Proton-Coupled, Low-Energy Pathway for Electrocatalytic CO₂ Reduction at Re(Diimine) Complexes with a Conjugated...

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• Rhenium(α-diimine)(CO)3Cl complexes with pyrazinyl linkages are explored for CO2 reduction.
• Nonmonotonic dependence of CO2 reduction overpotential on ligand conjugation size is observed.
• Understanding this dependence is key for efficient heterogeneous catalyst design.

Purpose of the Study:

• Investigate the role of the conjugated pyrazinyl moiety in electrocatalytic CO2 reduction.
• Elucidate the mechanism behind the nonmonotonic dependence of overpotential on ligand conjugation.
• Identify strategies to improve energy efficiency in CO2 reduction catalysts.

Main Methods:

• Synthesis of Re(α-diimine)(CO)3Cl complexes with varying pyrazinyl ligand conjugation.
• Electrocatalytic CO2 reduction experiments to measure overpotential and selectivity.
• Spectroscopic and electrochemical analyses to identify reaction intermediates and pathways.

Main Results:

• The conjugated pyrazinyl moiety enables a proton-coupled, lower-energy pathway for CO2 reduction.
• Moderate ligand conjugation sizes lead to novel intermediates and decreased CO2 reduction overpotential.
• The effectiveness of this pathway is limited by the basicity of the pyrazinyl nitrogen, imposing a limit on conjugation size.

Conclusions:

• The pyrazinyl nitrogen's basicity is crucial for the proton-coupled pathway in CO2 reduction.
• Ligand design must consider this basicity to optimize energy efficiency and catalyst performance.
• This finding facilitates the rational design of heterogeneous molecular catalysts for selective CO2 reduction.