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Cell Performance (cell + performance)
Kinds of Cell Performance Selected AbstractsControl of Solid-State Dye-Sensitized Solar Cell Performance by Block-Copolymer-Directed TiO2 SynthesisADVANCED FUNCTIONAL MATERIALS, Issue 11 2010Pablo Docampo Abstract Hybrid dye-sensitized solar cells are typically composed of mesoporous titania (TiO2), light-harvesting dyes, and organic molecular hole-transporters. Correctly matching the electronic properties of the materials is critical to ensure efficient device operation. In this study, TiO2 is synthesized in a well-defined morphological confinement that arises from the self-assembly of a diblock copolymer,poly(isoprene- b -ethylene oxide) (PI- b -PEO). The crystallization environment, tuned by the inorganic (TiO2 mass) to organic (polymer) ratio, is shown to be a decisive factor in determining the distribution of sub-bandgap electronic states and the associated electronic function in solid-state dye-sensitized solar cells. Interestingly, the tuning of the sub-bandgap states does not appear to strongly influence the charge transport and recombination in the devices. However, increasing the depth and breadth of the density of sub-bandgap states correlates well with an increase in photocurrent generation, suggesting that a high density of these sub-bandgap states is critical for efficient photo-induced electron transfer and charge separation. [source] A CdSe Nanowire/Quantum Dot Hybrid Architecture for Improving Solar Cell PerformanceADVANCED FUNCTIONAL MATERIALS, Issue 9 2010Yanghai Yu Abstract Incorporating colloidal CdSe quantum dots (QDs) into CdSe nanowire (NW)-based photoelectrochemical solar cells increases their incident-photon-to-carrier conversion efficiencies (IPCE) from 13% to 25% at 500,nm. While the effect could, in principle, stem from direct absorption and subsequent carrier generation by QDs, the overall IPCE increase occurs across the entire visible spectrum, even at wavelengths where the dots do not absorb light. This beneficial effect originates from an interplay between NWs and QDs where the latter fill voids between interconnected NWs, providing electrically accessible conduits, in turn, enabling better carrier transport to electrodes. The presence of QDs furthermore reduces the residual polarization anisotropy of random NW networks. Introducing QDs therefore addresses an important limiting constraint of NW photoelectrochemical solar cells. The effect appears to be general and may aid the future design and implementation of other NW-based photovoltaics. [source] SOFCo Planar Solid Oxide Fuel CellINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2004Liang A. Xue SOFCo-EFS Holdings LLC has developed a multi-layer, planar solid oxide fuel cell (SOFC) stack that has the potential to provide superior performance and reliability at reduced costs. Our approach combines state-of-the-art SOFC materials with the manufacturing technology and infrastructure established for multi-layer ceramic (MLC) packages for the microelectronics industry. With the proper selection of SOFC materials, implementation of MLC fabrication methods offers unique designs for stacks. Over the past two years, substantial progress has been made in the design and manufacturing development of our second-generation stack. Effective stack and manifold seals have been developed. Cell performance has been improved and relatively low non-cell contributions to stack resistance have been achieved. Stack development has been facilitated through the implementation of two key test methods: (1) a 10-cm single-cell test to bridge the gap in performance data obtained from button cell tests (used for cell R&D) and stack tests; and (2) a novel instrumented short stack (<5 cells) that allows for effective isolation of individual contributions to stack resistance. As a result of progress made to date, a clear pathway for improving stack performance has been established, thereby building confidence that commercial stack performance targets will be reached. [source] Transport mechanisms and performance simulation of a PEM fuel cellINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2008Geng-Po Ren Abstract A three-dimensional, gas,liquid two-phase flow and transport model has been developed and utilized to simulate the multi-dimensional, multi-phase flow and transport phenomena in both the anode and cathode sides in a proton exchange membrane (PEM) fuel cell and the cell performance with different influencing operational and geometric parameters. The simulations are presented with an emphasis on the physical insight and fundamental understanding afforded by the detailed distributions of velocity vector, oxygen concentration, water vapor concentration, liquid water concentration, water content in the PEM, net water flux per proton flux, local current density, and overpotential. Cell performances with different influencing factors are also presented and discussed. The comparison of the model prediction and experimental data shows a good agreement. Copyright © 2007 John Wiley & Sons, Ltd. [source] Thermal