Why Membranes Matter: Ion Exchange Membranes in Holistic Process Optimization of Electrochemical CO₂ Reduction

Abstract Reducing carbon dioxide to value‐added chemicals by electrolysis is a promising strategy to substitute fossil‐based processes. Research on CO₂ electrolysis has vastly progressed, focusing on catalysis and electrode design, leaving an essential question on the central part of the electrolyzer: Which type of ion exchange membrane is best suited for CO₂ electrolysis from an economic perspective? To address this question, holistic process optimization of CO₂ reduction and product purification is applied. The findings demonstrate that CO₂ electrolysis with an anion exchange membrane shows competitive production costs for CO of 796 €/t_CO, outperforming cation exchange and bipolar membranes. Unlike often described, the CO₂ pumping effect does not significantly impair the economics but offers an efficient indirect regeneration of dissociated CO₂. Furthermore, the results emphasize selective reduction of CO₂ rather than co‐electrolysis of CO₂ and H₂O. While pointing to a positive economic perspective, life‐cycle assessment highlights the need to minimize CO₂ emissions related to electricity consumption and incomplete CO₂ utilization.