Solvent-free synthesis and decomposition of Y(BH4)3

The implementation of a future hydrogen society relies on safe and economic ways to produce, store and distribute hydrogen. Among different techniques to store hydrogen, solid-state hydrogen storage in borohydrides M(BH4)n (M = Li, Na, Mg, Ca, Al, etc.; n = 1, 2, 3, 4) is attractive due to the high gravimetric and volumetric hydrogen density in these compounds. Some of the most intensively investigated tetrahydroborates (e.g. LiBH4, Ca(BH4)2 and Mg(BH4)2) exhibit a rather high hydrogen desorption temperature because of the thermodynamic stability or because of a kinetic barrier. Other borohydrides such as Al(BH4)3 are thermodynamically unstable and decompose spontaneously at ambient conditions.

Theoretical predictions based on density functional calculations suggested Y(BH4)3 to be stable at room temperature and to decompose in a clean way, without the evolution of poisonous diborane.

We achieved the direct and solvent-free synthesis of yttrium borohydride by reactive ball milling of yttrium hydride in diborane/hydrogen atmosphere. The product contains only the solid elemental hydride as remaining contaminant. Yields above 75% were obtained. The product crystallizes in the cubic a phase and releases hydrogen above 460 K. The decomposition was measured by in situ X-ray diffraction and the hydrogen release was monitored gravimetrically in conjunction with infrared gas analysis. No diborane was detected during the decomposition.

Details of the solvent free synthesis and the hydrogen release are going to be published in Scripta Materialia, doi:10.1016/j.scriptamat.2011.11.010. Details of the solvent free synthesis and the hydrogen release are published in Scripta Materialia, 66 2012 280.