modeling and simulation of an integrated solid oxide fuel cell and charcoal gasification systemENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY, Issue 3 2009C. Ozgur Colpan Abstract In this study we propose a novel integrated charcoal gasification and solid oxide fuel cell (SOFC) system, which is intended to produce electricity and heat simultaneously. This system mainly consists of an updraft gasifier using air and steam as the gasification agents, a planar and direct internal reforming SOFC and a low temperature gas cleanup system. The performance of this system is assessed through numerical modeling using a pre-developed and validated heat transfer model of the SOFC and thermodynamic models for the rest of the components. These models are used to simulate the performance of the cell and system for a case study. In addition, a parametric study is conducted to assess the effect of Reynolds number at the fuel channel inlet of the SOFC on the cell performance, e.g., fuel utilization and power density, and the system performance, e.g., electrical efficiency, exergetic efficiency, and power to heat ratio. The number of stacks is also calculated for different Reynolds numbers to discuss the economical feasibility of the integrated system. The results show that the electrical efficiency, exergetic efficiency and power to heat ratio of this system are 33.31%, 45.72%, and 1.004, respectively, for the base case. The parametric study points out that taking the Reynolds number low yields higher electrical and exergetic efficiencies for the system, but it also increases the cost of the system. © 2009 American Institute of Chemical Engineers Environ Prog, 2009 [source] Non-Corrosive, Non-Absorbing Organic Redox Couple for Dye-Sensitized Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Dongmei Li Abstract A new colorless electrolyte containing an organic redox couple, tetramethylthiourea (TMTU) and its oxidized dimer tetramethylformaminium disulfide dication ([TMFDS]2+), is applied to dye-sensitized solar cells (DSCs). Advantages of this redox couple include its non-corrosive nature, low cost, and easy handling. More impressively, it operates well with carbon electrodes. The DSCs fabricated with a lab-made HCS-CB carbon counter-electrode can present up to 3.1% power conversion efficiency under AM 1.5 illumination of 100 mW·cm,2 and 4.5% under weaker light intensities. This result distinctly outperforms the identical DSCs with a Pt electrode. Corrosive experiments reveal that Al and stainless steel (SS) sheets are stable in the [TMFDS]2+/TMTU-based electrolyte. Its electrochemical impedance spectrum (EIS) is used to evaluate the influence of different counter-electrodes on the cell performance, and preliminary investigations reveal that carbon electrodes with large surface areas and ideal corrosion-inertness toward the sulfur-containing [TMFDS]2+/TMTU redox couple exhibit promise for application in iodine-free DSCs. [source] Solution Processable Fluorenyl Hexa- peri -hexabenzocoronenes in Organic Field-Effect Transistors and Solar CellsADVANCED FUNCTIONAL MATERIALS, Issue 6 2010Wallace W. H. Wong Abstract The organization of organic semiconductor molecules in the active layer of organic electronic devices has important consequences to overall device performance. This is due to the fact that molecular organization directly affects charge carrier mobility of the material. Organic field-effect transistor (OFET) performance is driven by high charge carrier mobility while bulk heterojunction (BHJ) solar cells require balanced hole and electron transport. By investigating the properties and device performance of three structural variations of the fluorenyl hexa- peri -hexabenzocoronene (FHBC) material, the importance of molecular organization to device performance was highlighted. It is clear from 1H NMR and 2D wide-angle X-ray scattering (2D WAXS) experiments that the sterically demanding 9,9-dioctylfluorene groups are preventing ,,, intermolecular contact in the hexakis-substituted FHBC 4. For bis-substituted FHBC compounds 5 and 6, ,,, intermolecular contact was observed in solution and hexagonal columnar ordering was observed in solid state. Furthermore, in atomic force microscopy (AFM) experiments, nanoscale phase separation was observed in thin films of FHBC and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) blends. The differences in molecular and bulk structural features were found to correlate with OFET and BHJ solar cell performance. Poor OFET and BHJ solar cells devices were obtained for FHBC compound 4 while compounds 5 and 6 gave excellent devices. In particular, the field-effect mobility of FHBC 6, deposited by spin-casting, reached 2.8,×,10,3,cm2 V,1 s and a power conversion efficiency of 1.5% was recorded for the BHJ solar cell containing FHBC 6 and PC61BM. [source] Study of the Catalytic Layer in Polybenzimidazole-based High Temperature PEMFC: Effect of Platinum Content on the Carbon SupportFUEL CELLS, Issue 2 2010J. Lobato Abstract In this work, the effect of platinum percentage on the carbon support of commercial catalyst for electrodes