Single-Atom Ce Enables Interfacial Pathway Regulation of Fe2 Atomic Pairs in Alkaline Oxygen Reduction

Abstract

Fe2 atomic pairs are among the most active motifs in Fe–N–C catalysts for the alkaline oxygen reduction reaction (ORR), but their performance is limited by an activity–stability trade-off. In alkaline media, slow interfacial water dissociation restricts proton-coupled electron transfer (PCET). Under these proton-deficient conditions, the more proton-demanding 4e– pathway is suppressed, whereas the competing 2e– route becomes more favorable, leading to peroxide/reactive oxygen species (ROS) accumulation and accelerated Fe demetalation. Here we show that atomically dispersed Ce can mitigate this limitation by regulating the interfacial reaction environment around Fe2 atomic pairs. In situ spectroscopy, kinetic isotope measurements, and theoretical calculations indicate that Ce promotes the main 4e– pathway by improving the interfacial water/proton environment, while also reducing peroxide-related species formed through the competing 2e– route near Fe2 sites. Accordingly, the resulting FeAPCeSA-NHCS catalyst, consisting of Fe2 atomic pairs and isolated Ce species on N-doped hollow carbon spheres, delivers a high half-wave potential of 0.92 V with a peroxide yield of only 1.6% in alkaline media. It also mitigates Fe demetalation, retains 96% of its current after 50,000 s of ORR operation, sustains Zn–air battery cycling for over 1100 h, and achieves peak power densities of 1.0 W cm–2 in anion-exchange membrane fuel cells. This work establishes an interfacial pathway-regulation strategy for decoupling activity and stability in alkaline ORR catalysis.