Revealing insights into the axial coordination effect of M–N4 catalysts on electrocatalytic activity towards the oxygen reduction reaction,Journal of Materials Chemistry A

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Revealing insights into the axial coordination effect of M–N4 catalysts on electrocatalytic activity towards the oxygen reduction reaction
Journal of Materials Chemistry A ( IF 10.7 ) Pub Date : 2023-10-11 , DOI: 10.1039/d3ta03701k
Youxuan Ni ₁ , Weiwei Xie ₁ , Jun Chen ₁

Affiliation

Axial coordination is a powerful strategy to effectively regulate the activity of M–N₄ catalysts. However, the underlying mechanism is still not clear. Here, we explore the influence of axial coordination on the activity of Fe/Co/Ni-tetraphenylporphyrin covalent organic frameworks (Fe/Co/Ni-TPP COFs) towards the oxygen reduction reaction (ORR) using the DFT method. It is found that the widely used descriptors (e.g., d-band centers) are not applicable to explain the axial coordination effect on metal reactivity. The reason is that the hybridization of the d_z² orbital of metal centers and p_z orbital of axial coordination atoms leads to the formation of new active orbitals, where the effect of the p_z orbital should be considered in the design of the activity descriptor. Based on this, an activity descriptor using the total number of electrons in d_z² and p_z orbitals is proposed. The results show that the reactivity of the metal center is enhanced by axial coordination if N(d_z²) + N(p_z) > 2, while it is reduced if N(d_z²) + N(p_z) ≤ 2. The application of the descriptor is further extended to explain the activity change of Fe/Co/Ni-TPP COFs by different types of axially coordinated atoms. This work provides new insights into the regulation mechanism of the axial coordination effect on metal reactivity.

中文翻译：

揭示 M-N4 催化剂的轴向配位效应对氧还原反应电催化活性的影响

_{轴向配位是有效调节M–N 4}催化剂活性的有力策略。然而，其根本机制仍不清楚。在这里，我们利用 DFT 方法探讨了轴向配位对 Fe/Co/Ni-四苯基卟啉共价有机骨架 (Fe/Co/Ni-TPP COF) 氧还原反应 (ORR) 活性的影响。研究发现广泛使用的描述符（例如d带中心）不适用于解释轴向配位对金属反应性的影响。原因是金属中心的d _{z ²}轨道与轴配位原子的p _z轨道杂化导致形成新的活性轨道，在活性描述符的设计中应考虑p _z轨道的影响。在此基础上，提出了使用 d _{z ²}和 p _z轨道中电子总数的活性描述符。结果表明，当N (d _{z ²} ) + N (p _z ) > 2时，轴向配位会增强金属中心的反应活性，而当N (d _{z ²} ) + N (p _z ) ≤ 2时，会降低金属中心的反应活性。该描述符的应用被进一步扩展，以解释不同类型的轴配位原子对 Fe/Co/Ni-TPP COF 的活性变化。该工作为轴向配位效应对金属反应性的调控机制提供了新的见解。

更新日期：2023-10-11

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