| Popis: |
Density functional theory calculations employing a hybrid implicit/explicit solvation method were used to explore a new strategy for electrochemical conversion of CO2 using an electro-organocatalyst. A particular structural motif is identified that consists of an electron-rich >N−C=C−N< (enediamine) backbone which is capable of activating CO2 by formation of a C−C bond while subsequently facilitating the transfer of electrons from a chemically inert cathode to ultimately produce formaldehyde. Unlike transition metal-based electrocatalysts, the electroorganocatalyst is not constrained by scaling relations between the formation energies of activated CO2 and adsorbed CO, nor is it expected to be active for the competing hydrogen evolution reaction. The rate limiting steps are found to occur during two proton-coupled electron transfer (PCET) sequences and are associated with the transfer of a proton from a proton transfer mediator to a carbon atom on the electro-organocatalyst. The difficulty of this step in the second PCET sequence necessitates an electrode potential of −0.94 V vs. RHE to achieve the maximum turnover frequency. In addition, it is postulated that the electro-organocatalyst should also be capable of forming long chain aldehydes by successively carrying out reductive aldol condensation to grow the alkyl chain one carbon at a time. While much effort is still required to bring this conceptual design to reality, we are optimistic that the new directions for CO2 conversion opened up by this initial work will one day result in a practical device for electrochemical conversion of CO2 into multicarbon products. |
