Unexpected Solvent Effect in Electrocatalytic CO

Area of Science:

• Electrochemistry
• Catalysis
• Sustainable Chemistry

Background:

• Electrochemical carbon dioxide (CO2) reduction is crucial for sustainable fuel and chemical production.
• Metalloporphyrin complexes are investigated as catalysts for this process.
• Understanding the role of functional groups in catalyst design is essential for improving efficiency.

Purpose of the Study:

• To investigate the role of a 2-hydroxylphenyl functional group in metalloporphyrin catalysts for CO2 reduction.
• To design and synthesize minimal metalloporphyrin complexes (TPOH) for straightforward mechanistic studies.
• To evaluate the catalytic performance of various metal-substituted TPOH complexes (Mn, Fe, Co, Ni, Cu).

Main Methods:

• Electrochemical CO2 reduction experiments were conducted using synthesized TPOH complexes.
• Catalyst performance was evaluated in acetonitrile and dimethylformamide solvents.
• The effect of adding weak Brønsted acids (water, phenol) on catalytic activity was studied.
• Product analysis was performed to identify the reduction products.

Main Results:

• The iron-substituted TPOH complex demonstrated robust CO2 reduction to carbon monoxide in acetonitrile.
• Addition of Brønsted acids resulted in a ~100-fold increase in turnover frequency for the iron catalyst.
• The iron catalyst showed poor performance in dimethylformamide solvent.
• A mechanistic model was proposed involving the hydroxyphenyl group acting as a proton source and hydrogen bond donor.

Conclusions:

• The 2-hydroxylphenyl group plays a critical role in enhancing electrocatalytic CO2 reduction efficiency.
• The proposed mechanism highlights the importance of local proton transfer and hydrogen bonding interactions.
• These findings offer insights for designing improved electrocatalytic systems for CO2 conversion.