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An Iron Pyridyl-Carbene Catalyst for Low Overpotential CO2 reduction to CO: Mechanistic Comparisons with the Ruthenium Analogue and Photochemical Promotion

preprint
submitted on 02.03.2020 and posted on 02.03.2020 by Sergio Gonell, Julio Lloret, Alexander Miller

Electrocatalysts for CO2 reduction based on first row transition metal ions have attracted attention as abundant and affordable candidates for energy conversion applications. We hypothesized that a successful strategy in ruthenium electrocatalyst design, featuring two chelating ligands that can be individually tuned to adjust the overpotential and catalytic activity, could be equally applicable in the analogous iron complexes. New iron complexes supported by a redox-active 2,2':6',2''-terpyridine (tpy) ligand and strong trans effect pyridyl- N-heterocyclic carbene ligand (1-methyl-benzimidazol-2-ylidene-3-(2-pyridine)) were synthesized, and these isostructural analogues to leading ruthenium catalysts were also found to be active CO2 reduction electrocatalysts. Electrochemical and computational studies reveal completely distinct mechanisms for the iron and ruthenium complexes, with hemilability in the iron system enabling electrocatalysis at overpotentials as low as 150 mV (ca. 500 mV lower than the ruthenium analogue). Cyclic voltammetry studies elucidated the mechanism of the net 4e–/2H+ process that occurs within the single reductive feature, with an iron solvento complex undergoing reduction, CO2 activation, and further reduction to an iron carbonyl. The mechanistic insight guided development of photoelectrocatalytic conditions under a continuous flow of CO2 that exhibited improved performance, with Faradaic efficiency up to 99%.

Funding

Alliance for Molecular PhotoElectrode Design for Solar Fuels (AMPED)

Basic Energy Sciences

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MRI: Acquisition of a Mass Spectrometer

Directorate for Mathematical & Physical Sciences

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Horizon 2020 Marie Skłodowska-Curie Fellowship (grant no.794119, Fe-RedOx-Cat)

European Commission ERC-CG-2014-648304

Spanish Ministry of Science for the project CTQ2016-80038-R

History

Email Address of Submitting Author

ajmm@email.unc.edu

Institution

University of North Carolina at Chapel Hill

Country

United States

ORCID For Submitting Author

0000-0001-9390-3951

Declaration of Conflict of Interest

no conflict of interest

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