Hydrogen-generating solid-state hydride/hydroxide reactions

Solid-state reactions of ionic hydrides with alkaline hydroxides are shown to produce hydrogen gas and metal oxides. These reactions are analogous to the well-known hydrolysis reactions of ionic hydrides. Both classes of reactions are generally exothermic and are thermodynamically favored; DeltaGdegrees < 0 near room temperature. However, solid-state hydride/hydroxide reactant mixtures are kinetically stable at room temperature and can be prepared by mechanical milling without appreciable reaction. Thus, optimally stoichiometric mixtures are possible and nearly theoretical amounts of hydrogen can be generated. Reaction occurs upon heating with H, evolution beginning at similar to50degreesC and complete reaction occurring by 200-300degreesC. The reaction rate can be enhanced with additives such as TiCl3. Specifically, we discuss the reactions LiH + LiOH, 2LiH + NaOH, LiBH4 + 4LiOH, and 3LiBH(4) + 4LiOH.H2O. The 3LiBH4 + 4LiOH.H2O reaction generates approximately 10 wt.% hydrogen with more than 5 wt.% produced at temperatures below 100degreesC. (C) 2004 Elsevier B.V. All rights reserved.