Appearance of a Novel Pressure Plateau in RNi<SUB>5</SUB>-H (R = Rare Earth) Systems

Abstract

We investigated the hydrogen storage properties in a HoNi 5 -H system combined with TbNi 5 -H and DyNi 5 -H systems. Pressurecomposition (P-C) isotherms in the HoNi 5 -H system show one reversible pressure plateau during hydrogen absorption and desorption with a hysteretic phase transition. The maximum hydrogen storage capacity was found to be H/HoNi 5 ¼ ca. 2, and no second plateau similar to that observed in other RNi 5 -H (R: rare earth) systems was observed, even at 196 K. Two pressure plateaux found in light rare earth-based R L Ni 5 -H (R L ¼ La, Pr, Nd, Sm and Gd) systems tend to disappear in TbNi 5 -H and DyNi 5 -H systems and are scarcely present in HoNi 5 -H system. On the other hand, a novel pressure plateau appears at low hydrogen content in these systems due to the presence of a new hydride phase, and the plateau region extends from TbNi 5 -H and DyNi 5 -H to HoNi 5 -H systems. Contrary to the other plateaux, the pressures of the novel plateau during both hydrogen absorption and desorption decrease with decreasing unit cell volume of RNi 5 compounds or with increasing atomic number of the R element in RNi 5 -H systems. To clarify the effect of 4f electrons in the R element in RNi 5 -H systems on the novel plateau, we have evaluated the hydrogen storage properties in an YNi 5 -H system. Our results show that YNi 5 compound with lattice constants similar to those of TbNi 5 and DyNi 5 compounds has a similar P-C isotherm, suggesting that 4f electrons has no direct influence on the appearance of the novel plateau.

Improvement of reversible H storage capacity by fine tuning of the composition in the pseudo-binary systems A2-La Ni7 (A = Gd, Sm, Y, Mg)

“…followed by a second one of 2H/f.u. at much higher pressure (above 20 MPa at 25°C) [38,39]. Moreover, the hysteresis between absorption and desorption is quite high for these two compounds.…”

Особенности электронной структуры интерметаллических соединений CeNi-=SUB=-4-=/SUB=-M (M=Fe, Co, Ni, Cu)

“…Значительный магнитокалорический эффект, обнаруженный у отдельных представителей этих классов [3], также показывает перспективы их использования в устройствах магнитного охлаждения. Другим важным направлением применения таких интерметаллических соединений может стать водородная энергетика [4,5].…”