Effect of ionic liquid additives on oxygen evolution reaction and corrosion behavior of Pb-Ag anode in zinc electrowinning Nabil Sorour a, * , Chaoran Su a , Edward Ghali a , Georges Houlachi b a Department of Mining, Metallurgical and Materials Eng., Laval University, Qu ebec, G1V 0A6, Canada b Hydro-Qu ebec Research Institute (LTE), Shawinigan, QC, G9N 7N5, Canada article info Article history: Received 20 August 2017 Received in revised form 14 November 2017 Accepted 15 November 2017 Available online xxx Keywords: Zinc electrowinning Ionic liquids Additives Oxygen evolution reaction Corrosion of lead-silver anode abstract 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]ESO 4 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]ESO 4 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 ~25e42% by the addition of [EMIM]ESO 4 or [EMIM]Br. Corrosion current was found to be decreased in the order of [EMIM]ESO 4 < [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. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Lead has been used since many decades as anode material in the zinc electrowinning industry. However, pure lead is a weak material that tends to creep and deform during operation [1]. In addition, it has significant shortcomings during electrolysis, such as high over- potential of oxygen evolution reaction (OER), low corrosion resistance and lead contamination of cathodic zinc [2,3]. The OER overpotential could be reduced if lead is alloyed with specific elements. Small amounts of silver (0.3e1.0%) alloyed with lead were found to decrease the overpotential by 80e120 mV compared to that of pure lead [4]. Also, the benefits of silver on improving the corrosion resistance of the anode during electrolysis cannot be neglected [5]. Two main reactions occur on the lead-based anode during zinc electrodeposition, the evolution of oxygen gas and the formation of PbSO 4 (Eqs. (1) and (2)) [6]. H 2 O / 2H þ þ 2e  þ 1 2 O 2ðgÞ E o ¼ 1:23 V vs SHE (1) Pb þ SO 2 4 / PbSO 4 þ 2e  E o ¼ 0:35 V vs SHE (2) The oxidation of water to oxygen is theoretically possible at 1.23 V, but production of oxygen is only observed at potentials higher than the equilibrium potential for the PbSO 4 /PbO 2 (Eq. (3)). Therefore, the evolution of oxygen gas requires overpotential. PbSO 4 þ 2H 2 O / PbO 2 þ H 2 SO 4 þ 2H þ þ 2e  E o ¼ 1:685 V vs SHE (3) Approximately, 60% of the consumed energy during the zinc electrowinning process is used for the anodic reactions [7]. Although many studies and attempts have been carried out on improving the anode material, they mainly focused on lead-based alloys and metal-based coated anode such as Ti and Ni [8e11]. Mixed metal oxides (MMO) anodes are being recently developed to reduce the overpotential of OER. Results using MMO anodes with different oxides (TiO 2 - Ta 2 O 5 - IrO 2 - RuO 2 ) were obtained in terms of voltage reduction and service life [12,13]. However, more work is required to improve and evaluate the electrochemical performance and corrosion resistance of these anodes in the electrowinning industry. A low cost method to improve the performance of lead-based anode is to use appropriate additives. Cachet et al. [14] have * Corresponding author. E-mail address: nabil.sorour.1@ulaval.ca (N. Sorour). Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta https://doi.org/10.1016/j.electacta.2017.11.108 0013-4686/© 2017 Elsevier Ltd. All rights reserved. Electrochimica Acta xxx (2017) 1e8 Please cite this article in press as: N. Sorour, et al., Effect of ionic liquid additives on oxygen evolution reaction and corrosion behavior of Pb-Ag anode in zinc electrowinning, Electrochimica Acta (2017), https://doi.org/10.1016/j.electacta.2017.11.108