Microstructural study of hydrogen desorption in 2NaBH4 + MgH2 reactive hydride composite

The desorption mechanism of as-milled 2NaBH4 + MgH2 was investigated by volumetric analysis, X-ray diffraction and electron microscopy. Hydrogen desorption was carried out in 0.1 bar hydrogen pressure from room temperature up to 450 °C at a heating rate of 3 °C min−1. Complete dehydrogenation was achieved in two steps releasing 7.84 wt.% hydrogen. Desorption reaction in this system is kinetically restricted and limited by the growth of MgB2 at the Mg/Na2B12H12 interface where the intermediate product phases form a barrier to diffusion. During desorption, MgB2 particles are observed to grow as plates around NaH particles.

► A multi-step dehydrogenation of 2NaBH4 + MgH2 composite has been demonstrated.
► Desorption reaction is kinetically restricted and limited by the growth of MgB2.
► Intermediate products form a barrier to diffusion at the Mg/Na2B12H12interface.
► MgB2 grow as plates around NaH particles, during dehydrogenation reaction.