非平衡等离子体放电模式及反应器结构对氨气分解制氢的影响

在常压下研究了不同等离子体放电模式及反应器结构对氨分解制氢反应的影响.实验中调节反应器结构分别产生了介质阻挡放电和交流弧放电两种放电模式.通过对两种放电模式的放电图像、电压-电流波形和氨分解过程中等离子体区活性物种的发射光谱(OES)研究发现,与介质阻挡放电相比,交流弧放电为局部强放电,具有更高的电源效率和电子密度.因此,在介质阻挡放电中氨气分子大部分通过生成电子激发态物种NH3*,再与载能电子碰撞断裂N―H键进行氨分解反应;而在交流弧放电中载能电子具有更高的平均电子能量,可直接断裂氨气分子的N―H键生成NH2和NH等高活性物种,促进氨分解反应的进行.结果表明,交流弧放电的氨分解效果要明显优于介质阻挡放电.在交流弧放电模式下不同类型反应器对氨气分解转化率由高到低的顺序为:管-管管-板针-板板-板.在输入功率为30 W,气隙间距为6 mm时,管-管交流弧放电的氨气转化率达到60%左右,而板-板介质阻挡放电的氨气转化率仅为4%.     

Development of an Atmospheric Pressure Glow Discharge Detector for Capillary Column Gas Chromatography

 The use of the change in the oscillation frequency of the current of a new atmospheric helium glow discharge for sensitive signal detection for gas chromatography is studied. The effluent of a capillary column is directed into the glow discharge cell perpendicular to the axis of the glow discharge that existed between a platinum anode and cathode. A stable discharge is obtained when several hundred volts are applied between the 0.2-mm gap between the anode and cathode. The effects of the electrode gap, discharge voltage and gas flow rate on the baseline frequency and discharge current were investigated. The chromatogram shows that the discharge current and discharge gap have a strong influence on the detector response. The discharge current shows positive peaks; however, frequency peaks are positive or negative depending on the discharge conditions. The response of the detector is in the femto-mole and pico-mole range for nonane and decane. Received August 5, 1997. Revision September 2, 1999     

Diagnosis of OH Radical by Optical Emission Spectroscopy in Atmospheric Pressure Unsaturated Humid Air Corona Discharge and its Implication to Desulphurization of Flue Gas

OH radical in the corona discharge with pipe–nozzle–plate electrode has been diagnosed by optical emission spectroscopy. Spatial variations of OH radical emission in discharge gap have been measured. Relative intensity of OH radical emission spectroscopy increases with increasing water vapor flux injected into the reactor or intensity of electric field supported. In positive pulsed corona discharge, relative intensity is higher than that in positive DC corona discharge and lower than that in negative DC corona discharge. Strongest intensity of OH radical spectrum appears within the range of 5 mm near the discharge nozzle- electrode. In addition, it is proved that the efficiency of desulphurization from flue gas by pulsed corona discharge plasma processes can be improved when OH radical is produced in the reactor.     

The effect of oxygen pressures on the electrochemical profile of lithium/oxygen battery

The influences of oxygen pressure on the performance of a lithium/oxygen battery using non-aqueous electrolyte were investigated in this paper. Oxygen pressures were adjusted from 1 to 10 atm. It was found that, at all examined discharge rates from 0.1 to 1.0 mA cm⁻², the discharge capacity increased with the increasing of oxygen pressure, especially at a high discharge rate. The morphology of the discharge product was found to relate to discharge rate and oxygen pressure by scanning electron microscopy observation.     

Overview of Atmospheric Pressure Discharges Producing Nonthermal Plasma

Recently, much attention has been paid to gas discharges producing nonthermal plasma because of many potential benefits in industrial applications. Historically, past work focused on Dielectric Barrier (silent) Discharges (DBD) and pulse-periodical corona discharges. Recently, a number of new different discharge techniques succeeded in producing stable gas discharge at atmospheric pressure. Among these are repetitively pulsed glow discharge; continuous glow discharge in a gas flow; hollow-cathode atmospheric pressure discharge; RF and microwave (MW) discharges. Several new variants of the DBD have been demonstrated over a rather wide range of frequencies. All these forms of gas discharge are characterized by a strong nonequilibrium plasma state. We attempt to classify these discharges with respect to their properties, and an overview of possible applications is made. Conditions for the existence of homogenous and filamentary forms of each of the discharge types are discussed.     

