Understanding the Effect of Alkali Metal Addition on the Electrochemical Upgrade of MEA-Captured CO2

The growth of industries over the past century has led to an ever-increasing amount of CO₂ in the atmosphere. In 2020, the concentration of CO₂ reached its highest level at 412.5 ppm (part per million). This increase in carbon has a direct effect on climate change. We are expected to remain dependent on familiar CO₂-producing energy sources like oil, natural gas, and coal for the foreseeable future. Therefore, CO₂ management remains the best option for influencing climate change in the upcoming decades.

The use of aqueous monoethanolamine (MEA) is one of the main ways that CO₂ is currently captured. One of the main questions which remain in CO₂ management is what to do with the captured CO₂. One proposed solution is to electrochemically upgrade CO₂ to CO, which can then be used in other chemical processes. However, this process’s energy requirements are unreasonable for commercial implementation. Recent work has shown that adding alkali metals to a system with a charged electrode and MEA-captured CO₂ improves the Faradaic efficiency in the electrochemical upgrade of CO₂¹. It is still unclear what effect the alkali metals had on the electron double layer (EDL) structure that led to this enhancement. This lack of understanding has made it difficult to improve this process.

In this study, we use molecular dynamics to simulate mixtures of MEA-CO₂, and different alkali metals (Li+, Na+, K+, Rb+, Cs+) sandwiched between 2 electrodes at varying potentials to understand the EDL structure of MEA-captured CO₂ with alkali metals on an electrode surface. By studying each system's electrical response, we can plot the potential and capacitance across the system. From this data, we gain a foundational understanding of the effect different alkali metals and electrode charges had on this system. This foundational understanding allows for improving and implementing this vital chemical technology, which will be a significant step toward a cleaner atmosphere.

(1) Lee, G.; Li, Y. C.; Kim, J.-Y.; Peng, T.; Nam, D.-H.; Sedighian Rasouli, A.; Li, F.; Luo, M.; Ip, A. H.; Joo, Y.-C.; Sargent, E. H. Electrochemical Upgrade of CO2 from Amine Capture Solution. Nat. Energy 2021, 6 (1), 46–53. https://doi.org/10.1038/s41560-020-00735-z.