Redefining CO₂ Reduction in Zero-Gap Cell: Exploring Alkaline Ionomers as Alternatives to Mobile Cations

Incorporating cations into the cathode catalyst layer (CL) is a well-established strategy to enhance reaction kinetics in CO2 electrolysis. However, cations are inherently mobile, leading to challenges such as carbonate precipitation, reducing hydrophilicity with subsequent flooding, and difficulty maintaining their presence near the catalyst. These issues limit the long-term stability and performance of CO2 reduction systems. Alkaline ionomers (AEIs), polymers with fixed positive charges, present a potential alternative to cations due to their immobility and compatibility with alkaline environments. Yet, the feasibility of AEIs as a replacement for cations in cation-free systems remains uncertain. In this study, gas diffusion electrodes (GDEs) were prepared with varying contents and types of AEIs, and their performance was systematically evaluated in a cation-free environment. Electrochemical tests were conducted to assess CO2 reduction activity, selectivity, and stability. Morphological and structural analyses examined AEI distribution and its interaction with the catalyst surface. The results demonstrated that AEI content and type significantly influence the electrochemical performance and stability of the system. Thus, AEIs are a crucial design parameter, especially in cation-free systems. More specifically, the quantity and density of fixed positive charges significantly increase the reaction's kinetics. These findings underline the importance of tailoring AEI properties to optimize their role in facilitating CO2 reduction. This study provides valuable insights into the engineering of AEIs for cation-free CO2 electrolysis, paving the way for developing more stable and efficient cathodes.