Ozone and Nitrogen Oxides Generation in Gas Flow Enhanced Hollow Needle to Plate Discharge In Air

Siemens made the first ozone generation system by corona discharge about hundred and fifty years ago. At present mainly two types of atmospheric pressure electrical discharges - corona discharge and dielectric barrier discharge are used for production of ozone. Another type of discharge, which can be used for this purpose, is multineedle to plate electrical discharge enhanced by the gas flow. Contrary to the conventional arrangement when the gas is flowing around the needles we studied the discharge in which the gas was pumped through the needles. Results of studies of ozone and nitrogen oxides production by DC electrical discharge in air at atmospheric pressure with a single hollow needle to plate electrode configuration enhanced by the flow of air through the needle for both polarities of the needle, different airflow rates and currents are presented in this paper.     

质子交换膜燃料电池两维、两相流动模型

提出了考虑电池内部两相流动的质子交换膜燃料电池数学模型,模拟了阳极、阴极两侧的流道和扩散层中同时发生两相流动时电池内部的各种传递特性,并用实验数据验证了该模型的准确性。模拟结果显示,当电池阴极扩散层中有液态水存在时会大大降低膜中的局部电流密度;质子交换膜中水的净通量方向可正、可负,因此电池的增湿策略应根据不同的运行工况而不断变化。     

Study of Internal and External Leaks in Tests of Anode‐Supported SOFCs

A planar anode‐supported solid oxide fuel cell (SOFC) has been tested to investigate gas tightness of the electrolyte and the applied seals. Gas leaks reduce the efficiency of the SOFC and it is thus important to determine and minimise them. Probe gases (He and Ar) and a Quadrupole Mass Spectrometer were used to detect both internal (through electrolyte) and external (through seals) gas leaks. The internal gas leak through the electrolyte was quantified under different conditions, as was the external leak from the surroundings to the anode. The internal gas leak did not depend on the pressure difference between the anode and the cathode gas compartment, and can thus be described as diffusion driven. External leaks between the surroundings and the anode, but not the cathode gas compartment was observed. They were influenced by the pressure difference and are thus driven by both concentration and pressure gradients. The measured gas leaks deduced from the probe gas experiments and the total leak calculated from the deviation between the Emf defined by the gases and the cell OCV (which contains all gas leaks as well as effects of electronic leaks) were compared. Good agreement between the two measures was observed.     

Localized fabrication of carbon nanotubes forest at a needle electrode by atmospheric pressure corona discharge

Characteristics of the growth of multi-walled carbon nanotubes (CNTs) at a localized surface of a needle-shaped graphite cathode by corona discharge were investigated with varied temperature, 400–1000 °C. For the CNTs' growth, C₂H₄ in H₂ stream was used as carbon source. The CNTs were observed in aligned form on the tip of a needle-shaped cathode under the present condition. It was observed that the temperature range for the CNTs' growth with corona discharge, 600–800 °C, was lower than that that without corona discharge, 700–1000 °C. In the relevant reaction system, strong electric field at the cathode tip enforced the CNTs to grow straightly to form the free-standing aligned CNT forest at a specifically narrow tip zone of the needle cathode.     

Advances in Mixed‐Reactant Fuel Cells

The mixed‐reactant fuel cell (MRFC) is a new concept, in which a mixture of aqueous fuel and gaseous oxygen (or air) flows directly through a porous anode‐electrolyte‐cathode structure or through a strip‐cell with an anode‐electrolyte‐cathode configuration. These structures can be single cells or parallel stacks of cells and may be in a planar, tubular or any other geometry. Selectivity in the electrocatalysts for MRFCs is mandatory to minimize mixed‐potential at the electrodes, which otherwise would reduce the available cell voltage and compromise the fuel efficiency. MRFC offers a cost effective solution in fuel cell design, since there is no need for gas‐tight structure within the stack and, as a consequence, considerable reduction in sealing, manifolding and reactants delivery structure is possible. In recent years, significant advances have been made in MRFCs, using methanol as a fuel. This paper reviews the status of mixed reactant fuel cells and reports some recent experimental data for methanol fuel cell systems.     

