Abstract
Freestanding membrane electrodes with a high electrocatalytic activity and stability are desirable for use in highperformance metal-air batteries. Here, we report a gas-phase fluorination-assisted method to anchor single atom Fe-Nx moieties on a freestanding single-wall carbon nanotube (SWCNT) film that involves fluorination and defluorination/ammoniation processes. It is shown that the fluorination followed by defluorination/ammoniation harvests Fe atoms from the residual Fe nanoparticles used for SWCNT growth to form high density of Fe-Nx active sites, while retaining the flexibility, integrity and high quality of the films so that they can be directly used as a bifunctional oxygen electrode for rechargeable Zn-Air batteries. The single-atom Fe-Nx loaded SWCNT film shows an even better catalytic activity than commercial Pt/C-Ir/C catalysts, and an assembled Zn-Air battery using it exhibits a low charge-discharge voltage gap of 0.84 V under 20 mA/cm2, a high peak power density of 210 mW/cm2, and excellent long-time cycling stability. In addition, a flexible all-solid-state Zn-Air battery was assembled which has a stable open circuit voltage when bent to different angles.