Electrocatalytic CO2 Reduction with a Homogeneous Catalyst in Ionic Liquid: High Catalytic Activity at Low Overpotential

David C Grills; Yasuo Matsubara; Yutaka Kuwahara; Suzanne R Golisz; Daniel A Kurtz; Barbara A Mello

doi:10.1021/jz500759x

Electrocatalytic CO2 Reduction with a Homogeneous Catalyst in Ionic Liquid: High Catalytic Activity at Low Overpotential

J Phys Chem Lett. 2014 Jun 5;5(11):2033-8. doi: 10.1021/jz500759x. Epub 2014 May 28.

Authors

David C Grills¹, Yasuo Matsubara^{1

2}, Yutaka Kuwahara^{1

3}, Suzanne R Golisz¹, Daniel A Kurtz¹, Barbara A Mello¹

Affiliations

¹ †Chemistry Department, Brookhaven National Laboratory, P.O. Box 5000, Upton, New York 11973-5000, United States.
² ‡PRESTO, Japan Science and Technology Agency (JST), Chiyoda-ku, Tokyo 102-0076, Japan.
³ §Department of Applied Chemistry and Biochemistry, Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan.

PMID: 26273891
DOI: 10.1021/jz500759x

Abstract

We describe a new strategy for enhancing the efficiency of electrocatalytic CO2 reduction with a homogeneous catalyst, using a room-temperature ionic liquid as both the solvent and electrolyte. The electrochemical behavior of fac-ReCl(2,2'-bipyridine)(CO)3 in neat 1-ethyl-3-methylimidazolium tetracyanoborate ([emim][TCB]) was compared with that in acetonitrile containing 0.1 M [Bu4N][PF6]. Two separate one-electron reductions occur in acetonitrile (-1.74 and -2.11 V vs Fc(+/0)), with a modest catalytic current appearing at the second reduction wave under CO2. However, in [emim][TCB], a two-electron reduction wave appears at -1.66 V, resulting in a ∼0.45 V lower overpotential for catalytic reduction of CO2 to CO. Furthermore, the apparent CO2 reduction rate constant, kapp, in [emim][TCB] exceeds that in acetonitrile by over one order of magnitude (kapp = 4000 vs 100 M(-1) s(-1)) at 25 ± 3 °C. Supported by time-resolved infrared measurements, a mechanism is proposed in which an interaction between [emim](+) and the two-electron reduced catalyst results in rapid dissociation of chloride and a decrease in the activation energy for CO2 reduction.

Keywords: EC(cat) mechanism; carbon dioxide reduction; electrochemistry; homogeneous catalyst; ionic liquid; time-resolved infrared spectroscopy; ultramicroelectrode.