Main-Group Potassium-Assisted Dual-Site Relay Breaks the Activity–Stability Trade-Off in Acidic Oxygen Reduction

Abstract Fe–N–C catalysts are promising platinum-group-metal-free cathodes for proton-exchange membrane fuel cells. However, O2 activation on isolated FeN4 sites typically follows a single-center associative pathway, which limits (oxygen reduction reaction) ORR kinetics and is associated with peroxide formation and Fe demetalation under acidic operation conditions. Herein, an atomically dispersed Fe–K dual-site catalyst, FeN4–KN6/C, is reported for the first time, in which the N6-coordinated s-block K site (KN6) is introduced as a main-group auxiliary site to regulate FeN4 rather than as an isolated active center. The neighboring KN6 unit modulates the local electronic structure of FeN4 through K s/p-state-mediated perturbation, enabling bridge-type O2 activation and facilitating Fe-bound *OH desorption. Consequently, *OOH accumulation and H2O2 formation are suppressed, reactive oxygen species mediated degradation is mitigated, and Fe–N coordination is reinforced for improved Fe-site retention. FeN4–KN6/C exhibits an ORR half-wave potential of 0.850 V with a low H2O2 yield. Membrane electrode assemblies using FeN4–KN6/C cathodes deliver 47.0 mA cm–2 at 0.9 V under H2–O2 and 101 mA cm–2 at 0.8 V under H2–air conditions, with corresponding peak power densities of 1.30 W cm–2 and 0.71 W cm–2, respectively. Moreover, after 30,000 voltage cycles, the peak power density retention reaches 90.1% under H2–air and 92.3% under H2–O2 conditions. This work establishes an s-block alkali-metal-assisted Fe dual-site mechanism for acidic ORR and expands Fe-based dual-atom catalyst design beyond conventional transition-metal combinations.