Inspired by nature, Metal-N₄-complexes have been utilized as potential models to catalyze the sluggish oxygen reduction reaction (ORR) at cathode in fuel cells. Herein, we designed and synthesized dibenzo-N₄-[14]annulene metal complexes of Fe^II and Co^II metal ions and their nanocomposites with carbon black and characterized by various techniques. Computational and spectroscopic results suggested that the prepared complexes have saddle octahedral geometry. Further, the electrocatalytic activity of prepared nanocomposites towards ORR was investigated by using cyclic and linear sweep voltammetric techniques. The results exhibited that these nanocomposites are significantly ORR active; however, Fe-nanocomposite showed high ORR activity as compared to Co-composite. Theoretical studies indicated that the HOMO of Fe-complex was very near to the antibonding LUMO orbitals of dioxygen as compared to Co-complex, endowing high ORR activity.

中文翻译：

---

金属-N4-纳米复合材料的合成、表征和 ORR 活性

受自然启发，金属-N ₄配合物已被用作潜在模型，以催化燃料电池阴极处缓慢的氧还原反应 (ORR)。^{在此，我们设计并合成了 Fe II}和 Co ^II的二苯并-N ₄ -[14]环烯金属配合物。金属离子及其与炭黑的纳米复合材料，并通过各种技术进行表征。计算和光谱结果表明，制备的配合物具有鞍八面体几何形状。此外，通过使用循环和线性扫描伏安技术研究了制备的纳米复合材料对 ORR 的电催化活性。结果表明，这些纳米复合材料具有显着的 ORR 活性；然而，与 Co-composite 相比，Fe-nanocomposite 显示出较高的 ORR 活性。理论研究表明，与Co-络合物相比，Fe-络合物的HOMO非常接近分子氧的反键LUMO轨道，具有较高的ORR活性。