Tailoring the Ionomer Type to Optimize Catalyst Microenvironment for Enhanced CO₂ Reduction in Membrane Electrode Assemblies

Abstract

Electrocatalytic CO₂ reduction reaction (CO₂RR) represents an advanced technology for converting CO₂ into highly valuable chemicals. Although significant progress has been achieved in producing multi-carbon chemicals such as ethylene (C₂H₄), addressing (bi)carbonate salt formation and precipitation in alkaline electrolytes remains a critical challenge for achieving long-term stability during industrialization. We developed a Cu₂(OH)₂CO₃/Mg²⁺/C pre-catalyst, which transforms into a catalytically active Cu⁰/Cu²⁺/Mg²⁺ composite by electroreduction. Crucially, the application of different ionomers (specifically Sustainion XA-9) on this composite catalyst effectively alleviates salt precipitation issues, thereby enabling high-selectivity, durable CO₂-to-C₂₊ conversion. In a membrane electrode assembly, the maximum Faradaic efficiency for C₂₊ products reaches 80%, with stable operation at 200 mA cm⁻² for 50 h. In situ Raman spectroscopy reveals that only top-type *CO intermediate exists on the Cu⁰/Cu²⁺/Nafion cathode, whereas both bridge-type and top-type of *CO sites coexist on the Cu⁰/Cu²⁺/Mg²⁺/Sustainion XA-9 cathode. This dual adsorption configuration facilitates the C─C coupling kinetics on the catalyst, inducing a favorable microenvironment for selective C₂₊ formation. Therefore, strategic optimization of catalyst architectures and ionomer engineering enables CO₂RR with improved efficiency and durability, advancing green chemistry and carbon-neutral technologies.

Keywords

electrocatalytic CO₂ reduction reaction / ionomer / MEA / microenvironment

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2025 The Author(s). Carbon Energy published by Wenzhou University and John Wiley & Sons Australia, Ltd.