Low-coordinated Fe-N3 single atom with rapid protonation for boosting oxygen reduction reactions

Accurately constructing the coordination environment of single-atom catalysts (SACs) is an available avenue to promote multistep tandem catalytic reactions, but challenging. Herein, we construct a Fe SAC with low- coordinated Fe- N3 configuration for efficient oxygen reduction reaction (ORR). Low-coordinated Fe- N3 successfully breaks the electron distribution symmetry of the Fe- N4 unit to optimize the adsorption strength of the reactive species on it. In situ characterization techniques directly observed the bond stretching and increased electron density of Fe- N3 configuration facilitates the dissociation of *OOH intermediates and protonation of *O, thus accelerating the four-electron reaction kinetics. Therefore, this designed Fe- N3 catalyst exhibits a mass activity of 619 A g metal-1 at 0.85 V, nearly 39 times higher than commercial Pt/C (16 A g metal-1 ), and a high four- electron selectivity of 99.1 %. Furthermore, the catalyst shows high power density (125.3 mW cm- 2 ) in zinc- air batteries (ZABs), indicating its promising application potential. This work provides a new insight to construct well-defined SACs with coordination environment for efficient catalytic reactions.