Advancing CO₂ to CO conversion: Detailed impact analysis of atmospheric molecules in an ultrashort pulse laser filament plasma reactor

Capturing carbon dioxide (CO₂) and transforming it into valuable fuels offers a dual benefit: the potential to reduce atmospheric CO₂ levels and decrease our dependency on fossil fuels. Plasma-assisted CO₂ to carbon monoxide (CO) conversion stands out within the various CO₂ recycling methods, with research primarily emphasizing its energy efficiency and conversion efficacy. However, investigations of CO₂ conversion under real air conditions are relatively scarce, and the effects of the other atmospheric molecules on the CO₂ conversion process require further exploration. We have induced plasma chemical reactions by generating ultrashort pulse laser filaments inside a sealed-off cavity with variable air pressures. Simultaneously, we applied mid-infrared laser absorption spectroscopy to monitor the time evolution of the reaction products. The peak CO₂-to-CO conversion ratio was achieved at an air pressure of 8000 Pa, which resulted in a CO concentration of 82 ppm. The experimental results suggested that nitrogen (N₂) plays a promoting role in CO₂-to-CO conversion, while the presence of oxygen (O₂) seems to hinder the process. The hydroxyl radical (OH) arising from water molecules (H₂O) limits the accumulation of CO at lower air pressures. However, at higher air pressures, the reduced OH radical concentration shows negligible impact on the CO₂-to-CO conversion ratios. In addition, the study revealed that atmospheric plasmas produce a high concentration of hydrogen cyanide (HCN), which is directly proportional to the levels of ambient humidity. This research contributes to the development of strategies to mitigate the production of harmful gases like HCN in CO₂ conversion, thereby promoting the ecofriendly conversion of atmospheric CO₂.