Clarifying the dehydrogenation pathway of catalysed Li(NH)BH-LiH composites.

The effect of different metal oxides (CoO and NiO) on the dehydrogenation reaction pathways of the Li(NH)BH-LiH composite was investigated. The additives were reduced to metallic species i.e. Co and Ni which act as catalysts by breaking the B-H bonds in the Li-B-N-H compounds. The onset decomposition temperature was lowered by 32 °C for the Ni-catalysed sample, which released 8.8 wt% hydrogen below 275 °C. It was demonstrated that the decomposition of the doped composite followed a mechanism via LiNH and LiBN formation as the end product with a strong reduction of NH emission. The sample could be partially re-hydrogenated (∼1.5 wt%) due to lithium imide/amide transformation. To understand the role of LiH, Li(NH)BH-LiH-NiO and Li(NH)BH-NiO composites were compared. The absence of LiH as a reactant forced the system to follow another path, which involved the formation of an intermediate phase of composition LiBNH at the early stages of dehydrogenation and the end products LiNH and monoclinic LiBN. We provided evidence for the interaction between NiO and LiNH during heating and proposed that the presence of Li facilitates a NH-rich environment and the Ni catalyst mediates the electron transfer to promote NH coupling.