Protection of sealed NiCd cells from cell voltage reversal: I. experimental conditions for the formation of cadmium bridges

A common polyamide separator, used as the electrolyte carrier in sealed Ni/Cd cells, can also function as a carrier for the Cd/Cd²⁺ system, the deposition method being the same as that in the preparation of sintered Cd electrodes. A separator thus treated is suitable for sealed Ni/Cd cells. If it is cycled at least once in an excess of alkaline electrolyte prior to sealing, and if the cell capacity is limited by the positive electrode, the explosion hazard of the sealed cell due to voltage reversal can be eliminated by a proper choice of separator and cadmium loading. Cadmium bridges formed in the separator under these conditions prevent gas formation on either electrode, their properties depending on the quality of the separator and its loading with cadmium.     

Plastic-bonded electrodes for nickel-cadmium accumulators: VI. Oxygen recombination rate on sealed cell cadmium electrodes

The recombination (i.e., reduction) of oxygen on pocket-type cadmium electrodes, utilizable in sealed Ni-Cd cells, occurs on areas covered with a thin layer of alkaline electrolyte. Hence, in the presence of a non-woven electrolyte carrier with a low permeability for oxygen, or by blocking the side of the electrode facing the gas space of the cell (which is not in contact with the electrolyte carrier), the recombination of oxygen is reduced to an insignificant level for sealed Ni-Cd cells. A comparison of results obtained with pocket-type and plastic-bonded cadmium electrodes showed that oxygen is reduced on metal parts of the electrode (perforated pocket, current collector, contacting metal screen) which are covered with a thin electrolyte layer, are easily accessible to oxygen, and are short-circuited by the electroactive Cd/Cd²⁺ material. The latter has a sufficiently negative potential and electronic conductance to allow the electroreduction of oxygen to take place.     

Plastic-bonded electrodes for nickel-cadmium accumulators: VI. Oxygen recombination rate on sealed cell cadmium electrodes

The recombination (i.e., reduction) of oxygen on pocket-type cadmium electrodes, utilizable in sealed Ni-Cd cells, occurs on areas covered with a thin layer of alkaline electrolyte. Hence, in the presence of a non-woven electrolyte carrier with a low permeability for oxygen, or by blocking the side of the electrode facing the gas space of the cell (which is not in contact with the electrolyte carrier), the recombination of oxygen is reduced to an insignificant level for sealed Ni-Cd cells. A comparison of results obtained with pocket-type and plastic-bonded cadmium electrodes showed that oxygen is reduced on metal parts of the electrode (perforated pocket, current collector, contacting metal screen) which are covered with a thin electrolyte layer, are easily accessible to oxygen, and are short-circuited by the electroactive Cd/Cd²⁺ material. The latter has a sufficiently negative potential and electronic conductance to allow the electroreduction of oxygen to take place.     

Limitations in the use of plastic-bonded electrodes in sealed nickel-cadmium cells and their reasons: II. Button cells

The behaviour of commercial, sealed 225 mA h button cells with lamellar-type electrodes had been compared with similar cells containing plastic-bonded     

Influence of cell voltage and current on sulfur poisoning behavior of solid oxide fuel cells

The sulfur poisoning behavior of nickel-yttria stabilized zirconia (YSZ) cermet anodes in solid oxide fuel cells (SOFCs) was investigated under both potentiostatic and galvanostatic conditions. While the observed relative drop in cell power output caused by sulfur poisoning decreases as the cell-terminal voltage is lowered potentiostatically (thus more current passing through the cell), it increases as more current is drawn from the cell galvanostatically (thus leading to lower terminal voltage). The apparent contradictory trends in relative performance loss due to sulfur poisoning are explained using a simple equivalent circuit analysis, which was further validated by impedance measurements of cells before and after poisoning by trace amounts of hydrogen sulfide (H₂S) under different conditions. Results suggest that the relative increase in cell internal resistance caused by sulfur poisoning is smaller when more current is drawn from the cell (or the cell-terminal voltage is lowered) under either potentiostatic or galvanostatic conditions. Thus, the increase in anode polarization resistance, not the drop in cell power output, should be used to describe the degree of sulfur poisoning in order to avoid any confusion.     

