Nanoconfinement significantly improves the thermodynamics and kinetics of co-infiltrated 2LiBH₄-LiAlH₄ composites: Stable reversibility of hydrogen absorption/resorption

A uniformly distributed composite of 2LiBH₄-LiAlH₄ was successfully nanoconfined in mesoporous carbon scaffolds by using the solvent-mediated infiltration technique. The onset dehydrogenation temperatures of LiAlH₄ and LiBH₄ in the infiltrated 2LiBH ₄-LiAlH₄ composite are decreased to ∼80 and ∼230 C, respectively, and are 40 and 145 C lower for their post-milled counterparts. Isothermal measurements reveal that ∼10 wt.% H₂ could be released from the nanoconfined 2LiBH₄-LiAlH₄ composite at 300 C within 300 min, while less than 4 wt.% H₂ was released with respect to the post-milled mixture, even at 350 C. Moreover, by taking advantage of both nanoconfinement and thermodynamic destabilization, the release of toxic diborane from LiBH₄ was successfully suppressed. The dehydrogenation mechanism reveals that, under the structure-directing effects of carbon supports, the decomposition of the well-distributed 2LiBH₄-LiAlH ₄ composite favors the formation of AlB₂ instead of the thermodynamically stable Li₂B₁₂H₁₂, which has been verified to play a crucial role in enhancing the hydrogenation of the 2LiBH₄-LiAlH₄ composite. In combination with the extra LiH supplied by the in situ decomposition of nanoconfined LiAlH₄, the thus-tailored thermodynamics and kinetics of the 2LiBH₄-LiAlH ₄ composite endow it with significantly advanced reversible hydrogen storage properties, with a stable reversibility without apparent degradation after seven dehydrogenation/rehydrogenation cycles. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.