Suppression of the alpha -> beta-nickel hydroxide transformation in concentrated alkali: Role of dissolved cations

The presence of dissolved cations such as Al and Zn in alkaline electrolyte (6 M KOH) suppresses the alpha --> beta-nickel hydroxide transformation. The uptake of Al (10 mol%) and Zn (30 mol%) exhibited by the active material likely stabilizes the alpha-phase. Dissolved Al is deleterious to the performance of the nickel hydroxide electrode, whereas, dissolved Zn enhances the specific discharge capacity of nickel hydroxide by approximately 25% showing that the mode of metal uptake is different in the two cases

Nickel hydroxide electrodeposition from nickel nitrate solutions: Mechanistic studies

Nickel hydroxide electrodeposition by cathodic reduction of nitrate ions follows an electrochemical (EC) reaction followed by an irreversible chemical reaction mechanism. On subsequent cycling, the electrodeposited nickel hydroxide undergoes a reversible redox reaction. The mechanistic behavior of the nickel hydroxide electrodeposition from nickel nitrate solutions is investigated

Layered double hydroxides of Ni with Cr and Mn as candidate electrode materials for alkaline secondary cells

The use of layered double hydroxides (LDH) of Ni with Cr and Mn as electrode materials for alkaline secondary cells was studied. The presence of Cr and Mn suppresses β-nickel hydroxide formation which indicates their strong influence on the precipitation behavior of Ni2+. It is found that the LDH of Ni with Cr and Mn are electrochemically active and deliver capacities of 500 (Ni-Cr), 400 (Ni-Mn, x = 0.2) and 430 (Ni-Mn, x = 0.1) mAhg-1 of Ni respectively

Effect of lightweight supports on specific discharge capacity of β-nickel hydroxide

While the performance of βbc (bc: badly crystalline)-nickel hydroxide is relatively unaffected by the use of different lightweight supports, the specific discharge capacity of crystalline β-Ni(OH)2 doubles to approximately 355 mAh g–1 Ni (theoretical, 456 mAh g−1) when pasted to a fibre support compared with 170 mAh g–1 Ni when pasted to a nickel foam. Consequently, the fibre is a superior support as it is unaffected by the quality of the active material and extracts a consistently high performance irrespective of the degree of crystallinity, moisture content, morphology and composition of the active material. Electrochemical impedance measurements indicate that a lower charge-transfer resistance at low states-of-charge is responsible for the superior performance of fibre supported β-Ni(OH)2 electrodes

Electrochemically Impregnated Aluminum-Stabilized α-Nickel Hydroxide Electrodes

Nickel-positive electrodes obtained by electrochemical impregnation of aluminum-substituted α-nickel hydroxide are found to deliver a reversible discharge capacity of ca. 450 mAh/g. This is much higher than the capacity of β-nickel hydroxide electrodes 200 mAh/g: this work; 225 mAh/g: Dixit et al., J. Power Sources, 63, 167 (1996) prepared under identical conditions and pasted electrodes comprising cobalt-doped nickel hydroxide 345 mAh/g: Faure et al., J. Power Sources, 36, 497 (1991). These observations suggest that the theoretical target-capacity for high-performance nickel-positive electrodes must be revised from the currently accepted value of 289 mAh/g (1e exchange) to 491 mAh/g 1.7e exchange: Corrigan and Knight, J. Electrochem. Soc., 136, 613 (1989). © 1999 The Electrochemical Society. S1099-0062(98)08-044-4. All rights reserved

Electrochemical synthesis of α-cobalt hydroxide

Cathodic reduction of an aqueous solution of cobalt nitrate at low pH, high Co(II) ion concentration (â 1 M) and low current densities (< 0.3 mA cm-2) leads to the formation of a novel layered hydroxide of Co(II) with an interlayer spacing of 8.93 à . This hydroxy deficient phase is structurally and compositionally related to α-nickel hydroxide, but likely contains Co(II) ions in a mixed octahedral/tetrahedral coordination. Under other deposition conditions, the better known β-cobalt hydroxide (a= 3.17±0.01 à , c = 4.61 ± 0.02 à ) is obtained

Modified nickel hydroxide electrodes: Effect of cobalt metal on the different polymorphic modifications

Inclusion of Co metal as an additive during the preparation of pasted electrodes enhances the reversible discharge capacity of β-nickel hydroxide from 220 mAh g-1 of Ni to 400 mAh g-1 (theoretical, 456 mAh g-1 Ni). In contrast, the performance of βbc (bc badly crystalline) and α-nickel hydroxide is relatively unaffected by addition of Co. In electrodes comprising the crystalline-layered double hydroxide of Ni with Al, Co addition not only results in enhancement of the capacity from 375 to 585 mAh g-1 but also increases capacity retention

Suppression of the α → β-nickel hydroxide transformation in concentrated alkali: Role of dissolved cations

The presence of dissolved cations such as Al and Zn in alkaline electrolyte (6 M KOH) suppresses the α → β-nickel hydroxide transformation. The uptake of Al (10 mol%) and Zn (30 mol%) exhibited by the active material likely stabilizes the α-phase. Dissolved Al is deleterious to the performance of the nickel hydroxide electrode, whereas, dissolved Zn enhances the specific discharge capacity of nickel hydroxide by approximately 25% showing that the mode of metal uptake is different in the two cases

Factors governing the electrochemical synthesis of α-nickel (II) hydroxide

The electrodeposition of α-nickel hydroxide is promoted by the simultaneous chemical corrosion of the electrode by an acidic nitrate bath. Chemical corrosion results in the formation of a poorly ordered layered phase which is structurally similar to α-nickel hydroxide and provides nucleation sites for the deposition of the latter. Therefore under conditions which enhance corrosion rates such as low current density (<1.3 mA cm-2), high temperature (60 °C), high nickel nitrate concentration (â1 M) and the resultant low pH (approximately 1.7), α-nickel hydroxide electrodeposition is observed, while β-nickel hydroxide forms under other conditions. Further, α-nickel hydroxide deposition is more facile on an iron electrode compared to nickel or platinum