to be used in a Polybenzimidazole (PBI)-based PEMFC has been studied. Three percentages were studied (20, 40 and 60%). In all cases, the same quantity of PBI in the catalyst layer was added, which is required as a ,binder'. From Hg porosimetry analyses, pore size distribution, porosity, mean pore size and tortuosity of all electrodes were obtained. The amount of mesopores gets larger as the platinum percentage in the catalytic layer decreases, which reduces the overall porosity and the mean pore size and increases the tortuosity. The electrochemical characterisation was performed by voltamperometric studies, assessing the effective electrochemical surface area (ESA) of the electrodes, by impedance spectroscopy (IS), determining the polarisation resistance, and by the corresponding fuel cell measurements. The best results were obtained for the electrodes with a content of 40% Pt on carbon, as a result of an adequate combination of catalytic activity and mass transfer characteristics of the electrode. It has been demonstrated that the temperature favours the fuel cell performance, and the humidification does not have remarkable effects on the performance of a PBI-based polymer electrolyte membrane fuel cell (PEMFC). [source] Visualising Liquid Water in PEM Fuel Cells Using Neutron Imaging,FUEL CELLS, Issue 5 2009R. Mukundan Abstract In this article, we review the neutron imaging techniques that have been used to visualise liquid water in PEM fuel cells. A list of the various facilities engaged in this research is provided and the published literature in this field reviewed. Neutron imaging has been successfully used to visualise water dynamics in the flow channels of operating fuel cells. This technique has also been used to understand water removal mechanisms and the importance of membrane hydration and GDL flooding to optimal fuel cell performance. More recently this technique has been applied to imaging the water in fuel cell cross-sections in order to quantify the water contents in the different components of an operating fuel cell. Finally, this technique has also been utilised to examine ice formation during sub-zero operation of single fuel cells. With ongoing improvements in spatial and temporal resolution, neutron imaging can be expected to play a greater role in any fuel cell development related to water transport. [source] Testing a Vapour-fed PBI-based Direct Ethanol Fuel CellFUEL CELLS, Issue 5 2009J. Lobato Abstract This work is focused on the application and performance of a high temperature PBI-based direct ethanol fuel cell, studying the influence of some operating variables such as the temperature, ethanol concentration and oxygen partial pressure. An increase in the temperature resulted in an improvement of the cell performance due to the enhanced electrodic kinetic and electrolyte conductivity. An ethanol/water weight ratio between 0.25 and 0.5 was found to be suitable for providing both enough water and fuel availability to make the ethanol oxidation possible. Measurements of the ethanol crossover at different temperatures and concentrations were carried out. An intermittent lifetime test showed that the cell, after several hours, was able to reach stability. Moreover, its performance was completely reversible with no perceptible losses for 7,days. Finally, tests using bio-ethanol as fuel were performed, with no significant power losses. This final feature is of special interest from a practical ,green' point of view. [source] Charge Generation and Photovoltaic Operation of Solid-State Dye-Sensitized Solar Cells Incorporating a High Extinction Coefficient Indolene-Based SensitizerADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Henry J. Snaith Abstract An investigation of the function of an indolene-based organic dye, termed D149, incorporated in to solid-state dye-sensitized solar cells using 2,2,,7,7,-tetrakis(N,N -di- p -methoxypheny-amine)-9,9,-spirobifluorene (spiro-OMeTAD) as the hole transport material is reported. Solar cell performance characteristics are unprecedented under low light levels, with the solar cells delivering up to 70% incident photon-to-current efficiency (IPCE) and over 6% power conversion efficiency, as measured under simulated air mass (AM) 1.5 sun light at 1 and 10,mW cm,2. However, a considerable nonlinearity in the photocurrent as intensities approach "full sun" conditions is observed and the devices deliver up to 4.2% power conversion efficiency under simulated sun light of 100,mW cm,2. The influence of dye-loading upon solar cell operation is investigated and the thin films are probed via photoinduced absorption (PIA) spectroscopy, time-correlated single-photon counting (TCSPC), and photoluminescence quantum efficiency (PLQE) measurements in order to deduce the cause for the non ideal solar cell performance. The data suggest that electron transfer from the photoexcited sensitizer into the TiO2 is only between 10 to 50% efficient and that ionization of the photo excited dye via hole transfer directly to spiro-OMeTAD dominates the charge generation process. A persistent dye bleaching signal is also