Revealing the role of oxygen reduction in Mg anode self-corrosion and its mitigation through tailored electrolyte additives mixtures

In aqueous Mg batteries, self-corrosion of anode is mainly driven by the parasitic hydrogen evolution reaction (HER), the chunk effect, and the oxygen reduction reaction (ORR), with the first two processes significantly reducing anodic efficiency. Although ORR is an important secondary cathodic process on Mg anodes, its contribution to self-corrosion has often been overlooked, primarily due to the assumption that discharge products hinder O 2 diffusion and thus minimize its impact on anodic weight loss. Here, we directly assess the role of ORR and reveal that it contributes up to approximately 10% of the total anodic self-corrosion when a film-free anode surface is maintained by employing electrolyte additives. Building on this insight, we propose a novel binary mixture of electrolyte additives combining L-ascorbic acid (Vit. C), which depletes dissolved oxygen in the electrolyte, with Mg 2+ complexing agents that bind free Mg 2+ ions and maintain film-free anodic surface. This optimized electrolyte simultaneously improves discharge potential and utilization efficiency of Mg anodes, achieving a specific energy superior to previously reported individual-additive systems. • When the Mg anode surface is clean during discharge, the oxygen reduction reaction causes notable self-corrosion. • A novel binary mixture of electrolyte additives, combining the oxygen scavenger (Vit. C) and Mg 2+ complexing agents, simultaneously enhances the discharge potential and utilization efficiency of the Mg anode. • The optimized binary additive electrolyte achieves higher specific energy than that of most reported individual-additive systems.