Kinetically Controlling Surface Atom Arrangements in Thermally Robust, Amorphous High‐Entropy Alloy Nanoparticles by Solvent Selection

The ability to tailor nanoscale surface atom arrangements through multi-elemental compositional control provides high-entropy nanoalloys with promising functional properties. Developing a fundamental understanding of nanoalloy formation mechanisms during synthesis is therefore essential for effectively engineering the surface composition and resulting functional properties. Using the Cantor alloy (CrMnFeCoNi) as a model system, the investigation reveals how solvent selection during reactive, nanosecond-pulsed laser synthesis influences carbon doping and the resulting changes in nanoparticle morphology, structure, and composition. Supersaturated carbon incorporation, partitioned from the organic solvent molecules, produces amorphous nanoparticles with distinctive carbon shells, thermally stable up to 350 °C. Kinetically controlled particle formation mechanisms are proposed, rationalizing the criticality of the time scales between the competing reactions of carbon doping, carbon shell formation, and coalescence of metallic fragments, which rule compositional and morphological characteristics. Carbon shell thickness and the surface composition distribution are shown to influence the element-specific dissolution under electrochemical reaction conditions. This work demonstrates effective solvent-driven surface-compositional control in amorphous high-entropy nanoalloys. It introduces a novel synthesis approach for tailoring surface atom arrangements through carbon incorporation via reactive, pulsed laser synthesis.