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.