Thermodynamic destabilisation of MgH2 and NaMgH3 using Group IV elements Si, Ge or Sn

Abstract

a b s t r a c tThe addition of Group IV elements of Si, Ge or Sn to Mg-based hydrides has led to the successful destabilisation of MgH 2 or NaMgH 3 , resulting in hydrogen release at lower temperatures. This is the first time a direct comparison has been made with all the samples prepared and characterised using identical conditions. Pure MgH 2 desorbs hydrogen at a pressure of 1 bar at 282°C, a temperature too high for typical mobile applications. The addition of Group IV metals to MgH 2 causes the formation of intermetallic compounds (Mg 2 Si, Mg 2 Ge and Mg 2 Sn) upon hydrogen release. Theoretical calculations show promising thermodynamic equilibrium conditions for these systems. Experimentally, these conditions were difficult to achieve, however, hydrogen desorption results show that Ge has the most significant effect in allowing low temperature hydrogen release, followed by Sn, then Si. It was found that Si also has a beneficial effect on NaMgH 3 , reducing the desorption temperature.

Mg-based compounds for hydrogen and energy storage

“…When MgH 2 mixed with Si is heated until the hydrogen is released, it forms the intermetallic Mg 2 Si [13]. While the reaction is reversible in a ball-mill environment with hydrogen [14][15][16], application of pressures of hydrogen to Mg 2 Si up to 185 MPa and 350°C has not yielded a hydride phase [13,17] except when the Mg 2 Si particle size was reduced to 10 nm. Even then, the yield was low and the kinetics very poor [18].…”

Complex and liquid hydrides for energy storage

“…For example, the addition of Si (or Ge, Sn) metal to LiH or MgH 2 results in the formation of relatively stable group IV alloys upon dehydrogenation, effectively destabilizing the metal hydride and increasing the equilibrium hydrogen pressure at a given temperature [102,103]. Similarly, adding MgH 2 to LiBH 4 lowers the dehydrogenation enthalpy of the borohydride through the formation of MgB 2 [104].…”

Influence of Admixtures of Si, Fe, Ti on Temperature and Kinetics of Dissociation of MgH$_2$ Obtained by Reactive Mechanical Alloyage

“…В даному дослідженні, вибираючи в якості леґувальних елемен-тів Силіцій, Титан і Ферум, ми виходили з того, що Силіцій за да-ними [12][13][14] володіє істотним дестабілізувальним ефектом і може Рис. 7.…”