Abstract/Summary

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 [Mn(CO)3(2,2ʹ-bipyridine)Br] and [Mo(CO)4(6,6ʹ-dimethyl2,2ʹ-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(2,2ʹ-bipyridine)]2 and [Mo(CO)4(6,6ʹ-dimethyl-2,2ʹbipyridine)]•‒, respectively, generates the 2e‒-reduced, 5-coordinate catalysts, [Mn(CO)3(2,2ʹ-bipyridine)]‒ and [Mo(CO)3(6,6ʹ-dimethyl2,2ʹ-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.