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Published May 19, 2014 | Published + Supplemental Material
Journal Article Open

Studies of Cobalt-Mediated Electrocatalytic CO_2 Reduction Using a Redox-Active Ligand

Abstract

The cobalt complex [Co^(III)N_4H(Br)_2]+ (N_4H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(7),2,11,13,15-pentaene) was used for electrocatalytic CO_2 reduction in wet MeCN with a glassy carbon working electrode. When water was employed as the proton source (10 M in MeCN), CO was produced (f_(CO)= 45% ± 6.4) near the Co^(I/0) redox couple for [Co^(III)N_4H(Br)_2]+ (E_(1/2) = −1.88 V FeCp_2^(+/0)) with simultaneous H_2 evolution (f_(H2)= 30% ± 7.8). Moreover, we successfully demonstrated that the catalytically active species is homogeneous through the use of control experiments and XPS studies of the working glassy-carbon electrodes. As determined by cyclic voltammetry, CO_2 catalysis occurred near the formal CoI/0redox couple, and attempts were made to isolate the triply reduced compound ("[Co^0N_4H]"). Instead, the doubly reduced ("Co^I") compounds [CoN4] and [CoN_4H(MeCN)]+ were isolated and characterized by X-ray crystallography. Their molecular structures prompted DFT studies to illuminate details regarding their electronic structure. The results indicate that reducing equivalents are stored on the ligand, implicating redox noninnocence in the ligands for H_2 evolution and CO_2 reduction electrocatalysis.

Additional Information

© 2014 American Chemical Society. ACS AuthorChoice - This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Received: December 30, 2013; Published: April 28, 2014. This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. D.C.L. would also like to acknowledge the National Institutes of Health (Award Number F32GM106726). The authors would also like to thank Tzu-Pin Lin, Michael Takase, and Lawrence Henling for help with crystallography, and Kyle Cummins and Slobodan Mitrovic for help with XPS. Clifford Kubiak is also thanked for many insightful discussions.

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Published - ic403122j.pdf

Supplemental Material - ic403122j_si_001.cif

Supplemental Material - ic403122j_si_002.pdf

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August 20, 2023
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