Porous membranes enable selective and stable zero-gap acidic CO2 electrolysers

Zero-gap membrane electrode assembly (MEA) CO₂ electrolysers offer high energy efficiency and promise for industrial application. However, the transport of carbonates within an anion exchange membrane (AEM) electrolyser leads to CO₂ loss, thereby limiting carbon utilization efficiency. Emerging acidic anolyte electrolysers using cation exchange membrane (CEM) can address this challenge but face critical stability issues, including accelerated hydrogen evolution reaction (HER) and persistent salt precipitation. Here, we propose a porous membrane (PM) as an alternative to the CEM in acidic anolyte electrolysers. The system demonstrates continuous operation at 100 mA cm^-2 for 200 h without salt precipitation, while maintaining nearly 100% CO selectivity. Furthermore, large-scale device (100 cm²) also shows stable performance. Mechanism analysis suggests that enhanced water permeation and bidirectional ion transfer are critical for achieving stable performance in acidic anolyte electrolysers. These findings offer a feasible approach for high-performance, stable and scalable acidic MEA CO₂ electrolysers.