On the Electrochemical Deposition of Tin in Deep Eutectic Solvents

BOLZÁN, A.E.; GERVASI, C.A.; AZPEITIA, L.A.

Belgrado

Congreso; 71th Annual Meeting of the International Society of Electrochemistry; 2020

International Society of Electrochemistry

The electrodeposition of Sn from deep eutectic solvents (DES) on copper substrates was studied in the temperature range 303 -- 353 K using the mixtures of choline chloride with either ethylene glycol (ethaline) or urea (reline) in the ratio 1:2. For the characterisation of the electrochemical process, voltammograms were run between -0.25 and -1.0 V (vs. Ag wire quasireversible reference electrode). For both DES, the negative-going potential scans show first an underpotential deposition process, which is immediately followed by an overpotential electrodeposition process. The former is, however, considerably less distinguishable in DES compared with that obtained in aqueous acid solutions. Some significant differences were observed between the voltammetric profiles recorded in ethaline and reline. First, the current densities are much lower in reline, at all temperatures, probably related to the much higher viscosity and much lower conductivity of reline. Secondly, in ethaline the voltammogram presents a main single cathodic current peak while in reline, depending on the temperature, two or three electroreduction current peaks can be recorded. By means of a rotating disc electrode, Levich plots were obtained from which the diffusion coefficient of Sn(II) ions was determined at the different temperatures within the studied range. Moreover, while a limiting current plateau is recorded bellow -0.4 V during the electrodeposition of tin from etaline, in reline the limiting current is preceded by a series of three small cathodic peaks. From the corresponding Arrhenius plots, the activation energy for the diffusion process was determined and compared to data from acid aqueous solutions. Both, voltammetric and chronoamperometric measurements provided evidence of a nucleation and growth process. Non-dimensional plots derived from chronoamperometric experiments at different electroreduction potentials were consistent with the occurence of a 3D instantaneous nucleation and growth process under diffusion control during the overpotential deposition. Impedance data recorded between 60kHz and 10 mHz showed the presence of two capacitive time constants in the potential range related to the underpotential deposition process and a single capacitive time constant at potentials related to the overpotential electrodeposition of Sn ions. SEM images obtained for the deposits formed in both DES show the presence of different morphologies according to both, the nature of the electrolyte and the electrodeposition routine employed