Magnesium Anode Efficiency in Nonchloride Na ₄ EDTA Solutions for Aqueous MgAir Primary Batteries

The anodic behavior of magnesium in chloride‐free Na 4 EDTA solutions was investigated. A mechanism is proposed according to which dissolution proceeds via a passive state that includes two main stages: (i) magnesium ionization ( E < −1.45 V) accompanied by a sharp increase in the anodic current density; (ii) magnesium ionization and formation of a Mg(OH) 2 layer followed by its dissolution ( E ≳ −1.45 V). At stage (ii), the processes of hydroxide formation on the surface and its dissolution with the formation of the [MgEDTA] 2− complex are balanced, resulting in a stable anodic current density (7 ± 1 mA·cm −2 ) at E = −1.3…−0.5 V. The rate‐limiting step is the complexation: Mg(OH) 2 + EDTA 4− → [MgEDTA] 2− + 2OH ‐ . This is evidenced by a 20–50% increase in anodic current under hydrodynamic conditions. With increased anodic polarization, anode efficiency increases to over 90%. This effect is attributed to the growth of the barrier layer on the magnesium surface due to enhanced adsorption of EDTA 4− ions, as confirmed by impedance spectroscopy data. The test results of the Mg–air cell with an Ag‐nanostructured cathode showed the compatibility of the Na 4 EDTA electrolyte, which gives the prospect of functioning membrane‐free batteries.