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 (Co-1-SAC) with superior oxygen reduction reaction (ORR) performance. Co-1-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-N-4, which facilitate both the electronic hybridization with O-2 and the subsequent protonation of adsorbed O-2* toward the formation of OOH*. Engineering Co-N3C1-SAC into a micro/mesoporous 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.