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Abstract

Sodium aluminum hydride has been extensively investigated for hydrogen storage applications whereas its intermediate decomposition compound Na₃AlH₆ received much less attention, despite having a lower dissociation pressure and a reasonable hydrogen storage capacity of 3.0 wt%. In this work, Na₃AlH₆ is synthesized through ball milling, starting from NaAlH₄ and 2 NaH in the presence of TiCl₃ catalyst precursor, and evaluated on its hydrogen sorption properties and cycle stability. Further addition of 8 mol% Al and 8 mol% activated carbon (AC) and their effect on both the hydrogen sorption properties and cycle stability have been investigated. In order to explore whether the introduction of the Al and AC additives would be more beneficial (in terms of hydrogen sorption behavior and cycle stability) after the Na₃AlH₆ synthesis or during its synthesis, pre-synthesized Na₃AlH₆-based measurements were also included in this work. TiCl₃-catalyzed NaAlH₄+2 NaH sample showed a stable reversible hydrogen storage capacity of 1.7 wt%, which was further increased to 2.1 wt% with the addition of Al-powder and activated carbon AC.