Impurity-Resistant CO2 Reduction Using Reactive Carbon Solutions

Abstract

Electrolyzers that electrochemically convert aqueous (bi)carbonate solutions (solutions containing captured CO2, or “reactive carbon solutions”) into commodity chemicals couple CO2 capture with CO2 conversion. Industrial exhaust streams contain nitrogen oxides (NOx) and sulfur oxides (SOx) that form redox-active anions in reactive carbon solutions that can interfere with downstream CO2 reduction. We therefore designed experiments to test how impurities produced from the dissolution of NOx (NO2– and NO3–) and SOx (SO32– and SO42–) impact the electrochemical conversion of (bi)carbonate to CO. We found that CO production was unaffected by SOx compounds in a 3.0 M KHCO3 feedstock, but 2000 ppm of NOx impurities decreased CO selectivity from ∼60% to <5%. This decrease was caused by the preferential reduction of NO2– and NO3– over CO2. Our study establishes tolerance limits for common flue gas impurities in reactive carbon solutions and provides strategies to mitigate toxification effects.