Mechanistic understanding of CoO-catalyzed hydrogen desorption from a LiBH4·NH3-3LiH system.

Abstract

Addition of a minor quantity of CoO significantly reduces the dehydrogenation temperature, accelerates the dehydrogenation rate and increases the hydrogen purity of the LiBH4·NH3-3LiH system. The LiBH4·NH3-3LiH-0.1CoO sample exhibits optimal dehydrogenation properties because it releases 8.5 wt% of hydrogen below 250 °C, which is approximately 90 °C lower than that of the pristine sample. At 200 °C, approximately 8.0 wt% of hydrogen is released from the LiBH4·NH3-3LiH-0.1CoO sample within 100 min, whereas only 4.1 wt% is released from the pristine sample under identical conditions. The EXAFS analyses reveal that upon heating, CoO is first reduced to metallic Co at 130 °C and then partially combines with B to form a Co-B species. The in situ formed Co and Co-B are finely dispersed in the dehydrogenated intermediates, and they play critical roles as active catalysts in favour of breaking the B-H bonds of the Li-B-N-H species. This effectively decreases the thermodynamic and kinetic barriers of the dehydrogenation reaction of the LiBH4·NH3-3LiH system.