CO2 conversion products in α and γ modes of radio frequency capacitively coupled plasma

Radio Frequency Capacitively Coupled Plasma (RF-CCP) exhibits excellent spatial uniformity, high stability, and the capability to generate plasma over large areas, making it highly promising for applications in CO2 resource utilization in space environments. This study investigates the CO2 conversion products under two typical discharge modes (α and γ modes) of RF-CCP and their product selectivity under Martian nominal pressure. The results indicate that the optical emission spectra in both α and γ modes contain CO2+, O, and CO spectral bands/lines. The overall spectral line intensity is enhanced in the γ mode compared to the α mode, indicating a higher electron density and ionization degree in the γ mode. The key product, CO, is primarily generated through electron collisions with CO2, while O2 is produced via the dissociative recombination of electrons with CO2+. After the transition from α to γ mode, the content of CO2 decreases, but the concentrations of electrons and CO2+ increase significantly. This results in CO being the dominant product in the α mode, while in the γ mode, the overall abundance of products is higher and there is a greater selectivity for O2. Therefore, by controlling the discharge mode of RF-CCP, it is possible to achieve targeted regulation of the CO2 conversion products.