Titanium Hydride Nanoplates Enable 5 wt% of Reversible Hydrogen Storage by Sodium Alanate below 80°C.

Abstract

Sodium alanate (NaAlH₄) with 5.6 wt% of hydrogen capacity suffers seriously from the sluggish kinetics for reversible hydrogen storage. Ti-based dopants such as TiCl₄, TiCl₃, TiF₃, and TiO₂ are prominent in enhancing the dehydrogenation kinetics and hence reducing the operation temperature. The tradeoff, however, is a considerable decrease of the reversible hydrogen capacity, which largely lowers the practical value of NaAlH₄. Here, we successfully synthesized a new Ti-dopant, i.e., TiH₂ as nanoplates with ~50 nm in lateral size and ~15 nm in thickness by an ultrasound-driven metathesis reaction between TiCl₄ and LiH in THF with graphene as supports (denoted as NP-TiH₂@G). Doping of 7 wt% NP-TiH₂@G enables a full dehydrogenation of NaAlH₄ at 80°C and rehydrogenation at 30°C under 100 atm H₂ with a reversible hydrogen capacity of 5 wt%, superior to all literature results reported so far. This indicates that nanostructured TiH₂ is much more effective than Ti-dopants in improving the hydrogen storage performance of NaAlH₄. Our finding not only pushes the practical application of NaAlH₄ forward greatly but also opens up new opportunities to tailor the kinetics with the minimal capacity loss.