Hydrogen storage properties of nanoconfined LiBH4–NaBH4

• Increased porosity obtained by CO2 activation of carbon aerogel.
• LiBH4–NaBH4; bulk and nanoconfined hydrogen storage properties are investigated.
• Nanocomposite reduces hydrogen desorption temperature by 100 °C compared to bulk.
• Nanocomposite H2 cyclic capacity more than 3 times higher than bulk material.

In this study a eutectic melting composite of 0.62LiBH4–0.38NaBH4 has been infiltrated in two nanoporous resorcinol formaldehyde carbon aerogel scaffolds with similar pore sizes (37 and 38 nm) but different BET surface areas (690 and 2358 m2/g) and pore volumes (1.03 and 2.64 mL/g). This investigation clearly shows decreased temperature of hydrogen desorption, and improved cycling stability during hydrogen release and uptake of bulk 0.62LiBH4–0.38NaBH4 when nanoconfined into carbon nanopores. The hydrogen desorption temperature of bulk 0.62LiBH4–0.38NaBH4 is reduced by ∼107 °C with the presence of carbon, although a minor kinetic variation is observed between the two carbon scaffolds. This corresponds to apparent activation energies, EA, of 139 kJ mol−1 (bulk) and 116–118 kJ mol−1 (with carbon aerogel). Bulk 0.62LiBH4–0.38NaBH4 has poor reversibility during continuous hydrogen release and uptake cycling, maintaining 22% H2 capacity after four hydrogen desorptions (1.6 wt.% H2). In contrast, nanoconfinement into the high surface area carbon aerogel scaffold significantly stabilizes the hydrogen storage capacity, maintaining ∼70% of the initial capacity after four cycles (4.3 wt.% H2).

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