Influence of molar stoichiometry on the decomposition pathways and hydrogen storage properties of NaNH2–MgH2 composites

Achieving low-temperature operation with reversible, high-capacity hydrogen release remains a key challenge for advanced solid-state hydrogen storage systems. Metal amide–hydride composites are promising candidates, though the role of composition is not yet fully understood. In this study, NaNH 2 –MgH 2 composites with molar ratios of 1:1, 1:2, and 2:1 were prepared under identical ball-milling conditions (2 h) and examined to understand their decomposition behaviour and hydrogen desorption characteristics. Among them, the 2:1 composition showed the earliest hydrogen release at around 130°C and delivered the highest capacity (∼4.64 wt%) compared to the other ratios. This improved performance is linked to the early formation of a reactive Na 2 Mg(NH 2 ) 4 phase, which readily transforms into NaMg(NH 2 )(NH), thereby lowering the decomposition temperature and minimising ammonia release. XRD and FTIR analyses confirmed the reaction pathway. Overall, the results highlight composition as a critical factor, with the 2:1 ratio offering the most favourable performance.