Electrostatic effect of specifically adsorbed electro-inactive ions upon electrode processes II. Perbromate electroreduction in the presence of Cl−, Br−, SCN−, and N3−

Abstract

The reduction rate kf of BrO4− in the presence of halides and pseudohalides at sufficiently negative potential with respect to the point of zero charge satisfies the well-known Butler-Volmer equation corrected for diffuse-layer effects according to Frumkin. On the other hand at less cathodic potentials, where halide and pseudohalide adsorption becomes appreciable, the rate constant kf at constant applied potential E, once corrected for diffuse-layer effects according to Frumkin, still depends on the charge density qi due to the specifically adsorbed halide and pseudohalide ions. Thus in the presence of Cl−, Br−, SCN−, and N3− the logarithm of kf,d=0 (where kf,d=0 denotes the rate constant at constant E corrected for diffuse-layer effects) decreases linearly with |qi, at least for |qi|>∼10 μC cm−2. The slopes of the various log kf,d=0vs. qi plots are in satisfactory agreement with a theoretical treatment proposed by two of the authors1,2, which accounts for the electrostatic interactions between the activated complex for the electrode reaction and the neighbouring specifically adsorbed ions within the compact layer.