Plastic bonded electrodes for nickel-cadmium accumulators II. Basic electrochemical parameters of the nickel oxide electrode

Plastic bonded nickel oxide electrodes, prepared at normal temperature by one-stage rolling onto a current collector of steel net or perforated sheet of a mixture of active mass used in pocket-type electrodes, a conducting component and a PTFE binder, were tested in alkaline electrolyte. At current loads of 3–100 mA/cm₂ the type of conducting admixture, the current collector and its surface treatment were found to have a pronounced influence on the current carrying capability of the electrode. The electrode performance, especially at 100 mA/cm² is dependent not only on the composition of the active layer but also on the quality (or nature) - but not degree of contact between it and the current collector.     

Plastic bonded electrodes for nickel-cadmium accumulators. III. Influence of active layer composition on galvanostatic and potentiostatic discharge curves

Studies on the addition of a conducting component (carbon black, graphite, carbonyl nickel) and poly(tetrafluoroethylene) as binder to the active material used in pocket-type nickel oxide electrodes have shown that the second discharge step, which is observed in the discharge curve of a pressed nickel oxide electrode in the potential range from ?100 to ?600 mV (Hg/HgO), can be markedly influenced or fully suppressed as in the case of a sintered nickel oxide electrode. The existence of this discharge step is attributed to differences in the ohmic contacts of the electroactive particles in the pressed electrode.     

Influence of pulse reversal on the PEC performance of pulse-plated CdSe films

This paper embodies the first report on the pulse reversal deposition of CdSe thin films. The as-deposited and heat-treated films were characterised by XRD, optical absorption spectroscopy and electrical properties. The polycrystalline deposits of CdSe obtained indicated a hexagonal structure after heat treatment at 550°C. From the optical absorption measurements the band gap was found to be 1.71 eV. At an illumination of 70 mW cm⁻² conversion efficiencies of 3.20% and 6.57% were obtained for the photoelectrodes without and with pulse reversal.     

Plastic-bonded electrodes for nickel—cadmium accumulators: VII. Influence of different metal screens on the oxygen recombination rate on plastic-bonded cadmium electrodes

The oxygen recombination (reduction) rate on plastic-bonded cadmium electrodes in sealed NiCd systems can be increased by using metal screens applied to the gas side of the plastic-bonded cadmium electrode.The metal screen applied should have an optimum geometry (mesh size, wire diameter) to provide optimum conditions for the existence of a uniform electrolyte film covering the total screen surface. The oxygen recombination rate in such a case is high enough to enable this type of cadmium electrode to be used in practical sealed cells.No major differences between steel and nickel screens were noticed, but with a silver plated screen a substantially enhanced oxygen recombination rate was observed.     

Study of the cell reversal process of large area proton exchange membrane fuel cells under fuel starvation

In this research, the fuel starvation phenomena in a single proton exchange membrane fuel cell (PEMFC) are investigated experimentally. The response characteristics of a single cell under the different degrees of fuel starvation are explored. The key parameters (cell voltage, current distribution, cathode and anode potentials, and local interfacial potentials between anode and membrane, etc.) are measured in situ with a specially constructed segmented fuel cell. Experimental results show that during the cell reversal process due to the fuel starvation, the current distribution is extremely uneven, the local high interfacial potential is suffered near the anode outlet, hydrogen and water are oxidized simultaneously in the different regions at the anode, and the carbon corrosion is proved to occur at the anode by analyzing the anode exhaust gas. When the fuel starvation becomes severer, the water electrolysis current gets larger, the local interfacial potential turns higher, and the carbon corrosion near the anode outlet gets more significant. The local interfacial potential near the anode outlet increases from ca. 1.8 to 2.6 V when the hydrogen stoichiometry decreases from 0.91 to 0.55. The producing rate of the carbon dioxide also increases from 18 to 20 ml min⁻¹.     

