The catalytic role of tungsten electrode material in the plasmachemical activity of a pulsed corona discharge in water

Abstract

The effects of tungsten material used as a high-voltage needle electrode on the production of hydrogen peroxide and the degradation of dimethylsulfoxide (DMSO) caused by a pulsed corona discharge in water were investigated. A reactor of needle-plate electrode geometry was used. The erosion of the tungsten electrodes by the discharge was evaluated. The yields of H 2 O 2 production and the decomposition of DMSO by the discharge, which were obtained using the tungsten electrodes, were compared with those determined for titanium electrodes. The electrode erosion increased significantly with an increase in the solution conductivity. A large fraction (50-70%) of the eroded tungsten electrode material was released into the solution in dissolved form as tungstate WO 2− 4 ions. A correlation between the amount of eroded tungsten material released into the solution and the chemical effects induced by the discharge was determined. Lower yields of H 2 O 2 and a higher degradation of DMSO by the discharge were obtained using the tungsten electrodes than were determined using titanium electrodes. Tungstate ions were shown to play a dominant role in the decomposition of H 2 O 2 , which was produced by the discharge using a tungsten electrode. The higher degradation of DMSO that was determined for tungsten was attributed to the tungstate-catalyzed oxidation of DMSO by H 2 O 2 , in addition to the oxidation of DMSO by OH radicals. Such a mechanism was supported by the detection of degradation by-products of DMSO (methanesulfonate, sulfate and dimethyl sulfone). The catalytic role of tungstate ions in the plasmachemical activity of the discharge generated using a tungsten electrode was also demonstrated on a pH-dependent decomposition of H 2 O 2 and DMSO.

Comparison and Evaluation of Electrode Erosion Under High-Pulsed Current Discharges in Air and Water Mediums

“…Meantime, some oxides of metal sediments lead to other mass loss of eroded electrodes. This result is almost consistent with [15], where the release rate of WO 2− 4 from the W electrode caused by erosion in the discharge indicates that 54% of the tungsten material was released into the water in dissolved form as tungstate ions.…”

“…When the tungsten electrode is immersed in H 2 O 2 solution, hydrogen peroxide is a positive feedback with the metal material, and the tungsten electrode might be oxidized in the solution to turn into WO 2− 4 ions [15] W…”

“…However, there is not much research on the characteristics and mechanism of the Manuscript electrode erosion under pulsed current in water. The electrode erosion rate under pulsed discharge in water has a great difference from that in gas [12]- [15]. The erosion degree and roughness level of the electrodes are closely related to the prebreakdown voltage, reliability, delay time, breakdown field strength, etc.…”

“…Winands et al [17] have studied the erosion characteristics of brass electrodes in air medium, and found that for one electrode about 40 cm 3 is likely to be evaporated with a pulse duration of 100 ns, and for a peak current of 300 A, a total charge transfer of 10 6 C. Goryachev et al [18] have reported that an increase in the pulse length increases the specific erosion, and the dependence between them is almost linear. Lukes et al [15] have evaluated that the erosion rate of the tungsten needle-plate electrode in a pulsed corona discharge in water is 1.9 μg/s with solution conductivity of 500 μS/cm. A higher solution conductivity means a higher concentration of ions in the liquid, causing a larger discharge current; meanwhile, with the increase of solution conductivity, the peak current amplitude strongly strengthens, and pulsewidth of the prebreakdown voltage is decreased [19].…”

Analysis of a gas-liquid film plasma reactor for organic compound oxidation

“…8 and 9). The H2O2 concentrations in the pure water cases show that this species is stable and does not dissociate or decrease in concentration over time after removal from the plasma, indicating that there is no significant reaction of any iron sputtered from the electrodes in contrast to reported experiments in direct discharge in liquids [67][68][69]. Adding…”