bluuebunny/crossref_metadata_2025 huggingface dataset:
A Theoretical Study of the Effects of Two-Phase Transport Properties of the Catalyst and Gas Diffusion Layers in the Cathode on the Performance of a PEMFC
Authors: Wang Xuhai , Nguyen T. V. V.
Published: September 2007

Two-phase transport exists in the cathode of a PEMFC because liquid water is generated during operation by the oxygen reduction reaction and electro-osmotic drag of water from the anode. Its presence affects the transport rate of oxygen to the reactive sites in the catalyst layer of the cathode by reducing the gas pore volume and blocking the catalyst surface. To study the impact of the two-phase transport properties of the GDL and CL on the liquid water transport rate and the effect of the liquid water saturation levels in these porous layers on the performance of a PEMFC, a two-phase model using experimentally measured two-phase transport properties is developed. The simulated results show that the fuel cell performance and the liquid water saturation levels in the CL and GDL depend on both the individual two-phase properties of these two components and their interactions at the GDL/CL interface.
PEMFC Poisoning with H2S: Dependence on Operating Conditions
Authors: Urdampilleta Idoia , Uribe Francisco , Rockward Tommy , Brosha Eric L. , Pivovar Bryan , Garzon F. H.
Published: September 2007

H2S is a well known poison for polymer electrolyte fuel cells. In this work we have found that the severity of H2S poisoning depends on H2S concentration, dosage, cell temperature and anode humidification. We found catalyst poisoning by H2S was cumulative and highly irreversible. After poisoning, further cell operation on neat hydrogen resulted only in modest performance recovery. Full recovery could usually be attained after repetitive cyclic voltammetry between 0 and 1.4 V. We discuss improvements of cell tolerance to H2S and performance recovery using other strategies, such as holding the cell at open circuit and anode air bleed during operation. We discuss the possible implications of H2S crossover on cathode performance.
Dual-Pathway Kinetics Assessment of Sulfur Poisoning of the Hydrogen Oxidation Reaction at High-Surface-Area Platinum/Vulcan Carbon Electrodes
Authors: Pietron Jeremy J.
Published: September 2007

Hydrogen oxidation reaction (HOR) kinetics were measured at films of high-surface-area platinum/Vulcan carbon (Pt/VC) exposed to aqueous solutions of mercaptopropionic acid (MPA), a water-soluble organosulfur compound, using rotating disk voltammetry. Results were fitted to a recently developed dual-pathway kinetics model. At all levels of sulfur coverage (0-96% of a monolayer of MPA), the potential-independent Tafel-Volmer pathway, or two-site HOR pathway, seems largely unaffected. Decreases in current at low overpotentials are accounted for entirely by loss in surface area of the electrode due to site occlusion by the adsorbed organosulfur. Rates for the single site, potential-dependent Heyrovsky-Volmer pathway decrease by a factor of 10 after the initial MPA exposure (50% of a monolayer), indicating an electronic effect of sulfur on the potential-dependent Heyrovsky reaction.
Start/Stop and Local H2 Starvation Mechanisms of Carbon Corrosion: Model vs. Experiment
Authors: Gu Wenbin , Carter Robert N. , Yu Paul T. , Gasteiger Hubert A.
Published: September 2007

This paper discusses fundamental models developed to predict cathode carbon support corrosion induced by start-stop and local H2 starvation in a PEM (proton exchange membrane) fuel cell. The model incorporating the electrode pseudo-capacitance agrees well with controlled start/stop experiments. When the pseudo-capacitive effect is included, the model not only captures the difference in CO2 evolution between start and stop, but also matches the measured spatially resolved mass activity and limiting current distribution of the damaged cathode electrode. For long H2/air-front residence times during start/stop, commonly used in accelerated materials tests, the electrode damage predicted by the capacitive model is similar to that predicted by previously published models that neglect pseudo-capacitive effects. However, for application relevant shorter residence times, significantly lower damages are predicted when capacitive effects are included, consistent with experiments. Because local H2 starvation occurs on a longer time scale, pseudo-capacitive effects are less significant.
Corrosion of Polymer-Electrolyte Fuel Cells Caused by Water at the Fuel Inlet
Authors: Darling Robert M. , Jayne David
Published: September 2007

