Nanofluid-Assisted Synthesis of High-Entropy Alloy Nanoparticles.

The synthesis of high-entropy alloy nanoparticles (HEA-NPs) has traditionally been guided by thermodynamic considerations, relying on static parameter optimization. Here, we introduce a kinetically controlled paradigm for directing nanofluid transport to craft strained HEA-NPs from ten dissimilar elements. This strategy employs Zn as an active propellant, constructing interconnected nanochannels that steer multimetal nanofluid flow and trigger alloying. Using in situ transmission electron microscopy, we directly observe the dynamics of long-range directional migration under nanoconfinement, which induces forced fusion and fission events pivotal for achieving homogeneous mixing and size control. These unique confinement dynamics further impart surface tensile strain to the resulting nanoparticles. When applied to electrocatalytic nitrate-to-ammonia conversion, the strained HEA-NPs achieve an exceptional Faradaic efficiency of 94.8 ± 4.34% and sustain stable operation for over 720 h. Mechanistic studies attribute this performance to the synergy between multielement active sites and the tailored surface strain, which collectively optimize intermediate adsorption. This work establishes a new design principle for complex nanomaterials by shifting the perspective from static thermodynamics to dynamic kinetic control, providing a scalable pathway for the development of advanced electrocatalysts.