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Misleading aspects of the viscosity effect on the heterogeneous electron transfer reactions

“…An example was reported recently in Ref. [24]: formal h values for Pt(II) chloride reduction exceed 5, but became below unity when corrected for the portion of mercury surface occupied by sucrose.…”

“…For the both reactants under comparison the ET rate can be obtained experimentally at low overvoltages (<0.15 V), so there are no problems which we met in Ref. [24] when studying the Pt(II) chloride reduction.…”

“…An idea to change viscosity with keeping the solvent nature by introducing some additives resulted in a number of studies in carbohydrate solutions [19][20][21][22][23][24]. In particular, sucrose [20] and glucose [21][22][23] were considered as 'inert' additives strongly affecting viscosity with a minor effect on static permittivity.…”

“…The dielectric behavior of the mixed aqueous carbohydrates solutions is a poorly understood and complicated problem. Finally, the adsorption of carbohydrates in a wide potential range also presents a serious complication [24]. Being specific for any certain reactant, the latter problem does not have any general solution.…”

“…As the carbohydrate adsorption [24] decreases at high electrode charges (sharply at negative, more smoothly at positive), we have chosen the electroreduction of Cr(III) ethylenediamminetetraacetate anion ([CrEDTA] À ) as a model reaction. Its rate on mercury can be measured experimentally at the electrode charge densities of À12 to À16 lC cm À2 .…”