Electroreduction of CO₂ From Flue Gas: Impurity Tolerance and Mechanistic Insights in Molecular Catalysis

Direct utilization of diluted CO₂ from industrial flue gas containing SO₂, NO₂ and O₂ impurities is economically appealing and circumvents capture and purification prior to conversion. We present experimental data and density functional theory (DFT) calculations for understanding the effect of those impurities during CO₂RR catalyzed by a model Re molecular catalyst, [Re(bpy)(CO)₃Cl] (bpy = bipyridine). Under both 10% and 1% v/v CO₂ gas streams, high selectivity toward CO production was maintained, with faradaic efficiency (FE_CO) above 90% and 70%, respectively. O₂ reduction reaction (ORR) on the electrode surface represents a substantial competitive reaction that accounts for ≈80% of the charge consumed when a realistic CO₂ source mimicking an industrial waste-incinerator stream (10% v/v CO₂, 10% v/v O₂, 100 ppm NO₂, and 50 ppm SO₂ in N₂ matrix) is used. Neither NO₂ nor SO₂ incorporated in the diluted CO₂ stream provoke a significant decrease in the CO production (FE_CO ≥ 82%). DFT calculations indicate low affinity of the catalyst for impurities, because they are in their reduced form at the CO₂RR potential. This is experimentally proven by cyclic voltammetry and ion chromatography. These findings call for new strategies that enhance the moderate O₂-tolerance exhibited by Re complex on CO₂RR from flue gas.