Improving hydrogen storage properties of MgH2 by addition of alkali hydroxides

In this study, alkali hydroxides (NaOH, LiOH, KOH) were attempted as new-type catalytic additives to improve the hydrogen storage properties of MgH2 by ball milling. It is shown that the additives readily react with the MgH2 to form perovskite-structured NaMgH3 and KMgH3, but not the LiMgH3. Although the in-situ formed perovskite hydrides remain stable during hydriding/dehydriding cycles, both NaMgH3 and KMgH3 show predominant catalytic role on the hydriding and dehydriding of MgH2. In contrast, the LiOH modified MgH2 presents much inferior sorption kinetics because of the absence of LiMgH3. The catalytic mechanism of perovskite hydrides can be explained by the high hydrogen mobility in the perovskite structure. This study shows that such cheap hydroxides could be used as efficient catalysts to improve the hydrogen storage properties of high-capacity metal hydrides and complex hydrides.