Atomic-level modulation of electronic density of metal-organic frameworks-derived Co single-atom sites to enhance oxygen reduction performance.

Tuning the electronic structure of single-atom active sites via engineering atomic configuration is an effective strategy to boost oxygen reduction reaction (ORR), but still remains challenging because of the lack of rational guidance and effective methods. Here, we demonstrate the correlation between atomic configuration induced electronic density of single-atom Co active sites and ORR performance by combining density functional theory (DFT) calculations and electrochemical analysis. Guided by DFT calculations, we designed and synthesized a MOFs-derived Co single-atom catalyst with the optimal Co 1 -N 3 PS active moiety incorporated in hollow carbon polyhedron (Co 1 -N 3 PS/HC). As predicted, Co 1 -N 3 PS/HC exhibits outstanding alkaline ORR activity with a half-wave potential of 0.920 V and superior ORR kinetics with record-level kinetic current and ultralow Tafel slope of 31 mV dec -1 , exceeding the Pt/C and almost all non-precious ORR electrocatalysts. Even in more challenging acidic media, the ORR kinetics of Co 1 -N 3 PS/HC still surpasses that of Pt/C. This work offers an atomic-level insight into the relationship between electronic density of active site and catalytic property, promoting rational design of highly efficient catalysts.