Modelling approach applied to SnIn coatings from choline chloride/ethylene glycol deep eutectic solvent

The objective of this work was to electrodeposit Sn-In coatings using a deep eutectic solvent consisting of choline chloride (ChCl), and ethylene glycol (EG) in the ratio 1:2 and to characterize the electrolytes employed, both experimentally and theoretically. Solutions containing 0.025 mol/L SnCl2 and/or 0.025 mol/L InCl3 in 1ChCl:2EG were studied by cyclic voltammetry and chronoamperometry. The diffusion coefficients of the metal ions were measured at temperatures between 297 and 343 K, with the values for Sn2+ being between 3.5 x 10-7 and 5.4 x 10-7 cm2 s- 1 and between 0.90 x 10-7 and 1.46 x 10-7 cm2 s- 1 for In3+. The morphology and chemical composition of Sn, In and Sn-In electrodeposits were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), the latter showing that Sn as the more noble metal was deposited preferentially. X-ray diffraction (XRD) showed the presence of an InSn4 intermetallic phase. Furthermore, to understand better the species present in the solution, the behaviour of Sn2+ and In3+ ions was theoretically analysed through computational simulations involving molecular dynamics, density functional theory and quantum theory of atoms in molecules at four different temperatures. The results indicated that both ions (Sn2+ and In3+) interacted more strongly with the Cl- ion (In-Cl and Sn-Cl) than with ethylene glycol (In -(O1, O2) and Sn-(O1, O2) and showed no interaction with choline (In-O3 and Sn-O3).