Precipitation Of Nickel Hydroxide Research Articles

Model of nickel electrodeposition from acidic medium

A step-wise computer model is presented for simultaneous deposition of nickel and nickel hydroxide in aqueous solutions. In acidic solutions ({pH} 1), the potentiostatic current-time transient response on glassy carbon or titanium was analysed with respect to nucleation and radial growth mechanism. pH changes influence the current-time response greatly. A marked maximum in the current transient appears for slightly acidic solutions ({pH} 4.5) and a consecutive decrease in the deposition current density at long times is obtained. This behaviour is attributed to early precipitation of nickel hydroxide due to a local pH increase at the cathode surface.

A simple and novel method for preparing Ni(OH)2 Part I: Structural studies and voltammetric response

Ni/Ni(OH)2 electrodes were prepared by in situ precipitation of nickel hydroxide into porous nickel substrates. The thermal decomposition of urea in solutions containing Ni2+ was used for the synthesis of the active material. The compound prepared by this method was a poorly crystallized β(II)-type phase. The electrochemical behaviour of Ni/Ni(OH)2 electrodes thus prepared was studied by cyclic voltamperommetry and the efficiency of the in situ precipitation was followed by the measurement of the cathodic charge obtained from the j-E response. The amount of incorporated material depends on the urea concentration and the electrochemical response of the electrodes was improved by increasing the number of impregnation cycles.

Comparative Potentiodynamic Study of Nickel in Still and Stirred Sulfuric Acid‐Potassium Sulfate Solutions in the 0.4–5.7 pH Range

The potentiodynamic behavior of polycrystalline nickel disk electrodes in the potential range of the active to passive transition was investigated in still and stirred sulfuric acid solutions containing potassium sulfate in the range. Voltammetric data derived with a nickel rotating disk electrode allow a distinction between the main competing processes associated with the active to passive transition of nickel in acid, through their different dependences on the potential sweep rate and on the rotation speed. The first process corresponds to the formation of a nickel hydroxide solid phase through a relatively simple mechanism initially involving adsorbed (OH) species. The second process comprises the chemical dissolution and precipitation of nickel hydroxide, producing the thickening of the anodic layer. At high positive potentials, this anodic layer progressively transforms into the passive layer. The overall reaction is discussed in terms of a complex reaction pathway in which the participation of water plays a fundamental role.

Electrochemical Precipitation of Nickel Hydroxide

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Thermogravimetric studies on nickel hydoxide electrode

Thermogravimetric analysis (TGA) has been used as a quick and accurate method for determining the content of Ni(OH) 2 for nickel hydroxide electrodes (NOE) prepared by the chemical precipitation of nickel hydroxide on sintered nickel plaque. The analysis can be carried out in a reducing atmosphere (Ar+4%H 2) or in air, and, while the final products differ, results for the two methods should be mutually consistant. The chemical reactions expected (in air vs. in hydrogen) are shown below: ▪ From the weight loss of this reaction the loading of Ni(OH) 2 can be determined since the weight loss from the decomposition of pure Ni(OH) 2 is 19.4%. ▪ Again the Ni(OH) 2 loading can be calculated since the theoretical weight loss for the above reaction (i) is 36.7% (for pure Ni(OH) 2). Portions of a commercial NOE were cut and used for the TGA experiments in air and in hydrogen atmospheres. These TGA experiments gave consistent results for the nickel hydroxide concentration of our NOE. X-ray diffraction (XRD) studies indicated the active material was crystalline nickel hydroxide. After TGA in air to 500°C, XRD showed only NiO (plus the Ni from the plaque), while after TGA in H 2 to 500°C XRD showed only Ni peaks. In addition to these two chemical reactions, a weight loss of 1–3% was observed between 80–180°C corresponding to the loss of adsorbed H 2O. The molar ratio of adsorbed water to the calculated Ni(OH) 2 loading was about 0.1M H 2O per mole of Ni(OH) 2. This water was adsorbed and not structural based on the X-ray results discussed in this paper.

The electrocatalytic activity of Ni(II)/Ni(III) oxide films in alkaline solutions

The reactions involved in the electroreduction and electroformation of O 2 on electrodes prepared by precipitation of nickel hydroxide on different conducting substrates (platinum or vitreous carbon) in alkaline solutions are investigated. The catalytic activity of these electrodes for the O 2 evolution reaction is independent of the nature of the substrate but depends on the ageing conditions of nickel hydroxide. The mechanisms for the O 2 evolution reaction are explained through the participation of both Ni(III) and very reactive Ni(IV) species. The electrocatalytic activity is related to the u-NiOOH species. The O 2 electroreduction occurs on the substrate surface and is mainly determined by the characteristic of the substrate.