Optimizing high-coordination shell of Co-based single-atom catalysts for efficient ORR and zinc-air batteries

Atom-level modulation of the coordination environment for single-atom catalysts (SACs) is considered as an effective strategy for elevating the catalytic performance. For the MNx site, breaking the symmetrical geometry and charge distribution by introducing relatively weak electronegative atoms into the first/second shell is an efficient way, but it remains challenging for elucidating the underlying mechanism of interaction. Herein, a practical strategy was reported to rationally design single cobalt atoms coordinated with both phosphorus and nitrogen atoms in a hierarchically porous carbon derived from metal-organic frameworks. X-ray absorption spectrum reveals that atomically dispersed Co sites are coordinated with four N atoms in the first shell and varying numbers of P atoms in the second shell (denoted as Co-N/P-C). The prepared catalyst exhibits excellent oxygen reduction reaction (ORR) activity as well as zinc-air battery performance. The introduction of P atoms in the Co-SACs weakens the interaction between Co and N, significantly promoting the adsorption process of *OOH, resulting in the acceleration of reaction kinetics and reduction of thermodynamic barrier, responsible for the increased intrinsic activity. Our discovery provides insights into an ultimate design of single-atom catalysts with adjustable electrocatalytic activities for efficient electrochemical energy conversion.