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 (NO x ) and sulfur oxides (SO x ) 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 NO x (NO2 – and NO3 –) and SO x (SO3 2– and SO4 2–) impact the electrochemical conversion of (bi)carbonate to CO. We found that CO production was unaffected by SO x compounds in a 3.0 M KHCO3 feedstock, but 2000 ppm of NO x 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.

Ethylene Production from Carbonate Using a Bipolar Membrane Electrolysis System

“…In contrast to carbonate electrolysis, bicarbonate electrolysis has shown relatively high CO 2 concentration in the outlet, meaning that not all the produced CO 2 is utilized . For context, under the same operating conditions of −100 mA/cm 2 , bicarbonate electrolysis (pH: 8.8) releases approximately five times more CO 2 than that in carbonate electrolysis (pH: 11.8) . Further evaluations revealed significantly low overall conversion efficiencies in carbonate electrolysis: 0.0015% for Cu and 0.0031% for Cu–Ag(0.5) at −100 mA/cm 2 (Figure S11).…”

“…24 For context, under the same operating conditions of −100 mA/ cm 2 , bicarbonate electrolysis (pH: 8.8) releases approximately five times more CO 2 than that in carbonate electrolysis (pH: 11.8). 41 Further evaluations revealed significantly low overall conversion efficiencies in carbonate electrolysis: 0.0015% for Cu and 0.0031% for Cu−Ag(0.5) at −100 mA/cm 2 (Figure S11). These low efficiencies correlate with the high concentration of reactants (5 M K 2 CO 3 ), the substantial flow rate (65 m/min), and overall low conversion of bicarbonate to CO 2 .…”

A minireview on electrochemical CO2 conversion based on carbonate/bicarbonate media

“…In-depth research revealed that the type of anion did not affect the in situ generation of CO significantly. Instead, it primarily influenced the conversion of CO 2 to CO. Pimlott et al 31 took into account the scenario of CO 2 capture from flue gas and examined the effects of nitrogen oxides (NO x ) and sulfur oxides (SO x ) existing in the flue gas on the HCO 3 − electrolyzers. The results indicated that SO x did not have a significant impact on the generation of CO.…”

Reactive Carbon Capture Enables CO2 Electrolysis with Liquid Feedstocks

“…The aqueous medium of a reactive carbon electrolyzer can be modified to affect the reaction environment in ways that are not possible with a gaseous feedstock. Given the impact that bulk and cathode surface pH, electrolyte composition, electrolyte concentration, and additives have on CO2RR, ,,− we contend that there is a broad parameter space available for exploration to improve both the reactive carbon electrolyzer as well as the coupled CO 2 capture unit.…”