Integrated CO₂ Capture and Conversion to Formate with a Molecular Platinum Bis(diphosphine) Electrocatalyst

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 that 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.