g-C₃N₄ promoted MOF-derived Fe single atoms anchored on N-doped hierarchically porous carbon for high-performance Zn-air batteries

Exploring efficient, easy-to-manufacture, and inexpensive bifunctional electrocatalysts with abundant accessible active sites is crucial for rechargeable zinc-air batteries (ZABs). Herein, we report the strategy consisting of the space confinement and pore-making engineering to fabricate single-atom catalyst enriched with Fe-N₄ sites anchored on N-doped hierarchically porous carbon (Fe-NC-C₃N₄). The optimized Fe-NC-C₃N₄ exhibits excellent oxygen reduction/evolution reaction (ORR/OER) activities with a half-wave potential (E_1/2) of 0.90 V vs. RHE and a promising low overpotential of 0.305 V vs. RHE at 10 mA·cm⁻² in alkaline electrolyte. These superior catalytic activities are attributed to the combined effect between the atomic active sites and the well-balanced micro-meso-macropore structures. The homemade liquid Zn-air battery (ZAB) assembled with Fe-NC-C₃N₄ catalyst displays a power density of 133.59 mW·cm⁻² and a significant energy density of 882.58 mAh·g⁻¹, exceeding those of the equipment with commercial Pt/C-RuO₂ (56.82 mW·cm⁻² and 643.87 mAh·g⁻¹, respectively). Particularly, the corresponding flexible wearable ZAB manifests outstanding foldability and cyclical stability. This work opens a new perspective for the structural design of single-atom catalysts in the energy storage and conversion area.