Element-Specific Local Chemical Order of High-Entropy Nanoalloys

Multi-elemental nanoalloys have shown significant promise in applications like catalysis, due to unique structural features that arise from their complex structure. A key feature of particular interest is local chemical order (LCO) at the scale of a single neighboring bond length. LCO has proven challenging and inconclusive to interpret and verify in these materials, particularly in samples containing elements with similar atomic numbers. Herein we present a methodology combining experimental X-ray absorption spectroscopy and computational simulations, allowing for the reliable verification and quantification of LCO in a five-element high entropy alloy (HEA-5) on a truly element-specific basis. The analysis identifies a distinctive type of LCO involving the Ru-Ir bonding pair, which correlates with the high catalytic performance of HEA-5 in the ammonia decomposition reaction. The versatility of this element-specific methodology is further demonstrated through its application to an extremely complex 15-element HEA sample, where consistent LCO trends are observed. These findings contribute to LCO theory, element-specific structural analysis, and the catalytic design of high-entropy nanoalloys.