The most cited key substances for hydrogen storage are summarized in Table . As discussed above, carbon is the most prevalent element of H2 storage (Fig. ). Carbon is a major part of various carbonaceous sorbents such as activated carbon, graphene, MOFs, as well as liquid organic hydrogen carriers and polymers. Magnesium is another key element found in hydrides, borohydrides and hydrogen storage alloys (MgH2, Mg (BH4)2, Mg 2Ni). Transition metals, namely Ni, La, Ti, and Fe, are important components of H2 storage alloys (LaNi5, FeTi) and metal oxides (Ti4Fe2O, Ti4Ni2O). In addition, the growing interest in transition metal nanoparticles as dehydrogenation catalysts is since they can successfully replace expensive noble metals.