Modifying microstructures and hydrogen storage properties of 85Â mass% Mg-10Â mass% Ni-5Â mass% La alloy by ultra-high pressure

Herein, an ultrahigh pressure (UHP, under 5 GPa) technique was introduced to improve hydrogen storage properties of 85 mass% Mg-10 mass% Ni-5 mass% La (noted as 85 Mg-10Ni-5La) alloy by modifying the microstructures. The phase composition, phase morphologies and hydrogen storage properties of the as-cast and UHP alloys were comparatively studied. Of particular interest is that UHP treatment effectively reduces the dehydriding onset temperature, as well as improves the hydrogen sorption kinetics, with the evidence that the amount of hydrogen desorption in the UHP alloy hydride is 3.51 wt.% at 573 K, which corresponds to 60.8% of the saturated capacity, while the values in the as-cast alloy change to 2.34 wt.% and 39.5%, respectively. The reversible hydrogen storage capacities and plateau hydrogen pressure of the as-cast and UHP alloys are close. X-ray diffractions and scanning electron microscopy results indicate the similar thermodynamic property of the two alloys is associated with the same hydrogen storage phases (Mg and Mg2Ni). The improvement in the hydriding/dehydriding kinetics is ascribed to a better catalytic effect of Mg2NiH4 and a higher volume fraction of phase boundary which acts as hydrogen diffusion channel, which is related with the formation of Mg6Ni phase after ultrahigh pressure treatment. The results demonstrate that the UHP treatment is an effective pathway to tune the hydrogen storage performances of those magnesium-nickel-rare earth alloys.