Electrosynthesis of Unusual Nonfcc Palladium Hydride Nanoparticles

Intercalation of hydrogen into the palladium atomic layers during the growth of Pd nanoparticles can lead to the synthesis of unique palladium hydride phases. Here, we discover an unusual nonfcc palladium hydride nanoparticle, a structure that is not face-centered cubic (fcc), formed through coreduction of water molecules and Pd ions in solution. Crystal structure determination based on atomic electron tomography points to potential triclinic unit cells, indicating the presence of more than one nonfcc phase with some of those being a stack of loosened and distorted close-packed layer of atoms. The probability of finding nonfcc phase in single crystalline particles varies depending on the number and distribution of contact area with other particles. Roughly half of the isolated and one side-coalesced single crystal particles exhibit nonfcc structure while fcc dominates multiple sides-coalesced single crystals as well as polycrystal particles, which suggests a coalescence-induced phase transition from a nonfcc to a stable fcc structure due to the metastable nature of the nonfcc phases. While hydrogen is proven to be a key component for the synthesis of the nonfcc structure, given the limited formation of the unusual phase in H₂ gas bubbling system, the proposed electrochemical approach can be a promising platform for the in situ creation and study of metastable nanomaterials.