Sub‐3 nm High‐Entropy Alloy Nanoparticles with Triple Functionalities for Efficient Electrolytic Hydrogen Production

Abstract High‐entropy alloys (HEA) exhibit great promise for alkaline hydrogen evolution reaction (HER) due to tunable structures, yet suffer from low atomic utilization, insufficient current density, and unclear catalytic mechanism. Herein, ultrasmall sub‐3 nm PtRuFeCoNiCu HEA nanoparticles are synthesized on carbon fiber paper (CFP) via a 0.5 s ultraquick thermal shock strategy (us‐HEA/CFP). The as‐prepared hybrid demonstrates the best‐level performance among reported catalysts, achieving ultralow overpotentials of 31.4 and 102.5 mV at ‐100 and ‐1000 mA cm −2 , respectively, in alkaline media. Such exceptional catalytic performance stems from the triple‐functional nature of the HEA surface: Ru‐dominated regions facilitating rapid H 2 O dissociation, FeCoNiCu sites enabling optimal H * diffusion kinetics, and Pt‐rich zones promoting efficient H * combination. This synergistic dissociation‐diffusion‐combination mechanism has been unequivocally validated via in situ Raman spectroscopy and density functional theory calculations. Practically, the assembled anion exchange membrane electrolyzer only requires 1.94 V to deliver 1000 mA cm −2 and can operate stably for 500 h, showing strong potential for large‐scale H 2 production.