Effect of ionic liquid additives on oxygen evolution reaction and corrosion behavior of Pb-Ag anode in zinc electrowinning

Three ionic liquid salts, 1-Ethyl-3-methylimidazolium chloride [EMIM]Cl, 1-Ehyl-3-methylimidazolium bromide [EMIM]Br, and 1-Ehyl-3-methylimidazolium ethyl sulfate [EMIM]ESO4 were chosen as additives in order to examine their effects on the oxygen evolution reaction (OER) and corrosion of Pb-0.7%Ag anode in zinc electrowinning. Results of 24 h of anodic polarization showed that the presence of these additives depolarized the OER. A reduction of 25 mV of anodic potential was obtained by addition of 5 mg L−1 of [EMIM]ESO4 to that obtained from free-addition electrolyte. Corrosion measurements employing linear polarization technique revealed that corrosion rate of Pb-0.7%Ag was decreased by ∼25-42% by the addition of [EMIM]ESO4 or [EMIM]Br. Corrosion current was found to be decreased in the order of [EMIM]ESO4 < [EMIM]Br < Gelatin ≤ Blank < [EMIM]Cl. Electrochemical impedance spectroscopy demonstrated that addition of ILS to the zinc sulfate electrolyte increased the charge transfer resistance of the anodic dissolution reaction except for [EMIM]Cl. Zero resistance ammeter and scanning reference electrode techniques showed the same corrosion tendency obtained from other techniques and proved that no localized corrosion was observed in the presence of Cl¯ ions.