A chloride-free electrolyte to suppress the anodic hydrogen evolution corrosion of magnesium anode in aqueous magnesium air batteries

Aqueous magnesium air batteries are promising energy conversion devices because of high theoretical energy density, inherent safety and low cost. However, their practical energy density is significantly limited due to the dramatic hydrogen evolution corrosion of Mg anode in conventional sodium chloride (NaCl) electrolyte. Herein, we suppress the hydrogen evolution reaction on the surface of Mg anode using sodium acetate (NaAc) electrolyte, in which Mg anode exhibits uniform anodic dissolution behavior without the notorious localized corrosion. It is demonstrated that acetate ion (Ac-) averts the localized passive film breakdown of Mg anode in virtue of its large diffusion energy barrier within the film. Therefore, the anodic hydrogen evolution phenomenon amid discharge is evidently repressed. This enables Mg anode to achieve a high utilization efficiency of 84 % at 10 mA cm-2 compared with 59 % in NaCl electrolyte. Mg air battery tests manifest that its specific energy based on the anode weight is boosted from 1370 to 1770 Wh kg-1. Finally, the practicality of NaAc electrolyte is confirmed in a commercial Mg air battery. This work provides a simple and scalable solution for high performance Mg air battery.