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Carbon dioxide is a potentially valuable feedstock for carbon-based fuels or commodities but is only available in dilute streams. Many studies have focused on either the capture and concentration of CO₂ or the reduction of pure CO₂ streams. The direct reduction of sorbent-captured CO₂ in an integrated process would skip the energy-intensive CO₂ concentration and sorbent regeneration step. Herein, we report the electrocatalytic reduction of 1,3-bis(2,6-diisopropylphenyl)imidazolium-2-carboxylate (IPr·CO₂), which forms quantitatively from the reaction of sorbent 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) with 10% and 0.04% CO₂ streams, by catalyst [Pt(dmpe)₂](PF₆)₂ (dmpe = 1,2-bis(dimethylphosphino)ethane) to formate with >70% Faradaic efficiencies. Unexpectedly, experimental studies indicate thatmore » the proton source phenol facilitates rapid decarboxylation of IPr·CO₂ to release CO₂, which is the substrate for reduction. Kinetic studies determined the rate of hydride transfer from a catalytic intermediate [HPt(dmpe)₂](PF₆) to form the C–H bond in formate to be 0.22 M^–1s^–1. Further details on the mechanism, transition state energy, and structure for hydride transfer to CO₂, a common step in CO₂ reduction, were explored using computational methods.« less

CO₂ is a potential feedstock for carbon-based fuels or materials, but is only available in dilute streams. Integrated processes for CO₂ capture and conversion directly valorize the CO₂ captured by sorbent materials, skipping the energetically expensive sorbent regeneration step. Amines are the most heavily studied liquid-phase sorbent materials for CO₂ capture from dilute streams. Amines react with CO₂ in a 2:1 ratio to form the corresponding ammonium carbamate. Ammonium carbamate [NH₄][H₂NCO₂] was tested as the substrate using the highly selective and robust CO₂-to-formate reduction electrocatalyst [(^tBuPOCOP)Ir(H)(NCCH₃)₂], where (^tBuPOCOP) is the tridentate pincer ligand 2,6-bis(ditert-butyl-phosphonito). When ammonium carbamate was used asmore » the substrate instead of CO₂, only hydrogen was produced. An equivalent electrolysis with ammonium hexafluorophosphate with CO₂ also resulted in primarily hydrogen. Methyl carbamate and urea were also tested as substrates as proxies for carbamate that do not contain an equivalent of ammonium, and there was also negligible reduction to carbon-based products. These results indicate that the loss of selectivity observed for aminecaptured CO₂, or ammonium carbamate, is likely due to the generation of the acidic ammonium equivalent as well as the greater challenge of reducing carbamate compared to CO₂. This study illustrates that catalysts with high selectivity for concentrated CO₂ can favor hydrogen evolution and loss of carbon-based products when amine-captured CO₂ is used instead.« less