Tellurium electrodeposition on gold from a eutectic mixture of choline chloride and ethylene glycol

The electrodeposition of Tellurium (Te) on gold surface from a eutectic mixture of choline chloride and ethylene glycol, in molar ration of 1:2, was investigated. TeCl4 was Te source, Ag/AgCl was the pseudo-reference electrode and the used electrochemical techniques were cyclic voltammetry and chronoamperometry techniques. The working temperature varied between 30°C and 100°C. The crystallographic structure and surface morphology of the Te electrodeposits were assessed by X-ray diffraction (XRD) and field emission gun–scanning electron microscopy (FEG-SEM) coupled with energy dispersive X-ray spectroscopy (EDS). The cyclic voltammograms presented two electrochemical processes in the cathodic scan. The first had a –0.22 and –0.07 V peakspotentialsat30 and 100 °C, respectively, which were attributed to the reduction of Te4+/Te, suggesting that this electrochemical process occurred via one step with four electrons transfer. In addition, the last one, with peak potential positioned at –0.63 V at temperature of 30 °C was related to the reduction of Te toTe 2–. Furthermore, in the reverse sweep a cathodic current crossover loop was observed. Therefore, the electrodeposition of Te on gold substrate is typical nucleation-growth rate controlled process. Moreover, a potentiostatic study at diffusional regime was conducted and the diffusion coefficient of Te4+ species in 1ChCl:2EG eutectic mixture fitted with like-Arrhenius equation. The apparently activation energy for the diffusion Te4+ ions was 18.3 kJ mol–1. Furthermore, the current-time curves were also analyzed using the Scharifker-Hills’ model. These results suggested that the Te deposition occurred by the mechanism of progressive nucleation and three-dimensional growth with diffusion-limited. FEG–SEM micrographs displayed that the surface morphology of Te films at 100 °C was strongly dependent of the deposition charge, which changing from dense and composed deposits at 2 Ccm–2 to wires uniform distribution at 0.5 C cm–2. XRD pattern of deposits showed metallic Te with hexagonal structure growing along to {101} planes at all temperatures, as confirmed by ICSD card file 4000.