M–Nx–C (M = Fe, Zn) bi-active sites booting oxygen reduction reaction and zinc-air battery performance

Abstract

Fe/N/C is recognized promising catalyst for oxygen reduction reaction (ORR), playing a pivotal role in advancing the commercialization of proton exchange membrane fuel cells. However, an inadequate ORR activity hinders its potential applications. Here, we present the preparation of M–Nx–C (M = Fe, Zn) bi-active sites for promoting ORR. By the pyrolysis of benzimidazole salts, a porous coin-like iron-zinc-based nitrogen-doped carbon materials (FeZn-NC) catalyst was synthesized with abundant active sites. X-ray photoelectron spectroscopy and transmission electron microscopy characterizations indicated the successful doping of Zn and Fe within the carbon framework. Electrochemical measurements demonstrated great positive half-wave potential (0.90 V), high limiting current density (5.15 mA·cm−2), excellent methanol resistance, and good stability of FeZn-NC, compared to commercial Pt/C catalysts. Furthermore, an investigation into correlation between doping content of Fe and the ORR performance was carried out. As an cathode catalyst of zinc-air battery, FeZn-NC exhibited more significant advantages, including a high open-circuit voltage (1.54 V), enhanced power density (199.89 mW·cm−2), good specific capacity (771.9 mAh gZn−1), and enhanced stability compared to Pt/C. By presenting an approach for the controlled synthesis of metal-doped carbon materials, this work establishes the groundwork for potential applications in catalytic fields, as demonstrated by the prepared FeZn-NC.