Synthesis of ammonia in high-frequency discharges

The synthesis of ammonia from nitrogen-hydrogen plasma prepared using radiofrequency discharge and microwave discharge was studied under the same experimental conditions except the driving frequency. Twice larger amounts of ammonia were adsorbed on zeolite used as adsorbent in the microwave discharge than in the radiofrequency discharge. Relative intensities of NH band head (A³–X^3–,0–0) as well as hydrogen atomic line (H\) observed in the plasma prepared using microwave discharge were one order of magnitude larger than those in the plasma prepared using radiofrequency discharge. Since NH_x radicals and H atoms are considered ammonia precursors, the advantage of microwave discharge over radiofrequency discharge on ammonia synthesis is discussed from the results obtained above and from the plasma parameters,kT _e andn _e , obtained by the electric double probe technique.Partly presented at the 8th International Symposium on Plasma Chemistry, August 31 to September 4, 1987, Tokyo, Japan.     

AlF3包覆对Li1.2Mn0.534Ni0.133Co0.133O2正极材料电化学性能的影响

通过共沉淀法制备锂离子电池富锂锰基正极材料Li1.2Mn0.534Ni0.133Co0.133O2,并对其进行AlF3包覆。实验结果表明,通过AlF3包覆,材料的电化学性能得到明显提高。在0.2C下,包覆前材料的首次放电比容量为253 mAh.g-1,首次充放电效率仅为88.8%。经过AlF3包覆,材料的首次放电比容量提高到294 mAh.g-1,首次充放电效率高达96.4%。同样,在1.0C下循环50次,未包覆材料的放电比容量由225 mAh.g-1降到185 mAh.g-1,容量保持率仅为82.2%。经过AlF3包覆,材料的放电比容量由230mAh.g-1仅降为222 mAh.g-1,容量保持率高达96.5%。     

Effect of TiO<Subscript>2</Subscript> on Various Regions of Active Electrode on Surface Dielectric Barrier Discharge in Air

For surface dielectric barrier discharge in air, we examined the effect of titanium dioxide on various regions of the active electrode on the electrical parameters of discharge, on its emission spectra, and for demonstration of the obtained results also on the concentration of ozone produced by the discharge. We used the active electrode in the form of nine interconnected parallel strips and a square counter electrode. The TiO₂ layer covered either only the strips, the region between the strips, or all active electrode. As reference discharge we used the discharge without any layer of TiO₂. We found that direct application potential has a version when the strips of the active electrode are covered with a layer of TiO_2, because the concentration of ozone produced by the discharge is the highest in all investigated cases. This finding could therefore be used for construction of more efficient ozone generators.     

Role of Bipolar Pulsed DBD on the Growth of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> in Three-Phase Discharge Plasma Reactor

Algae in drinking water supplies often bring about impact on the water treatment. In this study, a bipolar pulsed dielectric barrier discharge system in three-phase discharge plasma reactor was constructed for investigating its ability to control excessive growth of cyanobacteria, Microcystis aeruginosa. Experimental results show there was almost no change in optical density immediately after the interruption of electrical discharge, but the decreasing trend of optical density, cell density and chlorophyll-a content was obvious during the incubation period, indicating a significant residual effect of electrical discharge process on the algal growth inhibition. Scanning electron microscopy investigation of algae revealed surface damage, apparent leakage of intracellular contents and pores formed after electrical discharge process, which showed that algal cells had no potential to survive and grow. Compared with the control sample, it was observed that electrical discharge on the algal extracellular products has almost no residual effect and the growth rate of algae slightly decreased before three days storage. Hydrogen peroxide was produced by electrical discharge in the μM level and showed a first-order decay. But at such level, the external addition of hydrogen peroxide alone is not likely to cause the residual effect. These results implicated that the growth inhibition of M. aeruginosa was mainly caused by electrical discharge process, and it made the algal cells lose ability to survive, demonstrating the considerable potential of such an alternative process for efficient water purification.     

