(720h) Revealing the Hydration-Mediated Direct Vapor Pathway for Simultaneous Water Splitting and Hydrogen Liberation from LiAlH4

Lithium Aluminum Hydride (LiAlH4) offers outstanding potential for on-demand hydrogen generation via hydrolysis reactions with >95% yield at reaction temperature bellow 100℃. Research on LiAlH4 has primarily been focused on hydrogenation/dehydrogenation, tuning thermodynamics conditions, and improving the kinetics for on-demand H2 release. The advantage of vapor hydrolysis is that it simultaneously liberates framework hydrogen and splits water for a multiplier effect on hydrogen production potential; this is most applicable for on-demand H2 for transportation applications. However, reaction pathways for hydration mediated H2 liberation are not well understood. This research elucidates the complex reaction pathways for vapor hydrolysis of LiAlH4 using in situ and ex situ spectroscopic and reaction monitoring techniques.

First, the results reveal that for the reaction to reach completion, excess water vapor relative to stoichiometric amount is required. Ex situ X-ray Diffraction (XRD) shows that solid products from LiAlH4 hydrolysis are predominantly lithium-aluminum Layer Double Hydroxides (Li-Al LDH) with the chemical formula of LiAl₂(OH)₆.OH.2H₂O and LiOH.

Next, kinetic evaluation of powder hydrolysis shows an induction period for water uptake followed by hydrogen release, which when combined with in situ Fourier transformed diffuse reflectance spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and thermogravimetric analysis (TGA) supports a new mechanism for Li-Al LDH formation from LiAlH4 vapor hydrolysis. This new pathway proceeds by direct interfacial surface rearrangement and is dissimilar to conventional routes which follow dissolution-precipitation or salt imbibition (intercalation).

By observing O-H bending vibrations at 1400-1500 cm^-1, O-H stretching vibration at 3540-3550 cm^-1, the DRIFTS data was used to track how surface chemical changes influence the evolution of the bulk phase.

This new understanding is essential for identifying conditions for maximal, controlled, on-demand H₂ production from solid storage materials to power the next generation of long-range transportation.