Generalized analysis of the illumination intensity vs. open-circuit voltage of solar cells

A new technique to determine the current–voltage characteristics of solar cells based on simultaneously measuring the open-circuit voltage as a function of a slowly varying light intensity has been proposed recently [Sinton and Cuevas, Proc. 16th European Photovoltaic Solar Energy Conf., Glasgow, UK, May 2000, pp. 1152–1155]. This paper presents a detailed theoretical analysis and interpretation of such quasi-steady-state V_oc measurements (QssV_oc). The ability of this analysis to accurately obtain the true steady-state device characteristics even in the case of high lifetime, high resistivity devices is demonstrated experimentally. Besides reasonable choices for the light source (2 and 4 ms exponential flashes), we have also used a rapidly varying illumination (0.35 ms decay rate) to illustrate problems with the existing analysis. The new analysis results in an excellent agreement between the three QssV_oc measurements and the true steady-state and dark I–V curves. An important application of the QssV_oc technique is to determine the minority carrier lifetime, and the new model proves to be especially important to do this accurately.     

The effects of molecular structure on soot formation II. Diffusion flames

Soot thresholds, in the form of flame heights and fuel mass consumption rates at the smoke points, have been measured in atmospheric pressure, laminar diffusion flames of 42 pure hydrocarbons using a wick-fed burner. The smoke point fuel consumption rates were converted into threshold soot indices, TSIs, and compared with fuel structural parameters and with previous data from the literature. Averaged TSI values are given for 103 fuels.Soot particle emission temperatures and line-of-sight averaged soot volume fractions were measured at half the total smoke point flame heights, the location at which the soot concentration maximizes. All of the soot emission temperatures were between 1450 and 1550K, with aromatic fuels exhibiting the highest temperatures. Maximum soot volume fractions ranged from 2 to 11 × 10⁻⁶, with aromatic fuels producing the highest total soot concentrations.     

Effect of anode iridium oxide content on the electrochemical performance and resistance to cell reversal potential of polymer electrolyte membrane fuel cells

An ideal polymer electrolyte membrane fuel cell (PEMFC) is one that continuously generates electricity as long as hydrogen and oxygen (or air) are supplied to its anode and cathode, respectively. However, internal and/or external conditions could bring about the degradation of its electrodes, which are composed of nanoparticle catalysts. Particularly, when the hydrogen supply to the anode is disrupted, a reverse voltage is generated. This phenomenon, which seriously degrades the anode catalyst, is referred to as cell reversal. To prevent its occurrence, iridium oxide (IrO₂) particles were added to the anode in the membrane-electrode assembly of the PEMFC single-cells. After 100 cell reversal cycles, the single-cell voltage profiles of the anode with Pt/C only and the anodes with Pt/C and various IrO₂ contents were obtained. Additionally, the cell reversal-induced degradation phenomenon was also confirmed electrochemically and physically, and the use of anodes with various IrO₂ contents was also discussed.     

Study on the CCM breakdown voltage of proton exchange membrane fuel cells

Proton exchange membrane (PEM) short circuits are one of the failure forms of fuel cells. In this paper, the change in breakdown voltage (BV) after the preparation of PEMs into catalyst coated membranes (CCMs) is studied, and the impact of the catalyst layer (CL) and its composition on the BV of the CCM is analysed. The results show that the BV of the CCM is significantly lower than that of the uncoated PEM. The higher the platinum (Pt) loading of the coated CL is, the lower the BV. Further research finds that the BV of the single-side CL-coated CCM only decreases when the CL side is connected to the positive pole of the power supply, while it is comparable to that of the PEM when the CL side is connected to the negative pole. The experimental results demonstrate that the Pt and carbon particles in the CCM undergo electrochemical reactions during the breakdown process when the CL is connected to the positive pole, which eventually leads to thermal breakdown. Therefore, when the BV is chosen for detecting whether the CCM preparation process causes PEM damage, single-side CL-coated CCM should be adopted, and the CL should be connected to the negative pole of the power supply.     

Influence of unbalanced voltage on the steady-state performance of a three-phase squirrel-cage induction motor

The negative effects of a particular unbalanced voltage on the performance of an induction motor are studied in this paper. The paper suggests that the available definitions of unbalanced voltages are not comprehensive and complete. Therefore, the results of these analyses on motor performance are not very reliable. To prove this claim, a three-phase 25-hp squirrel-cage induction motor is analyzed under different unbalanced conditions. It is shown that it is necessary to define a more precise unbalanced factor for more accurate results. Experimental results verify the theoretical analysis.     