Electrical Features of Radio-frequency,Atmospheric-pressure,Bare-metallic-electrode Glow Discharges

Radio-frequency (RF), atmospheric-pressure glow discharge (APGD) plasmas with bare metallic electrodes have promising prospects in the fields of plasma-aided etching, deposition, disinfection and sterilization, etc. In this paper, an induced gas discharge approach is proposed for obtaining the RF, atmospheric-pressure, γ-mode, glow discharges with pure nitrogen or air as the primary plasma-working gas using bare metallic electrodes. The discharge characteristics, including the discharge mode, the breakdown voltage and discharge voltage for sustaining α mode and/or γ mode discharges, of the RF APGD plasmas of helium, argon, nitrogen, air or their mixtures using a planar-type plasma generator are presented in this study. The uniformity (no filaments) of the discharges is confirmed by the images taken by an iCCD with a short exposure time (10 ns). The effects of different gap spacings and electrode materials on the discharge characteristics, the variations of the sheath thickness and the electron number density are also studied in this paper.     

Rotational temperature of nitrogen glow discharge obtained by optical emission spectroscopy

Measurements of rotational temperature as low as several hundred Kelvin have been measured using optical emission spectroscopy (OES) in nitrogen direct current (DC) glow discharge. The strongest band of the first negative system of nitrogen was chosen to deduce the rotational temperature at four different positions in nitrogen DC glow discharge, the back of cathode; cathode sheath; positive column; and anode glow. In positive column the rotational temperature increased apparently with the increasing discharge voltage from 500 to 1000 V when the pressure was 10 Pa. But with pressure of 20 Pa the rotational temperature in positive column increased slightly with the increase of discharge voltage. On the contrary, the rotational temperature in cathode sheath took reverse tendencies when the discharge voltage varies from 500 to 1000 V. As regard the anode glow, the rotational temperature at 10 Pa decreased with the increase of discharge voltage, but that at pressure of 20 Pa increased. We attribute the different tendencies of the rotational temperature to the different discharge statues at different pressures. When the discharge voltage varies from 500 to 1100 V, the discharge with pressure of 10 Pa is normal glow and that with 20 Pa is abnormal glow.     

The electrochemical properties of Li/TEGDME/MoS2 cells using multi-wall carbon nanotubes as a conducting agent

We investigated the first charge–discharge behavior and cycling property of Li batteries using MoS₂ electrodes with multi-wall carbon nanotubes (MWNT) as a conducting agent. The MoS₂ electrode was prepared using MWNT as the conducting agent. The battery gave a high first discharge capacity of 440 mAhg^?1 with a plateau potential region at 1.1 V. The Li/MoS₂ battery using MWNT showed a higher discharge capacity compared to acetylene black. After ten cycles of the battery using MWNT, the discharge capacity decreased to 120 mAhg^?1, which corresponded to 30% of the first discharge capacity. Adding a carbon nanotube into the MoS₂ electrode improved the first discharge behavior, but did not affect the cycling property of the Li/MoS₂ cell.     

掺碳的钠离子电池正极材料NaVPO4F的电化学性能

添加适量的葡萄糖并用高温固相法合成钠离子电池正极材料NaVPO₄F。用X射线衍射仪、扫描电镜等对NaVPO₄F进行结构表征，采用循环伏安、交流阻抗技术等对其进行电化学性能测试，探讨了不同掺碳量对NaVPO₄F结构和电化学性能的影响。恒流充放电测试结果显示，掺碳10wt%的NaVPO₄F在0.1C倍率下首次充、放电容量分别达到151.5 mAh·g^-1和113 mAh·g^-1，充、放电平台分别为3.8 V和3.6 V，经过20次循环，放电比容量的保持率为初始的91.6%。循环伏安曲线出现明显的氧化还原峰，并分别与充、放电电位平台相对应。交流阻抗图谱显示，掺碳10wt%的NaVPO₄F样品充放电阻抗较小，可逆性较好。     

Acceleration of Acetone Destruction Process under Synergistic Action of Photocatalytic Oxidation and Barrier Discharge

Separate and joint work of photocatalytic oxidation based on TiO₂ and surface barrier discharge as a source of active oxygen and UV radiation is investigated for acetone vapors destruction under ambient air conditions. Experiments were carried out in a 404 l airtight Plexiglas chamber and used five different combinations of photocatalyst, barrier discharge and ultraviolet irradiation under identical initial concentration (∼170 ppm) of acetone. It is shown for the synergistic action of photocatalytic method and barrier discharge that the initial rate of acetone decomposition per watt of input power increases in more than 1.5 times compared to photocatalytic oxidation. Under operation of plasma of barrier discharge, intermediate products are formed such as CO, acetic acid, acetaldehyde and methane nitrate (CH₃NO₃). These products are not detected for photocatalytic oxidation. Some interesting features of kinetics of acetone decomposition and formation of intermediate products with participation of barrier discharge are revealed.     

