Effect of Argon or Helium on the CO sub(2) Conversion in a Dielectric Barrier Discharge

This paper demonstrates that the CO sub(2) conversion in a dielectric barrier discharge rises drastically upon addition of Ar or He, and the effect is more pronounced for Ar than for He. The effective CO sub(2) conversion, on the other hand, drops upon addition of Ar or He, which is logical due to the lower CO sub(2) content in the gas mixture, and the same is true for the energy efficiency, because a considerable fraction of the energy is then consumed into ionization/excitation of Ar or He atoms. The higher absolute CO sub(2) conversion upon addition of Ar or He can be explained by studying in detail the Lissajous plots and the current profiles. The breakdown voltage is lower in the CO sub(2)/Ar and CO sub(2)/He mixtures, and the discharge gap is more filled with plasma, which enhances the possibility for CO sub(2) conversion. The rates of electron impact excitation-dissociation of CO sub(2), estimated from the electron densities and mean electron energies, are indeed higher in the CO sub(2)/Ar and (to a lower extent) in the CO sub(2)/He mixtures, compared to the pure CO sub(2) plasma. Moreover, charge transfer between Ar super(+) or Ar sub(2) super(+) ions and CO sub(2), followed by electron-ion dissociative recombination of the CO sub(2) super(+) ions, might also contribute to, or even be dominant for the CO sub(2) dissociation. All these effects can explain the higher CO sub(2) conversion, especially upon addition of Ar, but also upon addition of He. This paper presents the effect of Ar and He addition on the CO sub(2) conversion and energy efficiency in a dielectric barrier discharge. The observed trends are explained from the Lissajous plots and the current profiles, and by analyzing the rates of electron impact dissociation of CO sub(2) in the pure CO sub(2), CO sub(2)/Ar, and CO sub(2)/He plasmas. Finally, charge transfer between the rare gas ions and CO sub(2), followed by electron-ion dissociative recombination of the CO sub(2) super(+) ions, is also discussed.