Impact of applied cell voltage on the performance of a microbial electrolysis cell fully catalysed by microorganisms

The effect of the operating voltage on the performance of a microbial electrolysis cell (MEC) equipped with both a bioanode and a biocathode for hydrogen production is reported. Chronoamperometry tests ranged between 0.3 and 2.0 V were carried out after both bioelectrodes were developed. A maximum current density up to 1.6 A m⁻² was recorded at 1.0 V with hydrogen production rate of nearly 6.0 ± 1.5 L m⁻² cathode day⁻¹. Trace amounts of methane, acetone and formate were detected in cathode's headspace and catholyte which followed the same trend as hydrogen production rate. Meanwhile substrate consumption in anolyte also followed the trend of hydrogen production and current density changes. The bioanode could utilise up to 95% of acetate in the tested voltage ranges, however, at a cell voltage of 2.0 V the bioanode's activity stopped due to oxygen evolution from water hydrolysis. Cyclic voltammograms revealed that the bioanode activity was vital to maintain the functionality of the whole system. The biocathode relied on the bioanode to maintain its potential during the hydrogen evolution. The overall energy efficiency recovered from both bioanode and external power in terms of hydrogen production at the cathode was determined as 29.4 ± 9.0%, within which substrate oxidation contributed up to nearly 1/3 of the total energy marking the importance of bioanode recovering energy from wastewater to reduce the external power supply.     

An experimental study on the dynamic process of PEM fuel cell stack voltage

The dynamic characteristics of the proton exchange membrane (PEM) fuel cell are of great importance in its design and applications. In this paper, the dynamic process of stack voltage is analyzed when the current is step inputted. We discuss the process from the following four aspects: voltage variation rate, initial value of dynamic voltage, time to reach steady state and dynamic resistance factor. The analysis results show that the dynamic process of stack voltage responding to current step-up is different from that to current step-down. Additionally, the operating current values also have significant influence on the dynamic characteristics of stack voltage.     

影响烧结过程最初液相形成的因素分析

试验考察添加SiO2、Al2O3和MgO对铁酸盐黏结相(20%CaO-80%Fe2O3)最初液相熔化行为的影响,同时考察对于最初液相形成矿石中脉石含量与CaO的关系。试验结果表明:矿石中的SiO2和Al2O3脉石成分对烧结过程中最初熔体的形成都有抑制作用,但从熔化温度区间考察,2%~6%SiO2的添加可以显著减小熔体的熔化时间,而不同含量Al2O3和MgO的添加都会增加熔体的熔化时间;同时随着矿石中脉石含量的增加,形成最低液相的CaO含量也在增加。     

电动汽车接入方式对配电网静态电压稳定裕度的影响分析

电动汽车负荷具有随机性、间歇性和源荷两重性,当其大规模无序接入配电网时,对电网的安全稳定和经济运行将产生严重影响。本文分析了不同类型电动汽车用户的行为特性,建立了电动汽车功率需求模型,采用蒙特卡洛法预测了未来配电网中各类电动汽车负荷的时空分布规律,在此基础上提出了配电网对电动汽车适应能力的测评方法。以IEEE33节点配电网应用为例,分析了电动汽车充电负荷在不同接入方式下对电网静态电压稳定裕度的影响。     

Influence of ceramic separator on the LiNi0.8Co0.15Al0.05O2 high power Li-ion battery performance

本文以普通聚烯烃隔膜作为对比,研究了不同工艺的聚烯烃基膜制作的陶瓷隔膜对于LiNi_0.8Co_0.15Al_0.05O₂动力锂离子电池性能的影响。表征了三种隔膜的本征性能,包括微孔形貌、透气度和离子电导率。干法基膜陶瓷隔膜、湿法基膜陶瓷隔膜和普通聚烯烃隔膜的透气度值分别为165 sec/100 mL、200 sec/100 mL和520 sec/100 mL;离子电导率分别为0.952 mS/cm²、0.703 mS/cm²和0.622mS/cm²。分别采用三种隔膜制作了容量为2 A·h的软包装电池,评估了电池的倍率性能、循环寿命以及荷电保持能力。结果发现,与普通聚烯烃隔膜相比,陶瓷隔膜可以提高电池的功率性能,并且干法聚烯烃基膜制作的陶瓷隔膜,其倍率增效作用较湿法基膜的陶瓷隔膜明显,尤其当放电倍率达到电池的设计极限时,干法聚烯烃基膜制作的陶瓷隔膜对于电池倍率性能的增效作用更加显著。