Study of Hydrogen Peroxide Generation by Water Surface Discharge

The fundamental physics underlying non-thermal plasmas produced by pulsed discharges at atmospheric pressure is of great interest, especially considering the technological and environmental applications of these plasmas. Discharge dynamics is highly dependent on experimental conditions, such as the propagation medium and the voltage polarity. Herein, we investigate pulsed nanosecond discharges produced by a negatively polarized voltage in a medium of air in-contact with water. Electrical and optical characterization of the discharges is achieved using the appropriate probes and ultrafast imaging, respectively. The time-integrated images are acquired under varying conditions of applied voltage, and the discharge emission is shown to be a homogenous disk at voltages between −4 and −15 kV. When the voltage is increased (absolute value) beyond −15 kV, the homogeneous emission is superimposed with filaments. The temporal evolution of the discharge emission (1 ns integration time) shows that it remains homogeneous and has a ring-like ionization front. At higher voltages and during the falling period, the discharge reignites as filaments that significantly elongate and decrease in intensity until extinguishment. A comparison of discharge emissions obtained at positive and negative polarities indicates that the features of both may be controlled by manipulating the space charge formation dynamics.

Atmospheric water surface discharge is a promising method for water treatment. The selection of discharge gap distance must take a pair of conflicting aspects into account: the chemical efficiency grows as the discharge gap distance decreases, while the spark breakdown voltage decreases as the gap distance decreases. To raise the spark breakdown voltage and the chemical efficiency of atmospheric pressure water surface discharge, resistive barrier discharge is introduced in this paper. Both the high voltage electrode and the ground electrode are suspended above water surface to form an electrode-water-electrode discharge system. The water layer plays the role of a resistive barrier which inhibits the growth rate of discharge current as voltage increases. Experiments conducted at different discharge gap distances and water conductivities indicate that both the spark breakdown voltage and the chemical efficiency are remarkably raised in comparison with traditional water surface discharge. After parameter optimization, the discharge reactor is scaled up with activated carbon fiber electrodes and advantages of water resistive barrier discharge are kept.

This paper reports the streamer discharge generation in different types reactor and evaluate the chemical efficiency. We have used point to plane electrode arrangement for generation of underwater discharge (UWD) and water surface discharge (WSD). We have also generated gas bubbling discharge (GBD) in water employing a point to mesh electrode arrangement. A magnetic compression pulsed power modulator able to deliver 25kV, 100Hz was used as a high voltage pulse source to initiate discharge in reactors.Chemical efficiency of streamer discharge plasma was evaluated in UWD, WSD and GBD reactors by measurement of hydrogen peroxide (H 2 O 2 ) from discharged water. The amount of H 2 O 2 indicates the formation of chemical species by discharge plasma in all reactors. In addition, orange II organic dye solution was treated as polluted water sample to understand the plasma chemical activity of streamer discharge generated in different reactors. The experimental results reveal that the chemical species formation and degradation of orange II dye was influenced by streamer discharge propagation in underwater, water surface and gas bubbling reactors depending on their physical processes. Highest production of H 2 O 2 was in UWD and faster degradation of orange II dye was in WSD.

High-pressure nanosecond pulsed discharges (NPDs) have attracted increasing attention in recent years due to their wide potential applications. In this study, a barrier-free NPD in pure helium plasma at 120 Torr was numerically investigated by a one-dimensional self-consistent fluid model, and its current–voltage characteristics show very different behaviors from those in pulsed dielectric barrier discharges (DBDs), indicating an entirely distinctive discharge evolution in pulsed discharges with or without barriers on electrodes. Without the control of barriers, the computational data suggest that the discharge current increases very sharply during the plateau phase of the pulsed voltage and reaches its peak value at approximately the instant when the pulsed voltage starts to drop, together with a gradual reduction in the sheath thickness and an increase in electric field in the sheath region, which is in good agreement with experimental observations. By increasing the voltage plateau width and repetition frequency, the discharge current density from the simulation can be substantially enhanced, which cannot be observed in conventional pulsed DBDs, and the spatial distributions of the electric field and charged particles are given to unravel the underlying physics. From the computational data, the distinctive discharge characteristics in barrier-free NPDs are deeply understood, and could be further optimized by tailoring the waveform of the pulsed voltage to obtain desirable plasmas for applications.

