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

Abstract

Electrochemical CO2 reduction (eCO2R) stands as a pivotal technology for carbon recycling by converting CO2 into value‐added products. While significant strides have been made in generating multi‐carbon (C2+) products like ethylene (C2H4) and ethanol (C2H5OH) 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 CO2 availability. The impact of cation and anion exchange ionomer layers, specifically Nafion and Sustainion XA‐9 are examined on overall eCO2R 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 C2+ formation. This cation‐infused bilayer ionomer (CIBLI) achieves a high partial current density of ≈284 mA cm−2 toward C2+ products maintaining a stable eCO2R performance for 24 hours (h). This scalable approach of directly deposited ultra‐thin CIBLI offers a minimal conversion energy of 117 GJ/ ton C2+ products with an energy efficiency (EE) of 29% at 350 mA cm−2 current density in one‐step CO2 conversion.