Influence of the Concentration of Different Amino Acids on the Corrosion Behavior of Mg Alloy AZ31—A Respirometric Study

In view of the potential use of Mg-based materials as biodegradable metals in temporary implantation, it is important to study the role of different components of the biological environment on the corrosion behavior. This work focuses on the effect of selected amino acids and their concentrations on time-dependent corrosion of Mg alloy AZ31. The influence of different concentrations of glycine, glutamine, phenylalanine, cysteine, glutamic acid, and aspartic acid in 0.1 M NaCl on the corrosion behavior of Mg alloy AZ31 was investigated with respirometric measurements, mass loss, and electrochemical methods. At low concentrations, all investigated amino acids exhibited cathodic inhibition. At higher concentrations, strong acceleration of corrosion was observed, which can be attributed to the buffering effect of the amphoteric amino acids, hence decelerating alkalization of the electrolyte caused by Mg corrosion. For all here studied amino acids except cysteine, Mg corrosion occurred with hydrogen evolution reaction (HER) as the dominant cathodic reaction with around 10% of the oxygen reduction reaction (ORR) of the total cathodic reactions. However, the presence of cysteine changes the cathodic reactions during Mg corrosion to around 30% ORR. Moreover, Mg ions were shown to act as a catalyst for the oxidation of cysteine to cystine.