The electroreduction of carbon dioxide (CO 2 ) to C 2 products is a promising approach to divert and utilize CO 2 emissions. However, the requirement of a purified CO 2 feedstock decreases the economic feasibility of CO 2 electrolysis. Direct utilization of industrial flue gas streams is encumbered by low CO 2 concentrations and reactive oxygen (O 2 ) impurities. We demonstrate that pressurization enables efficient CO 2 electroreduction of dilute CO 2 streams (15% v/v); however, with the inclusion of O 2 (4% v/v), the oxygen reduction reaction (ORR) displaces CO 2 reduction and consumes up to 99% of the applied current in systems based on previously-reported catalysts. We develop a hydrated ionomer catalyst coating strategy that selectively slows O 2 transport and stabilizes the copper catalyst. Applying this strategy, we convert an O 2 -containing flue gas to C 2 products at a faradaic efficiency (FE) of 68% and a non-iR-corrected full cell energetic efficiency (EE) of 26%.