Controllable synthesis of 2D TiH2 nanoflakes with superior catalytic activity for low-temperature hydrogen cycling of NaAlH4

Abstract

Nanosized titanium compounds are particularly effective in catalyzing hydrogen cycling by NaAlH4. Titanium hydride (TiH2), as a catalyst, is highly interesting since it contributes hydrogen in addition to active Ti. However, it has been challenging to fabricate nanosized TiH2 due to the strong affinity of Ti with oxygen. Herein, TiH2 nanoflakes with a lateral size of ~10 nm and thickness of ~1 nm are successfully synthesized through a novel facile one-pot solvothermal process. In an anhydrous THF solution, LiH reacts with TiCl4 rapidly at 100 °C forming TiH2 and LiCl. The newly formed TiH2 nucleates and grows epitaxially on the graphene surface due to the well-matched lattice parameters, giving rise to the formation of TiH2 nanoflakes. Both theoretical calculations and experiments reveal the generation of Cl· radicals and unsaturated CC bonds when TiCl4 reacts with THF, which promotes the formation of TiH2. The nanoflake-like TiH2 on graphene enables an outstanding hydrogen storage performance of NaAlH4, i.e., full dehydrogenation at 80 °C and hydrogenation at 30 °C and under 100 bar H2, with a practical hydrogen capacity of 4.9 wt%, which has been never reported before.