Tailoring tin electrodeposits in deep eutectic solvents. Electrodeposition on glassy carbon and copper electrodes in oxaline

Abstract

The formation of Sn films in acid media using a deep eutectic solvent was studied. For this purpose, a mixture of choline chloride and oxalic acid was used and glassy carbon and polycrystalline copper electrodes employed. From voltammetric and chronoamperometric runs the electrodeposition process was characterized as diffusion-controlled with a $D$(Sn(II)) = $6.04\times 10^{-7}$ cm${}^2$ s${}^{-1}$, being the initial stage an instantaneous nucleation followed by a 3D growth. Depending on the substrate, the electrodeposition process occurs under overpotential (GC) or underpotential + overpotential (Cu) conditions. Different morphologies are obtained depending on the nature of the substrate and the potentiostatic and galvanostatic routines applied. Images from constant potential electrodeposition show the formation of well-dispersed tetrahedral pyramidal crystals on the GC surface and faceted particles with two preferred sizes on Cu. At high overpotentials, letter-shaped crystals form on GC, and fairly compact films are produced on Cu. Galvanostatic square wave routines allow to obtain different morphologies and size distributions of Sn deposits, depending on the current density, the on/off time ratio and the perturbation application time. Well dispersed nanometric to complex tetrahedral micrometric particles are formed on GC electrodes. On the other hand, the diffusion of Sn atoms into the Cu lattice precludes the formation of low density nanometric particles. In this case low density deposits of micrometric particles and compact films consisting of particles of few hundreds of nanometres in size can be obtained depending on the characteristics of the galvanostatic routine.