Yubin Xian

Gliding arc is considered to be an efficient method for nitrogen fixation. In this study, an improved magnetic-driven rotating gliding arc method was adopted to investigate the effects of gas flow rate, current, magnetic field, nitrogen-to-oxygen ratio in the working gas, and relative humidity on nitrogen fixation efficiency. To further understand the relationship between the discharge mechanism and nitrogen fixation efficiency, the arc length, arc diameter, arc rotation frequency, and reaction pathway were studied to find the relationship between external parameters, discharge characteristics, and nitrogen fixation efficiency. The research results indicate that the discharge current and magnetic field not only change the rotation frequency of the gliding arc, but also affect its length and diameter, and the amount of ionizing gases involved in the working gas, thus affecting nitrogen fixation efficiency. When the nitrogen volume ratio in the feed gas is 60%, the lowest energy cost can be achieved, which is 18.6% lower than that of air. The energy cost of nitrogen fixation is closely related to the humidity of the air. As the humidity increases, the energy cost also increases. At the magnetic field strength of 160 mT, gas flow rate of 10 l min⁻¹, and current of 40 mA, the energy cost of 1.708 MJ mol⁻¹ is realized which is the current lowest for plasma nitrogen fixation in this study.

A novel three-level coupled rotating electrodes air plasma with nano-sized TiO₂ photocatalysts is developed for plasma-catalytic NO _x production. The effects of plasma catalysis on NO _x production with different air flow rates, different N₂ fractions and different humidity levels are evaluated. Final results show the exceptional synergistic effect between TiO₂ and three-level coupled rotating electrodes air plasma significantly increases the NO _x concentration by 68.32% (from 4952 to 8335 ppm) and reduces the energy cost by 40.55% (from 2.91 to 1.73 MJ mol⁻¹) at an air flow rate of 12 l min⁻¹ and relative humidity level of 12%, which beats the ideal thermodynamic energy limit ∼2.5 MJ mol⁻¹ for the thermal gas-phase process. A possible mechanism for enhanced NO _x production with TiO₂ is discussed: Highly energetic electrons in plasma contribute to the formations of the electron–hole pairs and oxygen vacancy (V_o) on the TiO₂ catalyst surface, which may facilitate the dissociative adsorption of O₂ molecules to form superoxide radical groups (like O₂ ⁻), and H₂O molecules to form surface hydroxyl groups (like OH^·), and thus, improving energy efficiency.

Minimizing the breakdown voltage and discharge current required to initiate direct in-liquid discharges, thus lowering power-source requirements and avoiding electrode ablation, is crucial for industrial applications of in-liquid plasmas. Here we demonstrate such considerable reductions by employing movable electrodes, without changing the electrode configuration or increasing the system complexity. The new mechanism is based on electrostatic electrode attraction resulting in a reduction in the discharge spacing by up to 6 times and facilitating a plasma initiation at lower breakdown voltages. The accumulated charges consumed by the discharge revert the electrodes to the initial positions, forming a gliding arc between the enlarged gaps and thus inhibiting current increases and electrode ablation.

For all volume dielectric barrier discharges (DBDs) reported, including both planar configuration volume DBDs and cylindrical or coaxial volume DBDs, the gap distance between the two electrodes is always a constant. In this paper, a non-equal gap distance DBD between a wedge electrode and a plane-shaped electrode is reported. It is found that the plasma can self-organize into a striped shape, which makes it possible to achieve a homogeneous plasma treatment effect by scanning the plasma over the surface. The high-speed photographs show that the discharge first occurs at the center of the wedge-shaped electrode where the gap distance is smallest, and it jumps to the next position with a relatively larger gap distance after a certain delay time. This is because of the build up of the reverse voltage due to the deposit of charges at the locations where discharge is ignited. Detailed analysis shows that the width of the equivalent charge deposit region is larger than that of the bright plasma stripe. According to the intensity ratio of N ₂ ⁺ (391.4 nm) and N ₂ (394.3 nm), the reduced electric field strength is evaluated to be in the range of 250–370 Td. It decreases with the increase in the gap distance. In addition, plasma of another type of non-equal gap distance DBD with a conical shape and a plane-shaped electrode is explored, and it is found that the plasma can also self-organize into concentric rings.