Electro-sorption of ammonium by a modified membrane capacitive deionization unit

A modified membrane capacitive deionization (MCDI) unit with additional flow channels in the anode and cathode chambers was used to study the performance of ammonium ion removal. The influences of operating parameters including initial ammonium concentration, flow rate and applied potential and the effect of flow in the anode and cathode chambers were investigated. Flow through the anode and cathode chambers significantly enhanced the electro-sorption efficiency. The electro-sorption of ammonium at 5 mL/min was about 65% greater than without flow.     

Study of a Single‐Chamber Solid Oxide Fuel Cell Microstack with V‐Shaped Congener‐Electrode‐Facing Configuration

Single‐chamber solid oxide fuel cell (SC‐SOFC) microstacks with V‐Shaped congener‐electrode‐facing configuration were fabricated and operated successfully in a box‐like stainless steel chamber. Two gas channels with small gas inlets were used to transport the fuel and oxygen to the anodes and cathodes, respectively. The temperature of an anode‐facing‐anode two‐cell stack was higher than that of a cathode‐facing‐cathode two‐cell stack during the test procedure. For a three‐cell stack, the cell in the middle region presented the highest power output. The open circuit voltage (OCV) and maximum power output of the three‐cell stack in a gas mixture of 100 sccm N₂, 120 sccm CH₄, and 80 sccm O₂ were 3.0 V and 413 mW, respectively.     

Influence of Oxygen and Dissolved Inorganic Additives on the Removal of Gaseous Acetylaldehyde by Use of a Wetted‐Wall Corona Discharge Reactor

A cylindrical wetted‐wall corona discharge reactor was used for the removal of acetaldehyde in gas mixtures of N₂ and O₂. Gaseous acetaldehyde was removed from the gas stream by simultaneous absorption and gaseous corona reaction. The acetaldehyde absorbed in water, was decomposed by the aqueous radical, OH, produced by contact of the gas corona with the water film. There is an optimized oxygen concentration for the effective removal. When oxygen coexists in the gas mixture at 5 %, acetaldehyde was effectively removed, resulting in overall sustainable removal of acetaldehyde. However, an increase in oxygen concentration resulted in a decrease in the extent of removal, when the corona current was excessively high. This is due to corona‐induced turbulence broadening the residence time distribution of gas in the reaction zone. The decompositions of absorbed acetaldehyde and TOC in water were obviously affected by the varied oxygen concentrations. Acetaldehyde was not removed in the absence of oxygen. The dissolved inorganic additives, NaOH and HCl, strongly affected the acetaldehyde absorbability into water and subsequently, the decomposition rate of the absorbed acetaldehyde.     

Removal of heavy metals in a flow‐through vertical microbial electrolysis cell

This work describes laboratory experiments aimed at evaluating the feasibility of removing heavy metals from metal‐contaminated water in flow‐through microbial electrolysis cells (MECs) with peat moss as a source of organic carbon. MECs were assembled in upflow glass columns containing granular activated carbon (GAC) bioelectrodes preceded by a layer of peat moss. The MECs were fed with metal‐contaminated surface water collected at a firing range. At hydraulic retention times (HRT) of 4–6 days, up to 99 % removal of Pb, Zn, Cu, and Fe was observed. The removal efficiency of Zn and Cu declined at an HRT of 1.7 days, while effluent Pb concentration remained below the detection limit for all of the HRTs tested. Metal extraction from MEC compartments showed an accumulation of metals in both the peat moss layer and the GAC cathode, i.e., the removal was achieved by a combination of anaerobic and bioelectrochemical pathways of metal reduction. A proliferation of sulphate reducing bacteria in the peat moss layer and electroactive species in GAC electrodes was confirmed by biomolecular analysis. The proposed flow‐through system, which combines sulphate‐reducing and electroactive microbial activities to achieve near‐complete metal removal, can be used for removing a broad range of heavy metals from contaminated water in a low‐cost passive flow treatment system.     

