(406d) On the Origin of Carbon Sources in the Electrochemical Upgrade of CO2 from Carbon Capture Solutions: Case-Studies of Ag, Au, and Cu Catalysts

Carbon capture and utilization (CCU) is a crucial technology to mitigate climate change, primarily fueled by carbon dioxide (CO₂) emission from all sectors of our economy. One approach to CCU is reactive carbon capture (RCC), which integrates 1) the capture and concentration of CO₂ in a capture media 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, circumventing a CO₂ release step. Thermal energy used to release the CO₂ into a concentrated stream for further transformation is energy-intensive and circumventing the release step can potentially reduce capital and operational costs. However, CO₂ capture media present a large degree of speciation, where carbon exists in different molecular configurations with different energy states and barriers to reaction, which adds to the complexity of RCC systems. Thus, understanding the source of carbon for transformation under RCC conditions is one of the main challenges in the field.

Utilizing a gastight rotating cylinder electrode (RCE) cell with well-defined transport properties at the gas/liquid and liquid/solid interfaces, we have carried out the electrochemical reduction of ammonium carbamate (AC), potassium bicarbonate and a CO₂-loaded MEA solutions. In all experiments, the maximum concentration of CO reached in the headspace of the cell was proportional to the partial pressure of CO₂. 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 and gold electrodes. The same studies with copper showed corrosion of the catalyst when in contact with the amine solution. Carbon in the CO₂-absorber complex occurs to directly serve as a second carbon source only at highly negative potential. This work provides a deeper understanding of the reaction mechanisms and the nature of the reacting species at the electrode interface by quantifying the transport of species in solution and by determining the competitive reaction pathways for the electroreduction of captured and dissolved CO₂, which is necessary for the rational design of catalysts and scale-up of RCC technologies.