Cation‐Infused Bilayer Ionomer Coating Enables High Partial Current Density Toward Multi Carbon Products in CO2 Electrolysis

Abstract Electrochemical CO 2 reduction (eCO 2 R) stands as a pivotal technology for carbon recycling by converting CO 2 into value‐added products. While significant strides have been made in generating multi‐carbon (C 2+ ) products like ethylene (C 2 H 4 ) and ethanol (C 2 H 5 OH) at industrial‐scale current densities with high Faradaic efficiency (FE), cathode flooding and (bi)carbonate salt accumulation remain a fundamental concern in an alkaline electrolyte. In this work, ion‐conducting polymers are used to tailor the micro‐environment mitigating cathode flooding and salt precipitation and thus, enhancing the local CO 2 availability. The impact of cation and anion exchange ionomer layers, specifically Nafion and Sustainion XA‐9 are examined on overall eCO 2 R performance. The use of an ultra‐thin bilayer configuration significantly reduces cathode flooding and salt accumulation by ≈58% compared to commercial anion exchange membrane (AEM). Alongside, cation infusion improves the C─C bond formation inducing a favorable micro‐environment for selective C 2+ formation. This cation‐infused bilayer ionomer (CIBLI) achieves a high partial current density of ≈284 mA cm −2 toward C 2+ products maintaining a stable eCO 2 R performance for 24 hours (h). This scalable approach of directly deposited ultra‐thin CIBLI offers a minimal conversion energy of 117 GJ/ ton C 2+ products with an energy efficiency (EE) of 29% at 350 mA cm −2 current density in one‐step CO 2 conversion.