Properties of Mg-based materials for hydrogen storage

In the presented paper, microstructures of as-cast MgNi14.0 and MgNi27.8 alloys are described. The alloys are composed of α(Mg) phase and Mg2Ni intermetallic (space group P6222) of primary and/or eutectic nature. The α(Mg)+Mg2Ni eutectic is characterized by an asymmetric zone of coupled growth. Primary Mg2Ni phase shows a branched dendritic morphology and eutectic Mg2Ni phase forms narrow and interconnected lamellae. The MgNi27.8 alloy was electrochemically hydrided in 6 M KOH. XRD proved that the hydriding led to a transformation of the Mg2Ni phase into Mg2NiHx (x=0–0.3) solid solution. It was shown that the hydriding rate increased with bath temperature and that the optimum voltage between cathode and anode was 1.5 V. Higher voltages resulted in H2 evolution which reduced hydriding efficiency. An 1 h hydriding at 90 °C and 1.5 V was able to produce almost 20 μm layer of the Mg2NiH0.3 phase. Further hydriding probably led to a formation of Mg2NiH4 hydride which retarded the inward diffusion of H.