In recent years, electrical discharge plasmas have been used as an effective method for treating water containing environmental pollutants. Some researchers have reported that species with high oxidation potential such as OH radical, O radical, and O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> are produced by pulsed discharge plasmas generated in or at water surface. Effective treatment of polluted water can be expected by these species. Previously, the degradation of phenol by nano-second (ns) pulsed discharge on the surface of solution was studied in our laboratory [1], with positive results for many methods. In this work, ns pulsed discharge was generated under a wastewater shower. The system aims to be more effective at water-surface treatment than ns pulsed discharge. This experiment utilized an ns pulse generator with a pulse duration of 5ns to decompose acetic acid, sodium dodecyl benzene sulfonate, and PFOS in an aqueous solution. In the presentation, the results of water treatment using 5 ns pulsed discharge and water shower will be reported.

This study investigates the paracetamol removal efficiency by multi-tip pulsed corona discharges, highlighting the conditions avoiding mutual effects between two consecutive streamer branching discharges generated by each tip. The results show that the production of reactive oxygen and nitrogen species (RONS) in the liquid phase and the efficiency of paracetamol removal are influenced by the distance between two contiguous tips due to the mutual effects for small inter-tip distances between 4 mm and 8 mm in the case of a fixed inter-electrode distance of 5 mm (i.e. distance between the tip summit and the water surface). Beyond an inter-tip distance of 12 mm (over twice the gap distance), the mutual effects of branching discharges were no longer observed since the field lines did not overlap, making the production and absorption of liquid-phase species more efficient. Furthermore, RONS production was almost linear when moving from one to four tip electrodes: [H2O2]1tip: 0.52 mg l–1 versus [H2O2]4tips: 1.99 mg l–1, a ratio of 3.82. Optimum values were reached for an inter-tip distance of 16 mm. In this case, the enhancement factor in this reactor configuration is the surface integration between the plasma and the liquid surface to be treated. Furthermore, the results show a quasi-exponential increase in the percentage of paracetamol degradation as a function of the number of electrodes, from 4% with a mono-tip configuration to over 78% for a treatment with a four tip one.

Discharge in dielectric liquid is an active field of research involved in many technological applications. Such multiple discharges are often applied during an experiment and that the electrode and liquid are altered by these stochastically behaving discharges. Therefore, it is important to address the variation of discharge characteristics as a function of discharge occurrence. In this study we analyze the electrical characteristics of multiple discharges run at low repetition rate (5 Hz) in a liquid of known initial composition using an electrode with a specific geometry. The discharges are run continuously until they fail to occur due to the increase in gap distance, and the recorded voltage and current waveforms are processed using an algorithm in order to determine the probability of discharge occurrence, breakdown voltage, discharge current, and discharge delay. The injected charge and energy of each discharge are also calculated. Furthermore, the effects of applied voltage, pulse width, electrode configuration, and liquid composition on the characteristics of the discharge are investigated. The obtained results demonstrate that the highest and lowest numbers of occurred discharges are achieved using the plate-to-plate and pin-to-pin configurations, respectively. Moreover, the composition of the liquid has an appreciable effect on the discharge current, as well as on electrode erosion. For discharges in water and cyclohexane, we measured the lowest and highest current, respectively. As for the erosion rate, it was comparable for the three liquid hydrocarbons but relatively smaller than that in water. The plot of breakdown voltage as a function of discharge current varies depending on the discharge parameters and displays regions that may be linked to the ignition mechanisms. The original data reported herein is of great significance for various applications that utilize repetitive discharges in liquid.

