Polymer‐Confined Pyrolysis Promotes the Formation of Ultrafine Single‐Phase High‐Entropy Alloys: A Promising Electrocatalyst for Oxidation of Nitrogen.

High‐entropy alloys (HEAs) made up of multiple metallic elements have gained attention for their excellent electrocatalytic performance. However, their application in the field of nitrogen (N2) oxidation reaction (NOR) remains underexplored. In this study, a "pomegranate‐like" carbon embedded with ultrafine AuPdPtRhIr HEA (HEA@C) is synthesized using a polymer‐confined pyrolysis strategy. Molecular dynamics (MD) simulations show that small‐sized metal nanoparticles formed by the confinement of polyvinyl alcohol (PVA) during the hydrothermal process can easily form a single‐phase HEA through a thermodynamically‐driven solid‐phase diffusion process during subsequent pyrolysis. Additionally, a porous carbon layer which in situ converted from the PVA shell can effectively inhibit the agglomeration of HEA nanoparticles and confine the surrounding N2. Experimentally, the HEA@C nanohybrid demonstrates a satisfactory NO3− yield rate of 23.8 µg h−1 mgcat.−1 and a high Faraday efficiency of 13.8% for the NOR process. By using operando Fourier Transform Infrared spectroscopy, online differential electrochemical mass spectrometry (DEMS), and density functional theory calculations, potential efficient active sites (Rh–Ir–o) and pathways for the electrochemical conversion of inert N2 to NO3− are revealed. This research provides an effective strategy for producing highly dispersed ultrafine HEA nanoparticles, showing a wide range of applications in advanced electrocatalysis. [ABSTRACT FROM AUTHOR]