Dense Gd2O3-containing film dictates the trade-off between corrosion resistance and discharge performance in Mg-1Mn-0.2Gd anode

The practical discharge performance of magnesium (Mg) anodes is severely limited by self-corrosion, accumulation of resistive byproduct films, and the chunk effect (CE). In this work, as-cast Mg-1Mn (M1) and Mg-1Mn-0.2Gd (MG11) alloys were prepared by microalloying, and the influence of Gd on microstructural evolution, corrosion resistance, and electrochemical discharge behavior was systematically investigated. Gd addition refines the average grain size from 46.41 μm to 39.68 μm, promotes Mg 5 Gd precipitation, and reduces the electrochemical potential mismatch between secondary phases and the Mg matrix from 113.6 mV to 87.9 mV. Consequently, severe localized pitting is replaced by uniform dissolution, and the hydrogen evolution rate drops by 64.8% (from 12.8 to 4.5 mm y −1 ). Although the static corrosion resistance is enhanced, the addition of Gd causes a dense Gd-containing composite film to form during discharge. This film severely hinders interfacial Mg 2+ diffusion and charge transfer. Consequently, discharge currents concentrate at film defects. This accelerates localized dissolution and the CE, ultimately deteriorating the discharge performance of MG11 relative to M1. At 20 mA cm −2 , the M1 alloy delivers a specific capacity of 1259.45 mAh g −1 and an anodic utilization efficiency of 57.39%, outperforming most previously reported Mg anodes. This study clarifies the contradictory mechanism between corrosion durability and anodic activity induced by Gd microalloying, offering essential theoretical guidance for designing Mg-air battery anodes that integrate high utilization efficiency with superior corrosion resistance.