Synergistic electronic interplay between Co[sbnd]Fe single atom and nitrogen on 2D carbon boosts bifunctional oxygen redox in metal-air batteries

Abstract

Enhancing oxygen redox reactions (ORR and OER) is crucial for improving energy storage and conversion technologies such as fuel cells and metal-air batteries. While single-metal catalysts like Fe-Nx and Co-Nx are widely used, bi-metallic catalysts offer a synergistic effect that enhances catalytic performance. However, achieving well-defined bi-metallic active sites remains a challenge. In this study, we developed a novel dual-metallic single-atom (DSA) electrocatalyst (CoFe-2DSA) on 2D nitrogen-doped carbon nanosheets, synthesized using a molten salt-assisted pyrolysis approach. The incorporation of zinc acetate and KCl during pyrolysis increased porosity and surface area by preventing structural collapse and facilitating the formation of N-doped carbon sheets. Density Functional Theory (DFT) calculations revealed that Co[sbnd]Fe dual-atom sites and nitrogen dopants synergistically optimize oxygen redox reactions. Graphitic nitrogen enhances charge transfer and metal‑oxygenate bonding, while pyridinic nitrogen introduces sp3 defects that accumulate charge, reducing further charge transfer and weakening metal‑oxygenate interactions. Coordination between nitrogen and metal sites facilitates electron transfer to Co[sbnd]Fe, tuning d-orbital energy levels and optimizing intermediate adsorption (*O₂, *OH, *OOH). As a result, CoFe-2DSA demonstrated outstanding bifunctional catalytic performance, with an ORR half-wave potential (E1/2) of 0.886 V (vs RHE) and an OER overpotential (η) of 290 mV at 10 mA.cm−2. As a zinc-air battery cathode, it achieved a power density of 229.6 mW.cm−2, a specific capacity of 811.5 mA.h.g−1, and exceptional cycling stability over 74 days (3552 cycles). This study provides a paradigm shift in understanding the synergistic interaction between transition metals and nitrogen-doped carbon in oxygen redox reactions.