Releasing 17.8 wt% H2 from lithium borohydride ammoniate

Abstract

Release of ca. 17.8 wt% of hydrogen was observed from the Co-catalyzed lithium borohydride ammoniate, Li(NH₃)_4/3BH₄ (with equivalent protic and hydridic hydrogen atoms, composed of solid Li(NH₃)BH₄ and liquid Li(NH₃)₂BH₄), in the temperature range of 135 to 250 °C in a closed vessel. The low NH₃ equilibrium vapor pressure of the ammoniate in the vessel results in the retention of the majority of NH₃ in the vicinity of LiBH₄, and thus, creates an environment favorable for the direct dehydrogenation rather than deammoniation. The dehydrogenation is a two-step process forming the intermediates Li₄BN₃H₁₀ and LiBH₄. The final solid residue is a mixture of BN and Li₃BN₂. The presence of nanosized Co catalyst effectively promote the hydrogen release.