The lack of a robust and standardized experimental test bed to investigate the performance of catalyst materials for the electrochemical CO₂ reduction reaction (ECO₂RR) is one of the major challenges in this field of research. To best reproduce and mimic commercially relevant conditions for catalyst screening and testing, gas diffusion electrode (GDE) setups attract rising attention as an alternative to conventional aqueous-based setups such as the H-cell configuration. Zero-gap electrolyzer designs show promising features for upscaling to the commercial scale. In this study, we scrutinize further our recently introduced “zero-gap GDE” setup or more correct half-cell MEA design for the CO₂RR. Using an Au electrocatalyst as a model system we simulate the anode conditions in a zero-gap electrolyzer and identify/report the key experimental parameters to control the catalyst layer preparation to optimize the activity and selectivity of the catalyst. Among others, it is demonstrated that supported Au nanoparticles (NPs) result in significantly higher current densities when compared to unsupported counterparts, however, the supporting also renders the NPs prone to agglomeration during electrolysis.