Effects of interfacial structure of Pd–Pt nanoparticles on hydrogen solubility

Nanoparticles (NPs) of Pd are known for their high hydrogen storage capacity. The addition of a small amount of Pt has been found to further enhance the storage capacity, highlighting the important role of Pd-Pt interactions in the interfacial region. In this work, we investigated the element-specific local structure of core (Pd)-shell (Pt) NPs and their solid-solution alloy phase, which is formed through the process of hydrogen absorption and desorption (PHAD). To unveil the mechanism of enhanced hydrogen storage capacity in the solid-solution (SS) phase, we used extended X-ray absorption fine structure spectroscopy and investigated the local structure around the Pd and Pt. A notable stress in the Pd structure and a higher atomic pair distance than that of bulk Pd was observed in the core-shell NPs. Additionally, a Pd-Pt alloy formed in the interfacial region shows a deviation in local structure compared with both bulk Pd and Pt resulting from disorder and anharmonic distributions in both Pt-Pt and Pt-Pd atomic pair distances. In the solid-solution phase, the strained Pd NPs relaxed with a significant fraction of Pd remaining in the fcc structure. Moreover, the interfacial alloy was distributed homogeneously in the SS phase. This novel alloy phase has unique structural properties and provides active binding sites for hydrogen storage. The uniform distribution of the alloying phase, which acts as a source of active binding sites, facilitates high coverage resulting in an enhanced hydrogen storage capacity. (C) 2019 Elsevier B.V. All rights reserved.