Mg-RE Alloy Anode Materials for Mg-Air Battery Application

Commercial purity Mg, Mg-RE alloys ZE10A (UNS M11600), and EV31A (UNS M12310) were evaluated in the as-received condition for potential application as anode for Mg-air battery. Anodic and cathodic polarization studies were performed in 0.6 M of NaCl, 0.5 M of NaNO 3 and 0.1 M of Na 2 SO 4 . Hydrogen evolved during anodic polarization was measured at different current densities. Electrochemical impedance spectroscopy was carried out at open circuit conditions, and galvanostatic conditions. The results showed that commercial purity magnesium had higher corrosion resistance than the Mg-RE alloy specimens in all the electrolytes tested. All the specimens showed negative difference effect (NDE) where the rate of hydrogen evolution increased with increased anodic polarization. The NDE was more pronounced on ZE10A than on other materials. The results suggest that EV31A could be a potential anode material for Mg-air battery due to its better discharge capabilities. The surface layer formed on the Mg specimen showed predominantly a p-type semiconductivity with a charge carrier density in the order of 10 21 cm −3 . The Mg-RE alloys showed a dual layered surface layer with bottom n -type and top p -type characters. The p -type behavior could be associated with the formation cation vacancies due to dissolution of Mg from its lattice site, and the n -type semiconductivity could be attributed to segregation of trivalent rare earth cations at the metal/oxide interface. The enhanced NDE behavior of the Mg-RE alloys could also be attributed to the surface enrichment of Zr, and presence of Mg x RE y type secondary phases.