Modeling Fe/N/C Catalysts in Monolayer Graphene

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• 作者：Xiao-Dong Yang ; Yanping Zheng ; Jing Yang ; Wei Shi ; Jin-Hui Zhong ; Cankun Zhang ; Xue Zhang ; Yu-Hao Hong ; Xin-Xing Peng ; Zhi-You ZhouShi-Gang Sun
• 刊名：ACS Catalysis
• 出版年：2017
• 出版时间：January 6, 2017
• 年：2017
• 卷：7
• 期：1
• 页码：139-145
• 全文大小：450K
• ISSN：2155-5435

文摘

Pyrolyzed Fe/N/C is one of the most promising non-precious-metal catalysts for the oxygen reduction reaction (ORR), which is supposed to boost the commercialization of proton exchange membrane fuel cells (PEMFC). However, the nature of the active sites of Fe/N/C is not clear and has long been debated. The challenges mainly come from highly heterogeneous structures formed during the pyrolysis process as well as no suitable surface probes. To elucidate the active sites, the most effective approach is building well-defined model catalysts as single-crystal planes in surface sciences. Herein, we designed a single-atomic-layer Fe/N/C model catalyst based on monolayer graphene (FeN-MLG) to explore the active sites. The model catalyst was prepared by 950 °C heat treatment of graphene with controlled defects under an FeCl₃(g)/NH₃ atmosphere. The as-prepared model catalyst exhibits ORR activity and SCN^– suppressive effect comparable to those of normal nanoparticle-like Fe/N/C catalysts, indicating that active sites are successfully created in the model catalyst. The effect of defect density, the layer number of graphene, and nitrogen species on the ORR activity has been investigated. The main content of nitrogen species on FeN-MLG is N_x-Fe, and quantitative correlation between N_x-Fe and ORR activity demonstrates that N_x-Fe species are the active site of Fe/N/C catalysts. The proposed model catalyst serves to simplify the catalyst structures and to simulate the topmost atomic layer of normal Fe/N/C, where ORR is catalyzed. This model system opens an opportunity to further understand the highly heterogeneous Fe/N/C catalysts.