Hydrogen Evolution During Anodic Polarization of Mg Alloyed with Li, Ca, or Fe

The origin of high rates of hydrogen evolution (HE) on dissolving Mg, the so-called negative difference effect, remains of practical interest. Recent studies have suggested that the ability of Mg to support the cathodic reaction is enhanced during dissolution and that enrichment of noble impurity elements at the dissolving Mg surface may also play a role in enhanced rates of HE. To begin to uniquely address the role played by other elements, Mg was intentionally alloyed with Li, Ca, or Fe. Hydrogen collection was performed during anodic galvanostatic polarization tests. An Mg-Li alloy containing 33 at% Li exhibited similar rates of anodic HE as pure Mg. Because Li dissolves with a valence of 1, any mechanism of anodic HE involving a lower valence state such as Mg⁺, is therefore ruled out. Mg-Ca and Mg-Fe alloys exhibited higher rates of anodic HE than pure Mg. They also exhibited a minimum of the HE rate under cathodic polarization instead of at the open-circuit potential, the latter being the case for pure Mg and Mg-Li. The role of alloying elements in the HE on Mg and the implications for the mechanism of anodic HE are discussed.