Concentrated KOH + K2Zn(OH)4 + H2O and KOH + H2O electrolytes were investigated by cyclic voltammetry and hydrogen-electrode rest potential measurements. The adsorption of zincate ions on the platinum electrode is demonstrated by modifications of the voltammograms and shifts in rest potentials. Interference with the hydrogen reactions in the voltammograms by zincate ions prevents the use of the H-2/Pt reference electrode for rest potential measurements in zincate-containing solutions.