observed, and assigned to a remarkably high density of electrons "trapped" within the dye phase, equivalent to 1.8,×,1017,cm,3 under full sun illumination. it is believed that this localized space charge build-up upon the sensitizer is responsible for the non-linearity of photocurrent with intensity and nonoptimum solar cell performance under full sun conditions. [source] Effects of Solvent Mixtures on the Nanoscale Phase Separation in Polymer Solar Cells,ADVANCED FUNCTIONAL MATERIALS, Issue 12 2008Yan Yao Abstract The mixed solvent approach has been demonstrated as a promising method to modify nanomorphology in polymer solar cells. This work aims to understand the unique role of the additive in the mixture solvent and how the optimized nanoscale phase separation develops laterally and vertically during the non-equilibrium spin-coating process. We found the donor/acceptor components in the active layer can phase separate into an optimum morphology with the additive. Supported by AFM, TEM and XPS results, we proposed a model and identified relevant parameters for the additive such as solubility and vapor pressures. Other additives are discovered to show the ability to improve polymer solar cell performance as well. [source] Cover Picture: Tuning the Dimensions of C60 -Based Needlelike Crystals in Blended Thin Films (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 6 2006Mater. Abstract A new ordered structure of the C60 derivative PCBM is obtained in thin films based on the blend PCBM:P3HT, as detailed by Swinnen, Manca, and co-workers on p.,760. Needlelike crystalline PCBM structures, whose dimensions and spatial distribution ca be tuned by adjusting the blend ratio and annealing conditions, are formed. In typical solar-cell applications of these blended films, these results indicate that during long-term operation under normal conditions (50,70,°C) morphology changes and a decrease in cell performance could occur. A new ordered structure of the C60 derivative PCBM ([6-6]-phenyl C61 -butyric acid methyl ester) is obtained in thin films based on the blend PCBM:regioregular P3HT (poly(3-hexylthiophene)). Rapid formation of needlelike crystalline PCBM structures of a few micrometers up to 100,,m in size is demonstrated by submitting the blended thin films to an appropriate thermal treatment. These structures can grow out to a 2D network of PCBM needles and, in specific cases, to spectacular PCBM fans. Key parameters to tune the dimensions and spatial distribution of the PCBM needles are blend ratio and annealing conditions. The as-obtained blended films and crystals are probed using atomic force microscopy, transmission electron microscopy, selected area electron diffraction, optical microscopy, and confocal fluorescence microscopy. Based on the analytical results, the growth mechanism of the PCBM structures within the film is described in terms of diffusion of PCBM towards the PCBM crystals, leaving highly crystalline P3HT behind in the surrounding matrix. [source] A finite volume method for multicomponent gas transport in a porous fuel cell electrodeINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 6 2003John M. Stockie Abstract We present a mathematical model for multicomponent gas transport in an anisotropic fuel cell electrode. The model couples the Maxwell,Stefan equations for multicomponent diffusion along with Darcy's law for flow in a porous medium. The equations are discretized using a finite volume approach with the method of lines, and the resulting non-linear system of differential equations is integrated in time using a stiff ODE solver. Numerical simulations are performed to validate the model and to investigate the effect of various parameters on fuel cell performance. Copyright © 2003 John Wiley & Sons, Ltd. [source] A Conjugated Polymer for Near Infrared Optoelectronic Applications,ADVANCED MATERIALS, Issue 20 2007E. Perzon A new conjugated polymer, LBPP-1, with an unusually low band-gap (ca.,1.0,eV) is presented. Light absorption and photovoltaic response up to 1200,nm in composites with a fullerene is demonstrated. Solar cell performance is presented and the polymer's suitability for photodetection in the infrared region is discussed. [source] Effect of anode current collector on the performance of passive direct methanol fuel cellsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2009Qin-Zhi Lai Abstract The effect of anode current collector on the performance of passive direct methanol fuel cell (DMFC) was investigated in this paper. The results revealed that the anode of passive DMFC with perforated current collector was poor at removing the produced CO2 bubbles that blocked the access of fuel to the active sites and thus degraded the cell performance. Moreover, the performances of the passive DMFCs with different parallel current collectors and different methanol concentrations at different temperatures were also tested and compared. The results indicated that the anode parallel current collector with a larger open ratio exhibited the best performance at higher temperatures and lower methanol solution concentrations due to enhanced