ni + Co) were routinely prepared. Raman spectra consists of five lines. The intensities of the ones located at 3605 and were found to change as a function of the particle size and the Co content. Indeed, the line at , ascribed to adsorbed water, appears and grows when the particle size decreases (e.g., when the surface/volume ratio increases), while the line located at is enhanced by the presence of coprecipitated cobalt. A direct correlation between the intensity of the Raman line and the electrochemical capacity of the nickel hydroxide sample is found. Raman spectroscopy can then be used as a powerful nondestructive tool to differentiate “high capacity” from low capacity nickel hydroxide samples.

Effect of cobalt addition to nickel hydroxide as a positive material for rechargeable alkaline batteries

Nickel hydroxide powder is used widely as an active material in pasted-type nickel electrodes. The effect on the electrochemical behaviour of cobalt addition (0.19–9.9 wt.%) to the nickel hydroxide powder is investigated. The physical properties of several nickel hydroxide powders containing different amounts of cobalt compound are examined by inductively coupled spectroscopy, laser diffraction, BET, X-ray diffraction and scanning electron microscopy measurements. The interlayer distance of the layered nickel hydroxide diminishes to a small value with increase in cobalt content. Moreover, the charge and discharge potentials of nickel hydroxide samples decrease with an increase in cobalt content. The chemical diffusion coefficients of the proton (D̄) in the nickel hydroxide samples with different amounts of cobalt are measured by a current-pulse relaxation technique. The D̄ and D 0 values increase with an increase in cobalt content, and the activation energy for proton diffusion is in the 0.20–0.33 eV range.

New apparatus for the measurement of the self-discharge of the nickel hydroxide electrode

In this report a new method of measurement and equipment [1, 2] are described, that allow easy determination of the activation energy value of the self-decomposition process of the charged Ni(OH) 2/NiOOH electrode. A theoretical description of the method is given and its experimental practicability is demonstrated in addition to preliminary results obtained on differently doped nickel hydroxide samples.