 Abstract membrane electrode assemblies enable CO2 electrolysis at industrially relevant rates, but their operational stability is often limited by the formation of solid precipitates in the cathode pores. This is caused by cation crossover from the analyte due to imperfect ion exclusion by anion exchange membranes. The amount of cation crossover can be controlled by varying the concentration of the analyte solution, which has a significant effect on the behaviour of copper catalysts in catholite-free CO2 electrolyzers. Furthermore, the presence of cations also plays a key role in determining the reaction pathway for carbon dioxide reduction, even when there are no liquid catholites present. This article was authored by