Electrocatalytic CO2 reduction is an attractive strategy to mitigate the continuous rise in atmospheric CO2 concentrations and generate value-added chemical products. A possible strategy to increase the activity of molecular systems for these reactions is the co-catalytic use of redox mediators (RMs), which direct reducing equivalents to the active site from the electrode. Recently, we demonstrated that a sulfone-based RM could trigger co-electrocatalytic CO2 reduction via an inner-sphere mechanism under aprotic conditions. Now, we have synthetically modulated the mediator to increase activity at lower overpotentials under protic conditions, providing support for inner-sphere cooperativity. Furthermore, we have evidence that the intrinsic performance of the Cr-centered catalyst and its co-catalytic performance can be enhanced by ligand design. By tuning both reaction components appropriately, an optimized co-electrocatalytic system with quantitative selectivity for CO at an overpotential (η) of 360 mV and turnover frequency (TOF) of 5.58 x 105 s–1 is obtained, representing a significant improvement over our original report, and situating it among the best reported for molecular electrocatalysts.

Improving co-electrocatalytic activity for CO2 reduction at lower overpotentials through redox mediator tuning and catalyst design

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ACS Fall 2022

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