  Hydrogen is a promising alternative to fossil fuel, however storing it
efficiently poses challenges. One promising solution is to adsorb hydrogen on
solid materials demonstrating quasi-molecular bonding with hydrogen. The
hydrogen adsorption energy can be tuned by changing the morphology or
stoichiometry of bimetallic nanoparticles. Here we used complementary
techniques to unveil the chemical compositional and morphological
transformation undergone by PdxNi100-x nanoparticles during H2 adsorption. Our
findings reveal NiO-rich shell and Pd-rich core as confirmed by X-ray
photoelectron spectroscopy, X-ray scattering, and electron energy loss
spectroscopy. During hydrogen adsorption, which mainly occurs on Pd atoms, the
Pd-rich core fragments into small pockets, increasing its surface area. This
process is more pronounced for nanoparticles with lower Pd loading, emphasizing
the role of NiO. These results shed light on the atomic changes occurring in
the PdxNi100-x nanoparticles during hydrogen adsorption and can be applicable
on multi-metallic systems to improve hydrogen storage properties.
