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Plasma in contact with water has been widely investigated for the production of reactive species such as H2O2 and OH radicals [1]. In this research, both positive and negative pulsed corona discharges, with duration of the order of microseconds, were used to investigate hydrogen peroxide formation in a pin-to-water electrode system.
Under positive pulsed corona discharge, hydrogen peroxide formation was observed to increase linearly with time and reached 15 µmol, 5.5 µmol, 9.9 µmol and 11.5 µmol after a treatment time of one hour in oxygen, air, nitrogen and helium, respectively. The corresponding ratio of the electric charge transferred to the water surface and H2O2 formed (yield) is 1:1.8, 1:1, 1:15 and 1:1.4. The OH radical dimerization contributes to 7%, 86% and 46% of the H2O2 formation using air, nitrogen and helium, respectively. The solution conductivity was observed to increase linearly with time under positive corona discharge and reached 200 µScm-1 and 150 µScm-1 in air and nitrogen, respectively; no change was observed in helium.
The formation of H2O2 under negative pulsed corona discharge is generally much lower than that for positive polarity, being 8 µmol, 0.2 µmol, 1.1 µmol and 2.3 µmol for one hour of treatment in oxygen, air, nitrogen and helium, respectively; no significant change was observed to the solution conductivity. The results highlight the polarity effect, suggesting the involvement of different reaction mechanisms in H2O2 formation for positive and negative pulsed corona discharges.
[1] S. M. Thagard and K. Takashima. “Chemistry of the Positive and Negative Electrical Discharges Formed in Liquid Water and Above a Gas–Liquid Surface Plasma”, Chemistry and Plasma Processing, 2009, 29, pp. 455–473.