非平衡等离子体消除乙硫醇

采用脉冲电晕放电等离子体对乙硫醇进行消除实验,探索了气体流量（停留时间）、气流中水分含量对消除率的影响规律。结果表明,随着气体流量的增大,乙硫醇在反应器内的停留时间减小,能量密度减小,消除率降低;消除率随水分含量的变化并非呈单方向增大或减小,而是存在一个最佳范围,从实验结果来看,水分含量为3.2～3.5 g/m3,消除率明显高于水分含量低于3.2 g/m3或高于3.5 g/m3时的消除率。采用GC-MS、FTIR和SGA94-SO2型单项气体分析仪等仪器对乙硫醇的消除产物进行了分析,主要产物为CO2、H2O和SO2,未检测到有机产物。根据实验数据分析了乙硫醇的反应动力学特征,发现乙硫醇在脉冲电晕等离子体体系中的反应符合一级反应动力学特征,反应速率常数为0.0729 s－1。     

Study of arc stability and erosion behaviour of a transferred arc with graphite DC electrodes

The arc stability and erosion behaviour of a hollow graphite DC cathode were studied using a graphite anode in an argon atmosphere. The main factors controlling the arc stability were the geometry of the cathode tip and the argon gas flow rate. It is suggested that high argon gas flow rates might shift the electron emission mechanism of the cathode from the thermionic‐field to the thermionic emission regime. Arcs were generally stable if the cathode is in the thermionic emission regime. The erosion rate of the cathode at 150 A was strongly dependent on the arc stability and higher for the unstable arc operation. Meanwhile, the erosion rates at 300 and 400 A showed the opposite trend because of carbon redeposition.     

Development of a Self‐Adaptive Direct Methanol Fuel Cell Fed with 20 M Methanol

A passive and self‐adaptive direct methanol fuel cell (DMFC) directly fed with 20 M of methanol is developed for a high energy density of the cell. By using a polypropylene based pervaporation film, methanol is supplied into the DMFC's anode in vapor form. The mass transport of methanol from the cartridge to the anodic catalyst layer can be controlled by varying the open ratio of the anodic bipolar plate and by tuning the hydrophobicity of anodic diffusion layer. An effective back diffusion of water from the cathode to the anode through Nafion film is carried out by using an additive microporous layer in the cathode that consists of 50 wt.% Teflon and KB‐600 carbon. Accordingly, the water back diffusion not only ensures the water requirement for the methanol oxidation reaction but also reduces water accumulation in the cathode and then avoids serious water flooding, thus improving the adaptability of the passive DMFC. Based on the optimized DMFC structure, a passive DMFC fed with 20 M methanol exhibits a peak power density of 42 mW cm^–2 at 25 °C, and no obvious performance degradation after over 90 h continuous operation at a constant current density of 40 mA cm^–2.     

A Three‐Dimensional Two‐Phase Model for a Membraneless Fuel Cell Using Decomposition of Hydrogen Peroxide with Y‐Shaped Microchannel

A three‐dimensional, two‐phase, multi‐component mixture model in conjunction with a finite‐volume‐based computational fluid dynamics (CFD) technique is applied to simulate the operation of membraneless fuel cell with Y‐shape channel. Hydrogen peroxide is employed both as fuel and oxidant, which are dissolved in diluted sodium hydroxide and sulfuric acid solutions, respectively. Almost all transport phenomena occurring in the fuel cell such as fluid flows, mass transport, electrochemical kinetics, and charge transport are accounted in this model. The oxygen O₂ gas, which is a product on the anode electrode, is assumed to be insoluble. The presence of gas phase acts to prevent the processes of reactant supply and product removal. Thus, the cell performance is hindered, while it is operated at the normal current density situation. On the other hand, the capillary action is found to enhance the electrolyte transport in the anode porous electrode, which may slightly improve the cell performance at the high‐current density situation. Besides, a secondary vortex flow is induced due to the transportation of the gas phase, which drifts from the bottom to the top of the channel. The mixing zone is then inclined, which may result in serious fuel crossing phenomenon.     

