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.