Hydrogen generation from a sodium borohydride–nickel core@shell structure under hydrolytic conditions

Sodium borohydride (NaBH₄) is an attractive hydrogen carrier owing to its reactivity with water: it can generate 4 equivalents of H₂ by hydrolysis (NaBH₄ + 4H₂O → NaB(OH)₄ + 4H₂). Since using NaBH₄ in the solid state is the most favorable way to achieve a high gravimetric hydrogen storage capacity (theoretical maximum of 7.3 wt%), we have investigated the possibility of developing a core@shell nanocomposite (NaBH₄@Ni) where a metallic nickel catalyst facilitating the hydrolysis is directly supported onto NaBH₄ nanoparticles. Following our initial work on core-shell hydrides, the successful preparation of NaBH₄@Ni has been confirmed by TEM, EDS, IR, XRD and XPS. During hydrolysis, the intimately combined Ni⁰ and NaBH₄ allow the production of H₂ at high rates (<i>e.g.</i> 6.1 L min^-1 g^-1 at 39 °C) when water is used in excess. After H₂ generation, the spent fuel is composed of an aqueous solution of NaB(OH)₄ and a nickel-based agglomerated material in the form of Ni(OH)₂ as evidenced by TEM, XPS and XRD. The effective gravimetric hydrogen storage capacity of nanosized NaBH₄@Ni has been optimized by adjusting the required amount of water for hydrolysis and an effective hydrogen capacity of 4.4 wt% has been achieved. This is among the best reported values.