Hydrogen absorption of nanoscale pd particles embedded in ZrO 2 matrix prepared from Zr-Pd amorphous alloys
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Yue Chang Zhang and Yoshiaki Arata Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan (Received 27 November 2001; accepted 11 March 2002)
Nanocomposite materials consisting of ZrO2 and Pd phases were prepared by heating the amorphous Zr65Pd35 alloy for 24 h at 553 K in air. The maximum hydrogen absorption amount is about 2.4 mass% (H2/Pd) at 323 K and 2.2 mass% (H2/Pd) at 423 K at hydrogen pressure of 1 MPa. The absorption amount of Pd nanoparticles in the nanocomposite is a few times larger than those for the bulk and powder Pd metals. The remarkable increase in the hydrogen absorption/desorption amounts seems to result from the isolated dispersion state of Pd nanoparticles in the ZrO2 phase containing a tremendously large interface area in the nanocomposite.
I. INTRODUCTION
Recently, nanostructured materials have attracted rapidly increasing interest because of anomalous effects caused by the nanometer-scale structure. Amorphous alloys containing large amounts of solute elements have been regarded as one of the best starting materials to fabricate nanoscale mixed materials. In 1992, some of the present authors have reported that the oxidation of Zr–M (M ⳱ Cu, Ni, Pd) binary amorphous alloys in air leads to the synthesis of nanoscale composite materials in which nanoscale metallic (M) particles are distributed and embedded isolately in a monoclinic and cubic ZrO2 matrix.1,2 For instance, the Pd particles in a ZrO2 phase prepared from an amorphous Zr65Pd35 alloy have a spherical morphology with an average diameter of 10 nm and distribute homogeneously in an isolated state. Subsequently, we have performed a number of studies on the formation mechanism of the novel nanoscale mixed structure and various characteristics such as catalytic effects3 and mechanical properties4 of the mixed materials for the past 1 decade. In general, there are two stages in the process of hydrogen absorption of hydrogen storage materials such as Pd. The first stage of absorption is the solution of hydrogen into the ␣ phase, and the second stage, the hydrogenation of the material itself, accompanying the change from ␣ phase (Pd) to  phase (Pd hydride). There have been experimental and theoretical studies on hydrogen absorption of nanoscale Pd particles.5,6
a)
Address all correspondence to this author. J. Mater. Res., Vol. 17, No. 6, Jun 2002
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Zuettel et al. reported that hydrogen absorption of solitary nanoscale Pd clusters decreased with a decrease of cluster size.5 Pundt et al. studied hydrogen absorption of the composite material consisting of isolated Pd clusters dispersed in a polymer matrix and reported that hydrogen solubility of the composite material increased and the miscibility gap became narrower as compared with those of the bulk Pd metal.6 Moreover, hydrogen absorption studies on Pd nanocrystals have also been performed.7,8 Eastman et al. showed that the hydrogen solubility of nanocrystalline and coarse-grained Pd metals increased with decreasing grain s
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