Matsumoto Koki, Onoda Akira, Kitano Tomoyuki, Sakata Takao, Yasuda Hidehiro, Campidelli Stéphane, Hayashi Takashi
Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita 565-0871, Japan.
Faculty of Environmental Earth Science, Hokkaido University, North 10 West 5, Sapporo 060-0810, Japan.
ACS Appl Mater Interfaces. 2021 Apr 7;13(13):15101-15112. doi: 10.1021/acsami.0c21321. Epub 2021 Mar 15.
Pyrolytically prepared iron and nitrogen codoped carbon (Fe/N/C) catalysts are promising nonprecious metal electrocatalysts for the oxygen reduction reaction (ORR) in fuel cell applications. Fabrication of the Fe/N/C catalysts with Fe-N active sites having precise structures is now required. We developed a strategy for thermally controlled construction of the Fe-N structure in Fe/N/C catalysts by applying a bottom-up synthetic methodology based on a N-doped graphene nanoribbon (N-GNR). The preorganized aromatic rings within the precursors assist graphitization during generation of the N-GNR structure with iron-coordinating sites. The Fe/N/C catalyst prepared from the N-GNR precursor, iron ion, and the carbon support Vulcan XC-72R provides a high onset potential of 0.88 V (vs reversible hydrogen electrode (RHE)) and promotes efficient four-electron ORR. X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS) studies reveal that the N-GNR precursor induces the formation of iron-coordinating nitrogen species during pyrolysis. The details of the graphitization process of the precursor were further investigated by analyzing the precursors pyrolyzed at various temperatures using MgO particles as a sacrificial template, with the results indicating that the graphitized structure was obtained at 700 °C. The preorganized N-GNR precursors and its pyrolysis conditions for graphitization are found to be important factors for generation of the Fe-N active sites along with the N-GNR structure in high-performance Fe/N/C catalysts for the ORR.
热解制备的铁氮共掺杂碳（Fe/N/C）催化剂是燃料电池应用中氧还原反应（ORR）很有前景的非贵金属电催化剂。目前需要制备具有精确结构的含Fe-N活性位点的Fe/N/C催化剂。我们通过应用基于氮掺杂石墨烯纳米带（N-GNR）的自下而上合成方法，开发了一种热控构建Fe/N/C催化剂中Fe-N结构的策略。前驱体中预组织的芳环在生成具有铁配位位点的N-GNR结构过程中有助于石墨化。由N-GNR前驱体、铁离子和碳载体Vulcan XC-72R制备的Fe/N/C催化剂提供了0.88 V（相对于可逆氢电极（RHE））的高起始电位，并促进高效的四电子ORR。X射线吸收精细结构（XAFS）和X射线光电子能谱（XPS）研究表明，N-GNR前驱体在热解过程中诱导形成铁配位氮物种。通过使用MgO颗粒作为牺牲模板分析在不同温度下热解的前驱体，进一步研究了前驱体石墨化过程的细节，结果表明在700℃获得了石墨化结构。发现预组织的N-GNR前驱体及其石墨化热解条件是在用于ORR的高性能Fe/N/C催化剂中与N-GNR结构一起生成Fe-N活性位点的重要因素。
