Spin-Polarized PdCu–Fe₃O₄ In-Plane Heterostructures with Tandem Catalytic Mechanism for Oxygen Reduction Catalysis

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 O₂ molecules limits further improvement of ORR kinetics. Herein, the precise synthesis of nanosheet assemblies of spin-polarized PdCu–Fe₃O₄ in-plane heterostructures for drastically activating O₂ 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 O₂ molecules, which make PdCu–Fe₃O₄ 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–Fe₃O₄─Fe sites that initially activate molecular O₂ and generate oxygenated intermediates being transferred to Pd sites to finish the subsequent proton-coupled electron transfer steps.