Density Functional Study of Size-Dependent Hydrogen Adsorption on Ag n 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 H 2 with small-sized Ag n Cr ( n = 1-12) using density functional theory calculations. It is found that the cluster structures are preserved during the adsorption of H 2 either molecularly or dissociatively. Ag 3 Cr-H 2 , Ag 6 Cr-H 2 , and Ag 9 Cr-H 2 clusters are identified to be relatively more stable from computed binding energies and second-order energy difference. The dissociation of adsorbed H 2 on Ag 2 Cr, Ag 3 Cr, Ag 6 Cr, and Ag 7 Cr 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 Ag 4 Cr 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.