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

Abstract

Hydrogen evolution (HE) on anodically polarized Mg, commonly referred to as Negative Difference Effect, was studied by galvanodynamic measurements coupled with real-time gravimetric H 2 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.

A Critical Review of the Application of Electrochemical Techniques for Studying Corrosion of Mg and Mg Alloys: Opportunities and Challenges

“…Since the development of the gravimetric method for HE, GDP measurements have shown to reliably monitor the real-time evolution of H 2 from a Mg surface. Using GDP instead of GSP allows for an easy determination of the HE current density in a single GDP measurement by interpolation in a HE current density vs. applied current density plot [16] (see Figure 7). This has shown to be particularly useful when short timescales are needed or when limited amount of material is available and a large range current densities need to be applied.…”

“…These authors also have used SVET for studying the behavior of a range of potential anionic inhibitors, selected on the basis of their ability to form insoluble precipitates with aqueous Mg 2+ ions [46]. Their results using SVET for investigating the source of hydrogen evolution from high purity Mg anodically polarized are also significant [14,16,47].…”

Role of Segregated Iron at Grain Boundaries on Mg Corrosion

“…The well-known increase of the HER rate under anodic polarization of Mg seems to be in contradiction with the kinetic models of charge transfer electrochemical reactions (Butler-Volmer equation), predicting that the cathodic current should decrease exponentially with increasing anodic potential. This phenomenon called "the negative difference effect" (NDE) [9][10][11][12][13][14][15][16] and more recently "the anodic hydrogen evolution" process 17,18 has been also observed for other metals than Mg such as Al, Li. [19][20][21][22] Despite the abundant literature on Mg corrosion and many models of Mg corrosion (such as: the formation of Mg(I) as an intermediate product, 23,24 the formation and breakdown of the partially protective film, 11,[25][26][27] the formation of hydride intermediates, [28][29][30][31][32] or the catalytic activity of alloying elements and noble metal impurities) 22,33,34 the mechanisms still remain unclear.…”

Corrosion Performance of Friction Stir Linear Lap Welded AM60B Joints

“…[16][17][18]22 However, the ability of the sub-surface Al distribution and any associated Al enrichment layer to alter the surface film to avoid cathodic activation has not been investigated in a unified context. The scanning vibrating electrode (SVET) technique has eloquently revealed that breakdown of Mg 23,24 and single phase Mg-Al alloys [25][26][27] in NaCl (aq) electrolytes involves laterally-spreading focal anodes that leave behind cathodically-activated corrosion products. Thus, identifying microstructural features that can alter surface films to avoid cathodic activation is desirable from a corrosion performance perspective.…”