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

Electrochemical CO 2 reduction must move beyond purified CO 2 to use real-world sources like flue gas or captured CO 2 . But such low-concentration feeds pose two problems: residual O 2 poisons the reaction, triggering competing oxygen reduction reaction, cutting carbon efficiency, and degrading the catalyst, while low CO 2 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% CO 2 , 5% O 2 , 80% N 2 ), Bi@PEG demonstrates record-breaking performance for CO 2 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 CO 2 conversion of 72.5%, and maintains this performance even at 8% O 2 . Mechanism studies show the PEG layer selectively admits CO 2 (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 CO 2 enrichment. In contrast, O 2 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 CO 2 concentration and oxygen interference, this work establishes “armored catalysis” as a universal approach for electrochemical CO 2 conversion using realistic, low-concentration, oxygen-containing carbon sources.