Introduction to metal hydrides of AB5 compounds
This chapter provides an introduction to metal hydrides of AB5 compounds.
Hydrogen absorption by AB5 intermetallic compounds with CaCu5 structure type was discovered almost simultaneously by Zijlstra and Westendorp [69Z1] and Neumann [69N1] in the late 1960s. A first complete report of the hydriding properties of various AB5 compounds including LaNi5 was made by Van Vucht et al. [70V1], followed by Van Mal [76V1] who presented a significant study of the effects of substitutions. In contact with hydrogen gas, this compound may readily and reversibly absorb 6 H/f.u. at room temperature under a pressure of 2 bar. This remarkable property has made this intermetallic compound a good candidate as a hydrogen storage material. Later on, the possible use as negative electrode material in Ni-MH batteries was reported [76B1, 77P1].
LaNi5 and its substituted derivatives represent, with palladium alloys, the best studied and best known hydrogen storage compound family. This is not only because of the simplicity of the metallurgy of this system, the relative easiness to synthesize compounds (the congruent melting and the presence of an homogeneity domain for LaNi5 helps a lot in the synthesis of single phase compounds), and the ability to perform substitution of La and Ni by many different metals in a large amount. This is also because LaNi5 has the largest absorption capacity among AB5 compounds, the hydrogenation reaction is generally easy to activate, proceeds with fast kinetics, and is highly reproducible. Last but not least, the incredible richness of the fundamental properties (both thermodynamic and structural) and the real applications these compounds have found as electrode materials for Ni-MH batteries and as hydrogen gas storage materials are worth to mention.
Therefore, the following review will be focused on CaCu5-type compounds and among them centered on the properties of LaNi5 and its substituted derivatives. The properties of other hydrogen absorbing AB5 compounds will, however, be addressed.
- [69N1]Neumann, H. H.: Ph.D. Thesis, Technische Hochschule, Darmstadt (1969)Google Scholar
- [70V1]Van Vucht, J.H.N., Kuijpers, F.A., Bruning, H.C.A.M.: Philips Res. Rep. 25, 133 (1970)Google Scholar
- [76V1]Van Mal, H. H.: Philips Res. Rep. (Suppl. 1), 1 (1976)Google Scholar
- [77P1]Percheron-Guégan, A., Achard, J.C., Sarradin, J., Bronoël, G.: Hydrides for Energy Storage, Geilo, Norway, p. 485. Pergamon Press, Oxford (1977)Google Scholar