Developing a Suitable Anion Exchange Layer Structure for Pure Water Fed Bipolar Membrane CO2 Electrolysis

Anion exchange membrane (AEM)-based CO2 electrolyzers powered by renewable energy provide a promising pathway for a sustainable CO2-to-CO conversion. However, they suffer from CO2 crossover via the formation of (bi)carbonates, limiting carbon utilization to 50%, and electrolyte-driven salt precipitation, which shortens device lifetime. A forward-biased bipolar membrane (BPM) addresses these issues by operating with pure-water and regenerating CO2 at the bipolar junction. Nevertheless, instability of the bipolar interface, lower faradaic efficiency, and high cell potential remain open challenges. Here, we present a BPM incorporating a porous anion exchange layer (AEL) to facilitate CO2 release out of the bipolar junction. Two BPM configurations are compared with porous or dense AEL deposited either onto a silverbased gas diffusion electrode (GDE) or onto the CEM. Porous AEL-coated GDEs achieved enhanced stability, lower cell potentials, and partial current densities for CO up to 214 mA cm-2 at 3.25 V. Implementation of this BPM architecture reduces CO2 crossover by at least 80% compared with an AEM-based electrolyzer, although CO2 losses to the anode persist, highlighting the need for further optimization. These findings establish porous AEL-coated GDEs as a promising strategy for advancing BPM CO2 electrolysis.