Toward O₂-tolerant CO₂ electro-reduction for direct flue gas utilization

The electrochemical CO₂ reduction reaction (CO₂RR) is a promising strategy for converting CO₂ into value-added chemicals. Beyond the conventional use of purified CO₂, direct flue gas utilization offers a pathway to improve the technoeconomic viability of carbon conversion by eliminating costly CO₂ purification processes. However, O₂ present in flue gas poses a major challenge, as the thermodynamically favored oxygen reduction reaction (ORR) can dominate cathodic reactions and substantially hinder selective CO₂ conversion. This review examines the impact of O₂ on the CO₂RR and highlights recent advances in systems that maintain CO₂RR selectivity in the presence of O₂, including substrate selection, ionomer engineering, gas-feed engineering, electrolyte engineering, and catalyst design. Particular attention has been paid to the design principles for suppressing the ORR and enabling the selective CO₂RR under O₂-containing conditions, with emphasis on controlling local reactant transport and interfacial reaction environments. Finally, key challenges and future opportunities for a practical direct flue gas CO₂RR are discussed in this review, particularly in the context of integrated system design and MEA-based operation.