Hutchison Phillips, Smith Logan E, Rooney Conor L, Wang Hailiang, Hammes-Schiffer Sharon
Department of Chemistry, Yale University, New Haven, Connecticut 06520, United States.
Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.
J Am Chem Soc. 2024 Jul 24;146(29):20230-20240. doi: 10.1021/jacs.4c05444. Epub 2024 Jul 10.
Immobilized cobalt phthalocyanine (CoPc) is a highly promising architecture for the six-proton, six-electron reduction of CO to methanol. This electroreduction process relies on proton-coupled electron transfer (PCET) reactions that can occur by sequential or concerted mechanisms. Immobilization on a conductive support such as carbon nanotubes or graphitic flakes can fundamentally alter the PCET mechanisms. We use density functional theory (DFT) calculations of CoPc adsorbed on an explicit graphitic surface model to investigate intermediates in the electroreduction of CO to methanol. Our calculations show that the alignment of the CoPc and graphitic electronic states influences the reductive chemistry. These calculations also distinguish between charging the graphitic surface and reducing the CoPc and adsorbed intermediates as electrons are added to the system. This analysis allows us to identify the chemical transformations that are likely to be concerted PCET, defined for these systems as the mechanism in which protonation of a CO reduction intermediate is accompanied by electron abstraction from the graphitic surface to the adsorbate without thermodynamically stable intermediates. This work establishes a mechanistic pathway for methanol production that is consistent with experimental observations and provides fundamental insight into how immobilization of the CoPc impacts its CO reduction chemistry.
固定化钴酞菁（CoPc）是一种极具前景的体系结构，可用于将CO通过六质子、六电子还原反应生成甲醇。这种电还原过程依赖于质子耦合电子转移（PCET）反应，该反应可以通过连续或协同机制发生。固定在诸如碳纳米管或石墨薄片等导电载体上会从根本上改变PCET机制。我们使用吸附在显式石墨表面模型上的CoPc的密度泛函理论（DFT）计算来研究CO电还原生成甲醇过程中的中间体。我们的计算表明，CoPc和石墨电子态的排列会影响还原化学。这些计算还区分了在向系统中添加电子时石墨表面充电与CoPc及吸附中间体还原之间的差异。这种分析使我们能够识别出可能是协同PCET的化学转化，对于这些体系，协同PCET定义为CO还原中间体质子化的同时，电子从石墨表面转移到吸附质且不存在热力学稳定中间体的机制。这项工作建立了一条与实验观察结果一致的甲醇生成机理途径，并为CoPc的固定化如何影响其CO还原化学提供了基本见解。