Advances in Organic Liquid‐Gas Chemical Heat Pumps

Compared with inorganic chemical heat pumps (CHPs), organic liquid‐gas CHPs are more amenable to be run as a continuous process because the reactants and products can be fed or removed continuously. Therefore, increasing attention has been paid to investigations of CHPs using the organic liquid‐gas reaction system. Relevant research topics involved reaction catalyst, chemical reaction kinetics, reactive distillation, energy efficiency evaluation, economic analysis, etc. Nevertheless, the research on an organic liquid‐gas CHP system is still in the elementary stage. A detailed review on the current research status of catalyst‐assisted CHPs employing an organic liquid‐gas reaction system has been performed. Existing problems are identified and future research directions are proposed.     

Influence of Temperature on SO2 Removal Enhanced by Water Vapor Using a Corona‐Discharge Reactor

A reactor using d.c. corona discharge of negative polarity was applied to remove sulfur dioxide from an oxygen‐nitrogen mixture in the presence or absence of water vapor for temperatures ranging from room temperature to 350 °C. It was observed that increasing the reactor temperature caused a decrease in the removal efficiency. Mixing water vapor with the process gas resulted in an increase of the removal efficiency. The effect of the presence of water vapor on improving the removal efficiency was significant under low temperature conditions, while it was relatively moderate under high temperature conditions. In addition, the solid deposit formed inside the reactor at two temperatures, room temperature and 200 °C, was analyzed with both a differential scattering calorimeter and an X ray diffractometer. The analysis indicated that SO₂ was ultimately converted to solid sulfur in both the presence and absence of water vapor in the gas flow.     

Understanding Water Transport in Polymer Electrolyte Fuel Cells Using Coupled Continuum and Pore‐Network Models

Water management remains a critical issue for polymer electrolyte fuel cell performance and durability, especially at lower temperatures and with ultrathin electrodes. To understand and explain experimental observations better, water transport in gas diffusion layers (GDLs) with macroscopically heterogeneous morphologies was simulated using a novel coupling of continuum and pore‐network models. X‐ray computed tomography was used to extract GDL material parameters for use in the pore‐network model. The simulations were conducted to explain experimental observations associated with stacking of anode GDLs, where stacking of the anode GDLs increased the limiting current density. Through imaging, it is shown that the stacked anode GDL exhibited an interfacial region of high porosity. The coupled model shows that this morphology allowed more efficient water movement through the anode and higher temperatures at the cathode compared to the single GDL case. As a result, the cathode exhibited less flooding and hence better low temperature performance with the stacked anode GDL.     

Mathematical Modelling of Proton‐Conducting Solid Oxide Fuel Cells and Comparison with Oxygen‐Ion‐Conducting Counterpart

Proton‐conducting solid oxide fuel cells (H‐SOFC), using a proton‐conducting electrolyte, potentially have higher maximum energy efficiency than conventional oxygen‐ion‐conducting solid oxide fuel cells (O‐SOFC). It is important to theoretically study the current–voltage (J–V) characteristics in detail in order to facilitate advanced development of H‐SOFC. In this investigation, a parametric modelling analysis was conducted. An electrochemical H‐SOFC model was developed and it was validated as the simulation results agreed well with experimental data published in the literature. Subsequently, the analytical comparison between H‐SOFC and O‐SOFC was made to evaluate how the use of different electrolytes could affect the SOFC performance. In addition to different ohmic overpotentials at the electrolyte, the concentration overpotentials of an H‐SOFC were prominently different from those of an O‐SOFC. H‐SOFC had very low anode concentration overpotential but suffered seriously from high cathode concentration overpotential. The differences found indicated that H‐SOFC possessed fuel cell characteristics different from conventional O‐SOFC. Particular H‐SOFC electrochemical modelling and parametric microstructural analysis are essential for the enhancement of H‐SOFC performance. Further analysis of this investigation showed that the H‐SOFC performance could be enhanced by increasing the gas transport in the cathode with high porosity, large pore size and low tortuosity.     

