Core composition controlled hydrogen adsorption and atomic pressure effects in Pd₃₂IrNRh6-N nanoclusters

Hydrogen adsorption on Pd-based nanoalloys was investigated for truncated-octahedral Pd ₃₂ Ir N Rh 6-N (N=0,3,6) nanoclusters using a hierarchical computational approach combining Gupta-based global optimization, molecular dynamics, local atomic pressure analysis, and spin-polarized DFT+ U calculations. Structural optimization reveals surface segregation of Pd atoms and the formation of an octahedral Ir/Rh core. Hydrogen adsorption energies depend strongly on core composition: Pd ₆ cores exhibit the strongest binding, Ir ₆ and Rh ₆ cores the weakest, while the mixed Ir ₃ Rh ₃ core yields intermediate adsorption strengths. Although Pd-H bond lengths remain largely insensitive to core identity, the average compressive pressure of the core atoms varies significantly with composition. Notably, the Ir ₃ Rh ₃ core displays an average core pressure approaching that of Pd ₆ , accompanied by a corresponding strengthening of hydrogen adsorption. Site-resolved analysis further demonstrates that adsorption energies depend on whether the subsurface core region beneath a given site is Ir-rich or Rh-rich. These findings identify average core pressure and subsurface composition as key descriptors governing hydrogen adsorption in Pd-based trimetallic nanoclusters.