Graphene (Gr) is a promising material in the fields of energy and catalysis. By means of a combination of surface-science spectroscopies and theory [1], we have investigated the mechanisms ruling the catalytic role of epitaxial Gr grown on transition-metal substrates for the production of hydrogen from water. Water decomposition at the Gr/metal interface at room temperature provides a hydrogenated Gr sheet, which is buckled and decoupled from the metal substrate. We have evaluated the performance of Gr/metal interface as a hydrogen storage medium, with a storage density in the Gr sheet comparable with state-of-the-art materials (1.42 wt.%). It is expected that decoration of Gr by Ca or transition-metal atoms and, moreover, the substitutional doping of Gr by N or B could further increase the gravimetric capacity. Moreover, thermal programmed reaction experiments show that molecular hydrogen can be released …