[lemma=storage] [tag=NNS] [!tag=IN] [□] □
[lemma=storage] [tag=NNS] [!tag=IN] [□=□] □
[lemma=storage] [tag=NNS] [!tag=IN] [!□] □
Of potential practical hydrogen storage materials , pure Mg would be best from the standpoint of hydrogen capacity per unit mass .