The influence of water management on corrosion in a polymer-electrolyte fuel-cell stack was explored. CO2 evolution from the cathode was monitored during operation with a simulated reformed hydrocarbon fuel. CO2 production was observed when the dew point of the fuel exceeded the cell temperature in the vicinity of the fuel inlet. Rapid CO2 evolution was absent when dry fuel was supplied to the stack. The potentials of individual cells within the stack fluctuated in concert with the CO2 signals.
Stability of Corrosion-Resistant Magnéli-Phase Ti4O7-Supported PEMFC Catalysts
Authors: Ioroi Tsutomu , Senoh Hiroshi , Siroma Zyun , Yamazaki Shin-ichi , Fujiwara Naoko , Yasuda Kazuaki
Published: September 2007

Sub-stoichiometric titanium oxide (Ti4O7)-supported Pt catalysts were prepared and their electrochemical properties, particularly the effects of high potential conditions on the activity and stability of Pt/Ti4O7 catalysts, were examined in comparison to those of Pt/C catalyst. Polarization measurements using MEAs revealed that the Pt/Ti4O7 cathode shows similar activity for the oxygen reduction reaction as Pt/C catalyst at 80oC. A high-potential holding test (1 hour holding at 1.0 - 1.5 V vs. anode) demonstrated that the Pt/Ti4O7 catalyst is quite stable against high potential up to 1.5 V. Similar results were obtained in potential step tests (0.9 V-30 sec./1.3 V-30 sec.). A single cell using a Pt/Ti4O7 cathode was operated at 80oC, and voltage stability for >350 hours with H2/O2 was also demonstrated.
Use of FTIR to Analyze Ex-Situ and In-Situ Degradation of Perfluorinated Fuel Cell Ionomers
Authors: Delaney William E. , Liu Wen
Published: September 2007

A vapor phase peroxide test was developed and compared to aqueous Fenton's test and to in-situ fuel cell operation. FTIR was used to examine the ratio of carboxyl created by degradation to a CF2 overtone band. A mechanism for attack of the PFSA ionomer in fuel cells is suggested.
Kinetic Analysis of Methanol Oxidation on Pt/C and PtRu/C Catalysts Under Different Temperatures
Authors: Zhang Lu , Cheng Xuan , Tu Haitao , You Mengdi , Zhang Ying , Fan Qinbai
Published: September 2007

The kinetic parameters including Tafel slope, exchange current density and activation energy of methanol oxidation on Pt/C and PtRu/C catalysts in different methanol concentrations (0.1, 0.5, 1, 2 mol-L-1) and different temperatures (30oC, 60oC, 80oC) were evaluated using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). It was found that the exchange current densities of Pt/C were nearly 104 lower than those of PtRu/C, while the activation energies of PtRu/C were larger than those of Pt/C, in particular at low methanol concentrations. The change of rate determination steps was suggested to be mainly responsible for the distinctive characteristics of methanol oxidation on PtRu/C and Pt/C catalysts.
Observation of PtRu Particle Aging in Methanol with X-ray Absorption Spectroscopy
Authors: Shyam Badri , Arruda Thomas , Ziegelbauer Joesph , Mukerjee Sanjeev , Ramaker David
Published: September 2007

The dissolution/agglomeration of Ru and Pt from supported PtRu/C in an electrochemical cell, with potential cycling between 0.02 and 0.8 V, are reported. Two different commercial PtRu black catalysts (Johnson-Matthey and Tanaka) were utilized in 1M TFMSA and 0.3 M methanol and their properties compared. The Tanaka catalyst had relatively large RuOn islands on the surface; and underwent little Ru dissolution/agglomeration after 40 cycles, while the Johnson-Matthey catalysts with very small Ru islands underwent considerable Ru dissolution/agglomeration and thus, degradation of the catalyst. The Tanaka catalysts showed some Pt dissolution/agglomeration, but this appeared to increase the rate of CO oxidation (improve performance) after 40 cycles.
Distribution Profile of Specific Resistance in Polymer Electrolyte Membrane During Load Change for PEFC
Authors: Takaichi Satoshi , Uchida Hiroyuki , Watanabe Masahiro
Published: September 2007

