Accurately regulating the adsorption-desorption behaviors of oxygenated intermediates on the active centers is crucial to control the catalytic activity and selectivity in the oxygen reduction reaction (ORR) domain, but remains a great challenge. Here, we propose a universal strategy of symbiotically growing atomically metal sites on the electronic state-rich metallic nanocrystals to tailor the electron structure of the catalytic active centers, enabling moderate adsorption capacity of oxo-hydroxy on the active centers toward high four-electron ORR selectivity. As a proof-of-concept experiment, three typical catalysts of atomically-dispersed Fe sites (Fe-SA/NC), symbiotic Fe complex by coupling atomically-dispersed Fe sites onto Fe nanocrystals (SBT-Fe-NC@SA), and Fe nanoparticles (Fe-NP/NC) were designed to flexibly alter the kinetic pathways of ORR. In situ synchrotron characterizations identified that a self-evolved Fe site adsorbed on the oxygen-bridge enhances the dinuclear Fe-Fe interaction under working conditions for SBT-Fe-NC@SA, which regulates the oxo-hydroxy adsorption capacity to be moderate for rapid breakage of O-O bond. As a result, the well-designed SBT-Fe-NC@SA exhibits the largest efficiency of four-electron ORR pathway and ultrahigh mass activity at the half-wave potential, tens of times those of control counterparts. These findings provide a unique perspective for optimally regulating intermediates adsorption capacity of active sites toward superior activity.
