Proton Relay Mediated by Atomic Sn Lewis-Acidic Sites for Accelerating Oxygen Reduction Kinetics in Fe-N-C Catalysts

The oxygen reduction reaction (ORR) is a critical but sluggish cathodic process in anion-exchange membrane fuel cells (AEMFCs), primarily constrained by slow protonation due to the insufficient proton supply from interfacial water. To address this challenge, we report an atomically Sn-mediated proton relay strategy that markedly accelerates alkaline ORR kinetics. Atomic-resolution characterizations and operando spectroscopy analysis confirm the successful construction of proximal Fe-Sn dual-atom sites, in which Fe serves as the oxygen intermediate adsorption center, while the adjacent Sn Lewis-acidic site facilitates interfacial water dissociation. The accelerated proton transfer kinetics are further verified by ab initio molecular dynamics (AIMD), revealing a barrierless process of the *O₂ protonation pathway on FeSn-N-C, contrasting sharply with the 0.46 eV barrier on Fe-N-C. Benefiting from the efficient proton relay, the as-designed FeSn-N-C exhibits a half-wave potential of 0.94 V (vs RHE) in 0.1 M KOH and a kinetic current density of 28.64 mA cm^-2 at 0.90 V, outperforming the Fe-N-C counterpart (0.899 V; 5.30 mA cm^-2). Remarkably, an AEMFC assembled with an FeSn-N-C cathode achieves a peak power density of 1.01 W cm^-2 and a current density of 159.61 mA cm^-2 at 0.9 V. This work provides a practical design principle to overcome proton supply bottlenecks in proton-involving electrocatalysis.