Electrocatalytic CO2 Reduction with a Half-Sandwich Cobalt Catalyst: Selectivity towards CO

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 Co-NHCU 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 Co-NHCU catalyst changed the selectivity of the products in this reaction.

Transition Metal Complexes as Catalysts for the Electroconversion of CO2 : An Organometallic Perspective

The electrocatalytic transformation of carbon dioxide has been a topic of interest in the field of CO2 utilization for a long time. Recently, the area has seen increasing dynamics as an alternative strategy to catalytic hydrogenation for CO2 reduction. While many studies focus on the direct electron transfer to the CO2 molecule at the electrode material, molecular transition metal complexes in solution offer the possibility to act as catalysts for the electron transfer. C1 compounds such as carbon monoxide, formate, and methanol are often targeted as the main products, but more elaborate transformations are also possible within the coordination sphere of the metal center. This perspective article will cover selected examples to illustrate and categorize the currently favored mechanisms for the electrochemically induced transformation of CO2 promoted by homogeneous transition metal complexes. The insights will be corroborated with the concepts and elementary steps of organometallic catalysis to derive potential strategies to broaden the molecular diversity of possible products.

Nanostructured Cobalt-Based Electrocatalysts for CO2 Reduction: Recent Progress, Challenges, and Perspectives

CO₂ reduction reaction (CO₂ RR) provides a promising strategy for sustainable carbon fixation by converting CO₂ into value-added fuels and chemicals. In recent years, considerable efforts are focused on the development of transition-metal (TM)-based catalysts for the selectively electrochemical CO₂ reduction reaction (ECO₂ RR). Co-based catalysts emerge as one of the most promising electrocatalysts with high Faradaic efficiency, current density, and low overpotential, exhibiting excellent catalytic performance toward ECO₂ RR for CO and HCOOH productions that are economically viable. The intrinsic contribution of Co and the synergistic effects in Co-hybrid catalysts play essential roles for future commercial productions by ECO₂ RR. This review summarizes the rational design of Co-based catalysts for ECO₂ RR, including molecular, single-metal-site, and oxide-derived catalysts, along with the nanostructure engineering techniques to highlight the distribution of the ECO₂ RR products by Co-based catalysts. The density functional theory (DFT) simulations and advanced in situ characterizations contribute to interpreting the synergies between Co and other materials for the enhanced product selectivity and catalytic activity. Challenges and outlook concerning the catalyst design and reaction mechanism, including the upgrading of reaction systems of Co-based catalysts for ECO₂ RR, are also discussed.