The electroreduction of carbon dioxide (CO₂) to C₂ products is a promising approach to divert and utilize CO₂ emissions. However, the requirement of a purified CO₂ feedstock decreases the economic feasibility of CO₂ electrolysis. Direct utilization of industrial flue gas streams is encumbered by low CO₂ concentrations and reactive oxygen (O₂) impurities. We demonstrate that pressurization enables efficient CO₂ electroreduction of dilute CO₂ streams (15% v/v); however, with the inclusion of O₂ (4% v/v), the oxygen reduction reaction (ORR) displaces CO₂ 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 O₂ transport and stabilizes the copper catalyst. Applying this strategy, we convert an O₂-containing flue gas to C₂ products at a faradaic efficiency (FE) of 68% and a non-iR-corrected full cell energetic efficiency (EE) of 26%.

The transport and phase change of a complex fluid mixture under nanoconfinement is of fundamental importance in nanoscience, and limits the recovery efficiency from tight oil reservoirs (<10%). Herein, through experiments and supporting theory we characterize the transport and phase change of a nanoconfined complex fluid mixture. Our nanofluidic platform, nanomodel, replicates shale reservoirs in terms of mean pore size (∼100 nm), permeability (∼μD) and porosity (∼10%). We screen conditions for the most promising shale EOR strategies, directly quantifying their pore-scale efficiency and underlying mechanisms. We find that immiscible gas (N₂) flooding presents a prohibitively large capillary pressure threshold (∼2 MPa). Miscible (CO₂) gas flooding eliminates this threshold leading to film-wise stable oil displacement with high recovery efficiency. Strong capillary forces present barriers as well as opportunities for recovery strategies unique to nanoporous reservoirs by transitioning from a miscible to an immiscible condition locally within the reservoir. These results quantify the fundamental transport and phase change mechanisms applicable to nanoconfined complex fluids, with direct implications in unconventional oil as well as nanoporous media more broadly.