Nickel hydroxide modeling

First of all let us consider the morphological structure of an agglomerate electrode [6] by way of example of the model shown in Figure 1. This schematic represents a multiphase system with no fixed connection between its components. As a rule, the active mass of an electrode is a mixture of Nickel hydroxide (oxyhydroxide) with conductive carbon or a metal, which are well dispersed mechanically in the matrix. 

The authors mentioned, that the dissolution of nickel hydroxide in alkaline solutions up to 15 M NaOH was so slight that only estimates of its solubility could be made. When the reported experimental data were re-evaluated it became evident that, at best, only one constant,, 3, can be determined. The solubility of Ni(OH)2(cr) increases with increasing NaOH molality, but the solubility curve flattens out at [OH ] > 1 m. This may be due to ion-ion interactions at the high ionic strengths, but there is no evidence whatever for formation of Ni(OH)4". Equation (A.7) can be fit reasonably to the data at lower NaOH molalities. When the SIT model is applied ... 

The redox reaction of nickel hydroxide and nickel oxide hydroxide, the electrochemi-cally active compounds at the positive electrode of a nickel battery, was investigated. The thermodynamics of non-ideal solid solutions were applied to the reversible potential as a function of the state-of-discharge. In a temperature range 5 to 55°C two parameter activity coefficient models perform significantly better than one parameter models. 

The cathode of a modem Ni-Cd battery consists of controlled particle size spherical NiO(OH)2 particles, mixed with a conductive additive (Zn or acetylene black) and binder and pressed onto a Ni-foam current collector. Nickel hydroxide cathode kinetics is determined by a sohd state proton insertion reaction (Huggins et al. [1994]). Its impedance can therefore be treated as that of intercalation material, e.g. considering H+ diffusion toward the center of sohd-state particles and specific conductivity of the porous material itself. The porous nature of the electrode can be accounted for by using the transmission line model (D.D. Macdonald et al. [1990]). The equivalent circuit considering both diffusion within particles and layer porosity is given in Figure 4.5.9. Using the diffusion equations derived for spherical boundary conditions, as in Eq. (30), appears most appropriate. 

M. Sinha, A Mathematical Model for the Porous Nickel Hydroxide Electrode. Ph.D. Dissertation, University of California, Los Angeles, 1982. 

Figlarz and his co-workers have suggested that the formula Ni(OH)2 nHzO is not the correct one for a - Ni(OH)2 [46, 47]. They studied -Ni(OH)2 materials made by precipitation of the hydroxide by the addition of NH4OH to solutions of various nickel salts. In addition to Ni(N03)2 and NiC03 they used nickel salts with carboxylic anions of various sizes. They found that the interlaminar distance in the a - Ni(OH)2 depended on the nickel salt anion size. For instance, when the nickel adipate was used the interlaminar distance was 13.2A. Infrared studies of a - Ni(OH)2 precipitated from Ni(N03)2 indicated that NO, was incorporated into the hydroxide and was bonded to Ni. They suggested a model based on hydroxide vacancies and proposed a formula Ni(OH)2 tA, B, H20... 

In 1899, the nickel-cadmium battery, the first alkaline battery, was invented by a Swedish scientist named Waldmar Jungner. The special feature of this battery was its potential to be recharged. In construction, nickel and cadmium electrodes in a potassium hydroxide solution, it was the first battery to use an alkaline electrolyte. This battery was commercialized in Sweden in 1910 and reached the Unites States in 1946. The first models were robust and had significantly better energy density than lead-acid batteries, but nevertheless, their wide use was limited because of the high costs. 

Using the ethanethiol system as a model, we investigated the dependence of the oxidation rate on the concentration of thiol, of oxygen, and of hydroxide ion. The results for the copper- (10"5M), cobalt-(10"3M), and nickel- (10 3M) catalyzed oxidations, together with the comparable system in the absence of added catalysts are recorded in Table V. 

From a study of the enzyme kinetics with a range of substrates and inhibitors, and the chemistry of related metal-ion complexes, Dixon et al. [39] proposed a model of the environment of the active site and reaction cycle. Although differing in details from the structure as now determined, this mechanism provided a basis for understanding the functions of the two metal ions. One nickel ion (Ni-1) binds the urea, and the other nickel ion (Ni-2) binds a hydroxide ion that makes a nucleophilic attack on the urea, leading to the formation of a tetrahedral intermediate. 

Numerous dinickel complexes have been reported as models for urease. As depicted in Scheme 5, a dinickel complex [Ni2( 4-0H)( j,-H20)(bdptz)(H20)2][0Ts]3 is capable of hydrolyzing a bound amide substrate by intramolecular nucleophilic attack of a coordinated hydroxide ion, either from a bridging position or from a transient terminally bound form. This amide hydrolysis mimics the hydrolysis of urea by urease in that a hydroxide nucleophile is generated by the dinickel center, and the coordination of the substrate to the dinickel center as well as a nickel-bound hydroxide ion serving as the nucleophile are crucial to hydrolysis. Protonation of the amine group by an acidic residue in the active-site results in loss of ammonia. 

Raney-type nickel catalysts are typically prepared by leaching aluminium from a Ni-Al alloy using a concentrated sodium hydroxide solution [1-3], This process of activation critically affects the structure and properties of Raney-type nickel catalysts. The initial structure and composition of the starting alloy also influence the performance of the final catalyst [4-7], In this paper, numerical modelling is compared to experimental measurements in an attempt to simulate both the 3D morphology of as-leached Raney-Ni catalyst material and investigate the nature of the exposed catalyst surfaces. 

Hessami and Tobias [70] extended the mechanisms of Bockris et al. and Matulis etal. of the deposition of single metals (Ni, Fe) to the mathematical modeling of codeposition of Ni—Fe alloys. This mathematical model for the anomalous alloy deposition describes the electrode processes using the calculated interfacial concentrations. The inhibition (reduction) of nickel partial current density during alloy deposition and the anomalous deposition are explained on the basis of the relative concentrations of metal-hydroxide ions, [MOH]+. Calculations show that the [FeOH]+ concentrations are higher than [NiOH]+ because it has a much smaller dissociation constant ([MOH]+ = (M2+)(OH )/A surface sites, and the result of this competition is inhibition (decrease) in Ni deposition in the presence of [FeOH]+ ions. Figure 30... 

In terms of kinetics and mechanisms, electroless deposition processes have many similarities. In an attempt to analyze the electroless deposition, several mechanisms such as atomic hydrogen, hydride ion, metal hydroxide, electrochemical, and universal have been proposed.1-3 It is important to note that these mechanisms were developed for cases of nickel and copper electroless deposition, which were the most widely studied metals in this respect. Based on the proposed mechanisms, most of the features of electroless deposition can be explained. However, there are some characteristics of electroless deposition, which cannot be explained using these mechanisms. The major problems arise when attempting to generalize the proposed models explaining the mechanistic aspects. 

Procedure Gradually add, in portions, ammonia solution to the green-colored nickel chloride solution until the color turns violet. Show and compare a 3D-model for the octahedron structure of the hexa ammine complex. Slowly add sodium hydroxide solution (drop by drop) into the violet-colored solution, for comparison also to the green-colored nickel chloride solution. 

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