Constructing a Fe3O4/Fe–Nx Dual Catalytic Active Center on an N-Doped Porous Carbon as an Oxygen Reduction Reaction Catalyst for Zinc–Air Batteries

As a novel type of clean and environmentally friendly energy storage and conversion technology, the zinc–air battery is considered a promising alternative to lithium-ion batteries. Nevertheless, because the oxygen reduction reaction (ORR) in the air cathode has the characteristic of a slow kinetic reaction, developing an electrocatalyst for ORR plays an important role in overcoming the limitation of low current density and large electrode polarization. To catalyze ORR, herein a high-efficiency and cheap ORR catalyst with a Fe3O4/Fe–Nx dual catalytic active center (Fe–N–CS) via molten-salt-assisted pyrolysis is designed and prepared. The bulk iron oxide is successfully encouraged to break its chemical bonds by the sodium chloride molten salt and subsequently trapped by the porous nitrogen-doped carbon skeleton and reduced to Fe3O4 by a carbothermal process. Meanwhile, the graphitization degree of the carbon skeleton increases obviously and some Fe–Nx sites are also generated because of the cooperation of Fe3O4 nanoparticles and Fe–Nx species. It has been found that Fe–N–CS exhibits excellent ORR performance, e.g., half-wave potential up to 0.90 V and an onset potential of 1.04 V. In addition, Fe–N–CS shows better stability than Pt/C catalysts in chronoamperometry (I–T) tests, where Fe–N–CS maintains a 91% retention rate after 1200 s compared to Pt/C (75.8%). When the Fe–N–CS catalyst is used in zinc–air batteries (ZABs), it still shows better performance than the traditional Pt/C catalyst.