Evaluation of the corrosion inhibitive performance of simple amino acids on copper in a choline chloride/ethylene glycol deep eutectic solvent

The electrochemical behavior of copper in choline chloride/ethylene glycol (Ethaline), a deep eutectic solvent (DES), and its amino acid-inhibited solutions (alanine, glycine, and leucine) was investigated using linear sweep voltammetry (LSV) and potentiodynamic polarization measurements (PDP). The Tafel slopes and polarization curves illustrate the different electrochemical processes at play, highlighting the impact of charge transfer kinetics, mass transport phenomena, and amino acid adsorption on the copper surface. In uninhibited Ethaline, the anodic current converted from charge transfer based current to mixed charge transfer-mass transfer behavior at potentials 0.03 V more positive than the corrosion potential (Ecorr.), eventually adopting a mass transfer-controlled shape beyond 0.3 V. The addition of amino acids modified the electrochemical response, with glycine and leucine shifting the corrosion potential to more noble values, indicating enhanced corrosion resistance. Alanine exhibited a pseudo-passivation effect, shifting the pseudo-passivation current by 0.12 V toward more positive potentials. The cathodic current was reduced in the presence of amino acids, though the change was less obvious compared to the anodic behavior. Binary amino acid mixtures further influenced the polarization behavior, with the alanine/leucine combination showing the strongest inhibition effect. The significant difference between forward and backward Ecorr. is observed which offers deep insights into dynamic surface interactions, film stability, and the effectiveness of corrosion inhibitors. The study highlights the complex interplay of organic adsorption, chloride complexation, and mass transport limitations in DESs, underscoring their distinct electrochemical behavior compared to aqueous systems. These findings provide insights into the corrosion inhibition mechanisms of amino acids in DESs and their potential applications in controlling metal dissolution.