CO ₂ ‐to‐CO Electrochemical Conversion With an Fe(I) Porphyrin Complex in Water

Iron porphyrin complexes constitute a well‐established and versatile class of molecular electrocatalysts for the reduction of CO 2 to CO. In both organic and aqueous media, the reaction mechanism is typically proposed to involve the interaction of CO 2 with a formally defined [(porphyrin)Fe 0 ] intermediate. In this work, we performed a mechanistic investigation of CO 2 reduction using the water‐soluble complex [( p TMA)Fe III Cl]Cl 4 under aqueous conditions. In situ scanning spectroelectrochemistry was employed, enabling the synchronized acquisition of UV–vis or IR spectra during cyclic voltammetry experiments. Our results provide strong evidence for CO 2 binding to the electrogenerated [( p TMA)Fe I ] 3+ species, followed by reductive C─O bond cleavage to yield a stable [( p TMA)(Cl)Fe II ‐CO] 3 + complex. This process corresponds to an overall two‐electron reduction per iron center. This mechanism, which has not been previously considered for molecular iron porphyrins in CO 2 reduction, is proposed to be facilitated by the charged porphyrin periphery and the hydrogen‐bonding network of the aqueous medium. These features may open new avenues toward achieving CO 2 reduction at lower overpotentials in water.