Hydrogen desorption of Mg–Mg2Ni hypo-eutectic alloys in air, Ar, CO2, N2 and H2

The hypo-eutectic Mg–Mg2Ni system can be modified by trace elemental additions of Na which change the microstructure and the functional properties of the alloy. The modified microstructure results in improvements to the hydrogen storage properties. In alloys of optimal composition, it has been shown that the reversible storage of 6.5–7 wt% H2 is possible at a rate of reaction that is realistic for industrial applications. This research investigates the release of H2 in air under atmospheric pressure as well as under 0.2 MPa atmospheres of Ar, CO2, N2, and H2. The release kinetics were characterised using in situ crystallographic phase transformation analysis obtained by synchrotron Powder X-ray diffraction (PXRD) at the Australian Synchrotron. The mole fraction of MgH2, Mg, Mg2Ni, and Mg2NiH4 was determined by Rietveld refinement using RIETAN-FP. It was found that the hydrogen release temperature largely depends on the atmosphere.

• This research utilises temperature and atmosphere controlled synchrotron XRD analysis. • It was found that the hydrogen release temperature largely depends on the atmosphere. • The results should be considered when comparing reported kinetics of Mg-based hydrides.