Engineering Local and Global Structures of Single Co Atoms for a Superior Oxygen Reduction Reaction

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/mesoporous core-shell structure dramatically enhances the mass transport and electron transfer, which further boosts the ORR and Zn-air battery performance (slightly outperforming Pt/C). Our findings open an avenue toward engineering of the local and global environment of SACs for a wide range of efficient electrochemical conversions. © 2020 American Chemical Society.