Long-term hydrogen storage performance and structural evolution of LaNi4Al alloy

Abstract

LaNi5-based hydrogen storage alloys have a strong application potential in many areas such as gaseous hydrogen storage, hydrogen compressing, Ni/MH batteries etc. But the cycling stability is always an important issue of concern. In this study, the changes in the hydrogen storage performance of the LaNi4Al alloy at 403, 423 and 443 K during 1000 hydrogen absorption/desorption cycles are studied, and the degradation mechanism is explored using EXAFS as a main study method. It is found that with increasing cycle number, the P-C-T plateau first becomes flattened then steepened, the plateau pressure and the hysteresis are decreased, the entropy change for both hydrogen absorption and desorption first increases and then decreases, and the hydrogen storage capacity decreases. Testing temperature does not have notable influence in the variation trend of the long-term hydrogen storage properties. The degradation is mainly reflected by the tilted P-C-T plateau and the reduced hydrogen storage capacity. Structural analysis results suggest that the strain-induced nanocrystalization and the atomic mis-location during hydrogen absorption/desorption might cause a high disorder state and a partial destruction in LaNi5 crystal lattice, resulting in the degradation in the hydrogen storage properties.