O₂-Tolerant Electroreduction of Dilute CO₂ to Formate at Industrial Current Density by a Kinetic Molecular Sieving...

Electrochemical CO₂ reduction must move beyond purified CO₂ to use real-world sources like flue gas or captured CO₂. But such low-concentration feeds pose two problems: residual O₂ poisons the reaction, triggering competing oxygen reduction reaction, cutting carbon efficiency, and degrading the catalyst, while low CO₂ concentration limits mass transfer and conversion. We solve both with a kinetic molecular sieve: polyethylene glycol-coated bismuth nanoparticles (Bi@PEG). Under simulated flue gas (15% CO₂, 5% O₂, 80% N₂), Bi@PEG demonstrates record-breaking performance for CO₂ electroreduction to formate, achieving a Faradaic efficiency of 94.1 ± 0.6%, a current density of 0.91 A·cm^-2, and a single-pass CO₂ conversion of 72.5%, and maintains this performance even at 8% O₂. Mechanism studies show the PEG layer selectively admits CO₂ (small size, quadrupole moment, strong Lewis acid, base interaction with ether oxygens; binding energy -27.4 kJ mol^-1; diffusion barrier 0.57 eV), resulting in interfacial CO₂ enrichment. In contrast, O₂ transport is significantly impeded due to a higher diffusion barrier (0.83 eV), weak binding affinity (-3.0 kJ mol^-1), and steric hindrance. By overcoming the dual challenges of low CO₂ concentration and oxygen interference, this work establishes "armored catalysis" as a universal approach for electrochemical CO₂ conversion using realistic, low-concentration, oxygen-containing carbon sources.