A self-catalyzing hydrogen-storage material.

Conventional (e.g. MgH2) and complex hydrides (e.g. alanates, borohydrides, and amides) are the two primary classes of solid-state hydrogen-storage materials. Many of these “high-density” hydrides have the potential to store large amounts of hydrogen by weight (up to 18.5 wt% for LiBH4) and/or volume (up to 112 gL!1 for MgH2), values that are comparable to the hydrogen content of gasoline (15.8 wt%, 112 gL!1). However, all known hydrides are inadequate for mobile storage applications due to one or more of the following limitations: a) unfavorable thermodynamics (they require high temperatures to release hydrogen), b) poor kinetics (low rates of hydrogen release and uptake), c) decomposition pathways involving the release of undesirable by-products (e.g. ammonia), and/or d) an inability to reabsorb hydrogen at modest temperatures and pressures (i.e. “irreversibility”). In spite of these drawbacks, renewed interest in complex hydrides has been stimulated recently by substantial improvements in their kinetics and reversibility provided by catalytic doping (e.g. TiCl3-doped NaAlH4), [7,8] and by thermodynamic enhancements achieved through reactive binary mixtures such as LiNH2/MgH2, [10,11] LiBH4/MgH2, [12] and LiNH2/LiBH4. These compositions, previously termed “reactive hydride composites”, represent the state-of-the-art in hydrogen-storage materials; compared to their constituent compounds, they exhibit improved thermodynamic properties, higher hydrogen purity, and, in some cases, reversibility. The desorption behavior of these previously studied composites is illustrated in Figure 1a. It is evident from the hydrogen desorption profile (top panel) that the composites generally desorb hydrogen at significantly lower temperatures than their individual components. For example, the lowest temperature reaction, which involves a