Cryogenic-membrane hybrid separation for closed-loop CO₂ recycle and saleable O₂ recovery in AEM-based CO₂ electrolyzers: Process design, TEA, and LCA

Anion-exchange membrane (AEM)-based CO₂ electrolyzers generate a CO₂/O₂-mixed anodic gas due to unavoidable (bi)carbonate crossover, resulting in significant loss of CO₂ and limited utilization of the O₂ byproduct. While previous studies focused on crossover mitigation or CO₂ recycle, the integrated economic and environmental value of simultaneous anodic CO₂ recycle and O₂ valorization remains unexplored. In this study, cryogenic CO₂/O₂ separation processes for AEM-based CO₂ electrolyzers are designed and evaluated through techno-economic analysis (TEA) and life cycle assessment (LCA). A freeze-out-aware design framework combining thermodynamic screening with a support vector machine (SVM) surrogate enables rapid operability assessment under cryogenic conditions. The proposed membrane-assisted double-column configuration ensures operation without solid-phase formation while achieving ' 99.9 mol% purity and 91.5% recovery for CO₂, and ' 95 mol% purity and 55.0–87.2% recovery for O₂. TEA results indicate that refrigeration dominates the cost structure; however, gaseous O₂ valorization substantially offsets separation costs, resulting in a net CO₂ recycle cost of 51–56 USD/tCO₂. LCA shows that avoided emissions from displacing O₂ production at conventional air separation units offset indirect emissions from increased electricity demand, yielding more than 25% reduction in carbon footprint. When integrated with AEM-based CO₂ electrolyzers, the cryogenic CO₂/O₂ separation increases carbon utilization efficiency from 46% to 89%, reducing the dependence on external CO₂ supply. This shifts the entire system from a CO₂ feed-dominated cost structure to an electricity-driven regime. Sensitivity analysis indicates that these benefits become more pronounced under scenarios of high CO₂ feed costs (e . g ., direct air captur e) and low-cost renewable electricity.