Atomistic modeling of H absorption in Pd nanoparticles

Size affects the properties of absorption of H in Palladium nanoparticles. Because of their higher proportion of surface atoms compared to the bulk, the pressure–composition (P–C) isotherms of the nanoparticles are modified. We performed atomistic simulations for different-sized Pd nanoparticles and for the bulk at different H concentrations using the Monte Carlo technique in the TPμN ensemble to calculate the P–C isotherms. The Pd–H interatomic potentials are of the Embedded Atom (EAM) type and have been recently developed by Zhou et al. [1]. From the related van’t Hoff equation we obtained |ΔH°| = (28 ± 7) kJ/0.5 mol of H2 and |ΔS°| = (71 ± 19) J/0.5 mol of H2·K for the PdH formation in the bulk. For Pd nanoparticles previous simulations results based on a different set of EAM potentials showed that H was absorbed primarily in the surface before diffusing into the inside of small Pd clusters [2]. Considering the better performance of Zhou's potentials [1] for the bulk, in this work we analyzed the evolution of the equilibrium microstructure of Pd nanoparticles as a function of their size and H concentration. Our simulations predict enhanced hydrogen solubilities and vanishing plateaux when compared to the bulk and that H is absorbed in the subsurface of the nanoparticles.