Facile Synthesis of 3D Fe/N Codoped Mesoporous Graphene as Efficient Bifunctional Oxygen Electrocatalysts for Rechargeable Zn–Air Batteries

Exploring the oxygen electrocatalysts with both high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) performance is crucial to developing the rechargeable Zn–air batteries (ZABs). Herein, we prepared a bifunctional three-dimensional graphene-like iron-nitrogen doped oxygen electrocatalyst (3D Fe/N-G#4, polyacrylamide (PAM):NaCl = 1:4, mass ratio) by a facile synthesis with PAM and iron as precursors and NaCl as template. The NaCl template melted during the pyrolysis process, which could fabricate a stable 3D network structure in the precursors to form more mesopores, higher specific surface area, and more exposed active sites and prevent the loss of precursors. The low-cost and water-soluble PAM as the N precursor provided abundant N and dissolved adequately with NaCl solution. The Fe precursor coordinated with the N to form Fe-Nx active sites that were investigated by HR-TEM, XRD, XPS, and RDE techniques. The 3D Fe/N-G#4 exhibited excellent electrochemical activity with a high half-wave potential (0.852 V vs RHE) for ORR and a low overpotential (393 mV at 10 mA cm–2) for OER in the alkaline conditions. In addition, the homemade rechargeable ZAB based on the prepared 3D Fe/N-G#4 exhibits high power density (168.2 mW cm–2) and excellent discharge-charge cycling stability (over 60 h) at 20 mA cm–2. This work provides a cost-efficient, simple, and eco-friendly method to synthesize excellent bifunctional non-noble electrocatalysts for commercialization of ZABs.