Electrodeposition of Zn - Ni Alloys from Protic Ionic Liquids

Electrodeposition of metals and alloys  is currently carried out from aqueous solutions despite the environmental problems associated to the complex baths  needed to obtain electrodeposits with controlled properties (composition, roughness, etc). In this context, ionic Liquids (IL) are  studied as an option to be used as new green solvents for electrodepositon due to their  interesting properties : non volatility, low fusion temperature, conductivity, viscosity, etc. However, commercial LIs are generally toxic and highly reactive in the presence of water which limits their application in many chemical and electrochemical processes.  In this work, we study the use of environmentally friendly and stable protic ionic liquids (PILs) as solvents in the electrochemical deposition of nanostructured metals (Ni and Zn) and their alloys. 

The studied PILs synthetized by using well-known amounts of a linear aliphatic amine and a single-chain carboxylic acid as precursors in order to get mixtures of controlled composition (e.g., pure PIL or mixture of a pure PIL and its pure acidic or basic precursor as a co-solvent) to be applied directly as the depositon bath in the electrochemical deposition of nanostructured nickel, zinc and their alloys.

The electrodeposition process was studied by electrochemical techniques and the obtained deposits were characterized by optical microscopy and also by SEM and AFM techniques.  For the electrodeposition of the studied single metals (Ni and Zn), results shown that nanostructured nickel and zinc deposits can be electrodeposited from these protic ILs with faradic efficiencies dependent on the composition of the IL and on the temperature; the influence of the physicochemical  properties of the studied  PILs and of the temperature  on the morphological characteristics of the obtained deposits were also  evaluated. The major effects were attributed to the influence of composition on mass and charge transfer properties of the PILs.

In the case of the electrodeposited Ni-Zn alloys, results allow to evaluate the influence of the composition of the ionic liquid on the composition of the electrodeposited alloys. In these media, it is observed that Zn-rich alloys  are commonly formed. The morphology of the obtained electrodeposits are strongly dependent on the temperature.

These results allow conclude that the studied PILs are good as new reaction media with tunable properties for electrochemical applications, allowing to propose them as new systems for electrodeposition processes, as new single solvents  without the use of organic additives.

Acknowledgements: Authors gratefully acknowledge financial support from SEP–CONACyT Program (Project CB 2011-1-168032). TBGR  is indebted to CONACYT for the fellowship.