Density Functional Study of Size-Dependent Hydrogen Adsorption on Ag Cr (n = 1-12) Clusters

Increasing interest has been paid for hydrogen adsorption on atomically controlled nanoalloys due to their potential applications in catalytic processes and energy storage. In this work, we investigate the interaction of H₂ with small-sized Ag Cr (n = 1-12) using density functional theory calculations. It is found that the cluster structures are preserved during the adsorption of H₂ either molecularly or dissociatively. Ag₃Cr-H₂, Ag₆Cr-H₂, and Ag₉Cr-H₂ clusters are identified to be relatively more stable from computed binding energies and second-order energy difference. The dissociation of adsorbed H₂ on Ag₂Cr, Ag₃Cr, Ag₆Cr, and Ag₇Cr clusters is favored both thermodynamically and kinetically. The dissociative adsorption is unlikely to occur because of a considerable energy barrier before reaching the final state for Ag₄Cr or due to energetic preferences for n = 1, 5, and 8-12 species. Comprehensive analysis shows that the geometric structure of clusters, the relative electronegativity, and the coordination number of the Cr impurity play a decisive role in determining the preferred adsorption configuration.