FeCo alloy/N, S co-doped carbon aerogel derived from directional-casting cellulose nanofibers for rechargeable liquid flow and flexible Zn–air batteries

Bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts with the advantages of excellent activity and stability are the vital components of air cathodes for rechargeable Zn–air batteries (ZABs). Herein, the carbon aerogel with honeycomb-like structure, N and S double doping and loaded with FeCo alloy nanoparticles (NSCA/FeCo) was prepared successfully as cathodes for rechargeable liquid flow and two-dimensional flexible ZABs by clever directional casting. The interaction between the bimetallic alloy and the double-doped carbon with specifical structure, large surface, and great conductivity endows NSCA/FeCo with effective ORR/OER active sites and small charge/mass transport barrier, thus achieving outstanding bifunctional catalytic performance. The NSCA/FeCo displays a half-wave potential of +0.85 V (vs. reversible hydrogen electrode (RHE)) for ORR and an overpotential of 335 mV at a current density of 10 mA·cm⁻² for OER, which is even comparable to the performance of noble-metal catalysts in relevant fields (Pt/C for ORR and RuO₂ for OER). Consequently, the rechargeable liquid flow ZABs assembled with NSCA/FeCo showed excellent performance (maximum power density: 132.0 mW·cm⁻², specific capacity: 804.5 Wh·kg⁻¹ at 10 mA·cm⁻², charge and discharge cycle stability of more than 250 cycles). Furthermore, the flexible NSCA/FeCo-based ZABs have a maximum power density of 43.0 mW·cm⁻², outstanding charging–discharge stability of more than 450 cycles, and exhibit good flexibility under different bending conditions. Therefore, this work has provided an efficient bifunctional electrocatalyst for OER/ORR and a promising strategy of air cathodes for rechargeable and wearable ZABs.