S and O Co-Coordinated Mo Single Sites in Hierarchically Porous Tubes from Sulfur-Enamine Copolymerization for Oxygen Reduction and Evolution.

The highly efficient bifunctional catalyst for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is the key to achieving high-performance rechargeable Zn-air batteries. Non-precious-metal single-atom catalysts (SACs) have attracted intense interest due to their low cost and very high metal atomic utilization; however, high-activity bifunctional non-precious-metal SACs are still rare. Herein, we develop a new nanospace-confined sulfur-enamine copolymerization strategy to prepare a new type of bifunctional Mo SACs with O/S co-coordination (Mo-OS-C) supported on the multilayered, hierarchically porous hollow tubes. The as-prepared catalyst can not only expose more active sites and facilitate mass transfer due to their combined micropores, mesopores, and macropores but also have the S/O co-coordination structure for optimizing the adsorption energies of the ORR intermediates. Its ORR activity is among the highest, and it shows a low overpotential of 324 mV for the OER at 10 mA cm in all of the reported Mo-based catalysts. When assembled in a Zn-air battery, it exhibits a high maximal power density of 197.3 mW cm and a long service life of 50 hours, superior to those of Zn-air batteries using commercial Pt/C+IrO.