CO₂ Reduction to Higher Hydrocarbons by Plasma Discharge in Carbonated Water

By discharging nanosecond high-voltage pulses in CO2-saturated water, we observe CO2 reduction to higher-order hydrocarbons, including acetic acid, formic acid, and oxalate. Here, the plasma emission spectra exhibit Swan bands, which correspond to C2 species, indicating that in addition to reducing CO2, C2-species are formed, which presents the possibility of converting a notorious greenhouse gas into liquid (i.e., dense) hydrocarbon fuels. In order to characterize various hydrocarbon products formed in this process, cryogenic NMR spectroscopy and liquid ion chromatography are performed ex situ. Here, we observe clear peaks corresponding to formic acid (CH2O2) and acetic acid (CH3COOH). We have also observed the presence of formate (HCO2–), acetate (C2H3O2–), and oxalate (C2O42–) using liquid ion chromatography. Plasma emission spectroscopy exhibits spectral signatures associated with atomic hydrogen and atomic oxygen due to the plasma discharge in water, which facilitate (and compete with) the CO2-to-hydrocarbon conversion.