Plasma Conversion of CO2 in DC Glow Discharge with Distributed Gas Injection and Pumping

Abstract

Accumulation of carbon dioxide in the Earth's atmosphere leads to an increase in the greenhouse effect and, as a consequence, to significant climate change. Thus, the demand to develop effective technologies of carbon dioxide conversion grows year to year. Additional reason for research in this direction is the intention of Mars exploration, since 96% of the Martian atmosphere is just carbon dioxide, which can be a source of oxygen, rocket fuel, and raw materials for further chemical utilization. In the present paper, the plasma conversion of carbon dioxide have been studied in the dc glow discharge at the gas pressure of 5 Torr in a chamber with distributed gas injection and evacuation from the same side for the case of narrow interelectrode gap. The conversion coefficient and the energy efficiency of the conversion were determined using mass spectrometry of the exhaust gas mixture in dependence on CO₂ flow rate and the discharge current and voltage. Maximum conversion rate was up to 78% while the energy efficiency of the conversion was always less than 2%. It was found that the discharge at this pressure can operate in normal and abnormal modes and the transition between the modes corresponds just to the maximum value of the conversion coefficient for a given gas flow. It was shown that even in anomalous regime, when the cathode is completely covered by the discharge, the discharge contraction occurs in whole range of parameters studied. The anode glow and the plasma column outside the cathode layer occupy the central part of the discharge only that reduces the conversion efficiency. Optical emission spectra from the carbon dioxide plasma were measured in the range of 200-1000 nm, which allowed to make a conclusion that the Oxygen atom emission is mostly origins from the exited atoms appearing after dissociation rather than after electron impact excitation.