Achieving ambient temperature hydrogen storage in ultrafine nanocrystalline TiO₂@C-doped NaAlH₄

Sodium alanate (NaAlH₄) has attracted tremendous interest as a prototypical high-density complex hydride for on-board hydrogen storage. However, poor reversibility and slow kinetics limit its practical application. In this paper, we propose a novel strategy for the preparation of an ultrafine nanocrystalline TiO₂@C-doped NaAlH₄ system by first calcining the furfuryl alcohol-filled MIL-125(Ti) at 900 °C and then ball milling with NaAlH₄ followed by a low-temperature activation process at 150 °C under 100 bar H₂. The as-prepared NaAlH₄-9 wt% TiO₂@C sample releases hydrogen starting from 63 °C and re-absorbs starting from 31 °C, which are reduced by 114 °C and 54 °C relative to those of pristine NaAlH₄, respectively. At 140 °C, approximately 4.2 wt% of hydrogen is released within 10 min, representing the fastest dehydrogenation kinetics of any presently known NaAlH₄ system. More importantly, the dehydrogenated sample can be fully hydrogenated under 100 bar H₂ even at temperatures as low as 50 °C, thus achieving ambient-temperature hydrogen storage. The synergetic effect of the Al-Ti active species and carbon contributes to the significantly reduced operating temperatures and enhanced kinetics.