On the role of water in antimony electrodeposition from choline chloride/ethylene glycol/water mixture

Through experimental research and theoretical calculation, it was investigated the effect of water and temperature on the electrodeposition of antimony (Sb) on a platinum (Pt) electrode. The plating solutions were prepared by the addition of 0.05 mol L–1 SbCl3 to the mixtures of choline chloride (ChCl), ethylene glycol (EG) and water (W) in the following molar ratio: 1ChCl:2EG (bath 1), 1ChCl:2EG:0.45 W (bath 2), and 1ChCl:2EG:1.62 W (bath 3). Furthermore, the Sb coatings were electrodeposited at 297 and 338 K. The surface morphologies and crystalline structures of Sb electrodeposits were analysed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. In addition, to understand the interactions of Sb3+ species with the other components of the plating solution, models were created and calculated using density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM). The results of the voltammetric behaviour of Sb3+ species indicated that the reduction potential was shifted towards more positive values with increasing water content on the electrolyte, indicating that the water catalyses the electrochemical reduction of the Sb3+ species. The values of the diffusion coefficients for the Sb3+ species were calculated by applying the Cottrell equation, which increased with the addition of water and temperature increment. The water content and temperature increase affect the surface morphologies of the Sb electrodeposited coatings, which is attributed to the improvement of Sb electrodeposition rate. Moreover, Sb electrodeposited coatings were successfully obtained without adding a complexing agent, indicating that the procedure adopted for the Sb electrodeposition is environmentally friendly. The XRD results revealed the pure phase Sb films. DFT simulations indicated that the Sb-Cl interaction is stronger, which suggests the formation of Sb-Cl complexes. Adding H2O molecules favours the electron affinity of the systems, and QTAIM results suggested that this additive decreased the electron density of Sb3+ ions.