Computational and experimental evaluation of the corrosion inhibition of magnesium in the presence of acids/Esters in saline solutions

Abstract

Some additive compounds that have been noted to boost the performance of Mg batteries are herein investigated for their corrosion inhibition properties and mechanism of action on the Mg surface. Experimentally, hydrogen evolution tests were carried out in the presence and absence of the additives while molecular level computations were carried out using density functional theory (DFT) and molecular dynamic simulations (MDS) to evaluate the adsorption of the additives. These compounds include; analine, histidine, lysine, proline, and arginine, 1,3 2,4 dibenzylidene-sorbitol (DBS), hydroxyacetic acid, ethanedioate, nitrilotriacetic acid (NTAN) and ethylenediaminetetraacetic acid (EDTA). The additives inhibited the corrosion of Mg at different temperatures and additive concentrations. The compounds showed varying inhibition efficiencies at different concentrations of the additives, however at a concentration of 0.1 mg/L of the additives at 303 K, the trend of the inhibition efficiency is Glyocolate > EDTA > NTAN > DBS > Alanine > Histidine > Lysine > Oxalate > Proline > Arginine. The adsorption of the inhibitors were consistent with the langmuir adsorption isotherm and the values of Gibbs free energy of adsorption calculated indicates that the additives are physisorbed on the metal surface. The activation energy in the presence of the additives was higher than that of the blank solution suggesting an increase in the energy barrier needed to drive the corrosion process in the presence of the inhibitors. The Heat of adsorption values were negative and indicate that the adsorption process is exothermic. DFT calculations on the additives indicate that the molecular composition and bi polar nature of the amino acids have a pronounced effect on their adsorption characteristics in addition to the functional groups present. The molecular dynamics simulations indicated that the organic molecules all interact with the metal surface which was the driving force of the adsorption of the compounds on the metal surface.