Insights into Transformation of Icosahedral PdRu Nanocrystals into Lattice-Expanded Nanoframes with Strain Enhancement in Electrochemical Redox Reactions

Bimetallic icosahedral nanoframes have three-dimensional open structures, a high surface-area-to-volume ratio, and high surface site availability. Twin boundaries in these structures cause surface lattice expansion that leads to tensile strain over the nanoframes, which can improve their catalytic activity; however, robust methods for their synthesis in most metal systems are still lacking. In this work, we demonstrate a one-step synthetic strategy for the synthesis of both closed solid and hollow frame icosahedral PdRu nanoparticles (INPs) via a two-stage process of growth and dissolution. By extraction at different reaction times, INPs, concave-faceted icosahedral PdRu nanoparticles (CINPs), and icosahedral PdRu nanoframes (INFs) are obtained. High-angle annular dark-field scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy and inductively coupled plasma-optical emission spectrometry analyses show that the icosahedral nanostructures are PdRu alloys with ∼5 at. % Ru relative to Pd. We also carried out the electrochemical ethanol oxidation reaction (EOR) and CO₂reduction reaction over three types of catalysts, PdRu INPs, PdRu CINPs, and PdRu INFs, as well as commercial Pd NPs, to examine their catalytic properties. PdRu INFs showed a much higher mass activity than PdRu INPs, PdRu CINPs, and Pd NPs in the EOR. PdRu INFs exhibited the highest Faradaic efficiency of CO gas (34%), which suggests that the expansive strain in the framework catalyst structure improves selectivity and activity for CO₂conversion.