Li Xueli, Xiang Zhonghua
State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing, 100029, PR China.
Nat Commun. 2022 Jan 10;13(1):57. doi: 10.1038/s41467-021-27735-1.
The atomic configurations of FeN moieties are the key to affect the activity of oxygen rection reaction (ORR). However, the traditional synthesis relying on high-temperature pyrolysis towards combining sources of Fe, N, and C often results in the plurality of local environments for the FeN sites. Unveiling the effect of carbon matrix adjacent to FeN sites towards ORR activity is important but still is a great challenge due to inevitable connection of diverse N as well as random defects. Here, we report a proof-of-concept study on the evaluation of covalent-bonded carbon environment connected to FeN sites on their catalytic activity via pyrolysis-free approach. Basing on the closed π conjugated phthalocyanine-based intrinsic covalent organic polymers (COPs) with well-designed structures, we directly synthesized a series of atomically dispersed Fe-N-C catalysts with various pure carbon environments connected to the same FeN sites. Experiments combined with density functional theory demonstrates that the catalytic activities of these COPs materials appear a volcano plot with the increasement of delocalized π electrons in their carbon matrix. The delocalized π electrons changed anti-bonding d-state energy level of the single FeN moieties, hence tailored the adsorption between active centers and oxygen intermediates and altered the rate-determining step.
FeN部分的原子构型是影响氧还原反应（ORR）活性的关键。然而，传统的依靠高温热解来结合铁、氮和碳源的合成方法，常常导致FeN位点存在多种局部环境。揭示与FeN位点相邻的碳基质对ORR活性的影响很重要，但由于多种氮的不可避免连接以及随机缺陷，这仍然是一个巨大的挑战。在此，我们报告了一项概念验证研究，通过无热解方法评估与FeN位点相连的共价键合碳环境对其催化活性的影响。基于具有精心设计结构的封闭π共轭酞菁基本征共价有机聚合物（COPs），我们直接合成了一系列原子分散的Fe-N-C催化剂，这些催化剂具有与相同FeN位点相连的各种纯碳环境。实验结合密度泛函理论表明，随着这些COPs材料碳基质中离域π电子的增加，其催化活性呈现出火山图。离域π电子改变了单个FeN部分的反键d态能级，从而调整了活性中心与氧中间体之间的吸附，并改变了速率决定步骤。
