The Evolution of Anodic Hydrogen on High Purity Magnesium in Acidic Buffer Solution

Hydrogen evolution (HE) on anodically polarized Mg, commonly referred to as negative difference effect, was studied by galvanodynamic measurements coupled with real-time gravimetric H2 volume collection, the scanning vibrating electrode technique, and potentiodynamic polarization experiments. High purity Mg (99.96% Mg) electrodes were studied in chloride-free 0.1 M citric acid solution buffered at pH with the aim of determining the source of anodic HE and the role of the corrosion film on the process. In such conditions of pH, the typical dark corrosion product exhibited in neutral and alkaline solutions was not found, but the HE rate still increased with increasing potential. Evidence that HE on dissolving high purity Mg is associated with the regions dominated by the anodic dissolution reaction is provided. The role of noble impurity enrichment on the electrode surface during anodic polarization and the effect of Fe re-deposition are also discussed.