H concentrations and stresses in Pd nanoparticles

• Surface segregation and surface stress of nanoparticles.
• H-trap depth of Pd surface, H concentrations and stresses in both core and surface shell of Pd nanoparticles.
• Coupling between the stresses and H concentrations in the surface shell and core of the Pd nanoparticles.
• H concentrations in the core and surface shell generating tensile hydrostatic stress in the core.
• The tensile hydrostatic stress in the core enhancing the H concentration in the core.

Using the Gibbs-approach based adsorption isotherm and the experimental data of nominal H concentration in Pd nanoparticles with a mean diameter of 3.6 nm versus H2 partial pressure, we determined the H-trap depth of Pd surface, the H concentrations and stresses in both core and surface shell of the nanoparticles. The results indicate that in addition to the surface segregation of H atoms, the tensile hydrostatic stress induced by the difference in concentration between the core and the surface shell greatly enhances the H concentration in the crystalline core in comparison with that in the bulk Pd counterpart under the same H2 partial pressure.