Synergistic High‐Entropy and Anchoring Stabilization of PtPdIrRuCu Alloy Nanoparticles on N, O‐Doped Carbon Cage Fibers for Durable and Selective PET Upcycling

High‐entropy alloy nanoparticles (HEA NPs) are promising electrocatalysts, yet their ultrasmall size makes them vulnerable to migration‐induced coalescence (MIC), a sintering pathway that intrinsic high‐entropy effects cannot suppress. Herein, we anchor ultrasmall PtPdIrRuCu HEA NPs on N, O‐doped carbon cage fibers (NOCCFs). The N/O anchoring sites inhibit MIC through strong metal–support interactions, which, together with the intrinsic resistance of HEA to Ostwald ripening, synergistically suppress sintering. After 700 °C annealing, the PtPdIrRuCu NPs size increases from 2.8 nm to only 3.8 nm, whereas Pt/C aggregates from 2.3 nm to 21.8 nm. In ethylene glycol oxidation reaction (EGOR), the PtPdIrRuCu/NOCCFs delivers a mass activity of 7.66 A·mg Pt − 1 (7.3‑fold that of Pt/C) and a Faradaic efficiency of 95.8% toward glycolic acid (GA). A membrane electrode assembly (MEA) flow electrolyzer runs stably over 240 h with >90% GA selectivity. Mechanistic studies reveal that the PtPdIrRuCu/NOCCFs enhances *OH adsorption to promote the GA pathway, accelerates CO ads oxidation via oxophilic Ir/Ru sites to prevent catalyst poisoning, and elevates both C–C cleavage and overoxidation barriers to suppress byproducts.