Hollow Conjugated Microporous Polymer Nanosphere-Derived Fe–N–C Electrocatalysts for the Oxygen Reduction Reaction

Fe–N–C catalysts are some of the most promising catalysts for the oxygen reduction reaction (ORR). However, there are still some problems in the pyrolysis of precursors, such as the destruction of the carbon skeleton and low utilization of active sites. In this work, we synthesized hollow pyridine N-containing conjugated microporous polymers (CMPs) by coupling polymerization. The bipyridine units in CMPs’ skeleton can anchor Fe3+ to form a stable coordination structure, which was effectively converted into Fe–N–C catalysts by one-step pyrolysis. Due to the rigid skeleton of precursors, the hollow structure was preserved in catalysts, which is favorable to O2 diffusion and mass transport of intermediates. X-ray photoelectron spectroscopy and Fe K-edge X-ray near-edge spectroscopy revealed approximate FeN4 structures within the framework of the catalysts. As a result, the resulting CMP-derived catalysts exhibited satisfactory ORR activity in alkaline media with a limiting current density of 4.40 mA cm–2. Furthermore, the Fe,N–C1–900 catalyst demonstrated exceptional methanol immunity with a mere negative shift of 0.01 mA cm–2 in limiting current density compared with the commercial Pt/C catalyst, indicating remarkable stability.