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Abstract The long-term hydrogen storage performance of a CaCu 5 -type LaNi 4 Co alloy is studied by detailed analysis of its P-C-T curves and structural changes within 1000 cycles. The alloy shows one absorption plateau (α→β phase transition) and two desorption plateaus (γ→β and β→α phase transitions). With increasing cycle number, the plateau pressures for both α→β and β→α phase transitions decrease due to the increase in cell volumes. The increased crystal cells also provide more space to accommodate the simultaneous occupations of 12° and 6 m sites, and thus β→α and β→γ desorption plateaus become less distinguishable. During cycling, partial phase decomposition, crystal grain destruction and surface oxidation occur, resulting in the loss of hydrogen storage capacity. In addition, due to the increase in the atomic disorder and internal microstrains and defects, the average slope factors (SF / H %) of the hydrogen absorption/desorption plateaus are increased. Particularly, the SF / H % value of the γ→β plateau is always higher than those of the α→β and β→α plateaus, and it also increases faster with cycling, reaching about 4 times of the other two plateaus at the 1000th cycle. It is considered that the improvement of the γ→β phase transition process is significant to promote the cycling behavior and practical applications of this alloy system. Graphical abstract Image 1 Highlights • Hydrogen storage properties of the LaNi 4 Co alloy within 1000 cycles are studied. • Changes in PCT curves with double desorption plateaus are investigated in detail. • Phase decomposition, lattice expansion, crystal damage and surface oxidation occur. [ABSTRACT FROM AUTHOR]

LaNi 5 -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 LaNi 4 Al 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 LaNi 5 crystal lattice, resulting in the degradation in the hydrogen storage properties. [ABSTRACT FROM AUTHOR]

In this work, the microstructure and hydrogen storage properties of Ti 1- x Ce x V 0.45 Mn 1.5 (x = 0, 0.05, 0.10, 0.15, and 0.20) alloys have been studied. It shows that the x = 0 alloy consists of a C14 Laves single phase. Moreover, alloys containing Ce can exhibit the CeO 2 phase, whose content rises as Ce content does. Furthermore, CeO 2 phase aggregation causes the alloy to fracture and the hydrogen diffusion channel to enlarge. According to the PCT curves (25 °C), the plateau pressure increases with increasing Ce content, and the hydrogen storage capacity decreases with increasing Ce content due to increase in Ce content which does not absorb hydrogen. And it is also found that increase in Ce substitution for Ti results in better dynamic properties for the alloys. And the dehydrogenation kinetics curves show that hydrogen desorption rate substantially increases with x getting larger. This is because CeO 2 phase acts as the "hydrogen pump" to increase the rate of hydrogen discharge in the alloy, The fastest hydrogenation kinetics are shown, the best hydrogen storage performance is achieved, and the ma x imum hydrogenation is reached in less than 100 s. • According to the PCT curves, the plateau pressure increases with increasing Ce content and the hydrogen storage capacity decreases with increasing Ce content. • In this study, CeO 2 phase acts as the "hydrogen pump" to increase the rate of hydrogen discharge in the alloy. • CeO 2 phase aggregation leads to cracks in the alloy. [ABSTRACT FROM AUTHOR]