Axial Oxygen Ligands Regulating Electronic and Geometric Structure of Zn-N-C Sites to Boost Oxygen Reduction Reaction.

Zn-N-C possesses the intrinsic inertia for Fenton-like reaction and can retain robust durability in harsh circumstance, but it is often neglected in oxygen reduction reaction (ORR) because of its poor catalytic activity. Zn is of fully filled 3d 10 4s 2 configuration and is prone to evaporation, making it difficult to regulate the electronic and geometric structure of Zn center. Here, guided by theoretical calculations, five-fold coordinated single-atom Zn sites with four in-plane N ligands is constructed and one axial O ligand (Zn-N 4 -O) by ionic liquid-assisted molten salt template method. Additional axial O not only triggers a geometry transformation from the planar structure of Zn-N 4 to the non-planar structure of Zn-N 4 -O, but also induces the electron transfer from Zn center to neighboring atoms and lower the d-band center of Zn atom, which weakens the adsorption strength of *OH and decreases the energy barrier of rate determining step of ORR. Consequently, the Zn-N 4 -O sites exhibit improved ORR activity and excellent methanol tolerance with long-term durability. The Zn-air battery assembled by Zn-N 4 -O presents a maximum power density of 182 mW cm -2 and can operate continuously for over 160 h. This work provides new insights into the design of Zn-based single atom catalysts through axial coordination engineering.