Structural and Chemical Origin of Dual-Atom Sites for Enhanced Oxygen Electroreduction

Dual-atom catalysts have garnered widespread attention for the oxygen reduction reaction (ORR), yet achieving an in-depth comprehension of the reaction mechanism and the structure–activity relationship remains challenging. Herein, carbon nanosheets with FeCo–N6 active sites (FeCo-NCNS) are prepared via a straightforward self-sacrificing template and cascade anchoring strategy. Delicate structural control enables hierarchical porosity, providing adequate active site density (2.5 × 1019 sites g–1) and fast mass transfer, as revealed by in situ scanning electrochemical microscopy. Moreover, the structural and chemical origin of the dual-atom site for enhanced ORR activity is uncovered. FeCo–N6 can be spontaneously transformed to an oxygen-bridging structure (FeCo–N6–O) in the KOH electrolyte, triggering improved charge polarization, downshifted d-band center, and optimized adsorption behavior for oxygen-intermediates, thereby reducing the free energy barrier. Therefore, the FeCo-NCNS exhibits enhanced ORR activity regarding the half-wave potential (0.90 V), mass specific kinetic current density (9.54 A g–1), turnover frequency (2.35 e– site–1 s–1), and improved stability. This work not only provides an effective methodology to construct efficient electrocatalysts for energy conversation but also highlights the dynamic structural evolution and charge polarization in improving the electrocatalytic activity of dual-atom sites.