Effect of alkali cations,halides and thiocyanate on the Mn(Hg)/Mn(II) electrode reactions

The title subject has been studied by galvanostatic single-pulse, chronopotentiometric and equilibrium measurements on the Mn(Hg)/Mn(II) electrode (mainly saturated managanese amalgams) in one molar alkali chloride (LiCl, KCl and CsCl) and potassium iodide and thiocyanate solutions of pH 4 to 5 at 25°C. The Mn(Hg)/Mn(II) reactions are found to occur in two consecutive steps with monovalent ions as intermediate in all these solutions. The rates of both the ion-transfer step Mn(Hg)/Mn(I) and the electron-transfer step Mn(I)/Mn(II) appear independent of the cations Li⁺ and K⁺ and of the anions Cl^?, I^? and SCN^?, when differences in bulk activities of electroactive species are corrected for. The Cs⁺ ion, however, seems to retard the reactions more than expected from bulk activity changes, and this can be explained by Cs⁺ specific adsorption or by variations in the properties of the inner layer with the cation.