Microstructure and absorption/desorption kinetics evolutions of Mg–Ni–Ce alloys during hydrogenation and dehydrogenation cycles

Poor cycling stability limits the sustainable and long-life application of Mg as a hydrogen storage material. In the light of catalytic effects of rare earth elements and transition metals on de-/hydrogenation kinetics of Mg, binary Mg–20Ce, Mg–20Ni and ternary Mg–5Ni15Ce (wt%) alloys have been prepared with the aim of investigating the absorption and desorption cycling performance. Special attention is paid to the microstructure evolution during cycling and its interrelation with hydrogen storage properties. It is found that CeH_2.73 facilitates hydrogenation of Mg better than Mg₂Ni. Conversely, Mg₂Ni is more conducive to desorption. A synergistic catalytic effect between Mg₂Ni and CeH_2.73 is observed in Mg–5Ni15Ce alloy, the hydriding rate of which is faster than that of Mg–Ni and Mg–Ce binary alloys. The average particle size of each experimental alloy decreases significantly after 100 absorption/desorption cycles at 320 °C. Moreover, the particle sizes of CeH_2.73 and Mg₂Ni phases remain stable during cycling. The grain size of Mg increases significantly for binary alloys, while introducing Mg₂Ni and CeH_2.73 simultaneously can effectively inhibit the growth of Mg grains. The hydrogen absorption capacities increase gradually for Mg–20Ce and Mg–5Ni15Ce alloys due to reduced diffusion distance by particle pulverization and freshly exposed CeH_2.73 on newly formed particle surface. However, the capacity of Mg–20Ni alloy decreases slightly considering the facts that Mg grains agglomerate during cycling and Mg₂Ni possesses weak catalytic effect on absorption. Both the absorption and desorption kinetics keep stable during cycling for Mg–5Ni15Ce alloy.