Polypyrrole Template-Assisted Synthesis of Tubular Fe-NC Nanostructure-Based Electrocatalysts for Efficient Oxygen Reduction Reaction in Rechargeable Zinc-Air Battery

One-dimensional metal/N-doped carbons have exhibited promise for use as efficient catalysts of the oxygen reduction reaction (ORR). In this work, Fe,N-doped carbon nanotubes (Fe-NC@NCNT) are developed by pyrolyzing the precursor/template of a polypyrrole (PPy) nanotube-anchored Fe/Zn-based zeolite imidazole framework. Thanks to the hierarchical tubular nanostructure, high electronic conductivity, and abundant Fe-based species (Fe-N-x sites and Fe/Fe3C nanoparticles), the designed electrocatalyst exhibits a catalytic property comparable to that of commercial Pt/C. Specifically, the Fe-NC@NCNT catalyst undergoes a four-electron ORR pathway with an onset potential of 0.96 V and a half-wave potential of 0.88 V versus reversible hydrogen electrode, a small Tafel slope of 60.0 mV dec(-1), remarkable long-term cycle durability, as well as strong alcohol tolerance in an alkaline electrolyte. When applied to the air-electrode catalyst of rechargeable zinc-air batteries, the Fe-NC@NCNT-catalyzed liquid-state battery delivers an open-circuit voltage of 1.44 V and a maximum power density of 115 mW cm(-2) with a specific capacity of 814 mAh g(-1), outperforming those of the battery assembled with commercial Pt/C + RuO2. In addition, the as-assembled solid-state battery displays a desirable rechargeability and electrochemical flexibility. The present study establishes a facile dual-template approach to fabricate highly efficient and inexpensive ORR electrocatalysts toward the application of metal-air batteries.