Structural and\nChemical Origin of Dual-Atom Sites\nfor Enhanced Oxygen Electroreduction

Dual-atom\ncatalysts have garnered widespread attention\nfor the\noxygen reduction reaction (ORR), yet achieving an in-depth comprehension\nof the reaction mechanism and the structure–activity relationship\nremains challenging. Herein, carbon nanosheets with FeCo–N<sub>6</sub> active sites (FeCo-NCNS) are prepared via a straightforward\nself-sacrificing template and cascade anchoring strategy. Delicate\nstructural control enables hierarchical porosity, providing adequate\nactive site density (2.5 × 10<sup>19</sup> sites g<sup>–1</sup>) and fast mass transfer, as revealed by in situ scanning electrochemical\nmicroscopy. Moreover, the structural and chemical origin of the dual-atom\nsite for enhanced ORR activity is uncovered. FeCo–N<sub>6</sub> can be spontaneously transformed to an oxygen-bridging structure\n(FeCo–N<sub>6</sub>–O) in the KOH electrolyte, triggering\nimproved charge polarization, downshifted <i>d</i>-band\ncenter, and optimized adsorption behavior for oxygen-intermediates,\nthereby reducing the free energy barrier. Therefore, the FeCo-NCNS\nexhibits enhanced ORR activity regarding the half-wave potential (0.90\nV), mass specific kinetic current density (9.54 A g<sup>–1</sup>), turnover frequency (2.35 e<sup>–</sup> site<sup>–1</sup> s<sup>–1</sup>), and improved stability. This work not only\nprovides an effective methodology to construct efficient electrocatalysts\nfor energy conversation but also highlights the dynamic structural\nevolution and charge polarization in improving the electrocatalytic\nactivity of dual-atom sites.