Tuning the coordination environment of Fe atoms enables 3D porous Fe/N-doped carbons as bifunctional electrocatalyst for rechargeable zinc-air battery.

As one of the most promising candidates for power sources, the rechargeable Zn-air batteries have attracted much attention due to their high energy density. However, Zn-air batteries suffer from sluggish kinetics of oxygen reduction (ORR) and oxygen evolution reaction (OER) during the discharge and charge process. Herein, a FeN2-doped carbon with a unique three-dimensional (3D) porous structure (CeO2-FeNC-5) was synthesized as an electrocatalyst for Zn-air batteries by one-step pyrolysis and introducing CeO2 to tune the coordination environment of Fe atoms. Extended X-ray absorption fine structure (EXAFS) results indicate that the introduction of CeO2 can convert FeN3 moieties into FeN2 moieties. The CeO2-FeNC-5 exhibits a more positive half-wave potential of 0.902 V for ORR, and a low overpotential of 0.327 V at 10 mA cm-2 for OER. Furthermore, the Zn-air battery with CeO2-FeNC-5 achieve a maximum power density (169 mW cm-2), a high open voltage platform (1.47 V) and superior cycling stability (200 h). The unique 3D porous structure provides channels for mass transport and exposes sufficient active sites to facilitate the ORR and OER processes. Calculations prove that FeN2 moieties are beneficial to O2 adsorption on Fe/N-doped carbon surface. This work provides an effective strategy for designing and synthesizing FeNx-doped carbon matrix electrocatalysts for sustainable metal-air batteries.