Enriching Surface-Accessible CO₂ in the Zero-Gap Anion-Exchange-Membrane-Based CO₂ Electrolyzer

Zero-gap anion exchange membrane (AEM)-based CO₂ electrolysis is a promising technology for CO production, however, their performance at elevated current densities still suffers from the low local CO₂ concentration due to heavy CO₂ neutralization. Herein, via modulating the CO₂ feed mode and quantitative analyzing CO₂ utilization with the aid of mass transport modeling, we develop a descriptor denoted as the surface-accessible CO₂ concentration ([CO₂ ]^SA ), which enables us to indicate the transient state of the local [CO₂ ]/[OH^- ] ratio and helps define the limits of CO₂ -to-CO conversion. To enrich the [CO₂ ]^SA , we developed three general strategies: (1) increasing catalyst layer thickness, (2) elevating CO₂ pressure, and (3) applying a pulsed electrochemical (PE) method. Notably, an optimized PE method allows to keep the [CO₂ ]^SA at a high level by utilizing the dynamic balance period of CO₂ neutralization. A maximum j_CO of 368±28 mA cm_geo ^-2 was achieved using a commercial silver catalyst.