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Engineering strain critically affects the properties of materials and has extensive applications in semiconductors and quantum systems. However, the deployment of strain-engineered nanocatalysts faces challenges, in particular in maintaining highly strained nanocrystals under reaction conditions. Here, we introduce a morphology-dependent effect that stabilizes surface strain even under harsh reaction conditions. Using four-dimensional scanning transmission electron microscopy (4D-STEM), we found that cube-shaped core-shell Au@Pd nanoparticles with sharp-edged morphologies sustain coherent heteroepitaxial interfaces with larger critical thicknesses than morphologies with rounded edges. This configuration inhibits dislocation nucleation due to reduced shear stress at corners, as indicated by molecular dynamics simulations. A Suzuki-type cross-coupling reaction shows that our approach achieves a fourfold increase in activity over conventional nanocatalysts, owing to the enhanced stability of surface strain. These findings contribute to advancing the development of advanced nanocatalysts and indicate broader applications for strain engineering in various fields. 

Abstract Polyelemental nanoparticles (PE NPs), those consisting of four or more elements, exhibit unique properties from synergistic compositional effects. Examples include high entropy alloys, high entropy intermetallics, and multiphase types, including Janus and core‐shell architectures. Although colloidal syntheses offer excellent structural control for mono‐ and bi‐elemental compositions, achieving the same control for PE NPs remains challenging. Here, this challenge is addressed with a NP conversion strategy wherein different types of PE NPs – including high entropy alloy, high entropy intermetallic, and multiphase Janus nanoparticles – are achieved through thermal transformation of readily synthesized colloidal core‐shell NPs. Through systematic variations in stoichiometry and metal identity to the core‐shell precursor NPs, along with atomistic simulations that probe phase stabilities, we deduce that the final mixing states of the various NPs are governed by the balance between the enthalpy and entropy of mixing. Moreover, our annealing method allows us to trap NPs at intermediate states of mixing, creating distinct surface ensembles that were evaluated as catalysts for the hydrogen evolution reaction. This study is the first, to our knowledge, to report colloidally derived precursor NPs enabling the synthesis of all types of PE NPs in a single process. This NP conversion strategy offers a general route to diverse PE NPs.