Confinement of MgH2 Nanoclusters within Nanoporous Aerogel Scaffold Materials

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• 作者：Thomas K. Nielsen ; Kandavel Manickam ; Michael Hirscher ; Flemming Besenbacher ; Torben R. Jensen
• 刊名：ACS Nano
• 出版年：2009
• 出版时间：November 24, 2009
• 年：2009
• 卷：3
• 期：11
• 页码：3521-3528
• 全文大小：337K
• 年卷期：0
• ISSN：1936-086X

文摘

Nanoparticles of magnesium hydride were embedded in nanoporous carbon aerogel scaffold materials in order to explore the kinetic properties of hydrogen uptake and release. A new modified procedure for the synthesis of magnesium hydride nanoparticles is presented. The procedure makes use of monoliths (∼0.4 cm³) of two distinct types of nanoporous resorcinol−formaldehyde carbon aerogels loaded with dibutylmagnesium, MgBu₂. Excess MgBu₂ was removed mechanically, and the increase in mass was used as a measure of the amount of embedded MgH₂. Energy-dispersive spectrometry revealed that MgH₂ was uniformly distributed within the aerogel material. In situ synchrotron radiation powder X-ray diffraction showed that MgBu₂ transformed directly to MgH₂ at T ∼ 137 °C and p(H₂) = 50 bar. Two distinct aerogel samples, denoted X1 and X2, with pore volumes of 1.27 and 0.65 mL/g and average pore sizes of 22 and 7 nm, respectively, were selected. In these samples, the uptake of magnesium hydride was found to be proportional to the pore volume, and aerogels X1 and X2 incorporated 18.2 and 10.0 wt % of MgH₂, respectively. For the two samples, the volumetric MgH₂ uptake was similar, ∼12 vol %. The hydrogen storage properties of nanoconfined MgH₂ were studied by Sieverts’ measurements and thermal desorption spectroscopy, which clearly demonstrated that the dehydrogenation kinetics of the confined hydride depends on the pore size distribution of the scaffold material; that is, smaller pores mediated faster desorption rates possibly due to a size reduction of the confined magnesium hydride.