Photo‐Assisted Electrocatalytic Reduction of CO₂: A New Strategy for Reducing Catalytic Overpotentials

Abstract

Electrochemical and photochemical reduction of CO2 are both well‐established, independent catalytic routes toward producing added‐value chemicals. The potential for any cross‐reactivity has, however, hardly been explored so far. In this report, we assess a system primarily using spectroelectrochemical monitoring, where photochemistry assists the cathodic activation of precursor complexes fac‐[Mn(CO)3(2,2′‐bipyridine)Br] and [Mo(CO)4(6,6′‐dimethyl‐2,2′‐bipyridine)] to lower the catalytic overpotential needed to trigger the electrocatalytic reduction of CO2 to CO. Following the complete initial 1e− reduction of the parent complexes, the key photochemical cleavage of the Mn−Mn and Mo−CO bonds in the reduction products, [Mn(CO)3(2,2′‐bipyridine)]2 and [Mo(CO)4(6,6′‐dimethyl‐2,2′‐bipyridine)].−, respectively, generates the 2e−‐reduced, 5‐coordinate catalysts, [Mn(CO)3(2,2′‐bipyridine)]− and [Mo(CO)3(6,6′‐dimethyl‐2,2′‐bipyridine)]2− appreciably closer to the initial cathodic wave R1. Experiments under CO2 confirm the activity of both electrocatalysts under the photoirradiation with 405 nm and 365 nm light, respectively. This remarkable achievement corresponds to a ca. 500 mV positive shift of the catalytic onset compared to the exclusive standard electrocatalytic activation.

Electrochemically Driven Reduction of Carbon Dioxide Mediated by Mono‐Reduced Mo‐Diimine Tetracarbonyl Complexes: Electrochemical, Spectroelectrochemical and Theoretical Studies

“…Furthermore, IR‐SEC experiments performed in the dark yielded similar results to those carried out in daylight, thus excluding a photoactivated process. Noteworthy, complexes 2 and 3 displayed two new bands at 1920 and 1750 cm −1 , which were previously reported for the electrocatalytic reduction of CO 2 by Mo‐diimine complexes [12e,m] . The amplitude of these supplementary bands was shown to increase with water content.…”

“…redox potential) can be of high interest to enhance reactivity. In the particular case of group 6 metal carbonyl complexes, the combination of photochemistry with electrochemical methods appears as one of the most promising approach to lower the overpotential for CO 2 reduction by generating reactive species such as the putative [Mo(CO) 3 (L)] .− complex [12e] …”

Effect of the 2-R-Allyl and Chloride Ligands on the Cathodic Paths of [Mo(η3-2-R-allyl)(α-diimine)(CO)2Cl] (R = H, CH3; α-diimine = 6,6′-Dimethyl-2,2′-bipyridine, Bis(p-tolylimino)acenaphthene)

“…The subsequent reduction of [Mo(6,6′-dmbipy)(CO) 3 Y] − does not regenerate [ 1 -A] − . Instead, the ultimate reduction product is 5-coordinate [Mo(6,6′-dmbipy)(CO) 3 ] 2– (ν(CO): 1843, 1708, 1694 cm –1 ; Table 2 ), which is the active catalyst in the photoassisted reduction of CO 2 to CO. 23 …”

“… 21 This process can further be enhanced by photoassisted activation of [Mo(α-diimine)(CO) 4 ] •– . 23 …”

Supported metallic nanoparticles prepared by an organometallic route to boost the electrocatalytic conversion of CO2

“…The electrocatalytic reduction of CO 2 is a topic of large and increasing scientific interest, as indicated by many recent reviews [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Electrocatalysis is a key crucial technology to develop viable processes to yield chemicals using renewable energy sources [15].…”