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The ability to tune both local and global environments of a single-metal active center on a support is crucial for the development of highly robust and efficient single-atom electrocatalysts (SAECs) that can surmount both thermodynamic and kinetic constraints in electrocatalysis. Here, we designed a core–shell-structured SAEC (Co₁-SAC) with superior oxygen reduction reaction (ORR) performance. Co₁-SAC consists of a locally engineered single Co-N₃C₁ site on a N-doped microporous amorphous carbon support enveloped by a globally engineered highly conductive mesoporous graphitic carbon shell. Theoretical calculations reveal that Co-N₃C₁ exhibits near-Fermi electronic states distinct from those of Co-N₂C₂ and Co-N₄, which facilitate both the electronic hybridization with O₂ and the subsequent protonation of adsorbed O₂* toward the formation of OOH*. Engineering Co-N₃C₁-SAC into a micro …