A binary electrolyte strategy coupling cl^- and citrate to regulate anodic dissolution dynamics for high-performance...

Aqueous magnesium (Mg)-air batteries face serious challenges such as self-corrosion and anode passivation, which are caused by the disorderly accumulation of discharge products in traditional NaCl electrolytes, severely limiting their high-rate discharge performance. This study proposes a mixed electrolyte strategy consisting of 3.5 wt% NaCl and 0.1 M sodium citrate (NaCA) to regulate the interfacial kinetics of the AZ31 Mg alloy anode. Its corrosion and discharge behaviors were systematically investigated through electrochemical measurements, cross-sectional morphological characterization, and COMSOL Multiphysics® (COMSOL) simulations. The results indicate that the pure NaCl system leads to severe localized pitting corrosion and a porous product layer up to 406 μm thick, whereas the pure NaCA system, although exhibiting strong complexation and corrosion inhibition effects, suffers from severe voltage collapse at high current densities due to concentration polarization and significant ohmic voltage drops. In contrast, the mixed electrolyte exhibits a significant synergistic effect between corrosion and complexation dynamics: Cl^- continuously permeates the passivation film, reducing internal resistance and maintaining substrate activation; simultaneously, citrate ions (Cit^3-) rapidly complex with Mg²⁺, restructuring the product layer into a dense film (158 μm). This synergy promotes a transition of the anode from severe localized pitting corrosion to uniform shallow dissolution. As a result, even under a demanding current density of 20 mA cm^-2, the mixed electrolyte delivers an impressive anode utilization of 76.34 ± 1.7% alongside a specific energy of 1923.94 ± 51.00 mWh g^-1. This performance leads to simultaneous improvements in both discharge voltage and overall energy yield. The findings of this study provide important theoretical guidance for the design of next-generation electrolytes in advanced metal-air batteries.