Effect of group IV elements on the thermodynamic property of NaH + Al

The destabilizing effect of (X) group IV elements (C, Si, Sn and Ge) on NaH + Al was investigated. A significant decrease in the desorption temperature as well as the reaction enthalpy of NaH was achieved with additions of C, Si, Ge and Sn due to the formation of NaAlGe and NaAlSi ternary and NaSn binary compounds. Compared to a reaction enthalpy of 114 kJ mol−1 H2 for NaH above 400 °C, lower reaction enthalpies of 94 kJ mol−1 H2, 72 kJ mol−1 H2, 20 kJ mol−1 H2 and 2 kJ mol−1 H2 were obtained for the NaH + Al + C, NaH + Al + Si, NaH + Al + Ge and NaH + Al + Sn mixtures with onsets at 270 °C, 220 °C, 180 °C, and 130 °C respectively. Reversible hydrogenation was partly achieved in the NaH–Al–Si system with the formation of NaAlH4 + Si.

► The apparent destabilization of NaAlH4 by C, Si, Ge and Sn has been demonstrated.
► A significant decrease in sorption temperature and reaction enthalpy is achieved.
► Reversible hydrogenation is achieved in the NaH + Al + Si system to form NaAlH4 + Si.
► NaAlH4 is directly formed without the detection of any intermediates like Na3AlH6.
► Enhanced sorption kinetics is observed due to the catalytic effect of TiCl4.