Unveiling Direct and Indirect Pathways of Electrochemical CO₂ Reduction in Amine-Based Carbon Capture Electrolytes

Investigating the origins of carbon sources and mechanistic pathways in the electrochemical conversion of CO₂ from carbon capture electrolyte is essential for the rational design, optimization, and scale-up of reactive carbon capture processes; however, these mechanisms still remain inadequately understood. Therefore, clarifying the carbon source and reaction pathway is vital for efficient electrochemical CO₂ conversion in carbon capture electrolyte. In this study, in situ/operando attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), surface-enhanced Raman spectroscopy (SERS), and online differential electrochemical mass spectrometry (DEMS) are employed to identify (carbon sources) and elucidate reaction pathways during the electrochemical reduction of amine-CO₂ capture electrolyte. In electrolytes containing primary and secondary amines, CO₂ is captured to form carbamates (R₁R₂NCOO^-). These carbamates serve as key electrochemically active species during the electrochemical reduction process, which are directly reduced to carbon monoxide via a direct pathway. In electrolytes containing tertiary or sterically hindered amines, CO₂ is captured to form bicarbonate (HCO₃ ^-). This bicarbonate then undergoes an indirect reduction pathway: it first releases CO₂ in situ at the electrode surface. This released CO₂ acts as the primary reactive intermediate and is subsequently reduced to carbon monoxide. Notably, in both direct and indirect pathways, protonated amines serve as the primary proton source for the hydrogen evolution reaction (HER). This study employs multiple in situ/operando experimental techniques to demonstrate how different types of amines influence electrochemically active species and pathways during electrochemical reduction in carbon capture electrolyte. The findings provide deeper and novel insights into the mechanism of amine-based reactive carbon capture, providing guidance for optimizing dual-functional electrolytes, electrocatalysts, and reactor designs in reactive carbon capture.