Insights into corrosion and discharge behaviors of Mg-Er binary alloys as anodes for Mg-air batteries

In this work, the electrochemical performance and discharge behavior of Mg- x Er ( x = 0, 0.5, 1, 2, 4 and 8 wt.%) binary alloys were systematically investigated as anode materials for Mg-air batteries. The results demonstrate that the introduction of Er refines the grains of Mg-Er alloys and leads forming to the formation of the Mg₂₄Er_{5 s} phase, which acts as a cathodic site in micro-galvanic corrosion. With increasing Er content, the corrosion resistance of Mg-Er alloy first increases and then decreases. Among all compositions, the Mg–2Er alloy exhibits the highest discharge voltage at all current densities and shows the best overall discharge performance, achieving a discharge voltage of 1.355 V and a specific energy of 1297 m·Wh·g⁻¹ at 10 mA·cm⁻². These findings are attributed to the competing effects introduced by Er: an enhancement effect on surface electrochemical activity and an inhibiting effect associated with film formation during discharge. At low Er contents, both effects remain relatively weak, whereas excessive Er additions promote corrosion and strengthen the inhibitory action of surface films. The Mg–2Er alloy provides an optimal balance between enhancement and inhibition, making it a promising anode material for Mg–air batteries.