High‐Entropy Alloy Heterostructures with Tailored Interfacial Microenvironments for Efficient Electrocatalytic Water Splitting

High-entropy alloys (HEAs) offer a distinctive framework for tailoring surface affinities to reaction intermediates, enabling the design of efficient electrocatalysts. Notably, the heterogeneous interfaces within HEAs play a pivotal role in enhancing both intrinsic catalytic activity and durability, driven by the synergistic interactions among multiple metal atoms. Herein, a heterostructured bifunctional electrocatalyst, CrFeCoNiRu-RuNi (HEA-RuNi), is demonstrated to exhibit exceptional hydrogen and oxygen evolution reaction (HER and OER) activities, delivering overpotentials of 48 and 249 mV for HER and OER, respectively, at a current density of 10 mA cm^-2 in alkaline media, and robust stability in an anion exchange membrane water electrolysis device for 200 h. In situ Raman spectroscopy and electrochemical impedance spectroscopy revealed that the unique heterostructure of HEA-RuNi effectively modulates the local Ru microenvironment, redistributing the interfacial water hydrogen bond network within the electrochemical double layer, which facilitates water adsorption and dissociation. Theoretical calculations further unravel that the heterointerface of HEA-RuNi enables to tailoring of the electronic structure of the Ru active site, thus facilitating water dissociation in HER and moderating the adsorption ability of reaction intermediates in OER. The present work provides an insightful understanding of interficial engineering for electrocatalyst design in the field of energy storage and conversion.