State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, Wuhan 430070, China.
Nanoscale. 2017 Jun 8;9(22):7641-7649. doi: 10.1039/c7nr01925d.
Fe-N-C series catalysts are always attractive for their high catalytic activity towards the oxygen reduction reaction (ORR). However, they usually consist of various components such as iron nitrides, metallic iron, iron carbides, N-doped carbon and Fe-N moieties, leading to controversial contributions of these components to the catalysis of the ORR, especially iron nitrides. In this work, to investigate the function of iron nitrides, FeN nanoparticles (NPs) embedded in mesoporous N-doped carbon without Fe-N moieties are designed and constructed by a simple histidine-assisted method. Herein, the use of histidine can increase the N and Fe contents in the product. The obtained catalyst exhibits excellent ORR catalytic activity which is very close to that of the commercial Pt/C catalyst in alkaline electrolytes. Combining the catalytic activity, structural characterization (especially from Mössbauer spectroscopy), and the results of DFT calculations for adsorption energies of oxygen on the main surfaces of FeN including ε-FeN and ζ-FeN, it can be deduced that FeN NPs as active species make a contribution to the ORR catalysis, of which ε-FeN (x ≤ 2.1) is more active than ζ-FeN. In addition, we find that there exists an obvious synergistic effect between FeN NPs and N-doped carbon, leading to the greatly enhanced ORR catalytic activity.
铁氮碳系列催化剂因其对氧还原反应（ORR）具有高催化活性而备受关注。然而，它们通常由各种成分组成，如铁氮化物、金属铁、铁碳化物、氮掺杂碳和 Fe-N 部分，导致这些成分对 ORR 催化的贡献存在争议，尤其是铁氮化物。在这项工作中，为了研究铁氮化物的功能，通过一种简单的组氨酸辅助方法设计并构建了嵌入介孔氮掺杂碳中而没有 Fe-N 部分的 FeN 纳米颗粒（NPs）。在此，使用组氨酸可以增加产物中的 N 和 Fe 含量。所得催化剂在碱性电解质中表现出优异的 ORR 催化活性，非常接近商业 Pt/C 催化剂的活性。结合催化活性、结构表征（特别是来自 Mössbauer 光谱）以及 DFT 计算对包括 ε-FeN 和 ζ-FeN 在内的 FeN 主要表面上氧吸附能的结果，可以推断出 FeN NPs 作为活性物质对 ORR 催化有贡献，其中 ε-FeN（x ≤ 2.1）比 ζ-FeN 更活跃。此外，我们发现 FeN NPs 和氮掺杂碳之间存在明显的协同效应，导致 ORR 催化活性大大增强。
