Spin‐Polarized PdCu–Fe ₃ O ₄ In‐Plane Heterostructures with Tandem Catalytic Mechanism for Oxygen Reduction Catalysis

Abstract Alloying has significantly upgraded the oxygen reduction reaction (ORR) of Pd‐based catalysts through regulating the thermodynamics of oxygenated intermediates. However, the unsatisfactory activation ability of Pd‐based alloys toward O ₂ molecules limits further improvement of ORR kinetics. Herein, the precise synthesis of nanosheet assemblies of spin‐polarized PdCu–Fe ₃ O ₄ in‐plane heterostructures for drastically activating O ₂ molecules and boosting ORR kinetics is reported. It is demonstrated that the deliberate‐engineered in‐plane heterostructures not only tailor the d ‐band center of Pd sites with weakened adsorption of oxygenated intermediates but also endow electrophilic Fe sites with strong ability to activate O ₂ molecules, which make PdCu–Fe ₃ O ₄ in‐plane heterostructures exhibit the highest ORR specific activity among the state‐of‐art Pd‐based catalysts so far. In situ electrochemical spectroscopy and theoretical investigations reveal a tandem catalytic mechanism on PdCu–Fe ₃ O ₄ ─Fe sites that initially activate molecular O ₂ and generate oxygenated intermediates being transferred to Pd sites to finish the subsequent proton‐coupled electron transfer steps.