Removal of Toluene from Industrial Gas by Adsorption–Plasma Catalytic Process: Comparison of Closed Discharge and Ventilated Discharge

Degradation of adsorbed toluene over 13X zeolite, 5A molecular sieve and Al₂O₃ by non-thermal plasma was investigated. Different discharge modes, including closed and ventilated discharge were compared. The carbon balance and COx yield of 13X zeolite were increased by 17.6 and 19.4% by ventilated discharge, respectively, compared with closed discharge. But for 5A molecular sieve and Al₂O₃, the carbon balance and COx yield by closed discharge were greater than those by ventilated discharge. It meant that the closed discharge was more suitable for low-concentration of VOC and the residence time of reactants would be prolonged. Removal of high-concentration VOC by ventilated discharge was more appropriate because of more reactive oxygen species generated. Furthermore, the effect of discharge background gas was studied. Removal of adsorbed toluene over Co/13X by oxygen and air with different flow rate as background gas were compared. The removal efficiency was reduced as flow rate of background gas increased. The oxygen-discharge was more efficiency for toluene oxidation and inhibited the generation of nitrogen oxides.     

Effective-Medium Approximation in Studies of the Diffusion Discharge of the Positive Electrode in a Lead–Acid Battery

Application of the effective-medium approximation for studying diffusion-controlled electrochemical reactions that occur during the discharge of the positive electrode of a lead–acid battery is considered in detail. Effect of the electrode thickness on the discharge and development of percolation processes, following the clogging of pores by discharge products, is examined.     

Considerations in the design of a microwave induced plasma utilizing the TM010 cavity for optical emission spectroscopy

A procedure is presented to determine the resonant frequency shift of the TM₀₁₀ cavity when dielectric material (the plasma discharge tube) is inserted. This allows convenient adjustment of the cavity diameter to yield a resonance frequency near 2.450 GHz when the plasma is ignited.The design of a unique plasma discharge tube is presented. This discharge tube utilizes a tangential plasma support gas flow (He or Ar) to generate a suspended plasma discharge which does not touch the wall of the discharge tube. The resulting discharge has superior spatial and temporal stability compared to previously reported plasma discharges.The use of TM₀₁₀ resonant cavities having 2 and 3 cm internal thicknesses is discussed. These cavities result in physically longer plasmas providing greater analyte residence times and enhanced analytical performance. Results with and without prior aerosol desolvation are presented.     

Application of the synchronous detection to the identification of the characteristic lines of the neutral atoms sputtered and excited by a plasma

It is possible to excite by a Penning's discharge the neutral atoms sputtered during the bombardment of a target by positive ions and thus to increase the sensibility of the ionoluminescence analysis method. However, the characteristic lines of the target's elements may be masked by the discharge lines. We describe in this paper an arrangement using a lock-in amplifier which permits to reduce the discharge lines. The results obtained with a duraluminium target show that it is possible to identify the characteristic target's lines even when they are weak and near the discharge lines.     

Spectroscopic investigation of the discharge for PA-CVD of TiN

Investigations of the discharge for PA-CVD of TiN on steel substrates are carried out using optical emission spectroscopy. A great number of species could be identified in the discharge. The growth rate of dense layers shows a direct dependence on Ti⁺ intensities. The occurrence of TiN in the discharge leads to f aky, not compact layers, lowering the hardness of the layers.     

Synergistic effects of catalysts and plasmas on the synthesis of ammonia and hydrazine

The synergistic effects o1 driving frequency of the discharge and catalysis of iron and molybdenum wires when then are placed in nitrogen-h ydrogen radio-frequency and microwave plasmas mere investigated. The ammonia Yield increased in the plasmas prepared using both driving frequencies. but the hydrazine yield increased only in fire radio-frequency discharge with the catalysts. The direct adsorption of NH_x formed in the plasma on the catalyst surface followed by the formation of NH₃ and N₂H₄ are considered as a reaction scheme in the radio-frequency discharge. On the other hand, the adsorption of N atoms and/or formation of the metal- N bond favors the formation of ammonia but does not affect the hydrazine formation in the microwave discharge.