Reversible hydrogen decomposition of KAlH4

We report that potassium aluminum tetrahydride. KAIH(4), exhibits a rapid reversible hydrogen decomposition reaction without any aid of external catalysts. This is significantly different from the reaction mechanism of NaAlH4 and LiAlH4, in which the homogeneous doping of the transition metal catalyst is essential for the reversibility and fast kinetics. The reversible dehydrogenation and hydrogenation were clearly observed without a catalyst over a temperature range 250-340 degreesC under <10 bar of hydrogen. Hydrogen storage ability was above 3.5 wt.% (81.4% of the theoretical value of 4.2 wt.%). KAlH4 may be a competitive option with a lightweight but high-temperature metal hydride system such as Mg2NiH4. These findings will also provide renewed guidelines for understanding the reaction mechanism of the catalyzed alanates as reversible hydrogen storage materials. (C) 2002 Elsevier Science B.V. All rights reserved.