Fe–Co Dual-Atom Catalyst Prepared by a Defect-Confining Nitrogen-Rich Ion Strategy for Efficient Oxygen Reduction Reaction

Dual-atom catalysts demonstrate promising activity in the oxygen reduction reaction (ORR). In the present work, a two-step pyrolysis method was used to prepare an Fe/Co dual-atom catalyst (FeCo-NC). First, Fe-Zn-ZIF was pyrolyzed to fix the zeolitic-imidazolate framework (ZIF) structure and form defects with a negative charge via Zn evaporation. Second, the defect-rich carbon matrix was used to adsorb guest molecules with nitrogen-rich ([Co(en)3]3+), and then it underwent a secondary pyrolysis to yield FeCo-NC. The presence of defects can confine [Co(en)3]3+, and the abundant nitrogen within [Co(en)3]3+ facilitates coordination with Fe and Co atoms, effectively preventing the aggregation of metal species. Furthermore, there are a large number of nanotubes in FeCo-NC that combine with pyrolyzed ZIFs to enhance electron transfer. The density functional theory results suggest that the hydrogenation of OH* is the decisive step for ORR. The asymmetric charge distribution between Fe and Co atoms is able to lower the activation energy for the resolution step of OH*, which leads to a remarkable ORR performance with a positive E1/2 in 0.1 M KOH (0.92 V). Moreover, the assembled liquid Zn-air battery achieved a power density of 180.02 mW cm-2 and was able to operate continuously for more than 200 h. Solid Zn-air battery measurements confirm the practical applicability of the FeCo-NC.