Densely accessible Fe/Co-N_x dual-atom site coupled core-shell Co₃Fe₇@C as an efficient bifunctional oxygen electrocatalyst for rechargeable zinc-air batteries

The urgent demand for stable and highly efficient bifunctional electrocatalysts for the oxygen reduction/evolution reactions (ORR/OER) is pivotal in advancing energy conversion and storage technologies. Herein, we introduce a metal-organic framework (MOF)-derived bifunctional electrocatalyst Fe₃Co-NC@900, featuring synergistically coupled dual single-atom sites (Fe/Co-N_x) and core-shell Co₃Fe₇@C nanoparticles. Leveraging the synergistic interactions of Fe-N_x sites with associated Co-N_x sites and core-shell nanoparticles within the MOF-derived nitrogen-doped mesoporous sheets and nanotubes, Fe₃Co-NC@900 demonstrates outstanding ORR and OER performance, outpacing the Fe-NC@900 catalyst fabricated without Co incorporation. Specifically, it demonstrates superior ORR performance with a higher half-wave potential (E_1/2) of 0.88 V and a small Tafel slope of 62.1 mV dec⁻¹, surpassing the Pt/C benchmark (E_1/2 of 0.82 V) and Fe-NC@900 (E_1/2 of 0.788 V). Additionally, it demonstrates noteworthy OER performance, requiring a 1.572 V overpotential at 10 mA cm⁻² current density, resulting in a significant bifunctional activity with a potential gap (ΔE) of 0.692 V, surpassing the Pt/C + Ir/C combination (ΔE = 0.748 V). Moreover, serving as a bifunctional air electrode, Fe₃Co-NC@900 exhibits excellent performance in lab-made Zn-air batteries, with outstanding open circuit voltage, specific capacity, and cycling stability (>650 cycles), outpacing the Pt/C + Ir/C-based battery.