Mechanistic understanding of CoO-catalyzed hydrogen desorption from a LiBH4 center dot NH3-3LiH system

摘要

Addition of a minor quantity of CoO significantly reduces the dehydrogenation temperature, accelerates the dehydrogenation rate and increases the hydrogen purity of the LiBH4 center dot NH3-3LiH system. The LiBH4 center dot NH3-3LiH-0.1CoO sample exhibits optimal dehydrogenation properties because it releases 8.5 wt% of hydrogen below 250 degrees C, which is approximately 90 degrees C lower than that of the pristine sample. At 200 degrees C, approximately 8.0 wt% of hydrogen is released from the LiBH4 center dot 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 degrees 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 center dot NH3-3LiH system.