Nanoconfinement Mitigates the Size–Ordering–Loading Trade‐Off to Enable High‐Loading Sub‐3 nm Intermetallic PtCu for Oxygen Reduction

Pt-based intermetallic nanoparticles (NPs) are among the most effective electrocatalysts for the oxygen reduction reaction (ORR), yet simultaneously achieving high metal loading, ultrasmall particle size, and atomic ordering remains a longstanding challenge because the high-temperature annealing required for intermetallic ordering inevitably induces particle coarsening. Here, we demonstrate that mesopore-induced nanoconfinement mitigates this size-ordering-loading trade-off, enabling the synthesis of highly dense (∼40 wt.%), sub-3 nm intermetallic PtCu nanoparticles within ordered mesoporous carbon (CMK-3). In contrast, microporous carbon supports with comparable surface areas produce much larger nanoparticles (∼8.3 nm), highlighting the critical role of mesoporous confinement rather than surface area alone. Molecular dynamics simulations reveal that geometric confinement suppresses PtCu…