First stages of silver electrodeposition in a deep eutectic solvent. Comparative behavior in aqueous medium

The aim of the present work was to study the viability of a deep eutectic solvent (DES) solvent (consisting in a eutectic mixture of 1 choline chloride: 2 urea) as electrolyte for the electrodeposition of silver (I), paying special attention to the influence of the liquid on the mechanism of nucleation process. As this DES solvent is rich in chloride anion, which can act as complexing agent of the silver cation, parallel analysis was made, as reference, in aqueous media, both in free-chloride solution and in excess of chloride. These studies were made to analyze the role of chloride anion on the first stages of silver electrodeposition, but also to compare as nucleation mechanism changes depending on the medium, especially when DES solvent was used. For all solutions, cyclic voltammetry was useful to establish the potential range at which silver electrodeposition occurred, while potentiostatic technique was used to study the mechanism of the process. In all media, the deposition follows a nucleation and three dimensional growth governed by diffusion. The viability of the nucleation mechanism by Scharifker-Hills model was demonstrated. The analysis of the rising parts of the j-t transients confirms the obtained results by the model. Diffusion coefficients of silver species present in the solution were calculated from linear regression of j vs t−1/2 at long deposition times.