Numerical study on discharge characteristics and plasma chemistry in atmospheric CO2 discharges driven by pulsed voltages

In recent years, plasma technology as a new approach for CO2 splitting has attracted growing interest. The understanding of discharge characteristics and plasma chemistry is particularly important to improve the conversion of CO2 in applications. In this paper, the dissociation of CO2 driven by short pulsed voltages at atmospheric pressure is numerically investigated with 24 species and 137 reactions considered in the fluid model, to explore the discharge characteristics and plasma chemistry. The key reaction pathways of CO2 conversion are unveiled according to the simulation, and the calculated conversion and energy efficiency relying on the specific energy input agrees well with the experimental measurements. The simulation shows that by increasing the pulse rising rate of pulsed voltage, the breakdown voltage is enhanced and the densities of CO and O-2 are significantly improved with the increase in current density. From the simulation, a relatively strong electric field of 2.6 kV/cm always persists during the plateau phase to drive the heavy positive (CO2+) and negative ions (CO3-) to the electrodes, and the electric field induced by the surface charge significantly affects the discharge current during the pulse falling phase. As the duration of plateau phase increases from 200 to 1000 ns, the discharge current density during the pulse falling phase is enhanced from -20.9 to -116.0 mA/cm(2), indicating a very different discharge behavior from the atmospheric helium plasmas. This study provides deep insight into the atmospheric CO2 discharges driven by pulsed voltages, and according to the computational data the production of CO and O-2 can be effectively optimized by tailoring the waveforms of pulsed voltages in many applications.