1. Milorad Tomić,
Republic of Srpska, Bosnia and Herzegovina
Zinc electrodeposition on steel from non-aqueous solutions has drawn a lot of attention recently, due to the many benefits that it offers. Literature data on bulk pH and diffusion coefficients of various species in reline and ethaline, were used to calculate the expected pH change in the diffusion layer at the cathode, during the electrodeposition process. As expected (due to the lower diffusivity), a much higher increase in pH occurs in deep eutectic solvents, as compared to aqueous solution, suggesting the beneficial effect of utilizing hydrogen evolution inhibitor during electroplating from reline and ethaline.
The influence of 4-hydroxy-benzaldehyde (HBA), as an additive in ethaline deep eutectic solution (DES, 1: 2 choline chloride: ethylene glycol), on the current efficiency and deposit appearance was analyzed. The electrodeposition process was assessed by cyclic voltammetry and it was shown that the onsets of the cathodic current, as well as bulk electrolysis, were shifted to more negative potentials in the presence of HBA, resulting in the increased current efficiency. When Zn2+ ions were introduced in ethaline a cathodic peak appeared below the potentials of electrolyte degradation and another one during the backward anodic sweep. The cathodic peak for Zn2+ reduction in ethaline+HBA+Zn2+ ionic liquid resembled the zinc reduction in aqueous solution. Upon addition of Mn2+ ions in the plating electrolyte, there was no peak related to Mn2+ reduction, which is in agreement with earlier results for Zn-Mn plating from reline DES.