Metal-organic framework derived Fe₃C nanoparticles coupled single-atomic iron for boosting oxygen reduction reaction

Developing transition metal electrocatalysts, especially single-atom catalysts (SACs), is significant. However, most of the synthesis procedures of SACs involve the formation of nanoparticles (NPs), and the produced NPs always play an influential role during electrocatalytic processing, so exploring the synergistic effects between metallic and isolated metal species is of great interest. Herein, we report a Zn/Fe-metal-organic framework (MOF)-derived Fe₃C coupling FeN_x catalyst constructed via coordination confinement pyrolysis effect successfully. Compared with the Pt/C catalyst and most precious metal-free catalysts, the optimized catalyst Fe₃C-FeN_x/NC-7 demonstrates superior oxygen reduction reaction (ORR) activity in 0.1 M KOH. The half-wave potential (E_1/2) reaches up to 0.93 V with the limiting current density (j_L) of 5.65 mA/cm² at 5 mV/s scanning rate and 1600 rpm. The excellent performance originates from the synergistic effect of FeN_x and Fe₃C active units combined with wide-distributed nitrogen atoms. The Fe₃C NPs further optimize the electronic structure and adsorption/desorption free energy of the catalyst. The assembled primary Zn-air battery (ZAB) displays a satisfying open-circuit potential of 1.53 V and an excellent specific capacity of 835 mA·h·g^-1. The maximum power density achieves 283 mW/cm², outclassing the commercial Pt/C-based ZAB. This result demonstrates the promising application prospect of the catalyst-cooperated metallic NPs with isolated single metal species.