Reconfiguring FeN sites through axial FeO clusters to enhance d-orbital electronic delocalization for improved oxygen reduction reaction.

Effectively controlling the electronic configuration of metal sites within single-atom catalysts (SACs) is essential for improving their oxygen reduction reaction (ORR) performance. Here, we construct hybrid catalysts featuring Fe single atoms and FeO clusters (Fe SACs/FeO@NHPC) to realize highly efficient ORR. Specifically, the Fe SACs/FeO@NHPC delivers a remarkable half-wave potential (E) of 0.893 V and endures 30,000 cycles with only 12 mV E loss in alkaline media. Liquid zinc-air batteries (ZABs) utilizing Fe SACs/FeO@NHPC output a power density of 192.7 mW cm and demonstrate rechargeability over 370 h without noticeable voltage degradation. Furthermore, theoretical calculations indicate that the axially coordinated FeO clusters significantly promote electronic delocalization in the 3d orbitals of the Fe sites. This electronic structure regulation strategy optimizes the hybridization between Fe-3d orbitals and O-2p orbitals, thereby facilitating the *OH dissociation process. This research not only provides intensive insight into the synergistic interactions and complementary effects between single-atom sites and clusters in hybrid catalysts but also lays the groundwork for designing SACs.