Clean Technology 2010
J.-Ch. Buhl, C.H. Rüscher, L. Schomborg, F. Stemme
Leibniz University Hannover, DE
boron hydride sodalite, nanocrystalline solids, hydrogen storage, synthesis, thermal behaviour
Boron hydride is an interesting material for hydrogen storage but to become widely accepted in techniques, several problems like the high reactivity of NaBH4 under atmospheric conditions have to be solved. The latter offers a general safety problem according to the possibility of self ignition under influence of air moisture. Incorporation of the salt into a protective microporous sodalite matrix is a suitable way as recently found by us for microcrystalline BH4- sodalite. In the present work we investigate the synthesis and properties of nanocrystalline sodium boron hydride sodalite. Material of 25 nm average crystal size agglomerated by poorly crystalline hydrosodalite to bigger particles up to ~ 100 nm was observed from low temperature gel crystallization under hyperalkaline conditions. We show that the nanocrystalline sodalite host framework not only protects the BH4- ions from decomposition by air moisture but also exhibits two further important properties. Firstly hydrogen release already starts significantly above about 373 K. i.e. about 100K lower compared to the microcrystalline material. Secondly a 100% conversion rate was found for the BH4- anions in the nanocrystalline sample instead of only 40% under the same experimental conditions for the microcrystals. We conclude that the small particle size and the amount of water, available from the poorly crystalline hydrosodalite parts of the nanocrystalline sample control the complete hydrogen release reaction: BH4- + 2H2O => 4H2 + BO2-.