Advanced hydrogen storage of the Mg–Na–Al system: A review

A solid-state storage system is the most practical option for hydrogen because it is more convenient and safer. Metal hydrides, especially MgH2, are the most promising materials that offer high gravimetric capacity and good reversibility. However, the practical application of MgH2 is restricted by slow sorption kinetics and high stability of thermodynamic properties. Hydrogen storage performance of MgH2 was enhanced by introducing the Mg–Na–Al system that destabilises MgH2 with NaAlH4. The Mg–Na–Al system has superior performance compared to that of unary MgH2 and NaAlH4. To boost the performance of the Mg–Na–Al system, the ball milling method and the addition of a catalyst were introduced. The Mg–Na–Al system resulted in a low onset decomposition temperature, superior cyclability and enhanced kinetics performances. The Al12Mg17 and NaMgH3 that formed in situ during the dehydrogenation process modify the reaction pathway of the Mg–Na–Al system and alter the thermodynamic properties. In this paper, the overview of the recent progress in hydrogen storage of the Mg–Na–Al system is detailed. The remaining challenges and future development of Mg–Na–Al system are also discussed. This paper is the first review report on hydrogen storage properties of the Mg–Na–Al system.