EIS characterization of Sn|Sn(II), gluconic acid system

EIS and SEM techniques were applied to study processes occurring on the Sn electrode in Sn(II) gluconate solutions containing an excess of sulphate at 3 < pH < 5. Adsorption and kinetic parameters were obtained using the equivalent circuits derived for electrochemical processes involving adsorption steps.In the case of Sn(II)-free gluconate solutions, pH slightly affected impedance spectra. The most pronounced pH effect was observed for Sn(II) containing solutions: the impedance increased by 2 orders of magnitude, when pH was raised from 3 to 5. At the same time, a respective decrease in the capacitance of charged interface and in the exchange current density was detected.The revealed phenomena are interpreted in terms of formation of adsorption layer the inhibitive character of which is conditioned by species containing Sn2+ and OH− ions. The possible structure of adsorption layer is discussed.