An-Najah Staff

In this work the hydrogen absorption behaviour of two types of Pd-clusters, different in structure
but similar in size (3.1 nm), will be presented. First, icosahedral Pd clusters stabilised in surfactants; second,
cubic Pd clusters stabilised in a Teflon-AF matrix. The phase transition in these samples was monitored by
in-situ X-ray diffraction. It will be shown that the hydrogen uptake ability depends strongly on the lattice
structure, which is affected by the type of stabilizer. Teflon AF stabilised clusters (cubic clusters) show the
phase transition which is common for bulk Pd, whereas the surfactant stabilised clusters (icosahedral
clusters) show only weak lattice dilatation upon hydrogen absorption. Pressure - lattice parameter Isotherms
show that the cubic clusters absorb large amounts of hydrogen in comparison to the icosahedral clusters.
The measured lattice expansion is 0.130 Å at 105 Pa and 300 K, which is about 320 % the amount
measured for icosahedral clusters (0.04 Å). This suggests that surface sites are available for hydrogen in the

 Pd - Teflon-AF samples which are not accessible for Pd - surfactant -clusters, and that the icosahedral
lattice absorbs less hydrogen for similar external pressures.