Nanosecond pulsed plasma discharge over a flowing water film: Plasma characterization, hydrodynamic analysis, and hydrogen peroxide generation

Plasma discharges generated by moderate frequency, low energy pulses in a flowing carrier gas with liquid water have been shown capable of producing hydrogen peroxide at reasonably high energy yields. The leading hypothesis for the success of this production method is that the liquid water serves as both a source of water vapor from which hydroxyl radicals can be produced during the on cycle of the pulsed discharge, as well as a sink for hydrogen peroxide generated from these radicals during the off cycle of the pulse. Many reactor designs have been explored with various gas-liquid contact schemes in order to enhance the overall efficiency of this process. A continuously flowing, liquid film, reactor has been developed in our laboratory which we believe has a number of significant benefits over the previously explored configurations. In previous studies with this flowing film reactor, an automobile ignition coil was used to generate the pulsed plasma discharge. While this ignition coil provided high energy yields for hydrogen peroxide production, analysis of the system was difficult due to the large pulse widths required by the coil. Multiple arcing events were found to occur within these microsecond pulse widths which were extremely difficult to control or accurately measure and quantify. For this reason a nanosecond power supply is utilized in this study which is capable independently varying pulse width, input voltage, and pulse repetition. With this controllable power supply the plasma properties such as temperature and electron density can be measured for various input pulse characteristics to study the resulting effect on hydrogen peroxide generation on a per arc basis. High speed imaging of the hydrodynamic properties of the flowing liquid film is also performed in order to calculate gas and liquid residence times and provide physical insight on the gas-liquid interface across which the plasma propagates.