德国德累斯顿工业大学Xinliang Feng团队报道了在金属酞菁基二维共轭共价有机框架上促进氮向氨的电催化转化。相关研究成果于2021年11月16日发表于国际一流学术期刊《美国化学会杂志》。

环境条件下的电化学N₂还原反应（NRR）在替代当前的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，而精确调整活性位点的原理一直难以捉摸。

该文中，研究人员报告了第一例晶体二维共轭共价有机框架（2D c-COFs）与M–N4–C中心结合，作为新颖、明确和有效的催化剂，同时提高了电催化NRR对氨的活性和选择性。该2D c-COFs是基于金属酞菁（M=Fe、Co、Ni、Mn、Zn和Cu）和通过吡嗪键结合的芘单元合成的。值得注意的是，与具有其它M–N4–c中心的2D c-COFs相比，具有Fe–N4–C中心的2D c-COFs在0.1 V vs可逆氢电极下表现出更高的氨产率（33.6μg h^–1 mgcat^–1）和法拉第效率（FE，31.9%），使其成为最佳NRR电催化剂之一（产率>30μg h^–1 mgcat^–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–N4–C中心作为催化中心的作用。其显示了一种独特的电子结构，在费米水平上具有局域电子态，能够与N₂发生更强的相互作用，因此比其它M–N4–C中心更快的N₂活化和NRR动力学。

研究工作为开发金属-氮掺杂的富碳2D c-COFs作为优质NRR电催化剂打开了可能性，并为设计高性能NRR催化剂提供了M–Nx–C基电催化剂上NRR过程的原子理解。

附：英文原文

Title: Boosting the Electrocatalytic Conversion of Nitrogen to Ammonia on Metal-Phthalocyanine-Based Two-Dimensional Conjugated Covalent Organic Frameworks

Author: Haixia Zhong, Mingchao Wang, Mahdi Ghorbani-Asl, Jichao Zhang, Khoa Hoang Ly, Zhongquan Liao, Guangbo Chen, Yidan Wei, Bishnu P. Biswal, Ehrenfried Zschech, Inez M. Weidinger, Arkady V. Krasheninnikov, Renhao Dong, Xinliang Feng

Issue&Volume: November 16, 2021

Abstract: 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 mgcat–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 mgcat–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–Nx–C based electrocatalysts for designing high-performance NRR catalysts.

DOI: 10.1021/jacs.1c11158

Source: https://pubs.acs.org/doi/10.1021/jacs.1c11158