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 degrees C and then ball milling with NaAlH4 followed by a low-temperature activation process at 150 degrees C under 100 bar H-2. The as-prepared NaAlH4-9 wt% TiO2@C sample releases hydrogen starting from 63 degrees C and re-absorbs starting from 31 degrees C, which are reduced by 114 degrees C and 54 degrees C relative to those of pristine NaAlH4, respectively. At 140 degrees 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 H-2 even at temperatures as low as 50 degrees 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.