FeN2–CoN2 Dual-Atom Catalyst Derived by Mesoporous NH2-MIL-101 Adsorbing N-Rich Guest Molecules [Co(en)3]3+ for Efficient ORR in Zn–Air Batteries

The introduction of guest metal molecules into metal–organic frameworks (MOFs) is an outstanding method to prepare dual-atom catalysts (DACs) with good oxygen reduction reaction (ORR) activity. However, most of the MOF-derived dual-atom catalysts reported to date exhibit a microporous structure and, therefore, suffer from the underutilization of active sites and poor mass transfer. This study employed NH2-MIL-101 as a precursor to form defect-bearing mesoporous Fe-NC via one-step pyrolysis for adsorbing [Co(en)3]3+, followed by secondary pyrolysis to generate Fe–Co binuclear site catalysts. The mesopores of NH2-MIL-101 are beneficial to [Co(en)3]3+ introduction and can improve the mass transfer of the ORR. Furthermore, the elevated nitrogen content within the [Co(en)3]3+ complex facilitates the co-coordination of Fe and Co with nitrogen, thereby enhancing the formation of Fe–Co diatomic sites. As a result, the obtained FeCo-NC-40 catalyst showed excellent ORR performance with a half-wave potential of 0.915 V (vs RHE). In addition, the liquid-phase Zn–air battery employing FeCo-NC-40 as the cathode catalyst demonstrated a peak power density of 178.13 mW·cm–2 and achieved a discharge specific capacity of 806.13 mAh·g–1 at 10 mA·cm–2, and there was no significant decay in stability for 10 days of continuous cycling.