Theoretical modeling of metal–hydrogen interactions in Pd clusters

There is an enhancement in hydrogen solubility and narrowing of the two-phase plateau pressure region in the pressure-composition isotherm of Pd clusters compared to bulk Pd. Experimental data on the hydrogen solubility in bulk Pd and Pd clusters at 310 K have been utilised to obtain thermodynamic properties. The relative chemical potential of dissolved hydrogen (H) in the metal at infinite dilution and the apparent H–H interaction energy is lower in the case of Pd clusters. The solubility of H in Pd clusters was analysed by Fermi–Dirac statistics, using both single-site and two-site models. The two-site model assumed that H occupies both subsurface and interior sites. The subsurface sites have a lower energy compared to the interior sites thereby indicating that H would preferentially occupy these sites. The higher solubility of H in Pd clusters is due to the availability of subsurface sites of lower energy compared to bulk sites.