Synergistic enhancement of hydrogen storage and air stability via Mg nanocrystal-polymer interfacial interactions

The role of encapsulating polymers in nanocrystalline Mg air stability and hydrogen storage density was studied for a series of composites varying in both % Mg and polymer identity. In these materials, the Mg nanocrystals are completely dependent on the polymer for air stability. Remarkably, both air stability and hydrogen sorption capacity of poly(methylmethacrylate) composites were enhanced by reducing the amount of polymer. Composites consisting of 65 wt% Mg absorbed 6.95 wt% hydrogen and showed little oxidation after 3 months air exposure even after enduring the volume expansion induced by hydrogen sorption, whereas composites with 33.2 wt% Mg absorbed just 4.86 wt% hydrogen and were completely oxidized upon air exposure after hydrogen sorption. This surprising synergistic enhancement in stability and storage density is attributed to an increase in the tortuosity of the paths of gas molecules and increased interfacial structure-templating regions, which scale with % Mg loading and lead to nanoparticle entanglements, hindering polymer chain motion.