Surface-Engineered Core–Shell High-Entropy Alloy Nanoparticles with Reversible Structure for Low-Temperature NO Reduction

High-entropy alloy nanoparticles (HEA NPs) exhibit unique catalytic properties arising from the random distribution of constituent elements; however, precise control over surface active sites remains challenging. Herein, we report a surface composition engineering strategy to construct core-shell HEA@Rh nanoparticles via hydrogen spillover-driven synthesis of HEA NPs on CeO₂ nanorods, followed by galvanic replacement with Rh ions. The resulting HEA@Rh/CeO₂ catalyst exhibits markedly enhanced activity for the selective catalytic reduction of NO with H₂, particularly at low temperatures, compared to monometallic Rh and conventional HEA catalysts. In situ X-ray absorption fine structure analysis reveals that the HEA@Rh nanoparticles undergo reversible structural reconstruction under alternating oxidative and reductive atmospheres, while maintaining their particle size. This redox-responsive behavior contrasts with the irreversible structural evolution observed in conventional HEA systems, highlighting the advantage of controlled surface composition. Furthermore, the core-shell structure is preserved even after repeated redox cycling and under elevated temperatures in H₂, demonstrating exceptional structural robustness. The combination of dynamic structural reversibility and thermal robustness enables stable catalytic performance under realistic conditions. These results establish surface composition engineering as a powerful approach to unlock the full potential of high-entropy alloy catalysts by integrating structural dynamics with multicomponent synergy.