Engineering Favorable Morphology and Structure of Fe-N-C Oxygen-Reduction Catalysts through Tuning of Nitrogen/Carbon Precursors
Engineering Favorable Morphology and Structure of Fe-N-C Oxygen-Reduction Catalysts through Tuning of Nitrogen/Carbon Precursors
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DOI：
10.1002/cssc.201601397
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发表时间：
2017-02-22
期刊：
影响因子：
8.4
通讯作者：
Wu, Gang
中科院分区：
文献类型：
--
作者：
Gupta, Shiva;Zhao, Shuai;Wu, Gang
Fe-N-C 催化剂的结构和形貌被认为至关重要，因为活性位点的数量和局部键合结构控制着氧还原反应 (ORR) 的整体催化剂性能。然而，如何合理设计催化剂的知识仍然缺乏。通过结合不同的氮/碳前体，包括聚苯胺（PANI）、双氰胺（DCDA）和三聚氰胺（MLMN），我们的目标是调整催化剂的形态和结构以促进ORR。合成过程中使用了多种前体，而不是通常研究的单一前体；这提供了通过可能的协同效应促进催化剂活性和稳定性的新机会。由 PANI+ DCDA 衍生的性能最佳的 Fe-N-C 催化剂优于单独的 PANI 或 DCDA 衍生催化剂。特别是，与广泛探索的聚苯胺衍生催化剂相比，二元前体的半波电位增加了 0.83 V，并且在具有挑战性的酸性介质中电化学稳定性增强，表明活性位点数量显着增加，局部键合结构得到加强。阐明了与观察到的促进作用相关的多个关键因素，包括最佳孔径分布、最高电化学活性表面积、主要无定形碳的存在以及具有更多可能与活性原子铁键合的吡啶氮边缘位点的厚石墨碳层。
Structures and morphologies of Fe-N-C catalysts are believed to be crucial because of the number of active sites and local bonding structures governing the overall catalyst performance for the oxygen reduction reaction (ORR). However, the knowledge how to rationally design catalysts is still lacking. By combining different nitrogen/carbon precursors, including polyaniline (PANI), dicyandiamide (DCDA), and melamine (MLMN), we aim to tune catalyst morphology and structure to facilitate the ORR. Instead of the commonly studied single precursors, multiple precursors were used during the synthesis; this provides a new opportunity to promote catalyst activity and stability through a likely synergistic effect. The best-performing Fe-N-C catalyst derived from PANI+ DCDA is superior to the individual PANI or DCDA-derived ones. In particular, when compared to the extensively explored PANI-derived catalysts, the binary precursors have an increased half-wave potential of 0.83 V and an enhanced electrochemical stability in challenging acidic media, indicating a significantly increased number of active sites and strengthened local bonding structures. Multiple key factors associated with the observed promotion are elucidated, including the optimal pore size distribution, highest electrochemically active surface area, presence of dominant amorphous carbon, and thick graphitic carbon layers with more pyridinic nitrogen edge sites likely bonded with active atomic iron.