Structure of the catalytic sites in Fe/N/C-catalysts for O2-reduction in PEM fuel cells.
Structure of the catalytic sites in Fe/N/C-catalysts for O2-reduction in PEM fuel cells.
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DOI：
10.1039/c2cp41957b
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发表时间：
2012-09-07
期刊：
影响因子：
--
通讯作者：
Dodelet JP
中科院分区：
文献类型：
--
作者：
Kramm UI;Herranz J;Larouche N;Arruda TM;Lefèvre M;Jaouen F;Bogdanoff P;Fiechter S;Abs-Wurmbach I;Mukerjee S;Dodelet JP
通过Fe/N/C催化剂的57 Fe穆斯堡尔谱，确定了酸性介质中氧还原的铁基催化位点，该催化剂含有0.03至1.55wt%的Fe，其通过将乙酸铁浸渍在炭黑上，然后在950°C下在NH3中热处理而制备。在所有铁浓度下检测到四种不同的Fe物质：三种双峰分配给分子FeN 4样位点，其亚铁离子处于低（D1），中（D2）或高自旋状态（D3），另外两种双峰分配给由表面氧化氮化物纳米颗粒（FexN，x≤2.1）组成的单一Fe物质（D4和D5）。第五种Fe物种仅出现在Fe含量≥ 0.27wt%的催化剂中。它的特征是一个非常宽的单线态，这已被分配到不完整的FeN 4样网站，快速溶解接触酸。在这些催化剂中鉴定的五种Fe物种中，只有D1和D3在酸性介质中对氧还原反应（ORR）显示催化活性，其中D3具有与质子化的相邻碱性氮的复合结构，并且是迄今为止活性最高的物种，在0.8V vs RHE下ORR的估计转换频率为11.4 e− site−1 s−1。此外，所有D1位点和1/2至2/3的D3位点都是耐酸的。还提出了热处理后的网站形成机制的计划。这些催化剂中ORR活性位点的这种鉴定对于设计策略以改善这些材料的催化活性和稳定性至关重要。
Fe-based catalytic sites for the reduction of oxygen in acidic medium have been identified by 57Fe Mössbauer spectroscopy of Fe/N/C catalysts containing 0.03 to 1.55 wt% Fe, which were prepared by impregnation of iron acetate on carbon black followed by heat-treatment in NH3 at 950°C. Four different Fe-species were detected at all iron concentrations: three doublets assigned to molecular FeN4-like sites with their ferrous ion in low (D1), medium (D2) or high spin state (D3), and two other doublets assigned to a single Fe-species (D4 and D5) consisting of surface oxidized nitride nanoparticles (FexN, with x≤2.1). A fifth Fe-species appears only in those catalysts with Fe-contents ≥ 0.27 wt%. It is characterized by a very broad singlet, which has been assigned to incomplete FeN4-like sites that quickly dissolve in contact with an acid. Among the five Fe-species identified in these catalysts, only D1 and D3 display catalytic activity for the oxygen reduction reaction (ORR) in the acid medium, with D3 featuring a composite structure with a protonated neighbour basic nitrogen and being by far the most active species, with an estimated turn over frequency for the ORR of 11.4 e− site−1 s−1 at 0.8V vs RHE. Moreover, all D1 sites and between 1/2 to 2/3 of the D3 sites are acid-resistant. A scheme for the mechanism of site formation upon heat-treatment is also proposed. This identification of the ORR-active sites in these catalysts is of crucial importance to design strategies to improve the catalytic activity and stability of these materials.
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影响因子：
3.3
作者：
Jaouen, F;Marcotte, S;Lindbergh, G
通讯作者：
Lindbergh, G
影响因子：
6.2
作者：
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通讯作者：
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影响因子：
3.9
作者：
Hatchard, T. D.;Harlow, J. E.;Dahn, J. R.
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影响因子：
3.7
作者：
Herranz, Juan;Jaouen, Frederic;Lefevre, Michel;Kramm, Ulrike I.;Proietti, Eric;Dodelet, Jean-Pol;Bogdanoff, Peter;Fiechter, Sebastian;Abs-Wurmbach, Irmgard;Bertrand, Patrick;Arruda, Thomas M.;Mukerjee, Sanjeev
通讯作者：
Mukerjee, Sanjeev
影响因子：
3.3
作者：
Jaouen, F;Lefèvre, M;Cai, M
通讯作者：
Cai, M