CO2 Dissociation in Barrier Corona Discharges: Effect of Elevated Pressures in CO2/Ar Mixtures

Abstract

The formation of carbon monoxide, oxygen and ozone in a barrier corona discharge (BCD) operating in pure carbon dioxide (CO2) and binary mixtures of CO2 and argon is studied. The asymmetric electrode configuration of the BCDs allows plasma operation at pressures exceeding 1 atm, up to 6 bar, at moderate high-voltage amplitudes below 15 kV. Charge–voltage plots and an equivalent circuit model are employed to characterize the electrical parameters at different pressures and gas compositions. Depending on these conditions and the voltage amplitude, full or partial coverage of the electrodes with plasma is obtained. The existence of an optimum pressure for power dissipation for each given operation voltage amplitude and gas composition can be confirmed and explained by the equivalent circuit model. Increasing the CO2 concentration in the working gas increases the mean reduced electric field strength E/N while pressure reduces it in the BCD. The CO2 conversion shows a maximum efficiency of about 4% at 1.5 bar for the gas mixture Ar/CO2 = 1:1 and a voltage amplitude of about 10 kV. The calculation of thermodynamic equilibrium parameters reveals that a relatively small increase in pressure can affect both, the equilibrium parameters and the reaction rates. As a result, the specific required energy for the reaction ($$\Delta \mathrm{H}/\mathrm{SEI}$$ Δ H / SEI ) shows an optimum, but only 8% of the electrical input energy is spent for CO2 dissociation at these optimum conditions.

Electrical characterization and imaging of discharge morphology in a small-scale packed bed dielectric barrier discharge

“…We pay attention to the observation in many DBD arrangements that at low over-voltages only a distinct part of the electrode cross section is illuminated by plasma, which is related with a lower discharge power [40]. As also discussed in [42], the most likely reasons for this effect are slight variations of the discharge gap width and the thickness of the dielectric barrier due to tolerances of the tube walls, non-parallel alignments, improper electrode adhesion, local surface contaminations or edge effects at the electrodes. The extended equivalent circuit is given in figure 10(a).…”