Core-Shell Strategy Leading to High Reversible Hydrogen Storage Capacity for NaBH4

Owing to its high storage capacity (10.8 mass %), sodium borohydride (NaBH4) is a promising hydrogen storage material. However, the temperature for hydrogen release is high (>500 degrees C), and reversibility of the release is unachievable under reasonable conditions. Herein, we demonstrate the potential of a novel strategy leading to high and stable hydrogen absorption/desorption cycling for NaBH4 under mild pressure conditions (4 MPa). By an antisolvent precipitation method, the size of NaBH4 particles was restricted to a few nanometers (<30 nm), resulting in a decrease of the melting point and an initial release of hydrogen at 400 degrees C. Further encapsulation of these nanoparticles upon reaction of nickel chloride at their surface allowed the synthesis of a core-shell nanostructure, NaBH4@Ni, and this provided a route for (a) the effective nanoconfinement of the melted NaBH4 core and its dehydrogenation products, and (b) reversibility and fast kinetics owing to short diffusion lengths, the unstable nature of nickel borohydride, and possible modification of reaction paths. Hence at 350 degrees C, a reversible and steady hydrogen capacity of 5 mass %was achieved for NaBH4@Ni; 80% of the hydrogen could be desorbed or absorbed in less than 60 min, and full capacity was reached within 5 h. To the best of our knowledge, this is the first time that such performances have been achieved with NaBH4. This demonstrates the potential of the strategy in leading to major advancements in the design of effective hydrogen storage materials from pristine borohydrides.