Improved Hydrogen Storage Kinetics of Nanoconfined NaAlH₄ Catalyzed with TiCl₃ Nanoparticles

Abstract

Nanoparticles of NaAlH₄ have been infiltrated in nanoporous carbon aerogel with TiCl₃ nanoparticles in order to explore possible synergetic effects between nanoconfinement and a functionalized catalytic scaffold. Resorcinol formaldehyde carbon aerogels with an average pore size of 17 nm and total pore volume of 1.26 mL/g were infiltrated with TiCl₃ to obtain an aerogel doped with 3.0 wt % TiCl₃ nanoparticles. NaAlH₄ was melt-infiltrated into the functionalized carbon aerogel at 189 °C and <i>p</i>(H₂) ∼ 186−199 bar. Energy-dispersive spectrometry (EDS) combined with focused ion beam (FIB) techniques revealed the presence of Na, Al, Ti, and Cl inside the aerogel scaffold material. The infiltrated NaAlH₄ was X-ray amorphous, whereas ²⁷Al magic-angle spinning (MAS) NMR spectroscopy confirmed the presence of nanoconfined NaAlH₄. Temperature-programmed desorption mass spectroscopy (TPD-MS) and Sieverts’ measurements demonstrated significantly improved hydrogen desorption kinetics for this new nanoconfined NaAlH₄−TiCl₃ material as compared to nanoconfined NaAlH₄ without the catalysts TiCl₃ and to bulk ball-milled samples of NaAlH₄−TiCl₃. We find that the onset temperature for hydrogen release was close to room temperature (<i>T</i>_onset = 33 °C), and the hydrogen release rate reached a maximum value at 125 °C, which demonstrates favorable synergetic effects between nanoconfinement and catalyst addition.