Universal synthesis of high-entropy alloy nanostructures with femtosecond lasers.

High-entropy alloy nanostructures (HEA-NSs) hold promise in advanced catalysis and materials science, but lack a robust and universal synthetic strategy designed at an atomic level. Here, femtosecond lasers are used to prepare HEA-NSs, from single atoms to 100 nm nanoparticles, either free-standing or supported on a variety of substrates. Ultrafast excitation enables precise control over electron dynamics and instantaneously formed solvated electrons induce rapid, nonselective ion reduction ∼100 picoseconds post-irradiation, followed by stochastic atom nucleation and formation of atomically dispersed HEA-NSs through diffusion-controlled dynamics beyond nanoseconds. These processes are governed by the spatiotemporal confinement effect (STCE), with atomic diffusion restricted within nanoseconds, thereby enabling kinetic trapping of metastable nanoclusters with strict atomic-level dispersity. As a demonstration, FeCoNiRuPt achieved a peak power density of 2.1 W cm-2 for oxygen reduction reaction (ORR). Femtosecond lasers are robust and effective tools for the universal preparation of difficult-to-synthesize metastable nanoparticles by controlling electron dynamics.