Ligand-Controlled Product Selectivity in Electrochemical Carbon Dioxide Reduction Using Manganese Bipyridine Catalysts

• Published in: Journal of the American Chemical Society Vol. 142; no. 9; pp. 4265 - 4275
• Main Authors: Rønne, Magnus H, Cho, Dasol, Madsen, Monica R, Jakobsen, Joakim B, Eom, Seunghwan, Escoudé, Émile, Hammershøj, Hans Christian D, Nielsen, Dennis U, Pedersen, Steen U, Baik, Mu-Hyun, Skrydstrup, Troels, Daasbjerg, Kim
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 04.03.2020; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Multidisciplinary; Physical Sciences; Science & Technology; ELECTROCATALYTIC CO2 REDUCTION; ELECTRON-TRANSFER; FORMATE; ELECTROREDUCTION; COMPLEXES; WEAK BRONSTED ACIDS; CYCLIC VOLTAMMETRY; MOLECULAR CATALYSIS; LOCAL PROTON SOURCE; RHENIUM
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.9b11806

Electrocatalysis is a promising tool for utilizing carbon dioxide as a feedstock in the chemical industry. However, controlling the selectivity for different CO2 reduction products remains a major challenge. We report a series of manganese carbonyl complexes with elaborated bipyridine or phenanthroline ligands that can reduce CO2 to either formic acid, if the ligand structure contains strategically positioned tertiary amines, or CO, if the amine groups are absent in the ligand or are placed far from the metal center. The amine-modified complexes are benchmarked to be among the most active catalysts for reducing CO2 to formic acid, with a maximum turnover frequency of up to 5500 s–1 at an overpotential of 630 mV. The conversion even works at overpotentials as low as 300 mV, although through an alternative mechanism. Mechanistically, the formation of a Mn–hydride species aided by in situ protonated amine groups was determined to be a key intermediate by cyclic voltammetry, 1H NMR, DFT calculations, and infrared spectroelectrochemistry.