Mg Anode Corrosion in Aqueous Electrolytes and Implications for Mg-Air Batteries

Aqueous Mg-air primary batteries possess many favorable attributes for energy storage because Mg is affordable, abundant, and lightweight. However, parasitic corrosion of Mg in aqueous electrolytes generates H 2 and surprisingly increases with increasing current density during battery discharge (Mg oxidation), limiting the faradaic efficiency of aqueous Mg batteries. In this study, differential electrochemical mass spectrometry and H 2 pressure rise measurements were used to characterize Mg corrosion in Mg-air batteries employing aqueous electrolytes with salts (NaCl, NaNO 3 , NaPO 4 , and a NaCl/NaPO 4 mixture) that provide various degrees of Mg passivation. H 2 evolution rates were highest in NaCl electrolytes and lowest in NaNO 3 electrolytes. However, NaNO 3 salts reduced the H 2 -evolving corrosion rate at the expense of introducing a nitrate to nitrite corrosion reaction into the battery. The combined Mg corrosion rate in the nitrate-based electrolyte was still lowest among those electrolytes studied. The nitrate to nitrite corrosion reaction also lowered the magnitude of the Mg anodic potential and therefore decreased the overall Mg-O 2 battery voltage compared to the NaCl electrolyte. Nevertheless, Mg-O 2 batteries utilizing a NaNO 3 electrolyte allowed for 60% larger discharge capacity and 50% higher Mg oxidation faradaic efficiency compared to a NaCl electrolyte.