Simultaneous nitrification and denitrification with electricity generation in dual‐cathode microbial fuel cells

BACKGROUND: Nitrogen removal using microbial fuel cells (MFCs) is of great interest owing to the potential benefits of bioenergy production. In this study, simultaneous nitrification and denitrification in dual‐cathode MFCs was investigated. RESULTS: The dual‐cathode MFCs investigated were capable of generating electricity and removing nitrogen, influenced by operating methods, nitrogen loading rates and external resistance. Depending on the ammonium concentration in the anode chamber, 84–97% of the ammonium nitrogen was removed via nitrification in the aerobic cathode. The removals of nitrate and total nitrogen were relatively low (～50%) at the influent ammonium concentration of 80 mg NH₄⁺‐N L^?1, but were significantly improved to more than 90% at a lower ammonium input (40 and 20 mg NH₄⁺‐N L^?1). When the electrode couples were electrically connected for different purposes, with high power output from the anode/aerobic cathode and high current generation from the anode/anoxic cathode, nitrogen removal was also improved. An investigation of aeration suggested that factors other than carbon supply, possibly inefficient reactor configuration, also limited the performance of the developed MFC. CONCLUSION: The experimental results demonstrated that the proposed pathway was feasible with effective nitrogen and organic removal. This study provided valuable information for the further development of a continuously operated dual‐cathode MFC system. Copyright © 2011 Society of Chemical Industry     

Sequential Tape Casting of Anode‐Supported Solid Oxide Fuel Cells

A novel route was developed to fabricate anode‐supported solid oxide fuel cells with a high throughput and low manufacturing costs. In contrast to classical manufacturing routes, this novel route starts with the tape casting of the thin electrolyte followed by the tape casting of the anode and anode support. All three layers were cast green‐on‐green and finally sintered to yield a gas‐tight electrolyte. By carefully selecting the raw materials for all three layers, it is possible to manufacture near‐net‐shape half‐cells. The half‐cells were characterized with respect to thickness, microstructure, bending behavior, electrolyte gas leakage, shrinkage, electrolyte residual stresses, and mechanical strength. Finally, the cathode was screen‐printed and fired, and the full cell characteristics were obtained in single‐cell and stack tests. Additionally, a scale‐up to cell sizes of 200 × 200 mm² was verified. Electrolyte and anode thickness were around 20 μm, and the support was cast to 300–500 μm. The helium leak rates were better than the necessary internal threshold, and the characteristic bending strength obtained was in the range of 150–200 MPa. The single‐cell tests revealed current densities of 1.0 A cm^–2 at 700 mV and 800 °C (H₂/air). A first stack test proved their stackability and operational functionality.     

Removal of NOx with radical injection caused by corona discharge

Removal of NO_x (namely DeNO_x) from simulated flue gas with direct current (d.c.) corona radical shower system was investigated. Steady streamer coronas occur when the flow rates of the fed gases are adjusted properly. The experimental results show that both the composition and the flow rate of the gas fed into the nozzles influence the V-I characteristic of corona discharge. The vapor in the flue gas restrains the discharge, reduces the discharge current, but enhances the DeNO_x efficiency. Furthermore, removal of NO_x from flue gas by radical injection associated with alkali solution (26% by weight of NaOH in water) scrubbing was carried out. Oxygen together with water vapor is fed into the nozzle electrode and the oxygen and water molecules are decomposed in the corona zone. It is found that NO and NO₂ can be converted into HNO₂ and HNO₃, respectively, by radicals formed during the discharge process and the conversion efficiency of NO_x in the plasma reactor is more than 60%. The overall DeNO_x efficiency of the system reaches 81.7% after the flue gas was scrubbed by the NaOH solution.