Nanocluster-Assisted OH Ligand Modification Optimizes Activity and Stability of Fe-N-C Catalysts.

Achieving high activity and durability in platinum-metal-free electrocatalysts remains a challenge for proton-exchange membrane fuel cells. Fe/N-C catalysts are alternatives to platinum-based catalysts, but their performance is limited by the instability of Fe-Nx moieties under harsh operating conditions and site deactivation via uncontrolled ligand dynamics. Herein, we report a nanocluster-assisted ligand-anchoring strategy that establishes electronic coupling between Fe-Nx sites and adjacent Fe nanoclusters, which serve as auxiliary anchors to stabilize OH ligands on atomic Fe centers. Morphological characterization and density-functional-theory calculations reveal that charge redistribution between the single-atom site and neighboring clusters tailors the electronic environment of the Fe-Nx reaction center. Ab initio molecular dynamics simulations confirm the dynamic stability of this cluster-single-atom motif with OH-ligand modification under operating conditions. In situ Raman spectroscopy shows optimized evolution of oxygenated intermediates. The synergistic Fe single-atom and nanocluster (FeSA+NC-NC) catalyst exhibits a half-wave potential of 0.92 V, a kinetic current density of 183.57 mA cm-2 at 0.85 V, and retains 95% of its initial activity after 300 h of operation. The zinc-air battery delivers a peak power density of 154 mW cm-2. This work presents a new paradigm for designing single-atom catalysts by engineering the local coordination environment to overcome activity-stability trade-offs.