A thermal evaporation-trapping strategy to synthesize flexible and robust oxygen electrocatalysts for rechargeable zinc-air batteries

Great efforts have been devoted to the development of bifunctional electrocatalysts to accelerate the sluggish kinetics of cathodic oxygen reduction/evolution reactions (ORR/OER) in zinc-air batteries (ZABs). Here we report a thermal evaporation-trapping synergistic strategy to fabricate a bifunctional electrocatalyst of flexible N-doped carbon fiber cloth loaded with both CoFe-oxide nanoparticles and single-atom Co/Fe-N_x sites, in which the thermal evaporation process functions in both downsizing CoFe-oxide nanoparticles and trapping the evaporated Co/Fe species to generate Co/Fe-N_x sites. The obtained flexible electrocatalyst, directly serving as an oxygen electrode, displays a small potential gap of 0.542 V for the OER/ORR, large peak power densities (liquid-state ZAB: 237.4 mW cm⁻²; solid-state ZAB: 141.1 mW cm⁻²), and excellent charge-discharge cycling stability without decay after working more than 770 hours. Furthermore, in situ Raman spectroscopy characterization and theoretical calculations reveal that CoFe₂O₄ species is responsible for the OER while atomic Fe/Co sites play a key role in the ORR.