Diagnostic of spatiotemporal distribution of the electron density and temperature of atmospheric pressure plasma jets is a difficult task, as Thomson scattering, which is the most used measurement, suffers from the stray light induced by Rayleigh scattering. In this paper, a new strategy is reported to restrain the stray light in Thomson scattering. With a physical mask placed at the output of a single spectrometer, the scattering signal is obtained with a relatively high ratio of signal to noise. The electron density in a pulsed kHz‐driven atmospheric plasma jet interacting with a dielectric target is measured by using this method. A donut‐shaped distribution of electron density is observed at an axial position 1 mm away from the nozzle. The radius of the ring structure decreases with the reduction of the gas flow rate. The electron density reaches a maximum of about 4.5 × 10²⁰ m⁻³ at a delay time of 150 ns from the onset of the pulse. A similar time relationship between the electron density and plasma emission intensity is also identified. Higher applied voltage leads to a faster increasing and a higher peak value of the electron density. Pulse width shows little impact on the generation and decay of electrons.

The twisted behavior of a rotating electrode atmospheric-pressure argon plasma jet is reported and its mechanism is investigated. It is found that the plasma channel turns into a smooth pathway when about 5% of O ₂ or 3% of N ₂ are added to the main working gas, argon. Further investigation shows that the rotational frequency of the electrode, which can enhance the turbulence of the gas flow, does not affect the appearance of the plasma channel for both pure argon and argon mixed with different amounts of O ₂ /N ₂ . The optical emission spectra show that the emission intensities of the transitions from seven excited argon levels to two metastable states decrease dramatically when O ₂ /N ₂ is added. Detailed analyses suggest that when O ₂ /N ₂ is added, both the concentrations of argon in the two metastable states and their lifetimes decrease significantly, which results in a transition of the discharge channel from a turbulent pathway to a smooth pathway. In short, the metastable state of argon rather than the seed electrons plays the key role in the appearance of the plasma channel.

Novel plasma-based technologies that offer maximum efficiency at minimal environmental costs are expected to further promote the sustainable societal and economic development. Unique transfer of chemical reactivity and energy from gaseous plasmas to water takes place in the absence of any other chemicals, but results in a product with a notable transient broad-spectrum biological activity, referred to as plasma-activated water (PAW). These features make PAW a green prospective solution for a wide range of biotechnology applications, from water purification to biomedicine. Here, we present a succinct review of how novel, efficient methods based on non-equilibrium reactive plasma chemistries can be applied to low-cost natural water sources to produce a prospective product with a wide range of applications while at the same time minimising the process steps and dramatically reducing the use of expensive and/or hazardous reagents. Despite the recent exciting developments in this field, there presently is no topical review which specifically focuses on the underlying physics and chemistry related to plasma-activated water. We focus specifically on the PAW generation, origin of reactive species present in PAW, its related analytical chemistry and potentially different mechanisms that regulate the bio-activities of PAW in different biotech-applications and their roles in determining PAW efficacy and selectivity. We then review recent advances in our understanding of plasma-water interactions, briefly outlining current and proposed applications of PAW in agriculture, food and biomedicine. Finally, we outline future research directions and challenges that may hinder translation of these technologies into real-life applications. Overall, this review will provide much needed insights into the fundamental aspects of PAW chemistry required for optimization of the biochemical activity of PAW and translation of this environment- and human-health-friendly, and energy-efficient strategy into real life applications.

Recent years have witnessed successful applications of non-thermal plasmas (NTPs) as efficient and flexible tools for direct conversion of liquid alcohols into higher-value energy carriers at mild or even near-room-temperature conditions. Better understanding of the fundamental physical properties of the liquid alcohol discharges is needed for development and optimization of NTP-based applications. Here we investigate the discharge characteristics of a plasma-based liquid ethanol conversion under different process parameters and reveal the general trends of the discharge behavior. Two discharge modes, namely the self-pulsed and direct current (DC) modes, are sustained during the in-liquid discharge. These two modes can be easily interchanged and flexibly controlled by adjusting the processing parameters. The behavior of the bubbles generated during the discharge plays an important role in the transition between the discharge modes. When the discharge is sustained with the diffusion and floating of the bubbles, the DC mode is observed. Otherwise, the discharge develops into the pulse mode. The production rates and composition of the gaseous products are also shown to depend on the discharge modes.