The valorization of CO₂ into graphitic carbon quantum dots (CQDs) in a monoethanolamine (MEA)-CO₂ electrochemical system was successfully demonstrated at both lab-scale (50 mL) and a scaled-up 2 L setup, yielding approximately 10% CQDs from CO₂ conversion with energy cost as low as 2.1 MJ/kg CQDs. This process utilized chemisorbed CO₂ as the carbon source and required conditions that promoted excess electron accumulation on a confined Ag surface, stabilized by non-reducible N⁺-containing salts such as NH₄⁺ or [BMIM]+. Under these conditions, an intense localized electric field enhanced the electrochemical reduction of MEA-CO₂ adducts (MEACOO⁻) to gaseous CO while facilitating CO disproportionation and the interaction of CO* with CC*, leading to the formation of -CCCO linear acetylenic carbon species under elevated CO coverage at ambient conditions. Collaborative density functional theory (DFT) calculations suggest that these linear carbon species detach from the Ag surface into the electrolyte, where they undergo intermolecular cross-linking to form graphitic CQDs. The CQDs were efficiently separated and collected via dialysis and freeze-drying. The CO2-derived graphitic CQDs have been successfully used as strengthening additives for cement composites for the development of low carbon emission, high-performance construction materials. The capacity to convert captured CO2 into high-value carbon nanomaterials with minimal energy demand presents a novel approach to CO₂ capture and utilization, offering a promising pathway toward sustainable carbon management and negative carbon emissions.