In this paper, sealed-off laser sources based on pulsed surface discharge with expanding plasma are described. Plasma dynamics is analyzed. Data on electron number density obtained in our experiments are presented. Experimental results on laser action in plasma are discussed. Formation of inverse population as well as influence of plasma expansion on level population are considered. A construction of laser tube with pulsed surface discharge and additional illumination lamp is proposed. Data obtained with such a tube are presented.

Needle-to-plane geometry has been widely investigated and used in underwater pulsed discharges. The position relationship between the needle tip and insulation layer significantly affects the discharge patterns. We carried out experiments on underwater pulsed discharge with the needle tip protruding from, recessing into, and flushing with the insulating tube. The results are as follows. First, underwater pulsed discharge has a strong randomness under the experimental conditions. Different discharge patterns appeared under the same experimental environment. Second, recession into the insulator surface led to a higher probability of occurrence but a lower strength of spark discharge than protrusion. Third, between the needle tip protruding from and recessing into the insulation material, the average speed of propagation of underwater pulsed spark discharge decreased by an order of magnitude. The study shows that the optimum length of needle tip protruding from the insulation layer is 1 mm to obtain a strong underwater pulsed spark discharge.

Nanosecond pulsed streamer discharge has unique characteristics that differentiate it from longer discharges. The very fast voltage rise time, peak voltage plateau, short pulse duration, and fast fall time enable a large volume of uniform nonthermal plasma generation at atmospheric pressure. This review explains the physics of nanosecond discharge plasma through experimental and simulated studies for plasma processing techniques. The following are discussed and compared between sub-microsecond and nanosecond discharge plasma: discharge phase transition, discharge propagation, production of chemically active species, temperature change of gas during plasma propagation, electrode geometry, effect of voltage rise rate, voltage polarities, and N2/O2 gas composition ratio in air seeding gas. Nanosecond pulse discharge plasma is characterized by a considerably faster streamer head propagation velocity and reduced gas heating, resulting in a higher energy efficiency for plasma processing. Ozone generation, nitric oxide treatment and volatile organic compound treatment results are given as examples of plasma processing.

Plasma‐activated water (PAW) has been utilised in various application fields, and a deep understanding on the plasma chemistry is the foundation of application‐orientated optimisation. In this paper, a global model is built to study the chemical properties of PAW produced by a dielectric barrier discharge that is powered by nanosecond voltage pulses. The applied voltage is firstly repeated with 10 kHz frequency for 100 s, and then shut down for 200 s afterglow, providing a long‐term evolution regarding the production and consumption of some typical reactive oxygen/nitrogen species (RONS) in PAW. The calculated results agree principally with experimental measurements from literature. During the pulsed discharge, the water gradually acidises, and the long‐lived species accumulate; while in the afterglow, most of the aqueous RONS decay rapidly, except for O 3aq , , H 2 O 2aq and N 2 O aq , which might be the main sources to sustain long‐term effects. Furthermore, the effects of applied voltage and gap distance on RONS are investigated. Correlation analyses from Pearson correlation coefficient indicate that gaseous RONS are more sensitive to the gap distance, while the aqueous ones are more sensitive to the voltage amplitude, suggesting the possibility to independently regulating the gaseous and aqueous chemistry.

