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

ABSTRACT

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.