Immobilized Organic Cations Augment CO Electroreduction via Molecular Vibration Modulation.

Area of Science:

• Electrochemistry
• Catalysis
• Materials Science

Background:

• The catalyst-ionomer heterojunction (CIH) is crucial for electrochemical CO2 reduction to multicarbon (C2+) products.
• Current understanding of CIH primarily focuses on CO2 diffusion and activation, neglecting ionomer effects on CO adsorption.

Purpose of the Study:

• To investigate the impact of different immobilized cation groups in polynorbornene ionomers on CO electroreduction to C2+ products.
• To elucidate the mechanism by which ionomers influence CO adsorption and subsequent C-C coupling.

Main Methods:

• Electrochemical CO reduction experiments using Cu catalysts modified with various polynorbornene ionomers.
• Analysis of product selectivity and Faradaic efficiency for C2+ products.
• Spectroscopic investigation of CO adsorption states and vibrational frequencies on the catalyst surface.

Main Results:

• Imidazolium cations demonstrated the highest activity for C2+ products, achieving 83% Faradaic efficiency and 584 mA cm-2 partial current density.
• A correlation was found between imidazolium cation presence and modulated vibrational frequencies of adsorbed CO on Cu.
• Charge transfer between imidazolium cations and adsorbed CO was identified as the key factor weakening the C≡O bond.

Conclusions:

• Ionomers, specifically imidazolium cations, significantly impact CO adsorption and activation, which are critical for C2+ product formation.
• The charge transfer mechanism provides a new perspective on CIH function, extending beyond CO2 activation to influence CO reactivity.
• Optimizing ionomer structure offers a promising strategy to enhance selectivity and activity in electrochemical CO2 reduction.