Shen Jing, Kortlever Ruud, Kas Recep, Birdja Yuvraj Y, Diaz-Morales Oscar, Kwon Youngkook, Ledezma-Yanez Isis, Schouten Klaas Jan P, Mul Guido, Koper Marc T M
Leiden Institute of Chemistry, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands.
PhotoCatalytic Synthesis Group, MESA+ Institute for Nanotechnology, Faculty of Science and Technology, University of Twente, Meander 229, PO Box 217, 7500 AE Enschede, The Netherlands.
Nat Commun. 2015 Sep 1;6:8177. doi: 10.1038/ncomms9177.
The electrochemical conversion of carbon dioxide and water into useful products is a major challenge in facilitating a closed carbon cycle. Here we report a cobalt protoporphyrin immobilized on a pyrolytic graphite electrode that reduces carbon dioxide in an aqueous acidic solution at relatively low overpotential (0.5 V), with an efficiency and selectivity comparable to the best porphyrin-based electrocatalyst in the literature. While carbon monoxide is the main reduction product, we also observe methane as by-product. The results of our detailed pH-dependent studies are explained consistently by a mechanism in which carbon dioxide is activated by the cobalt protoporphyrin through the stabilization of a radical intermediate, which acts as Brønsted base. The basic character of this intermediate explains how the carbon dioxide reduction circumvents a concerted proton-electron transfer mechanism, in contrast to hydrogen evolution. Our results and their mechanistic interpretations suggest strategies for designing improved catalysts.
将二氧化碳和水电化学转化为有用的产物是促进封闭碳循环的一项重大挑战。在此，我们报道了一种固定在热解石墨电极上的钴原卟啉，它在相对较低的过电位（0.5 V）下于酸性水溶液中还原二氧化碳，其效率和选择性与文献中最好的基于卟啉的电催化剂相当。虽然一氧化碳是主要的还原产物，但我们也观察到甲烷作为副产物。我们详细的pH依赖性研究结果通过一种机制得到了一致的解释，即钴原卟啉通过稳定一个自由基中间体来活化二氧化碳，该中间体作为布朗斯特碱。与析氢相反，这个中间体的碱性特征解释了二氧化碳还原如何规避协同质子 - 电子转移机制。我们的结果及其机理解释为设计改进的催化剂提供了策略。
