On the origin of carbon sources in the electrochemical upgrade of CO2 from carbon capture solutions

Carbon capture and utilization (CCU) is a crucial technology for mitigating the effects of climate change. One approach to CCU is reactive carbon capture (RCC), which integrates (1) the capture and concentration of CO2 in a capture medium via the reversible formation of a chemical complex with a molecular capture agent, such as an amine, and (2) the direct transformation of the CO2 complex into a fuel or chemical. CO2 capture media present a large degree of speciation, where carbon exists in different molecular configurations with different energy states and barriers to reaction. In this work, a combination of first principle modeling and experimental electrochemical characterization methods reveal that unbound dissolved CO2 is the primary carbon species being consumed during the electrochemical reduction of bicarbonate and amine-based CO2 capture solutions on silver electrodes. Carbon in the CO2-absorber complex occurs to serve as a second carbon source only at highly negative potential.