mass transfer of methanol from the methanol solution reservoir to the gas diffusion layer. However, the passive DMFC with a smaller open ratio of the parallel current collector exhibited the best performance at lower temperatures and higher methanol solution concentrations due to the lower methanol crossover rate. Copyright © 2009 John Wiley & Sons, Ltd. [source] Behaviour modelling of a PEMFC operating on diluted hydrogen feedINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2008M. Minutillo Abstract The polymer electrolyte membrane fuel cell (PEMFC) using reformate gas as fuel is regarded as an attractive solution for the near-term introduction of fuel cells in stationary or mobile power generation market. With respect to hydrogen feeding, the reformate gas fuelling involves additional polarization losses because of the hydrogen dilution and the impurities contained in the gas. In this paper a one-dimensional model has been developed to investigate the behaviour of a PEMFC operating with reformate gas mixture. The model, based on a semi-empirical approach, considers the kinetic reactions in the anode side taking into account the effect of reverse water,gas shift (RWGS) due to the presence of CO2 in the fuel. As it is well known, the exhaust stream from fuel reformers can contain a high carbon dioxide concentration (>20%) that can have a detrimental effect on the fuel cell performance because of the combination of the dilution and the formation of CO by the RWGS reaction. The numerical simulation results have been compared with the experimental data, obtained in the test room of Industrial Engineering Department of Cassino University, and a good match has been observed. The model has been developed by using a simplified approach that, nevertheless, can allow to obtain a good numerical prediction of the fuel cell performance reducing the simulation time and computational efforts. Copyright © 2008 John Wiley & Sons, Ltd. [source] Transport mechanisms and performance simulation of a PEM fuel cellINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2008Geng-Po Ren Abstract A three-dimensional, gas,liquid two-phase flow and transport model has been developed and utilized to simulate the multi-dimensional, multi-phase flow and transport phenomena in both the anode and cathode sides in a proton exchange membrane (PEM) fuel cell and the cell performance with different influencing operational and geometric parameters. The simulations are presented with an emphasis on the physical insight and fundamental understanding afforded by the detailed distributions of velocity vector, oxygen concentration, water vapor concentration, liquid water concentration, water content in the PEM, net water flux per proton flux, local current density, and overpotential. Cell performances with different influencing factors are also presented and discussed. The comparison of the model prediction and experimental data shows a good agreement. Copyright © 2007 John Wiley & Sons, Ltd. [source] Along-channel mathematical modelling for proton exchange membrane fuel cellsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2005Wenbo Huang Abstract Proper water and thermal management is essential for obtaining high performance of proton exchange membrane fuel cells (PEMFCs). A steady, two-dimensional water and thermal management model was developed, aiming at considering pressure effects (i.e. the effects of local pressure on the cell performance), pressure drop, open circuit voltage variation with stack temperature, water vapour effects on membrane conductivity, which made the model physically more reasonable and more suitable for various operating conditions. The model could predict the distributions of a series of important parameters along the flow channel, and thus the effects of various operating and design parameters on the fuel cell performance could be investigated easily by numerical trial-and-error method. The modelling results compared well with the available experimental results from the literatures. The results also showed that the humidification of both anode and cathode is crucial for the performance of PEMFCs. The model could be a very useful engineering tool for the optimization of PEMFCs. Copyright © 2005 John Wiley & Sons, Ltd. [source] Intelligent structure design of membrane cathode assembly for direct methanol fuel cellINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2005K. Furukawa Abstract The performance and the structural model of membrane electrode assembly (MEA) have been developed and experimentally verified with fundamental calculations of the direct methanol fuel cell (DMFC). The model provides information concerning the influence of the operating and structural parameters. The composition and performance optimization of MEA structure in DMFC has been investigated by including both electrochemical reaction and mass transport process. In the experimentation, the effect of Nafion content and loading method in the catalyst layer of cathode for DMFC was investigated. For the spray method electrode (SME), the cell performance and cathode performance using