Destabilization of LiBH4 dehydrogenation through H+–H− interactions by cooperating with alkali metal hydroxides

Abstract

Destabilization by the alkali metal hydroxides LiOH, NaOH, and KOH in the solid-state dehydrogenation of LiBH₄ is reported. 6.5 wt% of hydrogen was liberated within 10 minutes at 250 °C. Destabilization originated from the interaction between H⁺ in [OH]⁻ and H⁻ in [BH₄]⁻. A larger Pauling's electronegativity of the alkali metal (Li > Na > K) led to a greater acidity of the proton donor [OH]⁻ site, and thus enhanced destabilization. The temperature of the predominant dehydrogenation was reduced to 207, 221, and 230 °C, for ball milled LiBH₄–LiOH, 2LiBH₄–NaOH, and 2LiBH₄–KOH, respectively. The LiBH₄: LiOH stoichiometry greatly affected the destabilization, by providing differing reaction pathways in LiBH₄-xLiOH (x = 1, 1.36, 4). The incremental increase in the LiOH content of LiBH₄-xLiOH increased the dehydrogenation rate, but the temperature increased from 207 °C (x = 1) to 250 °C (x = 4). 4.1 and 6.5 wt% of hydrogen was liberated within 10 minutes by LiBH₄–LiOH and LiBH₄–4LiOH, respectively. The incremental increase in dehydrogenation temperature was attributed to differing [BH₄]⁻⋯[OH]⁻ interactions, formed by the differing stoichiometric ratios.