Charged Macromolecular Rhenium Bipyridine Catalysts with Tunable CO₂ Reduction Potentials

Area of Science:

• Electrochemistry
• Polymer Science
• Catalysis

Background:

• Developing efficient electrocatalysts for carbon dioxide (CO₂) reduction is crucial for sustainable energy solutions.
• Tuning the performance of molecular catalysts through immobilization on polymeric supports offers a promising strategy.
• Rhenium(I) (Re^I) complexes are known electrocatalysts for CO₂ reduction, but their application in polymeric systems requires further investigation.

Purpose of the Study:

• To design and synthesize novel polymeric frameworks with functional assemblies to modulate the catalytic activity of covalently bound Re^I electrocatalysts.
• To investigate the effect of polymer charge on the electrochemical CO₂ reduction performance of immobilized Re^I catalysts.
• To explore the potential of these functionalized polymers as precursors for advanced catalytic materials.

Main Methods:

• Synthesis of norbornenyl polymers functionalized with quaternary ammonium (positive), phenyl (neutral), or trifluoroborate (negative) groups.
• End-labeling of polymers with a Re^I fac-tricarbonyl bipyridine electrocatalyst via cross metathesis.
• Electrochemical studies in acetonitrile under CO₂ saturation to determine reduction potentials and catalytic activity.

Main Results:

• Polymers with positively charged quaternary ammonium groups significantly lowered the CO₂ reduction potential to CO by approximately 300 mV compared to the free catalyst.
• Neutral phenyl polymers exhibited catalytic behavior consistent with the molecular Re^I catalyst.
• Negatively charged trifluoroborate polymers showed a negative shift in potential, and catalytic activity was not observed.

Conclusions:

• Immobilization of a single Re^I electrocatalyst onto a charged polymeric framework allows for environmentally tuned CO₂ reduction potentials.
• The charge of the polymer backbone plays a critical role in modulating catalyst performance.
• These functionalized polymer-catalyst systems hold potential for creating ordered catalytic structures like thin films and membranes.