a dynamic hydrogen electrode (DHE) as a reference electrode was improved in comparison with those of the PME electrode by decreasing cathode potential. From ac impedance measurements of the cathode, the adsorption resistance of the SME electrode was decreased compared with that of the PME electrode. The higher cell performance was mostly dependent on the adsorption resistance. In the modelling, the cathode overpotential was decreased with increasing ionomer content, due to increasing ionic conductivity for proton transfer and the larger reaction site. The resistance to oxygen transport was increased at the same time, and became dominant at higher ionomer loadings, leading to an increase in the voltage loss. The ratio of ionomer to void space in the cathode affected the cathode polarization, which had the lowest resistance of oxygen diffusion at the ratio of 0.1,0.2. Copyright © 2005 John Wiley & Sons, Ltd. [source] The impact of flow field pattern on concentration and performance in PEMFCINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2005A. Su Abstract In this study, we present a rigorous mathematical model, to treat prediction and analysis of proton exchange membrane fuel cells gas concentration and current density distribution in mass transfer area and chemical reaction area performed in 3-D geometry. The model is based on the solution of the conservation equations of mass, momentum, species, and electric current in a fully integrated finite-volume solver using the CFDRC commercial code. The influences of fuel cell performance with two kinds of flow channel pattern design are studied. The gas concentration of the straight flow pattern appears excessively non-uniform, resulting in a local concentration polarization. On the other hand, the gas concentration is well distributed for the serpentine flow pattern, creating a better mass transfer phenomena. The performance curves (polarization curves) are also well correlated with experimental data. Copyright © 2005 John Wiley & Sons, Ltd. [source] Numerical simulation of thermal,hydraulic characteristics in a proton exchange membrane fuel cellINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2003Y.M. Ferng Abstract The thermal,hydraulic characteristics of a proton exchange membrane fuel cell (PEMFC) are numerically simulated by a simplified two-phase, multi-component flow model. This model consists of continuity, momentum, energy and concentration equations, and appropriate equations to consider the varying flow properties of the gas,liquid two-phase region in a PEMFC. This gas,liquid two-phase characteristic is not considered in most of the previous simulation works. The calculated thermal,hydraulic phenomena of a PEMFC are reasonably presented in this paper, which include the distributions of flow vector, temperature, oxygen concentration, liquid water saturation, and current density, etc. Coupled with the electrochemical reaction equations, current flow model can predict the cell voltage vs current density curves (i.e. performance curves), which are validated by the single-cell tests. The predicted performance curves for a PEMFC agree well with the experimental data. In addition, the positive effect of temperature on the cell performance is also precisely captured by this model. The model presented herein is essentially developed from the thermal,hydraulic point of view and can be considered as a stepping-stone towards a full complete PEMFC simulation model that can help the optima design for the PEMFC and the enhancement of cell efficiency. Copyright © 2003 John Wiley & Sons, Ltd. [source] Photogalvanic effect in aqueous Methylene blue nickel mesh systems: Conversion of light into electricityINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2001Ilker S. Bayer Abstract The photogalvanic effect in electrochemical cells, employing aqueous Methylene blue and Fe(II)/Fe(III) couple electrolyte and nickel-mesh electrodes, were experimentally investigated. Five different standard H-cell configurations were set-up by modifying the electrolyte. Long-term open-circuit voltage measurements were conducted in order to test the stability of the cells. Light on,off reproducibility experiments were also carried out during lengthy cell operations. By comparing experimental quantum yield with theoretical predictions, it was found that the cells operate on differential electrode kinetics. Oxidation of the illuminated electrode was detected. This affected the current,voltage characteristics of the cells after a sufficiently long cell operation. Schottky junction treatment was used to model the electrolyte,electrode junction. After calculating the ratio between the majority carrier (electron) current density and minority carrier (hole) current density, we concluded that the oxidation of the electrodes contributes positively to the cell performance since the electrode,electrolyte interface shows unipolar Schottky diode characteristics. Copyright © 2001 John Wiley & Sons, Ltd. [source] The ethanol stress response and ethanol tolerance of Saccharomyces cerevisiaeJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2010D. Stanley