## 3 Results and Discussion  
### Experimental Results  
#### Gas Chromatography  
The inlet and outlet gases were analyzed with the gas chromatograph GC, Agilent 6890 N. The areas of chromatogram peaks are proportional to the concentrations of compounds in these gases. Then, the CO\({}_{2}\) conversion factor can be calculated from the areas of CO\({}_{2}\) peak, \(\left[CO_{2}\right]_{in}\) and \(\left[CO_{2}\right]_{out}\) by [33]:  
\[X_{CO_{2}}(\%)=\frac{\left[CO_{2}\right]_{in}-\left[CO_{2}\right]_{out}}{ \left[CO_{2}\right]_{in}}\times 100 \tag{24}\]  
In a similar way, the selectivity of CO and O\({}_{2}\) species were calculated by [32]:  
\[\begin{array}{c}S_{CO}(\%)=0.5\frac{\left[CO\right]_{out}}{\left[CO_{2} \right]_{in}-\left[CO_{2}\right]_{out}}\times 100\\ S_{O_{2}}(\%)=\frac{\left[O\right]_{out}}{\left[CO_{2}\right]_{in}-\left[CO_{2 }\right]_{out}}\times 100\end{array} \tag{25}\]  
Figure 4a shows the conversion factor of CO\({}_{2}\) and the selectivity of CO and O\({}_{2}\) obtained by gas chromatography for an applied voltage between 10 and 22 kV. A maximum value of the conversion factor of 25% was found at 22 kV voltage. This factor was also compared with that obtained by the 2-D model (see Section 3.2).  
The energy efficiency of this technique is given by [32]:  
\[\eta(\%)=X_{CO_{2}}(\%)\ \frac{\Delta H_{R}}{SEI*V_{m}} \tag{26}\]  
where \(V_{m}\) is the molar volume, that can be considered 24.5 L/mol, \(\Delta H_{R}\) is the reaction enthalpy for CO\({}_{2}\) splitting (CO\({}_{2}\)\(\rightarrow\) CO + \(\frac{1}{2}\)O\({}_{2}\)), i.e., 279.8 kJ/mol, and SEI is the specific energy input, that is calculated from discharge power and gas flow rate:  
\[SEI=\frac{Power}{Flow} \tag{27}\]  
The power consumed in discharge was estimated from measurements of the electrical current and HV voltage between the electrodes of the AC-PPP reactor. Then the energy  
Figure 4: (**a**) Dependence of CO\({}_{2}\) conversion and CO/O\({}_{2}\) selectivity on applied AC voltage. (**b**) Experimental dependence of energy efficiency on applied AC voltage.  
efficiency could be calculated. Table 3 shows the values of this efficiency for different applied voltages. In this case, the maximum efficiency was 6.1% for an applied voltage of 22 kV. This experimental energy efficiency of CO2 conversion is plotted in Figure 4b.  
In the review paper by [PERSON] et al. [7], a comparison of the conversion factor and the energy efficiency of different plasmas technologies for \(CO_{2}\) remediation was performed. Typical plasma technologies used for this purpose are dielectric barrier discharges (DBDs), microwave discharges (MWs), and gliding arc discharges (GAs). These systems are compared with the proposed AC-PPP reactor in Table 4.  
In general, the DBD plasma has a high conversion factor, but it is not energy efficient. Its maximum energy efficiency values were approximately 6%. The MW is the technology with the highest CO2 conversion with systems that have up to 80% energy efficiency. Some systems can also achieve a high energy efficiency of 40%, but the typical values for this technology are less than 10%. The power consumption of this system is usually very high. The worst CO2 conversion is obtained for the GA discharge. The reactor introduced in this study had a conversion factor value greater than GA and close to the maximum for DBD. Energy efficiency is low compared to the other technologies, but it has the advantages of its simple design and low power consumption, which are important factors for its industrial implementation.