Reversing the Irreversible: Thermodynamic Stabilization of LiAlH<sub>4</sub> Nanoconfined Within a Nitrogen-Doped Carbon Host.
basic_science · Level V
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- Record sourced from PubMed, PMID 34029480.
- Also identified by DOI 10.1021/acsnano.1c02079.
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Abstract
A general problem when designing functional nanomaterials for energy storage is the lack of control over the stability and reactivity of metastable phases. Using the high-capacity hydrogen storage candidate LiAlH<sub>4</sub> as an exemplar, we demonstrate an alternative approach to the thermodynamic stabilization of metastable metal hydrides by coordination to nitrogen binding sites within the nanopores of N-doped CMK-3 carbon (NCMK-3). The resulting LiAlH<sub>4</sub>@NCMK-3 material releases H<sub>2</sub> at temperatures as low as 126 °C with full decomposition below 240 °C, bypassing the usual Li<sub>3</sub>AlH<sub>6</sub> intermediate observed in bulk. Moreover, >80% of LiAlH<sub>4</sub> can be regenerated under 100 MPa H<sub>2</sub>, a feat previously thought to be impossible. Nitrogen sites are critical to these improvements, as no reversibility is observed with undoped CMK-3. Density functional theory predicts a drastically reduced Al-H bond dissociation energy and supports the observed change in the reaction pathway. The calculations also provide a rationale for the solid-state reversibility, which derives from the combined effects of nanoconfinement, Li adatom formation, and charge redistribution between the metal hydride and the host.