High-loaded oxygen reduction reaction (ORR) Pt intermetallic compounds with high performance expression under PEMFC operating conditions are prerequisite for practical application. Nevertheless, high metal-loading would lead to the severe agglomeration and nonuniformity of nanoparticles, imposing an enormous challenge on efficient synthesis. Herein we present a cobalt oxide aided structural evolution strategy to controllably synthesize high-loaded (44.7 wt%) sub-6 nm Pt1Co1 intermetallic compounds with a Pt-rich shell (Pt1Co1-IMC@Pt). Experiments and theory explicitly reveal that the ordered arrangement of Pt–Co atoms endows surface Pt with a lowered d band centre and enhanced oxidation-resistance of Pt/Co sites, thus simultaneously boosting the ORR activity and durability. The preeminent intrinsic ORR activity on an optimized catalyst reaches a mass activity as high as 0.53 A mg_(Pt) ⁻¹@0.90 V RHE⁻¹ (MA@0.9 V) in rotating disk electrode measurements. PEMFCs with such a catalyst deliver record-high power density (2.30/1.23 W cm⁻² under H₂–air/O₂ conditions at 80 °C) and extraordinary stability, ranking the highest fuel cell performance among the Pt-based electrocatalysts. Significantly, the MA@0.9 V calculated from fuel cell attains 0.46 A mg_(Pt) ⁻¹, exceeding the 2020 DOE target (0.44 A mg_(Pt) ⁻¹) and very close to the intrinsic value, definitely confirming the superiority of high-loaded Pt1Co1-IMC@Pt/C in activity expression under fuel cell conditions. This study paves a new way for the future practical application of low-Pt catalysts in PEMFCs.