To clarify the dynamic behavior of water content in a polymer electrolyte membrane (PEM) during load change in a fuel cell, distribution profiles of specific resistance (ρ) at various portions of the PEM were investigated with seven Pt potential probes inserted into the PEM. When the current density was stepped from 0.2 mA cm−2 to 100, 200, or 300 mA cm−2 at the cell temperature of 80{degree sign}C with supplying H2 and O2 humidified identically at 20% relative humidity (RH), it was found that the ratio of electro-osmotic drag (EOD) coefficient to water diffusion (WD) coefficient was constant irrespective of the current density. For the current step from 0.2 to 200 mA cm−2 under the reactant gases humidified identically at 20, 40 or 60% RH, the EOD coefficient decreased or the WD coefficient increased with increasing RH, which might be caused by a structure change in the PEM.
Spatial and Temporal Measurements of Temperature and Reaction Species in the Cathode Diffusion Layer of a Planar Air-Breathing PEM Fuel Cell
Authors: Fabian Tibor , O'Hayre Ryan , Prinz Fritz B. , Santiago Juan G.
Published: September 2007

Micron- and millimeter-scale sensors were employed to measure spatial and temporal distributions of temperature, oxygen partial pressure, and relative humidity in the layer immediately above the planar, horizontal cathode of PEM fuel cell driven by natural-convection. The sensors provide approximately 1 mm (or better) spatial resolution and 1 s temporal resolution. Substantial changes in temperature and reaction species concentrations were observed with increasing current density during a current-voltage (IV) scan. A linear decrease in oxygen partial pressure and a linear increase in water vapor partial pressure were observed with increasing current density. Spatially resolved profiles normal to the surface indicate that thermal and reaction species gradients extend up to 6 mm above the horizontal cathode surface. Complimentary horizontal profiles (parallel to the surface) reveal that the cell's cathode rib structure visibly influences oxygen distribution. Transient data reveal substantial differences in the time constants associated with oxygen, water, and heat transport.
Room Temperature Negative Differential Resistance in Au/Single ZnO Wire/Au Junction Structure
Authors: Zhang Yang , Chen Dai-Jang , Lee Ching-Ting
Published: September 2007

We have fabricated a novel device composed of a single ZnO wire bridged on a pair of Au electrodes. The charge transport in Au/single ZnO wire/Au is investigated by the current-voltage measurement. A negative differential resistance behavior (NDR) in current-voltage curve of single compound semiconductor wire is first observed at room temperature. A peak-to-valley current ratio is greater than 3:1. The NDR may be due to a specific metal-wire surface contact nanoscale contacts and electronic coupling between a single ZnO wire and Au electrodes. It is expected that ZnO wire can be applied to the nanoelectronic devices.
Frequency Response and Devices Performance of the Indium Zinc Oxide Thin Film Transistors
Authors: Wang Yu-Lin , Ren Fan , Covert Lance , Lin J , Lim Wantae , Pearton Steve
Published: September 2007

A 1um-gate length field effect thin film transistor was fabricated on a glass using indium zinc oxide (IZO) as the channel layer. The IZO film was deposited by rf magnetron sputtering at room temperature. A thin SiNx film was used as the gate insulator by plasma enhanced chemical vapor deposition. The depletion mode transistor has a threshold voltage -2.5V, maximum transconductance 7.5mS/mm at VDS=3V , and saturation current 2mA/mm at VGS=0V. The field effect mobility is 14.5 cm2.V-1.s-1, and the subthreshold voltage swing is 2.08V/decade. The on/off ratio is >105. The frequency response are measured at VGS=0V and VDS=3V. The cut-off frequency, ft, is 180MHz and the maximum oscillation frequency, fmax, is 155MHz.
Homoepitaxial Growth of Semi-Insulating 4H-SiC by Metal-Organic Precursors
Authors: Kim Hyeong Joon , Song Ho Keun
Published: September 2007

