Intermetallic hydrogen absorption

Buschow, K.H.J. (1984) Hydrogen absorption in intermetallic compounds. In Handbook on the Physics and Chemistry of Rare Earths, eds. Gschneidner Jr., K.A., and Eyring, L. (North-Holland, Amsterdam), Vol. 6, p. 1. 

The alloying effects on the electronic structures of LaNij and Mg Ni intermetallic hydrides are investigated by the DV-Xacluster method in order to understand the hydrogen absorption and desorption characteristics of these compounds. 

Apart from these specific hydrogen absorption and desorption properties, it is clear that the intermetallic compounds are more often used as precursors of new and more active catalysts. The decomposition of intermetallic compounds into transition-metal particles and rare-earth hydride, oxide or hydroxide in the course of the catalytic reaction was evidenced in a large number of catalytic reactions, especially those involving CO dissociation, which produces oxidizing species. The rise of catalytic activity was... 

As an intermetallic hydride undergoes repeated hydrogen absorption-desorption cycles, disproportionation, i.e. decomposition of the intermetallic compound, and loss of capacity may occur. This is illustrated in the following examples of eqs. (5) and (6). 

A high-temperature chemical heat pump system has been designed at JAERI to heat up waste heat of about 500 °C to above 1000 °C by using Ti/Cr metal hydride intermetallic compounds (Fig. 4-11). This method would improve the total energy efficiency of the hydrogen production system combined with the process heat provision by the HTTR. The system consists of a low-temperature and a high-temperature vessel with the metal hydride material. The exothermal process of hydrogen absorption by the metal is able to heat up helium to approx. 1000 °C as was demonstrated in a test system [36]. 

Fig. 6.15 Pressure composition isotherms for hydrogen absorption in a typical intermetallic compound on the left-hand side. The solid solution (a-phase), the hydride phase (/J-phase) and the region of the coexistence of the two phases. The coexistence region is characterized by the flat plateau...

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