In-Situ Atomic-Scale Phase Transformation of Mg under Hydrogen Conditions

The magnesium hydrogenation issue poses a serious obstacle to designing strong and reliable structural materials as well as offering a safe alternative for hydrogen applications. Understanding phase transformation of magnesium under hydrogen gas plays an essential role in developing high-performance structural materials and hydrogen-storage materials. Herein, we report in-situ atomic-scale observations of phase transformation of Mg and Mg-1 wt % Pd alloy under hydrogen conditions in an aberration-corrected environmental transmission electron microscope. Compared with the magnesium hydrogenation reaction, the magnesium oxidation reaction predominately occurs at room temperature even under pure hydrogen gas (99.9%). In comparison, magnesium hydrogenation is readily detected in the interface between Mg and Mg₆Pd, due to the catalytic role of Mg₆Pd. Note that the nanoscale MgH₂ compound transfers into MgO spontaneously, and the interface strain remarkably varies during phase transformation. These atomic-level observations and calculations provide fundamental knowledge to elucidate the issue of magnesium hydrogenation.