Phase transition and hydrogen storage properties of Mg17Ba2 compound

• The mechanism is revealed for the phase transition of Mg-Ba compound during the de/hydrogenation process.
• A new kind of fully reversible hydrogen storage Mg-Ba-H alloy is realized.
• An undefined barium magnesium hydride has been found with composition being Ba2Mg7H18.

Mg17Ba2 hydrogen storage alloy was obtained by induction melting, and its hydrogen storage properties and phase transitions have been investigated. The reversible hydrogen capacity of Mg17Ba2 compound was 4.0 wt% H2. A three-step dehydrogenation mechanism was revealed for the first time, and a new hydride (Ba2Mg7H18) was discovered during the dehydrogenation process. Enthalpy and entropy changes for the dehydrogenation of Mg17Ba2 were also calculated.

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