Elucidating magnesium-air battery anodes with excellent discharge performance by phase modulation with Gd element

Abstract

Magnesium-air batteries have a promising future as a potential green and clean energy source. The corrosion resistance and discharge performance of Mg-xGd (x = 0, 1, 3, 8, 15, 20 wt.%) alloys as anodes for magnesium-air batteries are systematically investigated. Gd exists in Mg alloys mainly in the form of the Mg₅Gd phase. The Mg₅Gd phase acts as the cathodic phase to promote the dissolution of magnesium substrate during corrosion and discharge processes. A higher content of Gd is not favorable to the improvement of corrosion resistance and discharge properties. Whereas, the corrosion resistance was improved over pure Mg with the addition of small amounts of Gd (1 and 3 wt.%). Mg-3Gd gives the best corrosion resistance. At the meantime, it exhibits the lowest amount of hydrogen evolution in the discharge state. The less hydrogen evolution side reaction is also favorable to reduce the accumulation of discharge products, and the flat discharge morphology is also favorable to product exfoliation, leading to the reduction of overpotential generated by discharge products and the increase of voltage. Mg-3Gd reaches a high voltage of 1.568 V at 2.5 mA cm^-2. The simultaneous attenuation of the hydrogen evolution reaction and the chunk effect gives Mg-3Gd an optimal discharge performance with a discharge efficiency of 60.7% at 40 mA cm^-2 and an energy density of 1681.4 mWh g^-1 at 20 mA cm^-2, a good candidate for anodes.