Hydrogen Storage Properties of New Hydrogen-Rich BH3NH3-MetaI Hydride (TiH2, ZrH2, MgH2, and/or CaH2) Composite Systems

摘要

Ammonia borane (AB - NH3BH3) is one of the most attractive materials for chemical hydrogen storage due to its high hydrogen contents of 19.6 wt %; however, impurity levels of borazine, ammonia, and diborane in conjunction with foaming and exothermic hydrogen release calls for finding ways to mitigate the decomposition reactions. In this paper we present a solution by mixing AB with metal hydrides (TiH2, ZrH2, MgH2, and CaH2) which can control impurity levels impurity levels from AB upon decomposition. The composite materials were prepared by mechanical ball milling, and their H2 release properties were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The formation of volatile products from decomposition side reactions, such as borazine (N3B3H6) was determined by mass spectrometry (MS). Sieverts type pressure-composition-temperature (PCT) gas-solid reaction instrument was adopted to observe the kinetics of the H2 release reactions of the combined systems and neat AB. In situ ~(11)B MAS NMR of AB/MgH2/TiH2 revealed for the first time a competing decomposition pathway via cyclic -BH2NH2- species, previously only observed in solution. We found that by adding specific metal hydrides to AB we can eliminate the impurities and mitigate the heat release.