Hydrogen absorption in Pd nanoparticles of different shapes

In order to analyze the influence of shape on the hydrogen absorption properties of Pd at the nano-scale we simulated pressure-composition (P-C) 300 K isotherms at the atomistic level for nanoparticles of similar sizes. The simulations were performed by the Monte Carlo (MC) technique in the TPμN ensemble and embedded atom type potentials (EAM) to model the interaction among atoms. We generated nanoparticles of different shapes (sphere, icosahedron, octahedron, cuboctahedron) and compared the resulting P-C isotherms with the bulk and a few available experimental results. Instead of the plateau corresponding to the α-β PdH equilibrium in the bulk, the nanoparticles isotherms show at least a two-plateaux behavior, corresponding to a subsurface hydride formation and a subsequent filling of the core of the nano-particle with H atoms. We also studied the evolution of the atomic pressure profiles inside nanoparticles. We used different criteria to define the atomic volumes at the surfaces and calculated the atomic stresses.