Summary Saccharomyces cerevisiae is traditionally used for alcoholic beverage and bioethanol production; however, its performance during fermentation is compromised by the impact of ethanol accumulation on cell vitality. This article reviews studies into the molecular basis of the ethanol stress response and ethanol tolerance of S. cerevisiae; such knowledge can facilitate the development of genetic engineering strategies for improving cell performance during ethanol stress. Previous studies have used a variety of strains and conditions, which is problematic, because the impact of ethanol stress on gene expression is influenced by the environment. There is however some commonality in Gene Ontology categories affected by ethanol assault that suggests that the ethanol stress response of S. cerevisiae is compromised by constraints on energy production, leading to increased expression of genes associated with glycolysis and mitochondrial function, and decreased gene expression in energy-demanding growth-related processes. Studies using genome-wide screens suggest that the maintenance of vacuole function is important for ethanol tolerance, possibly because of the roles of this organelle in protein turnover and maintaining ion homoeostasis. Accumulation of Asr1 and Rat8 in the nucleus specifically during ethanol stress suggests S. cerevisiae has a specific response to ethanol stress although this supposition remains controversial. [source] Mathematical modeling of solid oxide fuel cells at high fuel utilization based on diffusion equivalent circuit modelAICHE JOURNAL, Issue 5 2010Cheng Bao Abstract Mass transfer and electrochemical phenomena in the membrane electrode assembly (MEA) are the core components for modeling of solid-oxide fuel cell (SOFC). The general MEA model is simply governed with the Stefan-Maxwell equation for multicomponent gas diffusion, Ohm's law for the charge transfer and the current-overpotential equation for the polarization calculation. However, it has obvious discrepancy at high-fuel utilization or high-current density. An advanced MEA model is introduced based on the diffusion equivalent circuit model. The main purpose is to correct the real-gas concentrations at the triple-phase boundary by assuming that the resistance of surface diffusion is in series with that of the gaseous bulk diffusion. Thus, it can obtain good prediction of cell performance in a wide range by avoiding the decrement of effective gas diffusivity via unreasonable increment of the electrode tortuosity in the general MEA model. The mathematical model has been validated in the cases of H2H2O, COCO2 and H2CO fuel system. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Preparation of LiMn2O4 powders via spray pyrolysis and fluidized bed hybrid systemAICHE JOURNAL, Issue 7 2006Izumi Taniguchi Abstract A novel technique has been developed to directly produce fine ceramic powders from liquid solution using a spray pyrolysis and fluidized bed hybrid system. Using this technique, the preparation of lithium manganese oxides LiMn2O4, which are the most promising cathode materials for lithium-ion batteries, has been carried out for various superficial gas velocities U0 = 0.30-0.91 m/s, static bed heights Ls = 50-150 mm, and medium particle sizes dpm,g = 294-498 ,m. The resulting powders had spherical nanostructured particles that comprised primary particles with a few tens of nanometer in size, and they exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Moreover, the as-prepared powders showed better crystallinity and smaller specific surface area than those by conventional spray pyrolysis. The effects of process parameters on powder properties, such as specific surface area and crystallinity, were investigated for a wide range of superficial gas velocities and static bed heights. An as-prepared sample was used as cathode active materials for lithium-ion batteries and the cell performance has been investigated. Test experiments in the electrochemical cell Li/1M LiClO4 in PC/LiMn2O4 demonstrated that the sample prepared by the present technique was superior to that by the conventional spray pyrolysis and solid-state reaction method. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source] In situ observation of water distribution and behaviour in a polymer electrolyte fuel cell by synchrotron X-ray imagingJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2008Taihei Mukaide In situ visualization of the distribution and behaviour of water in a polymer electrolyte fuel cell during power generation has been demonstrated using a synchrotron X-ray imaging technique. Images were recorded using a CCD detector combined with a scintillator (Gd2O2S:Tb) and relay lens system, which were placed at 2.0,m or 2.5,m from the fuel cell. The images were measured continuously before and during power generation, and data on cell performance was recorded. The change of water distribution during power generation was obtained from X-ray images normalized with the initial state of the fuel cell. Compared with other techniques for visualizing the water in fuel cells, this