Metal Active-Site Engineering in High-Entropy Catalysts for Catalytic Applications.

High-entropy catalysts (HECs), including high-entropy alloys and high-entropy oxides, have emerged as a transformative class of catalytic materials owing to their exceptional compositional flexibility and entropy-stabilized structures. Unlike conventional catalysts, HECs possess a broad distribution of atomic configurations of surface-active sites that enable simultaneous modulation of reactants'/intermediates' adsorption and stabilization energetics, charge transfer, and reaction pathways. Such characteristics provide unique opportunities to overcome long-standing activity-selectivity-stability trade-offs in heterogeneous catalysis. Nevertheless, the extreme compositional complexity of HECs also creates major challenges in identifying the true catalytic active sites and elucidating the underlying reaction mechanisms. This review provides a perspective on how metal active-site engineering in HECs, including strain, ensemble effects, defect engineering, and dynamic surface reconstruction, regulates adsorption configurations, intermediate evolution, proton-coupled electron transfer, and catalytic pathway selectivity. By addressing knowledge gaps in the structure-activity relationship of high-entropy catalysts, this review aims to open a potential avenue for the translation of HEAs into practical implementations for a sustainable energy and environmental future.