We elucidate the origin of oxygen reduction reaction (ORR) activity enhancement on the FeN₄ site at the edge of a pyrolyzed Fe-N-C catalyst (FeN₄-edge) using a combination of density functional theory calculations and microkinetic simulations. The presence of graphitic edges facilitates the formation of FeN₄ active sites. Majority of these edge active sites have quite similar activities as in the case of a typical FeN₄ active site in the interior of graphene (FeN₄G). The ORR activity enhancement of this catalyst originates from the formation of two unique tilted-FeN₄ configurations at the edge of graphene, which have remarkable ORR activities. The first configuration is the tilted FeN₄ site at the zigzag edge, which can positively shift the onset potential for the associative reduction mechanism about 0.13 V higher than that on the typical FeN₄G system. The second configuration is the tilted FeN₄ site at the armchair edge, which has a low O₂ dissociation energy and a high onset potential for the dissociative reduction mechanism (0.26 V higher than the FeN₄G system).

中文翻译：

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在具有 FeN4 边缘活性位点的热解 Fe-NC 催化剂上形成倾斜的 FeN4 构型作为氧还原反应活性增强的起源

我们结合密度泛函理论计算和微动力学模拟阐明了热解 Fe-NC 催化剂（FeN ₄边缘）边缘的 FeN ₄位点上氧还原反应 (ORR) 活性增强的起源。石墨边缘的存在促进了FeN ₄活性位点的形成。这些边缘活性位点中的大多数具有与石墨烯内部的典型 FeN ₄活性位点 (FeN ₄ G)非常相似的活性。该催化剂的 ORR 活性增强源于两个独特的倾斜 FeN ₄的形成石墨烯边缘的构型，具有显着的 ORR 活性。第一种配置是在锯齿形边缘倾斜的 FeN ₄位点，它可以将缔合还原机制的起始电位正向移动，比典型的 FeN ₄ G 系统高约 0.13 V。第二种配置是扶手椅边缘的倾斜 FeN ₄位点，它具有低 O ₂解离能和高解离还原机制的起始电位（比 FeN ₄ G 系统高 0.26 V ）。