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

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.