The authors attempted to grow a semi-insulating silicon carbide (SiC) epitaxial layer by in situ doping using metal-organic precursors. The homoepitaxial growth of the 4H-SiC layer was performed by MOCVD using the organo-silicon precursor, bis-trimethylsilylmethane (BTMSM, [C7H20Si2]). In situ doping for semi-insulating property was carried out by the metal-organic precursors, bis-cyclopentadienylvanadium (verrocene, [C10H10V]) and t-butylferrocene ([C14H17Fe]). For the measurement of the highly resistive 4H-SiC epilayers, on-resistance of Schottky barrier diode was used. Based on the measurements of the on-resistance of the Schottky barrier diode fabricated using the semi-insulating epilayers, the free carrier concentration of the epilayers was decreased with increasing partial pressure of verrocene or t-butylferrocene. The resistivity of the in situ vanadium-doped 4H-SiC epilayer was about 107 Ωcm and 108 Ωcm for the Fe-doped epilayers. The free carrier concentration of semi-insulating 4H-SiC epilayers was 109 ~ 1011 cm-3.
Fabrication of Crack-Free Metal-Semiconductor-Metal Ultraviolet Photodetectors on Si (111) Substrates Based on Novel AlN/AlGaN Buffer Multilayer Scheme
Authors: Chuang Ricky W. , Chang S. J. , Chang S. P.
Published: September 2007

The GaN ultraviolet metal-semiconductor-metal (MSM) photodetectors epitaxially grown on Si (111) and sapphire (0001) substrates were prepared and characterized. By implementing our elaborate AlN/AlGaN buffer multilayer scheme on Si, the maximum responsivity of n-GaN MSM photodetector with TiW transparent electrodes achieved at an incident wavelength of 359 nm was 0.187 A/W, which corresponds to the quantum efficiency of 64.7%. Furthermore, for a given bandwidth of 1 kHz and a given bias of 5 V, the corresponding noise equivalent power (NEP) of aforementioned photodetector was 1.53x10^-12 W, which translates to a maximal detectivity (D*) of 1.31x10^12 cm-Hz^0.5W^-1.
Study of the Thin-Film GaN-Based LEDs with TiO2/SiO2 Omnidirectional Reflectors and PEC Roughened Surfaces
Authors: Chiu C.H. , Kuo H. C. , Lee C.E. , Lin C.H. , Cheng B. S. , Cheng P. C. , Huang H.W. , Lu T.C. , Wang S.C. , Leung K.M.
Published: September 2007

A novel GaN-based thin-film vertical injection light emitting diode (LED) structure with a TiO2 and SiO2 omnidirectional reflector (ODR) and an n-GaN rough surface is designed and fabricated. At a driving current of 350 mA and with chip size of 1 mm x 1 mm, the light output power and the external quantum efficiency of the LED with a TiO2/SiO2 ODR reaches 330 mW and 26.7%; increasing by 18% and 16%, respectively. The optical output power mainly increased within the 120 deg cone due to the higher reflectance of the TiO2/SiO2 ODR within the blue regime.
GaN and ZnO-Based Sensors for Gas, Nuclear Materials and Chemical Detection
Authors: Pearton Steve , Ren Fan , Kang Byoung Sam , Wang Hung-Ta , Gila B , Norton D , Tien L , Chancellor TJ , Lele Tanmay , Tseng Yiider , Lin J
Published: September 2007

There is strong current interest in the use of GaN- and ZnO-based materials for gas, biological and chemical sensing. Both ZnO and the AlGaN/GaN heterostructure systems are piezoelectric, leading to large changes in charge density when the ambient or surface condition is changed and nitride HEMTs are also being developed for next generation wireless communication systems. Therefore it is possible to integrate on-chip wireless data transmission with the sensors, providing remote sensing capability and the ability to integrate with blue or ultra-violet light-emitting diodes (LEDs) for directed cell growth or remediation. In this talk we will give examples of using ZnO nanorods and nitride HEMTs for pH sensing in the range of interest for human blood (7-8 pH), detection of DNA hybridization and detection of Hg. The mercury (II) (Hg2+) ion is one of the environmentally most important cations whose toxicity has long been recognized as a chronic environmental problem. Development of the basic science of improving the detection efficiency for nuclear agents such as Pu-240 (weapons-grade plutonium typically contains about 5 percent plutonium-240) is needed. In all of these sensor systems, integrating the resulting sensors with modern GPS and wireless communication systems in a convenient module is important for ease of use and monitoring applications.
In Situ Investigation of the Passive Films Formed on Chromium in Aqueous (pH8.4) Borate Buffer and Aqueous Chloride Solutions
Authors: Wang Feng , Harrington Scott , Devine Thomas M.
Published: September 2007

