Identification of catalytic sites for oxygen reduction in iron- and nitrogen-doped graphene materials
Identification of catalytic sites for oxygen reduction in iron- and nitrogen-doped graphene materials
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DOI：
10.1038/nmat4367
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发表时间：
2015-09-01
期刊：
影响因子：
41.2
通讯作者：
Jaouen, Frederic
中科院分区：
文献类型：
--
作者：
Zitolo, Andrea;Goellner, Vincent;Jaouen, Frederic
虽然迄今为止铂一直是酸性聚合物燃料电池中催化氧电还原的首选元素，但据报道，热解Fe-N-C材料取得了巨大进展。然而，其活性位点的结构仍然难以捉摸，推迟了进一步的进展。本文通过氩气或氨气热解合成了Fe-N-C准无晶体铁结构的材料。这些材料表现出几乎相同的穆斯堡尔光谱和相同的x射线吸收近边缘光谱（XANES），显示出相同的铁中心部分。然而，nh3热解Fe-N-C材料的高活度和碱性表明，铁中心部分的周转频率取决于载体的物理化学性质。通过深入的XANES分析，确定了两种具有不同O-2吸附模式的FeN4卟啉体系结构的详细结构。这些卟啉部分不容易集成到石墨烯片中，这与迄今为止在热解Fe-N-C材料中假设的铁中心部分相反。这些新的见解为自下而上的综合方法和站点支持相互作用的研究开辟了道路。
While platinum has hitherto been the element of choice for catalysing oxygen electroreduction in acidic polymer fuel cells, tremendous progress has been reported for pyrolysed Fe-N-C materials. However, the structure of their active sites has remained elusive, delaying further advance. Here, we synthesized Fe-N-C materials quasi-free of crystallographic iron structures after argon or ammonia pyrolysis. These materials exhibit nearly identical Mossbauer spectra and identical X-ray absorption near-edge spectroscopy (XANES) spectra, revealing the same Fe-centred moieties. However, the much higher activity and basicity of NH3-pyrolysed Fe-N-C materials demonstrates that the turnover frequency of Fe-centred moieties depends on the physico-chemical properties of the support. Following a thorough XANES analysis, the detailed structures of two FeN4 porphyrinic architectures with different O-2 adsorption modes were then identified. These porphyrinic moieties are not easily integrated in graphene sheets, in contrast with Fe-centred moieties assumed hitherto for pyrolysed Fe-N-C materials. These new insights open the path to bottom-up synthesis approaches and studies on site-support interactions.