Vertical-Space-Limit Synthesis of Bifunctional Fe, N-Codoped 2D Multilayer Graphene Electrocatalysts for Zn-Air Battery

Developing a green, cost-efficient air-cathode catalyst with high oxygen evolution and reduction reaction (OER/ORR) performance for rechargeable Zn-air batteries (ZABs) has gained attention. Iron-containing nitrogen-doped graphene (Fe/N-G) that contains Fe-N_x coordination sites is prepared by pyrolyzing the complex of iron ion and PANI sheets intercalated with the unique layer gaps of H-montmorillonite nanoreactors. The transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis confirm that there are no crystalline materials, such as iron lattice, iron carbide, or iron nitride. The as-prepared Fe/N-G show a high electrocatalytic activity in ORR with a 4e⁻ transfer process and the half-wave potential of Fe/N-G (0.877 V vs reversible hydrogen electrode—RHE), which is better than that of Pt/C in oxygen saturated 0.1 m KOH solution. In an acid electrolyte, the Fe/N-G possesses a half-wave potential similar to that of 20 wt% Pt/C. For OER, the Fe/N-G exhibits the overpotential of 400 mV versus RHE at 10 mA cm⁻². However, the Fe/N-G as the air-cathode of the homemade rechargeable ZABs exhibits a high power density (156.8 mW cm⁻²) and an excellent long discharge–charge cycling stability (787 cycles) at 20 mA cm⁻². This work provides an inspiring guideline to prepare a high-performance bifunctional air-cathode for a rechargeable ZAB.