CuFe Cooperativity\nat the Membrane-Electrode Interface\nElicits a Tandem 2e<sup>–</sup>+2e<sup>–</sup> Mechanism\nfor Exclusive O<sub>2</sub>‑To‑H<sub>2</sub>O Electroreduction

High O<sub>2</sub> reduction reaction (ORR) kinetics\nand exclusive\n4e<sup>–</sup> pathway selectivity are keys to realizing a\nsustainable society. However, nonprecious electrocatalysts at present\ncannot enhance the ORR turnover frequency and H<sub>2</sub>O Faradaic\nefficiency (FE) concurrently. To address these two challenges, hybrid\nbilayer membrane (HBM) electrodes with earth-abundant metal centers\nare developed to control proton-coupled electron transfer (PCET) in\nORR. Here, an oxidase-inspired CuFe active site is supported on a\ntris(2-pyridylmethyl)amine HBM and explored as a unique interface\nfor efficient ORR. This bimetallic HBM displayed an ORR activity 1.4\ntimes higher than the monometallic systems and exhibited the highest\nFE for H<sub>2</sub>O (∼94%) among Cu-, Fe-, Ni-, and Co-based\nHBMs. Contrary to previous studies where the ORR current decreases\nupon embedding the metal center in a hydrophobic lipid environment,\nhere, the incorporation of a nitrile-terminated proton carrier at\nthe HBM interface boosts the ORR current by 1.7 folds relative to\nthe case where the catalytic site is directly exposed to protons in\nsolution. This intriguing dual improvement is supported by density\nfunction theory calculations where an additional 2e<sup>–</sup>+2e<sup>–</sup> mechanism occurs in parallel to the direct\n4e<sup>–</sup> pathway, highlighting the synergistic effect\nof the CuFe HBM for facilitating high-performance ORR. A Zn-air battery\nis constructed using this CuFe HBM for the first time, further demonstrating\nthat the knowledge gained from this HBM technology holds practical\nvalues in real-life applications. These findings on interfacial PCET\nare envisioned to spark new design principles for future catalysts\nwith optimal electrochemical properties for advanced energy conversion\nschemes.