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 for the commercial silver catalyst.