Iron phthalocyanine (FePc) is a promising non-precious catalyst for the oxygen reduction reaction (ORR). Unfortunately, FePc with plane-symmetric FeN 4 site usually exhibits an unsatisfactory ORR activity due to its poor O 2 adsorption and activation. Here, we report an axial Fe–O coordination induced electronic localization strategy to improve its O 2 adsorption, activation and thus the ORR performance. Theoretical calculations indicate that the Fe–O coordination evokes the electronic localization among the axial direction of O–FeN 4 sites to enhance O 2 adsorption and activation. To realize this speculation, FePc is coordinated with an oxidized carbon. Synchrotron X-ray absorption and Mössbauer spectra validate Fe–O coordination between FePc and carbon. The obtained catalyst exhibits fast kinetics for O 2 adsorption and activation with an ultralow Tafel slope of 27.5 mV dec −1 and a remarkable half-wave potential of 0.90 V. This work offers a new strategy to regulate catalytic sites for better performance.
Zhengtao Jia,Yuxiang Zhu,Qiufan Sun,Xiang Zhong,Yan Wang,Sai Xu,Jianfeng Yao
This study presents the design and synthesis of isostructural metal coordination polymers (MCPs) incorporating iron and hexaazatrinaphthalene ligands functionalized with different substituents (FeHATN-X, X = NO 2 , CN, Br). The ligand variations enable fine-tuning of geometric structures, pore environments, and electronic properties due to the polarity and intraframework interactions. Among them, FeHATN-NO 2 exhibits an enhanced electrocatalytic ammonia yield rate of 87 μg h −1 mg −1 with a Faradaic efficiency of 24 % at −0.4 V vs. RHE, outperforming its counterparts. Comprehensive characterizations reveal that the nitro substituent promotes smaller nanorod formation, increasing active site exposure and improving mass transport. Moreover, the establishment of Fe−O coordination sites can modulate the Fe center, facilitate stronger nitrogen adsorption and concurrently suppress the competing hydrogen evolution reaction, thereby collectively contributing to improved electrocatalytic activity. Furthermore, in-situ spectroscopic analysis confirms that iron coordination centers act as effective electron acceptors, facilitating the formation of *NH 2 intermediates at the Fe center. The system achieves peak efficiency at −0.4 V vs. RHE, where the conduction band potential promotes the involvement of free electrons in the reaction. This work underscores the potential of tailoring coordination environments and morphologies in MCPs to enhance electrocatalytic ammonia synthesis performance.
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