A surface mechanism for O-3 production with N-2 addition in dielectric barrier discharges

Ozone, O-3, is a strong oxidizing agent often used for water purification. O-3 is typically produced in dielectric barrier discharges (DBDs) by electron-impact dissociation of O-2, followed by three-body association reactions between O and O-2. Previous studies on O-3 formation in low-temperature plasma DBDs have shown that O-3 concentrations can drop to nearly zero after continued operation, termed the ozone-zero phenomenon (OZP). Including small (<4%) admixtures of N-2 can suppress this phenomenon and increase the O-3 production relative to using pure O-2 in spite of power deposition being diverted from O-2 to N-2 and the production of nitrogen oxides, N (x) O (y) . The OZP is hypothesized to occur because O-3 is destroyed on the surfaces in contact with the plasma. Including N-2 in the gas mixture enables N atoms to occupy surface sites that would otherwise participate in O-3 destruction. The effect of N-2 in ozone-producing DBDs was computationally investigated using a global plasma chemistry model. A general surface reaction mechanism is proposed to explain the increase in O-3 production with N-2 admixtures. The mechanism includes O-3 formation and destruction on the surfaces, adsorption and recombination of O and N, desorption of O-2 and N-2, and NO (x) reactions. Without these reactions on the surface, the density of O-3 monotonically decreases with increasing N-2 admixture due to power absorption by N-2 leading to the formation of nitrogen oxides. With N-based surface chemistry, the concentrations of O-3 are maximum with a few tenths of percent of N-2 depending on the O-3 destruction probability on the surface. The consequences of the surface chemistry on ozone production are less than the effect of gas temperature without surface processes. An increase in the O-3 density with N-based surface chemistry occurs when the surface destruction probability of O-3 or the surface roughness was decreased.

Automated summary

Ozone (O-3) is a strong oxidizing agent commonly used for water purification. Research has shown that the concentration of O-3 can drop to nearly zero after continued operation in low-temperature plasma DBDs, known as the ozone-zero phenomenon (OZP). However, by adding a small amount of N-2, the OZP can be suppressed and O-3 production can be increased. This is hypothesized to occur because N-2 prevents the destruction of O-3 on the surfaces in contact with the plasma.