N-Doped Graphene-Rich Aerogels Decorated with Nickel and Cobalt Nanoparticles: Effect over Hydrogen Storage Properties of Nanoconfined LiBH4

We present the decoration of N-doped graphene entangled in mesoporous carbon by nickel and/or cobalt nanoparticles. The textural properties of the mesoporous materials were characterized by nitrogen desorption isotherms. The materials presented metallic nanoparticles of at least 20 nm and diffraction peaks typical of cubic cobalt or nickel. Transmission microscopy revealed the presence of graphene layers, organized mostly in an onion-like fashion around the metallic nanoparticles, suggesting these might promote the formation of extra graphene sheets from the surrounding amorphous carbon. The formation of a metallic alloy when nickel and cobalt were mixed is strongly suggested. Differential scanning calorimetry of these materials filled with LiBH4 evidenced that the presence of nanoparticles displaced the typical transition, melting and decomposition peaks of this hydride toward lower temperatures. Volumetric studies revealed that the liberation of hydrogen started at lower temperatures when nanoparticles ...