Nanostructured Zinc Electrodeposited from Protic Ionic Liquids: Comparison with Zinc Aqueous Electrodeposition Processes

Abstract

Zinc electrodepositon is one of the more important electrochemical process for surface treatment because of its application in anticorrosion protection and also as electrode material in zinc batteries. The main limitation of the electrodepositon of zinc from acidic or basic solutions in aqueous media, in addition to the very negative potential needed to carry out the electrodeposition, is associated to the simultaneous hydrogen evolucion reaction (HER) limiting the farad¡c efficiency of the electrochemical process. The HER has also a direct effect on the nucleation and on the electrocrystallization of zinc with some negative effects on the physical and structural proporties of zinc electrodeposits obtained from these solution (e.g. (poor adhesion, inhomogeneous deposits, etc). In this work the electrodeposition processes of zinc from protic ionic liquids is studied and compared with results of electrodeposition from aqueous solution in order to determine the avantages of electrodeposition from ionic liquids. Results show that in protic carboxylated ionic liquids, as ethanolammonium propionate, homogeneous electrodeposits of pure metallic zinc are obtained, with a narrow distribution of grain size in the range of 50-70nm, contrariously to electrodeposits obtained from aqueos solutions with grain sizes from 20 to 100nm. In addition, differences in the nucleation-electrocrystallization mechanism and on the electrodeposition rate are observed and they are dependent on the nature of the nature of the solvent. Results allow to conclude that zinc electrodeposits continous, homogeneous and with a well controlled grain sizes can be obtained from protic ionic liquids. These results allow to envisage that these deposits can be more effective for anticorrosion protection since this property is dependent on the homogeneity and contoinuity of an electrodeposit. ACKNOWLEDGEMENTS. The financial support provided by CONACYT (México), project Fondo Sectorial SEP-CONACYT CB 2011 168032 and The Engineering Research Council of Canada (NSERC) are gratefully acknowledged.