The films formed on chromium in the passive and transpassive regions in borate buffer (pH8.4) were investigated by a combination of cyclic polarization and in situ EQCM and SERS. In the passive region, chromium dissolves as well as forms a passive film. The passive film thickness increases slowly with potential (approximately 6Aå/V). At low passive potentials, the identity of the film is not yet known. At high passive potentials the film is very similar to Cr2O3. In the transpassive region chromium forms a thick Cr(III) film, tentatively identified as Cr(OH)3, plus two Cr(VI) species. Significant changes occur to the passive film when the sample is removed from the aqueous solution and exposed to air.
Coupled Multi-Electrode Investigation of Crevice Corrosion of 316 Stainless Steel and NiCrMo Alloy 625
Authors: Bocher Florent , Presuel-Moreno Francisco J. , Budiansky Noah D. , Scully John
Published: September 2007

Close packed coupled multi-electrodes arrays (MEA) simulating a planar electrode were used to measure the anodic current evolution as a function of position during initiation and propagation of crevice corrosion of AISI 316 stainless steel (UNS S31600) and Ni-Cr-Mo alloy 625 (UNS N06625). Scaling laws derived from polarization data guided the implementation of rescaled crevices providing spatial resolution. Crevice corrosion of AISI 316 stainless steel in 0.6 M NaCl at 50{degree sign}C was found to readily initiate close to the crevice mouth (i.e., xcrit ≈ 0) at modest applied potentials (e.g., 0 VSCE) and to spread inwards and outside the crevice with time. In the case of alloy 625, crevice corrosion initiates further inside the crevice (i.e., xcrit is large) and requires higher applied potential (e.g., 0.05 VSCE). The local crevice current density increased dramatically over a short period to reach a limiting value in both cases.
Predictive Model for Cut-Edge Corrosion of Galvanized Steels
Authors: Thebault Florian , Vuillemin Bruno Vuillemin , Oltra Roland , Allely C. , Dosdat Florence , Ogle Kevin
Published: September 2007

A numerical model for the electrochemical behavior of cut-edge of galvanized steels is proposed. Some experimental data of current densities above cut-edge immersed in a 0.03M NaCl solution have been measured, using a scanning vibrating electrode technique, and compared with some simulated ones. A good fit has been obtained. The model geometry has been modified by decreasing the electrolyte thickness in order to tend towards an atmospheric corrosion case; such situation that is not easily accessible by electrochemical studies. Three regions can be distinguished according to the efficiency of the galvanic coupling to protect steel.
Use of Coupled Electrode Arrays to Elucidate Copper Pitting as a Function of Potable Water Chemistry
Authors: Cong Hongbo , Budiansky Noah D. , Michels Harold , Scully John
Published: September 2007

The electrochemical pitting behavior of UNS C11000 copper was investigated in synthetic potable water and several other HCO3- , SO42- and Cl- containing waters using microelectrodes and coupled multi-electrode arrays. Studies were systematically conducted (pH from 6 to 10, [Cl2] (as NaOCl) from 1-5 ppm, and with or without Al(OH)3 additions). Studies of the effect of water chemistry on electrochemical properties of copper were accomplished using the cyclic voltammetry and cathodic polarization methods. Critical potentials for copper pitting are observed to be brought about and decreased by certain water chemistry variables. High [SO42-]/[HCO3-] and [Cl-]/ [HCO3-] lower pitting potentials (EPit) while high [HCO3-] and pH raise EPit. ClO- increases cathodic reaction rates and thus raises OCPs towards EPit. Certain water chemistries (pH from 8 to 10, [Cl2] > 2 ppm and with Al(OH)3) are found to promote pitting conditions where strong, persistent anodes developed at certain sites and pitting factor was raised.
Electro-oxidation of Biginelli Dihydropyrimidones
Authors: Aceves-Hernandez Juan M. , Miranda Rene , Kappe Oliver
Published: September 2007

