Studies of double-layer effects at single crystal gold electrodes II. The reduction kinetics of hexaaquairon(III) ion in aqueous solutions

The reduction kinetics of hexaaquairon(III) was studied at different concen trations of perchloric acid at four single-crystal gold electrodes. The ele ctron-transfer rate constants obtained at constant electrode potential incr ease in the following order: Au(210) < Au(110) < Au(100) < Au(111). The exp erimental transfer coefficients increase in the same order. An analysis of double-layer effects within the framework of the classical Frumkin approach was consistent with the transport of a reactant of charge 2+ through the d ouble-layer region and gave a value of the apparent transfer coefficient <a lpha>(a) equal to 0.3 for all single-crystal electrodes studied. The alpha (a) value was rationalized by the distribution of charges within the reacta nt and product. The differences between double-layer effects on the reducti on kinetics of hexaaquairon(III) and hexaamminecobalt(III) ions are discuss ed.