Metal/graphene nanocomposites synthesized with the aid of supercritical fluid for promoting hydrogen release from complex hydrides

Abstract

With the aid of supercritical CO2, Fe-, Ni-, Pd-, and Au-nanoparticle-decorated nanostructured carbon materials (graphene, activated carbon, carbon black, and carbon nanotubes) are synthesized for catalyzing the dehydrogenation of LiAlH4. The effects of the metal nanoparticle size and distribution, and the type of carbon structure on the hydrogen release properties are investigated. The Fe/graphene nanocomposite, which consists of ∼2 nm Fe particles highly dispersed on graphene nanosheets, exhibits the highest catalytic performance. With this nanocomposite, the initial dehydrogenation temperature can be lowered (from ∼135 °C for pristine LiAlH4) to ∼40 °C without altering the reaction route (confirmed by in situ X-ray diffraction), and 4.5 wt% H2 can be released at 100 °C within 6 min, which is faster by more than 135-fold than the time required to release the same amount of H2 from pristine LiAlH4.

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

“…The temperature-programmed desorption( TPD) profiles obtained for the various samples are showni nF igure 2. [27,37] The above results clearly indicate that the low-cost Fe/CNTs( withoutf urther purification) can be an effective dehydrogenation promoter for LiAlH 4 .T he CNTsc an help transfer electrons from Fe to [AlH 4 ] À and thus increaset he number of heterogeneousn ucleation sites for formation of dehydrogenated phases, which triggers the subsequent hydrogen release from the bulk. Although another hydrogen release was observed at~480 8C, this is relatively difficult to utilize, and thus is not considered in this work.…”

“…The initial dehydrogenation occurred at~100 8C, ad ecrease of 35 8Cc ompared to that for pristine LiAlH 4 .W hen incorporated, the Fe particles could donate electrons to [AlH 4 ] À ,m aking this complex anion unstable, which made it easy to release hydrogen from the AlÀHb onds. [27,37] The above results clearly indicate that the low-cost Fe/CNTs( withoutf urther purification) can be an effective dehydrogenation promoter for LiAlH 4 .T he CNTsc an help transfer electrons from Fe to [AlH 4 ] À and thus increaset he number of heterogeneousn ucleation sites for formation of dehydrogenated phases, which triggers the subsequent hydrogen release from the bulk. The high-strength CNTsa re effective grinding agents that enhance the mixing of Fe and reduce the particle size of the hydride (see Figure S2) whereas the incorporation of CNTsa lso creates microchannels in LiAlH 4 (see Figure S2), and both factors are desirable for the dehydrogenation reaction.…”

“…[21,[26][27][28] It is knownt hat as peciesw ith ag iven chemical composition can show superior catalytic performance when its dimensions are reduced. [21,[26][27][28] It is knownt hat as peciesw ith ag iven chemical composition can show superior catalytic performance when its dimensions are reduced.…”

“…Hybridizationw ith other catalysts to form composite additives hasb een proven to increase the dehydrogenation promotion ability of carbon-based materials. [21,[26][27][28] It is knownt hat as peciesw ith ag iven chemical composition can show superior catalytic performance when its dimensions are reduced. [17,21,29] Accordingly, as upercritical-CO 2 (SCCO 2 )-fluid-assisted deposition technique, which is knownf or being able to highly disperse nanoparticles onto high-surface-area supporting materials, [30][31][32] is used in this work to decorate carbon nanotubes (CNTs) with ac ontrolled amount of nanosized Ni particles( 5wt%,t oc ontrolc osts and achieve sustainability).…”

Catalytic and inhibitive effects of Pd and Pt decorated MWCNTs on the dehydrogenation behavior of LiAlH4

“…A recent study proposed decorating Fe, Ni and Pd nano-particles on carbon nano-materials to produce an effective catalyst for dehydrogenation of LiAlH 4 [31]. The aim of the current study is to further clarify the effects of Pd or Pt decorated MWCNTs on the dehydrogenation behavior of LiAlH 4 , and especially the catalytic and/or inhibitive effects.…”