The electrochemical oxidation of several Biginelli compounds in acetonitrile at different pH values was carried out. The influence of the substituents at the heterocyclic ring was studied in tetrabutylammonium perchlorate by linear and sweep voltamperometry with platinum rotatory disc. Cyclic voltamperometry, controlled potential electrolysis and EPR techniques were used in order to determine the oxidation mechanisms. In acidic medium all derivatives follow an oxidation mechanism with an ECE (Electrochemical, Chemical, Electrochemical process), sequence. On the other hand, in basic media the derivatives obey a DISP1 (Disproportionation) mechanism, whereas the uptake of the proton at N1 by the OH- ion of the medium was the rate determining step. The effect of different substituents in the compounds was studied by using the theoretical ionization potential and the half wave oxidation potential correlation, as. It was found that there is an acceptable relationship between these parameters. The electrosynthesis of the para-nitro derivative was carried out in order to characterize the corresponding oxidation product.
Redox Reaction of Catalytic Layer in the Electrochemical Reactor for NOx Decomposition
Authors: Hamamoto Koichi , Fujishiro Yoshinobu , Awano Masanobu
Published: September 2007

The influence of reduction and re-oxidation reactions on NOx decomposition properties of an electrochemical reactor with a catalytic layer (NiO/YSZ) has been studied. To clarify the correlation between the NOx decomposition properties and the redox reactions of NiO in the catalytic layer, we carried out the measurements of re-oxidation time (interval) dependence of electric current at between 350 and 600{degree sign}C. The electrochemical reactor with the catalytic layer was shown the highly effective NOx decomposition properties in the presence of excess oxygen. Even if the interval increases, the current efficiency for NOx decomposition was not deteriorated at less than 400{degree sign} C. However, the current efficiency has been decreased according to an increase in temperature and/or interval at over 450{degree sign}C. The deterioration of current efficiency occurs with the volume expansion of the catalyst layer by the re-oxidation of NiO.
Influence of Interface Recombination in Light Emission from Lateral Si-Based Light Emitting Devices
Authors: LeMinh Phuong , Hoang Tu , Holleman Jisk , Schmitz Jurriaan
Published: September 2007

The influence of interface recombination on the electroluminescence profile of a lateral p+/p/n+ light emitting diode fabricated on Silicon On Insulator (SOI) materials has been experimentally investigated. Our device resembles a MOSFET fabricated on SOI, except that the source region has opposite doping to the drain. By controlling the voltage bias at the poly gate on top of active emitting region in association with a bias on the silicon substrate under the active region we were able to diminish the non-radiative recombination component at Si/SiO2 interface and therefore enhance the radiative recombination in the thin film SOI. When the diode is working under constant current condition, we observe an increased light output of ~ 20 % as the gate and/or the substrate are biased negatively. The intensity profile across the device is also strongly influenced. To understand the device thoroughly, the structure has also been simulated showing agreement with experimental results.
The Lithium/Iodine-Polyvinylpyridine Pacemaker Battery - 35 years of Successful Clinical Use
Authors: Holmes C.
Published: September 2007

The lithium/iodine-polyvinylpyridine (PVP) battery has been in clinical use as a power source for pacemakers for 35 years. Since 1972, literally millions of lithium/iodine cells have seen clinical use, providing health-giving and life-saving therapy to patients throughout the world. Indeed, the battery has compiled an excellent record of reliability and safety. The cell reaction is the simple combination of lithium and iodine to form lithium iodide, but the chemistry of the cathode material is interesting and complicated.
Electrochemical Studies of Lewis Acid / Ketone Interactions in Ionic Liquids
Authors: Cheek Graham
Published: September 2007

The voltammetric behavior of 9-fluorenone, benzophenone, and benzil has been investigated in the ionic liquids 1-ethyl-3- methylimidazolium tetrafluoroborate (EMIm BF4) and 1-butyl- 2,3-dimethylimidazolium tetrafluoroborate (BDMIm BF4). At 100 mV/s, protonation of the radical anions of benzophenone and benzil by the EMIm cation is extensive; however, the protonation reaction is slow and is not significant at 1000 mV/s. Use of BDMIm BF4, in which the acidic 2 position is substituted, precludes protonation of these radical anions. It has been found that addition of BF3 etherate to solutions of benzophenone in BDMIm BF4 , and to benzil in EMIm BF4, results in formation of ketone : BF3 complexes.
Voltammetric Determination of Hydroxylamine at Platinum
Authors: ul Haque Inam , Bano Kiran
Published: September 2007

