Homogeneous Iron Porphyrin as a Molecular CO Shuttle Enables Electrochemical Multicarbon Product Formation from CO2

Homogeneous molecular catalysts for electrochemical CO2 reduction are generally limited to two-electron-reduced C1 products, primarily CO. Here we propose and demonstrate a fundamentally distinct role for molecular catalysts: as reversible CO shuttles that enhance the local CO activity at the electrical double layer. Using a water-soluble iron porphyrin as a CO shuttle, we observe the formation of isotopically verified C1-C4 hydrocarbons from CO2 in aqueous electrolyte. These products are not observed even in CO-saturated electrolyte in the absence of the iron porphyrin, indicating that the shuttle enhances local CO activity at the electrode surface beyond what bulk saturation can provide. Electrochemical and spectroscopic data support the formation of a stable FeII-CO species outside the compact layer, which releases CO upon further reduction at the electrode surface, consistent with an electrochemically gated shuttle mechanism. These findings suggest a potential design principle in which homogeneous catalysts function as molecular intermediate shuttles at the electrode surface and provide an alternative framework for interpreting beyond-CO products observed in heterogenized molecular catalyst systems.