Abstract
An optimized baseline pretreatment protocol effectively regulates transmembrane water transport in anion exchange membrane CO2 electrolyzers, mitigating performance artifacts and improving stability.
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The performance of CO2 electrolyzers is significantly affected by water transport through the anion exchange membrane (AEM). However, the role of membrane pretreatment in governing water transport behavior has seldom been investigated, and a standard pretreatment protocol remains absent. Therefore, we investigate the impact of the pretreatment protocol on CO2 electrolyzer performance in this work. We found that for two widely used commercial AEMs, the choice of pretreatment protocol exerts a profound influence on both performance and durability. In I-V polarization tests, the KOH-pretreated quaternary ammonium poly(N-methyl-piperidine-co-p-terphenyl) (QAPPT) membrane exhibited a Faradaic efficiency for CO product (FECO) of 81% at 500 mA cm−2, representing relative enhancements of 27% and 53% compared to K2CO3- and KHCO3-pretreated membranes, respectively. However, during durability tests for 50 h, the K2CO3-pretreated membrane achieved a stable FECO of 79%, a 16% relative improvement over the KOH-pretreated membrane. Furthermore, even though both were theoretically in the HCO3− form, the as-received poly(aryl piperidinium) (PiperION) membrane and the KHCO3-pretreated membrane displayed a distinct discrepancy in electrolyzer performance. This stability discrepancy is attributed to the water transport behavior across the AEM, which is determined by the pretreatment-induced membrane microphase separation morphology rather than the anion form, as evidenced by anode product analysis, attenuated total reflection infrared (ATR-IR), and atomic force microscopy (AFM) characterizations. Based on these findings, we propose a baseline pretreatment protocol to alleviate performance artifacts and improve cross-study comparability for similar AEM systems.