Electrodeposition of tin and tin based alloys from ionic liquids: nanowires, thin films and macroporous structures

Abstract

During the past decade, Ionic liquids have gained massive attention as perfect electrolytes in electrochemical processes and in industry due to their unique physicochemical properties. Tin is an important metal known for its corrosion resistance, optical properties and silver-like finish that makes it suitable for many applications such as decorations, corrosion protecting coatings, and also in lithium-ion batteries. However, the electrodeposition of tin from aqueous solutions is complicated. The results presented in this thesis show, for the first time, a comparative study on the electrodeposition of tin from two different ionic liquids containing the same cation namely, 1-butyl-1-methylpyrrolidinium dicyanamide ([Py1,4]DCA) and 1-butyl-1-methylpyrrolidinium trifluoromethylsulfonate ([Py1,4]TfO). The effect of the ionic liquid anion on the morphology of the obtained deposits was also studied by cyclic voltammetry, scanning electron microscopy (SEM), infrared (IR) spectroscopy and X-ray diffraction. The results showed that the morphology of the tin deposits changes upon changing the IL. Agglomerated tin deposits are obtained on gold and copper from [Py1,4]TfO. Tin dendrites were obtained both from [Py1,4]DCA and also from1-ethyl-3-methylimidazolium dicyanamide [EMIm]DCA. This study reveals that a change in the ionic composition (anion) of the IL can influence the morphology of electrodeposits of tin and presumably of other elements and compounds. Sn nanowires are electrodeposited from two different air- and water stable ionic liquids [EMIm]DCA and [Py1,4]TfO each containing 0.1 M SnCl2 as Sn precursor. The tin nanowires were synthesized at room temperature via a template-assisted electrodeposition process using track etched polycarbonate membranes as templates. Gold or copper thin films were sputtered on one side of the track-etched polycarbonate template to make it conductive to be used as a working electrode. A copper layer was deposited on the sputtered side in from 1 M CuCl/[EMIm]DCA to act as a supporting layer for the Sn nanowires. The electrodeposition of Zn-Sn films as well as free-standing nanowires from [Py1,4]TfO ionic liquid is reported. The nanowire arrays were obtained by using polycarbonate membranes. The study includes cyclic voltammetry, chronoamperometry, X-ray diffraction, and scanning electron microscopy/energy-dispersive X-ray analyses. The results reveal that the morphology of Zn-Sn deposits shows coarse Zn particles on a Sn-rich layer, indicating the formation of Zn/Sn co-deposits. The XRD results reveal the co-deposition of Zn-Sn films. Zn-Sn nanowires with average diameters of approximately 100 nm and lengths of 5 μm were synthesized. Free-standing Zn-Sn nanowires with different lengths and a diameter of approximately 200 nm were also synthesized. Macroporous CuSn films as well as free standing nanowires were electrodeposited from [EMIm]DCA. A uniform periodicity of macroporous CuSn films is obtained through potentiostatic deposition at -1 V for 10 minutes. Higher potentials destroy the obtained deposits and lead to honeycomb structure. The electrodeposition at -1 V for 15 minutes produces a three dimensional macroporous structure. Free standing CuSn nanowires were obtained via a template-assisted electrodeposition process using polycarbonate membranes as templates. The produced nanowires have an average diameter of 100 nm and an average length of 7 μm. Si, Sn and SiSn thin films were electrodeposited from [Py1,4]TfO. Microcrystals of Sn were obtained by the potentiostatic deposition at -1.3 V vs Pt. White greyish Si deposits were obtained galvanostatically at -20 μA. SiSn thin films containing tiny particles were obtained at -2 V for 1hr while hair-like SiSn nanowires are produced when the electrodeposition process is done after running CV, and increasing the applied potential leads to the synthesis of free standing nanowires.