A Library of Seed@High‐Entropy‐Alloy Core–shell Nanocrystals With Controlled Facets for Catalysis

Abstract High‐entropy‐alloy (HEA) nanocrystals hold immense potential for catalysis, offering virtually unlimited alloy combinations through the inclusion of at least five constituent elements in varying ratios. However, general and effective strategies for synthesizing libraries of HEA nanocrystals with controlled surface atomic structures remain scarce. In this study, a transferable strategy for developing a library of facet‐controlled seed@HEA nanocrystals through seed‐mediated growth is presented. The synthesis of seed@HEA core–shell nanocrystals incorporating up to ten different metallic elements, with control over the number of solid‐solution HEA atomic layers is demonstrated. Epitaxial HEA growth on nanocrystal seeds with low‐index and high‐index facets leads to the formation of seed@HEA catalyst library with composition‐ and facet‐dependent catalytic activities in both electrocatalysis and photocatalysis. In situ synchrotron X‐ray absorption spectroscopy and density‐functional theory calculations are employed to identify surface active sites of the HEA, rationalizing the high level of catalytic activities achieved. This work enables facet engineering in the multi‐elemental chemical space and unveils the critical needs for their future development toward catalysis.