Hydriding-dehydriding reactions

It is known that the electrochemical hydriding/ dehydriding reactions taking place at a hydrogen storage electrode in an alkaline solution may be simply expressed as follows ... 

Figure 2 shows the strong dependence of temperature on the plateau pressure. The higher the temperature, the higher is the plateau pressure. This is an important thermodynamic consequence of the heat of reaction Ah associated with Eq. 1. The hydriding reaction (->) is exothermic and the dehydriding reaction ( -) is endothermic. The plateau pressure Pp is related to the absolute temperature T by the Van t Hoff equation... 

Schematic drawing of dehydriding and hydriding reactions of borohydride, LiBH4. 

Nakamori Y, Ninomiya A, Kitahara G, Aoki M, Noritake T, Miwa K, Kojima Y and Orimo S (2006), Dehydriding reactions of mixed complex hydrides, J. Power Sources, 155, 447 55. 

Above 40 wt % hydrogen content at room temperature, zirconium hydride is brittle, ie, has no tensile ductiHty, and it becomes more friable with increasing hydrogen content. This behavior and the reversibiHty of the hydride reaction are utilized ki preparing zirconium alloy powders for powder metallurgy purposes by the hydride—dehydride process. The mechanical and physical properties of zirconium hydride, and thek variation with hydrogen content of the hydride, are reviewed in Reference 127. 

Figure 6. Schematic representation of the reaction paths for hydriding and dehydriding LaNis [331.

Heat of reaction is one of the most important hydride properties from a container design point of view. Because heat is generated during hydriding and required during dehydriding, the... 

Another effect is that confinement in pores might influence the phases formed for complex systems. Although not completely understood this is found experimentally, for instance, by Autrey ef al. for the confinement of ammonia borane in mesoporous Si02 and carbon (see Section 10.6.1) [74]. For complex materials often not only thermodynamic considerations but also kinetics have an import influence on which phases are formed upon hydriding or dehydriding. For instance, on decomposition of UBH4 the thermodynamically most favorable reaction is ... 

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