Site-Dependent Structural and Vibrational Properties of Hydrogenated Nanoscale Pd

The predictive design of novel Pd-based nanoscale materials for hydrogen sensing, storage, and purification necessitates a better understanding of the interplay between the adsorption of H and the evolution of the local structural environment on the atomic scale, as well as the ability to characterize this interplay under reaction conditions. We present a theoretical analysis of the interaction of H with atomistic nanostructured Pd models, quantifying the energetics of H–Pd interactions and predicting infrared (IR) absorption lines for such systems. The effects of local atomic structure, charge density distribution, and the presence of coadsorbed H and H₂O on the IR properties are also considered. We show that the IR absorption frequency and intensity reflect the local environment of the adsorbed H, with the number of neighboring Pd atoms being the most consequential factor in determining the vibrational characteristics and electronic structure changes induced by the adsorbed H. These correlations facilitate the interpretation of the experimentally observed IR spectra by providing a basis for the spectral decomposition into contributions associated with undercoordinated surface sites, ultimately allowing for the identification of the most likely H adsorption sites through nondestructive approaches to probing the bonding environment of H, such as in situ IR spectral monitoring.