Long-term hydrogen absorption/desorption properties of an AB5-type LaNi4.75Mn0.25 alloy

Abstract AB5-type hydrogen storage alloys have been extensively studied due to their wide applications, but their degradation process is still controversial, hindering the improvement in their cycling performance. In this work, the degradation mechanism of an AB5-type LaNi4.75Mn0.25 alloy with single CaCu5-type phase structure has been investigated based on its long-term hydrogen storage properties and the structural changes during cycling. It is found that within 1000 hydrogen absorption/desorption cycles in the temperature range of 343–383 K, the P-C-T curves remain a single plateau, but the plateau slope becomes steeper and the hydrogen storage capacity decreases. These degradation phenomena are caused by the structural evolution of the alloy including particle pulverization and crystal lattice damage. The internal driving force of the structural changes is found to be the microstrains generated during hydrogen absorption/desorption. But with cycling, the isotropic parameter c/a increases, decreasing the hysteresis and slowing down the degradation process.