FeCo Alloy Nanoparticles Coated by an Ultrathin N-Doped Carbon Layer and Encapsulated in Carbon Nanotubes as a Highly Efficient Bifunctional Air Electrode for Rechargeable Zn-Air Batteries

Development of inexpensive, efficient, and stable nonprecious-metal-based bifunctional catalysts for oxygen reduction (ORR) and evolution (OER) reactions remains an enormous challenge. This work reports on an excellent bifunctional electrocatalyst consisting of ultrathin N-doped carbon (1–3 graphitic carbon layers) coated Fe1.2Co nanoparticles and N-doped carbon nanotubes (Fe1.2Co@NC/NCNTs). The Fe1.2Co@NC/NCNTs have an extremely low Fe/Co content (6.7 wt %), but with highly efficient and durable bifunctionality for ORR and OER. Specifically, the Fe1.2Co@NC/NCNT exhibits onset potential (Eonset = 0.842 V vs RHE) and half-wave potential (E1/2 = 0.82 V vs RHE) for ORR and onset potential of 1.43 V vs RHE and overpotential of 355 mV at 10 mA cm–2 for OER. The potential gap (ΔE) between E1/2 of ORR and EOER at 10 mA cm–2 (Ej=10) for the Fe1.2Co@NC/NCNTs is 0.765 V, which surpasses the commercial Pt/C and Ir/C catalysts and most state-of-the-art bifunctional catalysts previously reported. Most notably, when used in the Zn-air battery, the Fe1.2Co@NC/NCNT exhibits superior efficiency and durability to the Pt–Ir/C catalysts. This strongly suggests that the Fe1.2Co@NC/NCNT can be used as an efficient bifunctional catalyst with potential applications in the field of clean electrochemical energy storage and conversion technologies.