Effect of Argon or Helium on the CO₂ Conversion in a Dielectric Barrier Discharge

Abstract

This paper demonstrates that the CO 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 2 conversion, on the other hand, drops upon addition of Ar or He, which is logical due to the lower CO 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 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 2 /Ar and CO 2 /He mixtures, and the discharge gap is more filled with plasma, which enhances the possibility for CO 2 conversion. The rates of electron impact excitation–dissociation of CO 2 , estimated from the electron densities and mean electron energies, are indeed higher in the CO 2 /Ar and (to a lower extent) in the CO 2 /He mixtures, compared to the pure CO 2 plasma. Moreover, charge transfer between Ar + or Ar 2 + ions and CO 2 , followed by electron‐ion dissociative recombination of the CO 2 + ions, might also contribute to, or even be dominant for the CO 2 dissociation. All these effects can explain the higher CO 2 conversion, especially upon addition of Ar, but also upon addition of He.