Herein, a novel binuclear active site structure, Co₂N_xC_y, is intentionally designed and successfully fabricated to efficiently catalyze the oxygen reduction reaction (ORR), which is achieved by precisely controlling the atomic scale structure of bimetal-organic frameworks before pyrolysis. Through discovering a two-atom site with Co-Co distance at 2.1–2.2 Å from aberration-corrected scanning transmission electron microscopy (STEM), as well as a novel shortened Co-Co path (2.12 Å) from the X-ray absorption spectroscopy, we for the first time identified the binuclear Co₂N_X site in the pyrolyzed catalyst. Combined with density functional theory (DFT) calculation, the structure is further confirmed as Co₂N₅. Excitingly, the Co₂N₅ site performs approximately 12 times higher activity than the conventional CoN₄ site and the corresponding catalyst shows unprecedented catalytic activity in acidic electrolyte with half-wave potential of 0.79 V, approaching the commercial Pt/C catalyst and presenting the best one among the Co-N-C catalysts. Theoretical density functional theory calculations reveal that the novel binuclear site exhibits considerably reduced thermodynamic barrier towards ORR, thus contributing to the much higher intrinsic activity. Our finding opens up a new path to design efficient M-N_x/C catalysts, thus pushing the fuel cell industry field one step ahead.

        https://doi.org/10.1016/j.nanoen.2018.02.025