Using dopamine interlayers to construct Fe/Fe3C@FeNC microspheres of high N-content for bifunctional oxygen electrocatalysts of Zn–air batteries

Abstract

High activity bifunctional oxygen electrocatalysts are crucial for the development of high performing Zn–air batteries. Fe–N–C systems decorated with Fe/Fe₃C nanoparticles have been identified as prospective candidates in which almost all the active sites need the presence of N. To anchor more N, an Fe₂O₃ microsphere template was covered by a thin layer of polymerized dopamine (PDA) before it was mixed with a high N-content source of g-C₃N₄. The PDA interlayer not only provides a part of C and N but also serves as a buffer agent to hinder fast reactions between Fe₂O₃ and g-C₃N₄ during pyrolysis to avoid the destruction of the microsphere template. The prepared Fe/Fe₃C@FeNC catalyst showed superior electrochemical performance, achieving a high half-wave potential of 0.825 V for ORR and a low overpotential of 1.450 V at 10 mA cm⁻² for OER. The rechargeable Zn–air battery assembled with the as-obtained Fe/Fe₃C@FeNC catalyst as a cathode offered a high peak energy density of 134.6 mW cm⁻², high specific capacity of 856.2 mA h g_Zn⁻¹ and excellent stability over 180 h at 5 mA cm⁻² (10 min per cycle) with a small charge/discharge voltage gap of ∼0.851 V. This work presents a practical strategy for constructing nitrogen-rich catalysts with stable 3D structures.