We study pulsed positive discharges in air in a cylindrically symmetric setup with an electrode needle close (about 1 mm) above the top of a dielectric cylindrical rod of 4 mm in diameter mounted at its bottom on a grounded plate electrode. We present ICCD (intensified charge-coupled device) pictures and evaluations of experiments as well as simulations with a fluid discharge model; the simulations use cylindrical symmetry. In the experiments, there is an initial inception cloud phase, where the cylindrical symmetry is maintained, and later a streamer phase, where it is broken spontaneously. At 75–150 mbar, discharges with cylindrical symmetry are not attracted to the dielectric rod, but move away from it. The dielectric rod plays the sole role of an obstacle that shades (in the context of photoionization) a cone-shaped part of the inception cloud; the cone size is determined by the geometry of the setup. The material properties of the dielectric rod, such as its dielectric permittivity and the efficiency of the photon induced secondary electron emission do not have a noticeable effect. This is due to the abundance of photoionization in air, which supplies a positive discharge with free electrons and allows it to propagate along the electric field lines. Using some simple field calculations, we show that field enhancement due to dielectric polarization does not play a significant role in our geometry as long as the discharge maintains its cylindrical symmetry. The field component towards the rod is insufficiently enhanced to cause the discharge to move towards the rod. Any additional electrons produced by the dielectric surface do not influence this discharge morphology. This interpretation is supported by both experiments and simulations. At higher pressures (400–600 mbar) or for larger gaps between the needle and the dielectric rod, the inception cloud reaches its maximal radius within the gap between needle and rod and destabilizes there. In those cases, streamer channels are more likely to turn into a surface streamer. All our experiments and simulations were performed at moderate pressures (75–600 mbar), but we expect that the results will be the same for other pressures assuming that all the lengths scales (including the rod) in the setup are rescaled according to the Townsend scaling of the discharge.

In this study, a two-dimensional fluid model is employed to simulate the streamer, pressure wave, and vortex in surface dielectric barrier discharge driven by nanosecond pulse voltage (ns-SDBD). It comprises a numerical model with two interconnected modules: discharge dynamics and gas flow dynamics. These modules are coupled through the physical variables including ‘EHD force’, ‘thermal source’, ‘velocity field’, ‘gas temperature’, and ‘gas pressure’. Our research primarily focuses on the underlying physical mechanisms of pressure waves and vortices for plasma-based flow control. The generation of pressure waves is attributed to the rapid gas heating by pulsed discharge, whereas the formation and development of the vortex are related to the ionic wind (EHD effect) provided by the plasma. To thoroughly understand and optimize flow control performance, an investigation into the effects of various discharge parameters, such as voltage amplitude and polarity, is conducted. Additionally, several SDBD modules are arranged in series, each featuring a dual three-electrode configuration. Subsequently, the dynamic behaviors of multiple streamers, pressure waves, and vortices, along with their interactions, are explored.

The experimental study was performed to clarify the basic behaviour of streamers traveling over the surface of oil-immersed polyethylene insulated wire under a standard lightning impulse voltage application. The effect of the grounded side electrode on the characteristics of creepage discharges, such as discharge inception voltage, discharge extension length, discharge current and charge, discharge figure has been studied. There is a remarkable difference in these characteristics between positive and negative polarities of the streamer. Though the approach of the grounded side electrode to the wire restrains the generation and progression of streamers, it leads to the reduction of a punch-through breakdown voltage of the wire insulator. The authors also measured the electric potential along the streamer channel and the streamer propagation velocity by means of a capacitive probe. It is indicated that the streamer continues to progress in a constant velocity and the streamer channel is not equipotential. The propagation of streamers appears to be stopped by a finite potential drop along the streamer channel.

All theories coupling electron emission theories ultimately approach the space-charge-limited current (SCLC) in vacuum, given by the Child–Langmuir (CL) law, for sufficiently high voltage, or the Mott–Gurney (MG) law for finite electron mobility and high (but not infinite) voltage. These analyses demonstrate the presence of an SCLC regime that cannot be described by either CL or MG. Here, we derive an exact solution for SCLC for general electron mobility and nonzero velocity. We recover the traditional CL with nonzero initial velocity at high voltage. For low mobility (or infinite collision frequency), we derive corrections to the MG law that depend on the ratio of initial velocity to the product of collision frequency and gap distance or initial velocity to drift velocity for low and high voltage, respectively. Increasing collisionality decreases the correction to SCLC for nonzero velocity, indicating that these corrections are less important for low-mobility materials (e.g., solids) than high-mobility materials (e.g., air or vacuum). For a given gap distance (collision frequency), increasing the collision frequency (gap distance) increases the voltage necessary to make the gap appear more like vacuum. These results provide a generalized SCLC for both collisionality and initial velocity when assessing the transitions between electron emission mechanisms.