Collect. Czech. Chem. Commun. 1997, 62, 1396-1402

The Thermodynamics of Solid Solutions of Ni(II)/Ni(IV) Oxo Compounds

Jan Baleja and Jiri Divisekb

a Consultant Bureau for Chemical Engineering, Johanniterstr. 28, 86609 Donauworth, Germany
b Institute of Energy Process Engineering (IEV), Research Center Julich (KFA), 52425 Julich, Germany


The measured data of equilibrium and rest potentials of higher nickel oxo compounds, E' (converted for 25 °C and aH2O = aKOH = aH2 = 1.0) selected in the range of the overall oxidation number of 2.0 < zNi ≤ 3.6, were newly evaluated with the aid of a simplified model of the quasi-binary solid solutions Ni(OH)2/Ni(OH)4 assuming unlimited miscibility. It was found that the dependence of E' on the composition of the redox system can be described by a Nernst equation in the entire range of zNi investigated, where the activity coefficients of individual components are expressed by relations for regular solutions. The so calculated activities of considered components showed positive deviations from the ideal behaviour of the solid solutions. All results obtained were discussed in more detail assuming the non-existence of Ni(III) oxo compounds in such solid solutions.

Keywords: Equilibrium potential; Activity coefficients; Nickel oxide electrode.