Surface reconstructed hollow Fe-doped CoO_x(OH)_y bifunctional electrocatalysts for rechargeable zinc–air batteries

The development of cost-effective and highly stable bifunctional electrocatalysts for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is essential for the advancement of rechargeable zinc–air batteries (ZABs). Herein, we report Fe-doped CoO_x(OH)_y, derived from the in situ transformation of Fe-doped CoS, as a bifunctional electrocatalyst for ZAB applications. By utilizing highly porous Ti-based metal–organic frameworks (MIL-125-NH₂) as a sacrificial template, the Fe-doped CoS pre-catalyst forms a hollow structure with a high surface area. During electrochemical activation, the Fe-doped CoS undergoes surface reconstruction into oxygen-containing species that serve as active sites for both OER and ORR. Our characterizations indicate that Fe doping enhances the adsorption and desorption of intermediates during ORR and improves charge distribution during OER. The rechargeable ZAB employing the hollow Fe-doped CoO_x(OH)_y catalyst achieves a high power density of 188.2 mW cm⁻², an open-circuit potential of 1.50 V, and demonstrates long-term charge–discharge performance over 500 h, outperforming commercial catalysts. This study presents an efficient strategy for synthesizing bifunctional electrocatalysts, significantly advancing the feasibility of rechargeable ZABs.