CO2 to CO Conversion using Flow Cells with Sustainion™

The work titled “Investigation of CO2 Single-Pass Conversion in a Flow Electrolyzer” was published in RSC Reaction Chemistry & Engineering by an independent group from the University of Delaware. Sustainion™ membrane was chosen as the membrane material because it has a relatively high ionic conductivity in bicarbonate electrolytes in compared to other anion exchange membranes. At the electrode-membrane interface, two side reactions, i.e., hydrogen evolution reaction through water reduction and carbonates formation between CO2 and hydroxide anions, also occur simultaneously. Both reactions compete with eCO2RR and have significant impacts on the CO2 single-pass conversion.

They found that the maximum amount of CO2 being converted to CO is limited to approximately 43% regardless of CO2 feeding rate, operating current density, and reaction temperature. The remaining CO2 feed was mainly consumed by the side reaction of carbonate formation between the CO2 feed and the hydroxide anions generated during the electrolysis as shown below.

Schematic diagrams of (a) the CO2 flow electrolyzer configuration and (b) the cathode Sustainion membrane/ionomer interface with multiple competing reactions.

The resulting gas effluent stream from the cathode chamber contains mainly CO (∼80%), together with 15% H2 and 5% unreacted CO2. Among all figures of merit, CO2 single-pass conversion is an important factor that can strongly affect the product separation cost of the whole process. These values are a little lower compared to previous publications where we have demonstrated CO% selectivity of greater than 98% in the catholyte effluent gas stream versus hydrogen. Using our specially prepared anodes and ionomer embedded cathodes with our membranes could bridge this gap. Visit our webstore to purchase these materials or buy the complete CO2 electrolyzer itself with higher selectivity and performance.