Cost-Effective Hierarchical Catalysts for Promoting Hydrogen Release from Complex Hydrides

Fe nanoparticles (∼10 nm), used to grow carbon nanotubes (CNTs), have an outstanding ability to catalyze the dehydrogenation of LiAlH₄. The CNTs help connect Fe and LiAlH₄ and create microchannels among the composite, thus promoting the release of hydrogen. Inspired by these results, a supercritical-CO₂-fluid-assisted deposition technique is employed to decorate the Fe/CNTs with highly dispersed nanosized Ni (∼2 nm in diameter) for better performance. With the incorporation of 10 wt% of this hierarchical catalyst (Ni/Fe/CNTs), the initial dehydrogenation temperature of LiAlH₄ is decreased from ∼135 to ∼40C. At 100C, this catalyzed LiAlH₄ takes only ∼0.1 h to release 4.5 wt% hydrogen, which is more than 100 times faster than the time needed with pristine LiAlH₄. The dehydrogenation mechanism of the complex hydride is examined using in situ synchrotron X-ray diffraction. No pressure, LiAlH₄, just release H₂: Highly effective Ni/Fe/carbon nanotubes (CNTs) hierarchical catalysts with low cost are constructed using a supercritical CO₂-assisted deposition technique. Using 10 wt% of this nanocatalyst, the initial dehydrogenation temperature of LiAlH₄ is decreased from ∼135C to ∼40C. At 100C, the catalyzed LiAlH₄ takes only ∼0.1 h to release 4.5 wt% hydrogen, which is more than 100 times faster than that required for pristine LiAlH₄.