Ni Lingmei, Gallenkamp Charlotte, Wagner Stephan, Bill Eckhard, Krewald Vera, Kramm Ulrike I
Department of Chemistry and Department of Materials and Earth Sciences, Catalysts and Electrocatalysts Group, TU Darmstadt, Otto-Berndt-Str. 3, 64287 Darmstadt, Germany.
Department of Chemistry, Theoretical Chemistry, TU Darmstadt, Alarich-Weiss-Str. 4, 64287 Darmstadt, Germany.
J Am Chem Soc. 2022 Sep 21;144(37):16827-16840. doi: 10.1021/jacs.2c04865. Epub 2022 Aug 29.
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 and Fe Mössbauer spectroscopy and quantum chemistry. A Mössbauer signal newly emerging under conditions, D4, is correlated with the loss of other Mössbauer signatures (D2, D3a, D3b), implying a direct structural correspondence. Pyrrolic N-coordination, , FeNC, 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.
为了在未来基于氢的能源经济中大规模应用燃料电池，需要价格合理且对环境无害的催化剂。热解获得的金属和氮掺杂碳（MNC）催化剂是这项任务的关键竞争者。对它们进行系统改进需要详细了解活性位点组成和降解机制。在FeNC催化剂中，活性位点是由嵌入扩展石墨烯片中的氮原子配位的铁离子。在此，我们基于57Fe穆斯堡尔光谱和量子化学构建了一个活性位点模型。在特定条件下新出现的一个穆斯堡尔信号D4与其他穆斯堡尔特征（D2、D3a、D3b）的损失相关，这意味着存在直接的结构对应关系。与吡啶氮配位相反，吡咯氮配位（-N=FeNC）被发现是整个催化循环在光谱和热力学上一致的模型。因此，这些发现克服了先前对活性位点相互矛盾的结构归属，此外，还识别并在结构上确定了FeNC催化剂氧还原反应中一个先前未知的中间体。
