The electrochemical N₂ reduction reaction (NRR) under ambient conditions is attractive in replacing the current Haber-Bosch process toward sustainable ammonia production. Metal-heteroatom-doped carbon-rich materials have emerged as the most promising NRR electrocatalysts. However, simultaneously boosting their NRR activity and selectivity remains a grand challenge, while the principle for precisely tailoring the active sites has been elusive. Herein, we report the first case of crystalline two-dimensional conjugated covalent organic frameworks (2D c-COFs) incorporated with M–N₄–C centers as novel, defined, and effective catalysts, achieving simultaneously enhanced activity and selectivity of electrocatalytic NRR to ammonia. Such 2D c-COFs are synthesized based on metal-phthalocyanine (M = Fe, Co, Ni, Mn, Zn, and Cu) and pyrene units bonded by pyrazine linkages. Significantly, the 2D c-COFs with Fe–N₄–C center exhibit higher ammonia yield rate (33.6 μg h^–1 mg_cat^–1) and Faradaic efficiency (FE, 31.9%) at −0.1 V vs reversible hydrogen electrode than those with other M–N₄–C centers, making them among the best NRR electrocatalysts (yield rate >30 μg h^–1 mg_cat^–1 and FE > 30%). In situ X-ray absorption spectroscopy, Raman spectroelectrochemistry, and theoretical calculations unveil that Fe–N₄–C centers act as catalytic sites. They show a unique electronic structure with localized electronic states at Fermi level, allowing for stronger interaction with N₂ and thus faster N₂ activation and NRR kinetics than other M–N₄–C centers. Our work opens the possibility of developing metal–nitrogen-doped carbon-rich 2D c-COFs as superior NRR electrocatalyst and provides an atomic understanding of the NRR process on M–N_x–C based electrocatalysts for designing high-performance NRR catalysts.

中文翻译：

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在基于金属-酞菁的二维共轭共价有机骨架上促进氮向氨的电催化转化

环境条件下的电化学 N ₂还原反应 (NRR) 在取代当前的 Haber-Bosch 工艺以实现可持续氨生产方面具有吸引力。金属杂原子掺杂的富碳材料已成为最有前途的 NRR 电催化剂。然而，同时提高它们的 NRR 活性和选择性仍然是一个巨大的挑战，而精确定制活性位点的原则一直难以捉摸。在此，我们报告了第一个与 M-N ₄ -C 中心结合的结晶二维共价有机骨架 (2D c- COFs)作为新型、明确和有效的催化剂，同时提高了电催化 NRR 的活性和选择性。氨。这样的 2D c-COF 是基于金属-酞菁（M = Fe、Co、Ni、Mn、Zn 和 Cu）和通过吡嗪键键合的芘单元合成的。值得注意的是，与可逆氢电极相比，具有 Fe-N ₄ -C 中心的 2D c -COF在 -0.1 V 与可逆氢电极下表现出更高的氨产率（33.6 μg h ^-1 mg _cat ^-1）和法拉第效率（FE，31.9%）与其他 M–N ₄ –C 中心，使它们成为最好的 NRR 电催化剂（产率 >30 μg h ^–1 mg _cat ^–1和 FE > 30%）。原位 X 射线吸收光谱、拉曼光谱电化学和理论计算揭示了 Fe-N ₄-C 中心充当催化位点。它们显示出一种独特的电子结构，在费米能级具有局部电子态，允许与 N ₂更强的相互作用，从而比其他 M-N ₄ -C 中心更快的 N ₂活化和 NRR 动力学。我们的工作开辟了将金属-氮掺杂的富碳二维c - COFs 开发为卓越的 NRR 电催化剂的可能性，并提供了对基于 M-N _x -C 的电催化剂的 NRR 过程的原子理解，以设计高性能 NRR 催化剂。