Tuning the hydrogen thermodynamics of NaAlH4 by encapsulation within a titanium shell

The use of NaAlH4 as a practical hydrogen storage material has seen extensive progress. However, it is still difficult to control the hydrogen storage properties of NaAlH4 and in particular its hydrogen thermodynamics. Herein, we demonstrate the potential of core-shell NaAlH4@Ti nanostructures in altering the hydrogen storage properties of NaAlH4. To this aim, a facile solvent evaporation method was developed to enable the making of freestanding NaAlH4 nanoparticles and their individual encapsulation within a Ti shell. These core-shell nanostructures enabled: (i) an effective confining environment for NaAlH4 and its dehydrogenation products, and (b) fast hydrogen kinetics due to a weakening of the Al–H bond and the shorter diffusion lengths. At 180 °C, a reversible hydrogen storage capacity of 4.4 mass% was observed. More remarkably, this core-shell approach enabled a shift in the equilibrium plateau pressure, therefore demonstrating the possibility to control the hydrogen thermodynamics of NaAlH4 at the nanoscale.