Atomic-Level CuO_x-CoO_x-Pd Interfacial Engineering Enables Hierarchical Synergy for High-Efficiency ORR Pathways and...

The sluggish kinetics of the oxygen reduction reaction (ORR) and the high cost of Pt-based catalysts remain major barriers for alkaline fuel cell (AFC) technologies. Here we report a Cu-decorated CoO@Pd catalyst in which atomic-to-subnanometer CuO_x species reconstruct the Pd-Co-Cu heterointerface and enable a cooperative multi-site ORR pathway. Structural and spectroscopic analyses reveal that low Cu loading produces atomically dispersed CuO_x motifs that enrich oxygen vacancies (O_V)s, preserve metallic Pd, and stabilize oxygen-deficient Co^{3 +} centers. Operando PFY-XANES/EXAFS further uncovers a synergistic mechanism in which O_Vs around Cu serve as rapid O₂ activation sites, Pd mediates lateral *O^ads spillover, and O_Vs around Co act as the primary *O^ads reduction centers. This division of labor maximizes four-electron ORR kinetics, yielding a on-set potential of 0.935 V and a mass activity (MA) of ∼1.6 × 10⁴ mA mg_Cu ^{- 1} without decay for 50k potential cycles, surpassing commercial Pt/C by over two orders of magnitude. When integrated into AFCs, the optimized catalyst (CPCu-1) delivers a peak power density of ∼430 mW cm^{- 2}, approximately 60% higher than Pt/C, and exhibits a characteristic three-stage durability governed by dynamic CuO_x-CoO_x interface reconstruction. These findings establish atomic CuO_x interface engineering strategy for designing high-performance, noble-metal-efficient ORR catalysts.