Comparative study on discharge characteristics of low pressure CO₂ driven by sinusoidal AC voltage: DBD and bare electrode structure

Abstract

The low-pressure atmosphere on Mars, rich in CO2 (~95%), makes the in-situ resource utilization of Martian CO2 and the improvement of oxidation attract widespread attention. It contributes to construct the Mars base which will support the deep space exploration. Conversion of CO2 based on high voltage discharge has the advantages of environmental friendliness, high efficiency and long service life. It has application potential in the in-situ conversion and utilization of Martian CO2 resources. We simulate the CO2 atmosphere of Mars where the pressure is fixed at 1kPa and the temperature is maintained at room temperature. A comparative study was carried out on the discharge characteristics of two typical electrode structures (with/without barrier dielectric) driven by 20kHz AC voltage. Combined with numerical simulation, the CO2 discharge characteristics, products and their conversion pathways were analyzed. The results show that the discharge mode changes from single discharge during each half cycle to multi discharge pulses after adding the barrier dielectric. Each discharge pulse of the multi pulses corresponds to a random discharge channel, which is induced by the distorted electric field of accumulated charge on the dielectric surface and the space charge. The accumulated charge on the dielectric surface promotes the primary discharge and inhibits the secondary discharge. Space charge will be conducive to the occurrence of secondary discharge. The main products in discharge process include CO%2B 2, CO, O2, C, O, etc. Among the products, CO is mainly produced by the attachment decomposition reaction of energetic electrons and CO2 at the boundary of cathode falling zone, and the contribution rate of the reaction can reach about 95%. O2 is mainly generated by the compound decomposition reaction of electrons and CO%2B 2 near the instantaneous anode surface or instantaneous anode side dielectric surface, and the contribution rate of the reaction can reach about 98%. It is further found that the dielectric does not change the generation position and dominant reaction pathway of the two main products, but will reduce the electron density (from 5.6×1016?m-3 to 0.9×1016?m-3) and electron temperature (from 17.2eV to 11.7eV) at the boundary of the cathode falling region, resulting in the reduction of CO production. At the same time, the deposited power is reduced, resulting in insufficient CO%2B 2 yield near the instantaneous anode surface and instantaneous anode side dielectric surface and further reduced O2 generation.