The synthesis, thermodynamic destabilisation and hydrogen absorption/desorption characteristics of the Li x Na 1-x MgH 3 system with (x=0, 0.2, 0.5 and 0.8 molar ratios) have been investigated. Samples were mechanically milled under argon for 5 hours; then characterised by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Diffraction peaks of NaMgH 3 phase shifted to higher angles and lattice parameters decreased due to the Li addition into the system. 2 and 3 endothermic reactions were observed for the Li x substituted samples (x=0, 0.2, 0.5, 0.8). Li 0.8 Na 0.2 MgH 3 hydride showed the best performance among the other quaternary hydrides (synthesised in this work) releasing 5.2 wt.% of H 2 at 314 °C. Rehydrogenation of the decomposed Li x Na 1-x MgH 3 (x=0, 0.2, 0.5 & 0.8) samples was experimentally confirmed under 10 bar H 2 at ~250 °C.

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