化学
催化作用
穆斯堡尔谱学
氮气
碳纤维
石墨烯
氢
氧气
金属
无机化学
活动站点
纳米材料基催化剂
光化学
化学工程
有机化学
结晶学
工程类
复合材料
复合数
材料科学
作者
Lingmei Ni,Charlotte Gallenkamp,Stephan Wagner,Eckhard Bill,Vera Krewald,Ulrike I. Kramm
摘要
For large-scale utilization of fuel cells in a future hydrogen-based energy economy, affordable and environmentally benign catalysts are needed. Pyrolytically obtained metal- and nitrogen-doped carbon (MNC) catalysts are key contenders for this task. Their systematic improvement requires detailed knowledge of the active site composition and degradation mechanisms. In FeNC catalysts, the active site is an iron ion coordinated by nitrogen atoms embedded in an extended graphene sheet. Herein, we build an active site model from in situ and operando 57Fe Mössbauer spectroscopy and quantum chemistry. A Mössbauer signal newly emerging under operando conditions, D4, is correlated with the loss of other Mössbauer signatures (D2, D3a, D3b), implying a direct structural correspondence. Pyrrolic N-coordination, i.e., FeN4C12, is found as a spectroscopically and thermodynamically consistent model for the entire catalytic cycle, in contrast to pyridinic nitrogen coordination. These findings thus overcome the previously conflicting structural assignments for the active site and, moreover, identify and structurally assign a previously unknown intermediate in the oxygen reduction reaction at FeNC catalysts.
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