Atomically Dispersed Rare Earth‐Confined High‐Entropy Alloy Nanocrystals for Efficient Ammonia Electrosynthesis

Rare earth (RE) elements with unique lanthanide contraction and electron configuration are promising for many important studies. Alloying RE with typical 3d/5d transition metals generates new or improved properties due to enhanced orbital coupling and thermodynamic stability. However, limited to ultralow reduction potential, strong oxophilicity and poor compatibility of RE, most research focused on high-temperature procedures and complex processing techniques, which hinders compositional and structural control, functional optimization and mechanistic investigation for diverse applications. Here we define a general wet-chemistry synthetic protocol for the creation of RE-confined high-entropy alloy (HEA-RE) nanocrystals (NCs) under mild conditions, featuring atomically dispersed RE embedded in Pt-based HEA framework, via sequential reduction kinetics of different metal precursors and high-entropy effect-induced confinement of RE atoms. The HEA-RE NCs with multi-site synergy switch from boosting simple reaction to complex process involving multiple reactants and intermediates. They achieve ∼99% Faradaic efficiency and superior yield rate toward nitrate-to-ammonia reduction, attributed to carved surface promoting mass transfer, tensile strain tuning adsorbate behavior, and delocalized RE electron regulating reaction pathways. Our study provides a new perspective for rational design and potential application of RE-based HEA nanostructures with atomic precision.