Fe-N₄and Co-N₄dual sites for boosting oxygen electroreduction in Zn-air batteries

Compared to individual metal sites,e.g.Fe-N₄sites, the synergistic effect of dual-metal sites can further adjust the interaction of reactants or intermediates with active sites, which is beneficial for boosting the oxygen reduction reaction (ORR) in Zn-air batteries. However, developing a simple and direct method instead of complicated procedures and post-treatment to realize well-defined dual-metal sites is still a grand challenge. Herein, a facile one-step impregnation-pyrolysis route without any post-treatment is developed to controllably synthesize Fe and Co dual-metal sites embedded in hierarchical N-doped carbon from metal-organic frameworks. X-ray absorption spectra coupled with density functional theory calculations demonstrate that the Fe-N₄and Co-N₄dual sites can synergistically enhance the ORR activity. Impressively, the well-controlled FeCo-N-C catalyst exhibits excellent ORR performance, with half-wave potentials (E_1/2) of 0.807 and 0.904 V in 0.1 M HClO₄and 0.1 M KOH, respectively. Benefiting from the highly active dual-metal sites and desired porous structure, FeCo-N-C serving as a cathode catalyst achieves an uplifting peak power density of 196.3 mW cm⁻²and a remarkable specific capacity of 728.6 mA h g_Zn⁻¹at a discharge current density of 20 mA cm⁻²in a practical liquid Zn-air battery. Besides this, such superb battery performance is demonstrated in an all-solid-state Zn-air battery.