Interesting influence of structure phases on hydrogen storage properties of AB5 type alloys

This study investigates the influence of phase composition and Sn for Ni substitution on the hydrogen storage characteristics of La–Ni–Sn alloys. Through a combination X-ray diffraction (XRD), scanning electron microscopy (SEM), Sieverts-type measurements, and ab initio calculations, we demonstrate that Sn substitution expands the unit cell volume, thereby lowering equilibrium plateau pressures and enhancing hydride stability. Alloys containing 30 wt% La, which exhibit the coexistence of two LaNi 5 -type phases, leads to an increase in the slope of the plateau and reduced hysteresis. In contrast, alloys with 40 wt% La exhibit a dual-phase microstructure consisting of LaNi 5 and LaNiSn, resulting in two-step hydrogenation process. Kinetic analysis via the JMAK model reveals that while the coexistence of two LaNi 5 -type phase slows down the hydrogen absorption, the presence of incoherent grain boundaries in multiphase alloys significantly reduces activation energy (down to 15.1 kJ/mol) by promoting rapid grain-boundary (Gb) hydrogen diffusion. These results demonstrate that Gb-mediated diffusion as a promising mechanism for tailoring both the thermodynamic and kinetic performance of AB 5 -type hydrogen storage materials.