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

Abstract

•Reacting bicarbonate and carbamate species on Ag electrodes requires energy input •On Ag electrodes, the carbon source is the free and dissolved CO2 during RCC •Carbamate species can only participate in RCC at highly negative potentials •Methods to measure and report dissolved CO2 concentration during RCC are developed 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. 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.