technique enables the water distribution and behaviour in the fuel cell to be visualized during power generation with high spatial resolution. In particular, the effects of the specifications of the gas diffusion layer on the cathode side of the fuel cell on the distribution of water were efficiently identified. This is a very powerful technique for investigating the mechanism of water flow within the fuel cell and the relationship between water behaviour and cell performance. [source] Electrode Properties of the Ruddlesden,Popper Series, Lan+1NinO3n+1 (n=1, 2, and 3), as Intermediate-Temperature Solid Oxide Fuel CellsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2010Suguru Takahashi The Ruddlesden,Popper phases, Lan+1NinO3n+1 (n=1, 2, and 3), were synthesized by a solid-state reaction for use as cathodes in an intermediate-temperature (500°,700°C) solid oxide fuel cell. The samples crystallized into an orthorhombic layered perovskite structure. The overall electrical conductivity increased with the increase of n in the intermediate temperature range. Single test-cells, which consisted of samarium-oxide-doped ceria (SDC; Sm0.2Ce0.8Ox) as an electrolyte, Ni,SDC cermet (Ni,SDC) as an anode, and Lan+1NinO3n+1 as a cathode, were fabricated for measurements of cell performance at 500°,700°C. Current interruption measurements revealed that both the ohmic and overpotential losses at 700°C decreased with the increase of n. La4Ni3O10 was found to exhibit the best cathode characteristics in the Lan+1NinO3n+1 series. Maximum test-cell power densities with La4Ni3O10 (n=3) were 10.2, 36.5, and 88.2 mW/cm2 at 500°, 600°, and 700°C, respectively. [source] Regeneration of large bone defects in sheep using bone marrow stromal cellsJOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE, Issue 5 2008P. Giannoni Abstract Bone repair was addressed in a critical-sized defect model in sheep, combining a ceramic biomaterial and mesenchymal progenitor cells. The defects in the tibial mid-diaphysis were treated with autologous bone or with a silicon-stabilized tricalcium phosphate biomaterial, implemented or not by the addition of expanded bone marrow stromal cells. An internal locking compression plate and an external fixator were applied for stabilization. Radiographies were taken during the 8 months follow-up: the pixel grey levels of the lesion areas were determined to evaluate the repair process radiologically. Microradiography, histology and vascular density tests were performed. The autologous bone-treated group performed best, as assessed radiologically, within 20,24 weeks after surgery. Very limited healing was detected in the other experimental group: a partial bone deposition occurred at the periphery of the bony stumps only in the cell-seeded scaffolds. Interestingly, this effect ended within 20,24 weeks, as for the autologous bone, suggesting similar kinetics of the repair processes involved. Moreover, bone deposition was located where a significant reduction of the ceramic scaffold was detected. Faxitron microradiography and histology data confirmed these results. Vascular density analysis evidenced that cell-seeded scaffolds supported an increased vascular ingrowth. Thus, the interactions with the proper microenvironment and the oxygen and nutrient supply in the inner part of the constructs seem fundamental to initiate scaffold substitution and to improve cell performance in tissue-engineered approaches to bone repair. Copyright © 2008 John Wiley & Sons, Ltd. [source] Electrochemical preparation of MoO3 buffer layer deposited onto the anode in organic solar cellsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2010M. Gacitua Abstract In this work the authors have studied the advantages of using electrochemically deposited molybdenum oxide as a buffer layer in an organic bilayer heterojunction solar cell arrangement. Furthermore, it has been probed that electrochemistry provides an alternative low cost, reproducible and less laborious method to prepare thin layered deposits. The precursor solution is composed by a concentrated molybdic acid solution in a sulphuric media in order to ensure the obtainment of low reduced molybdenum species. Therefore, by means of potentiostatic techniques, ITO/molybdenum oxide transparent anodes were tested for the photovoltaic device showing improved surface properties. XDR and AFM techniques were used to characterize the morphology of the deposits. The films with optimum thickness (5,nm) are amorphous. XPS analysis indicates that the best results in solar cell performance are in hand with a heterogeneous composition of the molybdenum oxide film presenting MoV and MoVI as predominant species. The MoO3 films deposited by cyclic voltammetry are not as homogeneous as those deposited by potentiostatic technique and only MoVI species are present. These differences may justify the different behaviour of the solar cells using these different buffer layers. Only buffer layers deposited by potentiostatic technique allow improving the cells performances in the same way than those achieved by evaporation. [source] | ||||||||||||||||||||||