Triggering highly stable catalytic activity of metallic titanium for hydrogen storage in NaAlH4 by preparing ultrafine nanoparticles

Abstract

Highly stable catalytic activity of metallic Ti and corresponding mechanistic understanding are of particularly critical importance for the development of sodium alanate (NaAlH₄) as an advanced on-board hydrogen storage medium. However, only limited catalytic effectiveness is observed for commercial metallic Ti powders due to their ductile behavior limiting the dispersion of large particles. Here, we successfully synthesize ultrafine metallic Ti nanoparticles (3–5 nm) supported on amorphous carbon (nano-Ti@C) through a facile, scalable calcination process. Unlike commercial metallic Ti powders, the nano-Ti@C exhibits remarkable catalytic activity for hydrogen storage in NaAlH₄, superior to other reported transition metals and rare earth metals. The 7 wt% nano-Ti@C-containing NaAlH₄ sample delivers a quite low onset temperature of dehydrogenation of 75 °C and a practically available hydrogen capacity as high as 5.04 wt%. Reloading of hydrogen is fully completed in <3 min at 100 °C and 120 bar H₂; this sorption kinetics is fastest among all catalytically enhanced NaAlH₄ systems known. Moreover, only 0.07 wt% of hydrogen capacity is lost after 100 cycles, exhibiting a highly stable cyclability. Theoretical calculations reveal the interaction between Ti and Al, which not only weakens the Al–H bonding but also facilitates diffusion of H in NaAlH₄, contributing to the superior catalytic activity of nano-Ti@C. Our findings greatly increase potentials towards practical applications of catalyst-doped NaAlH₄ for onboard hydrogen storage.