Three-Way Control on Product Selectivity in Electrocatalytic CO₂ Reduction Reaction Using a Single Molecular Co–NHC Catalyst

For a long time, molecular electrocatalysts have been developed to reduce CO₂ efficiently to value-added products such as CO and HCO₂H, along with H₂; however, selectivity remained as a major issue. Recent work toward addressing this issue showed that several different catalysts could be used to achieve product selectivity. It is desirable that instead of using different catalysts for specific products, a single catalyst should be able to produce the target products by subtle tuning of the reaction conditions. Toward this objective, herein we presented the organometallic Co electrocatalyst <b>Co-</b>^<b>NHC</b><b>U</b> and successfully utilized it in the electrochemical CO₂ reduction reaction (CO₂RR) to produce CO, H₂, and HCO₂H with notable selectivity. The reduction of CO₂ selectively produced CO with 81 ± 2% Faradaic efficiency (FE) in the presence of 5% H₂O as a proton source. The selectivity was changed toward H₂ with 80 ± 3% FE when 1.5 M triethylamine was added as an additive in the presence of 10% H₂O as a proton source. In the presence of 1.0 M morpholine as an external additive, the CO₂-saturated solution containing 10% trifluoroethanol as a proton source generates 55 ± 5% HCO₂H as the predominant product, with H₂ as a competitive side product. It was found that the combined effect of the proton source and the additive in association with the nature of the <b>Co-</b>^<b>NHC</b><b>U</b> catalyst changed the selectivity of the products in this reaction.