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

Abstract

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-O₂S₂-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^-2 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^-2 and a long service life of 50 hours, superior to those of Zn-air batteries using commercial Pt/C+IrO₂.