Collect. Czech. Chem. Commun. 1997, 62, 1663-1676

Diagrams Er-mKOH for Cobalt at 25-125 °C and at Total Pressure of 1-30 Bar

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


Diagrams Er-mKOH for cobalt were calculated in the range of molality mKOH = 2-18 mol kg-1, temperature t = 25-125 °C and total pressure P = 1-30 bar (0.1-3.0 MPa) on the basis of recent reliable data for individual reaction components. The water activity aH2O, the equilibrium pressure of the water vapour pH2O in or above the KOH solutions was considered. The results displayed differences from the original E-pH diagram for cobalt after Pourbaix. The direct oxidation of Co3O4 to CoO2 without any intermediate stage of Co(III) oxo compounds was found to be thermodynamically more favourable. Consideration of the reduced water activity in concentrated KOH solutions led to the finding that solid Co(OH)2 can be dehydrated to CoO at elevated temperatures in contact with KOH solutions. With rising temperature, dehydration can occur at lower KOH molality. CoO2, not known in a pure form, was assumed to exist as a pure substance in mixtures with other solid Co oxo compounds in lower states of oxidation.

Keywords: Corrosion; Cobalt oxo compounds; Alkaline water electrolysis.