Scandium functionalized carbon aerogel: Synthesis of nanoparticles and structure of a new ScOCl and properties of NaAlH4 as a function of pore size

• New synthesis approach for nanoporous Sc-functionalization carbon aerogel (Sc-CA).
• The new scandium oxochloride, ScOCl, structure is obtained.
• NaAlH4 nanoconfined in Sc-CA with pores ranging between 7 nm• Improved H2 release kinetics obtained with decreasing pore size.
• Nanoconfinement (Dmax=39 nm) retains 71% of the H2 capacity after four cycles.

A new method for scandium-functionalization of carbon aerogels forming nanoparticles of a new scandiumoxochloride, ScOCl is presented. Sodium aluminiumhydride, NaAlH4, is successfully melt infiltrated into the nano porous scaffolds with pore sizes of Dmax=7, 10, 13, 21, 26 and 39 nm, containing scandium based nano particles (<2.9 wt%) confirmed by elemental analysis and scanning electron microscopy. A systematic study of hydrogen storage properties of the nano composite materials is presented. An aqueous solution of ScCl3 was initially infiltrated and formed nanoconfined [Sc(OH)(H2O)5]2Cl4(H2O)2, which transforms to nanoparticles of a new scandium oxochloride, ScOCl at 192 °C and to Sc2O3 at 420 °C. ScOCl crystallizes in an orthorhombic unit cell a=3.4409(8), b=3.9613(6) and c=8.178(2) Å, space group Pmmn, and is built from layers of [ScO4Cl2] octahedra forming neutral ScOCl layers. Temperature programmed desorption mass spectroscopy shows slightly improved kinetics for release of hydrogen with decreasing pore size. Continuous cycling of hydrogen release and uptake measured by the Sieverts' method reveal a larger preserved hydrogen storage capacity for scandium-functionalized aerogel with the larger pores (39 nm).

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