Dissociation of CO2 by Argon Atmospheric Pressure Plasma Jet

The purpose of this study was to investigate the dissociation rate and efficiency of carbon dioxide (CO2) using Ar atmospheric pressure plasma jet (APPJ) at room temperature. Various process parameters, including CO2 flow rate, pulse frequency, and peak voltage, were used to study, under which the plasma characteristics, mainly electron temperature ( $T_{e}$ ), electron density ( $n_{e}$ ), and the intensity ratio of CO to CO2 ( $I_{\mathrm {CO}}$ / $I_{\mathrm {CO}2}$ ), were evaluated and correlated to the results of the dissociation rate and efficiency of CO2. The plasmas were characterized using optical emission spectroscopy (OES). In the experiment, the plasma consisted of Ar (10 slm) and CO2 (6, 9, 12, and 15 sccm). The pulse frequencies were 13.16 and 16.67 kHz, and the peak voltages of the square wave were 9, 9.5, and 10 kV. In the measurement and numerical analysis, the dissociation rate and efficiency of CO2 were measured by a newly developed way, which used a CO2 chemical sensor. The results show that the increase in CO2 flow rate would cause a decrease in plasma density due to high breakdown voltage of CO2 gas, which is not conducive to the formation of plasma. As a result, the CO2 dissociation rate and efficiency would also decrease. With the increase of pulse frequency, $n_{e}$ would be enhanced to promote more Ar atoms to be excited or ionized. These results would be advantageous toward improving the dissociation rate of CO2. According to the results obtained from $I_{\mathrm {CO}}$ / $I_{\mathrm {CO}2}$ ratio analysis, the trends were consistent with those measured and calculated dissociation efficiency and rate. To summarize, it can be concluded that the highest CO2 dissociation rate could be obtained at a low CO2 flow rate, high pulse frequency, and high peak voltage. The highest average dissociation efficiency obtained here was 67.71%, while the highest average dissociation rate was 0.48 g/h. This was obtained when the CO2 input was 6 sccm with a pulse frequency of 16.67 kHz and a peak voltage of 10 kV.