Exploring the (Dis)-Similarities of Half-Cell and Full Cell Zero-Gap Electrolyzers for the CO₂ Electroreduction

Carbon dioxide electroreduction (CO2R) is a promising technology for mitigating industrial CO2 emissions and generating valuable chemicals using renewable energy sources. Recent advances have centered on fine-tuning catalyst materials and their micro-environments, stimulating interest within the CO2R community. However, testing novel catalyst materials often occurs under conditions different from those relevant to industrial applications. In this study, we explore the transferability of CO2R results obtained using Ag-based gas diffusion electrode (GDEs) in an easy to fabricate, assemble and test zero-gap half-cell (ZGHC) to a zero-gap electrolyzer (ZGE). Our investigation reveals that the transferability of results is not only influenced by the reactor design, but also partially dependent on the type of additive used in the catalyst layer of the GDE. Moreover, we show that the humidity of the CO2 is a crucial operational parameter that not only impacts the selectivity of the electrode but also influences its stability during testing in the ZGHC. These findings highlight the importance of comprehensively considering operational conditions as well as reactor designs when comparing results between the ZGHC and ZGE, presenting finally a pathway on how to minimize such differences.