Significantly improved kinetics, reversibility and cycling stability for hydrogen storage in NaAlH4 with the Ti-incorporated metal organic framework MIL-125(Ti)

Abstract

A well-crystallized Ti-incorporated metal organic framework, MIL-125(Ti), synthesized using a solvothermal method, was introduced into NaAlH₄ as the catalyst precursor to improve the dehydrogenation–hydrogenation kinetics. Adding 5 wt% MIL-125(Ti) dramatically decreased the operating temperatures and improved the reaction kinetics for hydrogen storage in NaAlH₄. The starting temperature for hydrogen desorption from the sample containing MIL-125(Ti) was lowered by 50 °C relative to that of the pristine sample. The apparent activation energies of the first two dehydrogenation steps of the 5 wt% MIL-125(Ti)-added NaAlH₄ were ca. 98.9 and 96.3 kJ mol⁻¹, respectively; both these values are lower than those of the pristine sample. Mechanistic studies revealed that the catalytic function of the Ti-based active species and the nanopore effects of the dehydrogenation decreased the operating temperatures and increased the rate of the dehydrogenation–hydrogenation process in the MIL-125(Ti)-added sample. This understanding will facilitate further improvements in the hydrogen storage properties of metal alanates using optimized MOF-based additives.