The overlooked yet critical role of catholyte composition in microbial electrosynthesis

The circular economy should include CO₂ valorization, which could be achieved via microbial electrosynthesis (MES). In MES, the catholyte supplies all nutrients, yet its composition has been adopted from other biotechnologies, overlooking specific needs of MES. In this Perspective, we examine how catholyte design impacts MES performance at microbial, electrochemical, and process levels. We highlight mismatches in metal availability, electrode interactions, and medium origins. We propose reframing the catholyte as a key design parameter and introduce a decision-making framework for tailored formulation. This strategy has the potential to improve MES performance and serve as model for optimizing media in broader biotechnological applications.