CO₂-to-CO Electrochemical Conversion With an Fe(I) Porphyrin Complex in Water

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• Iron porphyrin complexes are known molecular electrocatalysts for CO2 reduction to CO.
• The typical mechanism involves a formal iron(0) intermediate interacting with CO2.
• Understanding aqueous phase mechanisms is crucial for developing sustainable CO2 conversion technologies.

Purpose of the Study:

• To investigate the mechanism of CO2 reduction using a water-soluble iron porphyrin complex, [(pTMA)FeCl]Cl4, in aqueous media.
• To explore a novel CO2 reduction pathway distinct from the conventional iron(0) mechanism.
• To identify factors facilitating efficient CO2 reduction in water.

Main Methods:

• Mechanistic investigation of CO2 reduction electrocatalysis.
• Utilized in situ scanning spectroelectrochemistry synchronized with cyclic voltammetry.
• Employed UV-vis and IR spectroscopy for real-time spectral acquisition during electrochemical experiments.

Main Results:

• Provided strong evidence for CO2 binding to an electrogenerated iron(I) species, [(pTMA)Fe(I)]3+.
• Observed reductive C-O bond cleavage leading to a stable iron(II)-carbonyl complex, [(pTMA)(Cl)Fe(II)-CO]3+.
• Demonstrated a two-electron reduction process per iron center, a previously unconsidered mechanism for iron porphyrins in CO2 reduction.

Conclusions:

• The charged porphyrin periphery and aqueous hydrogen-bonding network facilitate a novel CO2 reduction mechanism.
• This mechanism involves CO2 binding to Fe(I) followed by C-O bond cleavage.
• Findings suggest new strategies for achieving lower overpotentials for CO2 reduction in water.