Electrodeposition of zinc films from ionic liquids and ionic liquid/water mixtures

The electrodeposition of zinc films from zinc triflate (Zn(TfO)2) in two air and water stable ionic liquids namely, 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate, [Py1,4]TfO, and 1-ethyl-3-methylimidazolium trifluoromethylsulfonate, [EMIm]TfO, was studied. The influence of water on the deposition process was also investigated. The morphology of the obtained deposit is different in the two liquids. Dense and uniform silvery zinc deposits with good adherence were obtained from [EMIm]TfO while less adhering and dark gray zinc deposits were obtained from [Py1,4]TfO. The SEM results of the deposit obtained from [EMIm]TfO revealed a hexagonal zinc structure while a flower-like structure was observed for the deposits obtained from [Py1,4]TfO under the same conditions. Water added to the electrolyte has a distinct effect on the deposits obtained in [EMIm]TfO and [Py1,4]TfO, respectively. The difference in the structure might be attributed to the different interaction of the ions with the substrate. Furthermore, the addition of water to the solution decreases the electrochemical window of both ionic liquids and shifts the reduction of zinc(II) to less negative values. The XRD phase analysis showed that not only Zn was deposited in the dried ionic liquids also Zn-Au alloys were obtained. However, in ionic liquid/water mixtures only Zn was obtained, surprisingly. Furthermore, Zn deposits obtained at 50 °C showed a preferential orientation compared with those ones obtained at room temperature. Both the water concentration and the temperature affect the deposition process.