Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum catalysts for the oxygen reduction reaction (ORR) in fuel cells; however, their active site structures remain poorly understood. A leading postulate is that the iron-containing active sites exist primarily in a pyridinic Fe-N₄ ligation environment, yet, molecular model catalysts generally feature pyrrolic coordination. Herein, we report a molecular pyridinic hexaazacyclophane macrocycle, (phen₂N₂)Fe, and compare its spectroscopic, electrochemical, and catalytic properties for ORR to a typical Fe-N-C material and prototypical pyrrolic iron macrocycles. N 1s XPS and XAS signatures for (phen₂N₂)Fe are remarkably similar to those of Fe-N-C. Electrochemical studies reveal that (phen₂N₂)Fe has a relatively high Fe(III/II) potential with a correlated ORR onset potential within 150 mV of Fe-N-C. Unlike the pyrrolic macrocycles, (phen₂N₂)Fe displays excellent selectivity for four-electron ORR, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data demonstrate that (phen₂N₂)Fe is a more effective model of Fe-N-C active sites relative to the pyrrolic iron macrocycles, thereby establishing a new molecular platform that can aid understanding of this important class of catalytic materials.

铁和氮掺杂碳 (Fe-NC) 材料是替代燃料电池中氧还原反应 (ORR) 铂催化剂的主要候选材料；然而，它们的活性位点结构仍然知之甚少。一个主要假设是含铁活性位点主要存在于吡啶Fe-N ₄连接环境中，然而，分子模型催化剂通常具有吡咯配位特征。在此，我们报告了一种分子吡啶六氮杂环芳大环化合物（phen ₂ N ₂ ）Fe，并将其 ORR 的光谱、电化学和催化性能与典型的 Fe-NC 材料和原型吡咯铁大环化合物进行了比较。 (phen ₂ N ₂ )Fe 的 N 1s XPS 和 XAS 特征与 Fe-NC 的特征非常相似。电化学研究表明，(phen ₂ N ₂ )Fe 具有相对较高的 Fe(III/II) 电位，相关 ORR 起始电位在 Fe-NC 的 150 mV 范围内。与吡咯大环化合物不同，(phen ₂ N ₂ )Fe 对四电子 ORR 表现出优异的选择性，与 Fe-NC 材料相当。聚合光谱和电化学数据表明，(phen ₂ N ₂ )Fe 是相对于吡咯铁大环更有效的 Fe-NC 活性位点模型，从而建立了一个新的分子平台，可以帮助理解这一类重要的催化材料。