The electrochemical oxidation of hydroxylamine at a platinum semi-micro disk electrode in nitric acid solution has been studied. The plot of the peak, limiting and summit currents from cyclic voltammetry, normal pulse, and differential pulse voltammetry shows linear variation with the concentration of hydroxylamine. The peak current in DPV scaled linearly with the concentration of hydroxylamine from 25 micro-molar to 2.5 milli-molar. Lower limit of detection was found to be 15 micro- molar. The lowest detectable signal was observed at S/N=10.
Electrolytic Behaviour of Ferrocene
Authors: ul Haque Inam , Sadaf Shamaila , Fatima Gulzar
Published: September 2007

Electrochemical behavior of ferrocene at platinum was studied in two solvents: acetonitrile and ethanol. Cyclic voltammetry showed that the electro-oxidation of ferrocene followed different routes in these two solvents. Anode process of aniline in acetonitrile under electrolytic conditions was also investigated in the presence of ferrocene.
Electrochemistry Behind Electrocoagulation Using Iron Electrodes
Authors: Moreno Casillas Hector A. , Cocke David L. , Gomes Jewel A. , Morkovsky Paul , Parga Jose R. , Peterson Eric , Garcia C
Published: September 2007

Electrocoagulation (EC) has been known for more than a century. Applications in industries as a water and wastewater treatment process have been adapted for the removal of metals, non metals, suspended solids, organic compounds, COD and BOD. Iron electrodes have been preferred over aluminum due to their durability and cost. However, the electrochemical reactions occurring with EC using iron electrodes have not been systematically studied. For a better understanding of the mechanism and reactions for EC using iron electrodes, we present a review of the concept of green rust (GR) and its relationship to the current theory of EC. Experimental results obtained by measuring pH at different zones near the iron electrodes during the EC process are detailed, and are used to illustrate the mechanism and reactions that occur at both, the anode and cathode. Mechanism and reactions presented explain phenomena associated with EC and are congruent with solubility and Pourbaix diagrams.
Electrically Mediated Process for Functinal and Decorative Trivalent Chromium Electroplating: An Alternative to Hexavalent Chromium
Authors: Lozano-Morales Alonso , Renz Robert , Fortman John , Taylor E. Jennings
Published: September 2007

Research work performed to develop a functional and decorative trivalent chromium plating process from a single, simple to control trivalent-based electrolyte to replace hexavalent chromium plating will be reported. Hexavalent chromium plating has been used for many years to provide hard, durable coatings with excellent wear and corrosion resistance properties. However, hexavalent chromium baths have come under increasing scrutiny due to the toxic nature of the bath, effects on the environment, and workers' health. In this work, Faraday is updating its accomplishments to date to achieve properties comparable to existing hexavalent chromium plating for both functional and decorative applications. Continuing work on the bath chemistry, diffusion layer, hydrodynamics, and electrically mediated process parameters will also be discussed.
Nano Suspension of Porous Silicon in Water: Two Methods of Material Preparation and Modification by Surfactants
Authors: Pastor Ester L. , Balaguer Ramirez Maria , Bychto Leszek , Salonen Jarno , Letho Vesa P. , Chirvony Vladimir , Matveeva Eugenia S.
Published: September 2007

Luminescent silicon nanocrystals (Si-nc) are promising material for biomedical purposes. However, as-prepared Si-nc are H-terminated and not miscible with biological (aqueous) liquids. We used physical and chemical adsorption of undecylenic acid to make porous silicon (porSi, material containing Si-nc assemblies) miscible with water solutions. PorSi powders prepared by two different methods, electrochemical anodization and stain etching were modified and suspended in water. Luminescent properties of aqueous suspensions have been then monitored for long time. The many- fold buildup of initial luminescence intensity during the first 3-6 days has been observed for electrochemically prepared porSi material. This phenomenon was explained as disaggregating of the primary micelles formed from surfactant- covered porSi particles into smaller ones. Contrary to this, the stain etched porSi powder exhibited a continuous decrease of the luminescence intensity with time and, moreover, was much less luminescent. Thus, electrochemically prepared porSi is found more appropriate for photosensitizing biomedical applications.
Determination of c Lattice Parameter of LiCoO2 by Convergent-Beam Electron Diffraction
Authors: Xing Qingfeng , Gabrisch Heike
Published: September 2007

The convergent-beam electron diffraction technique of transmission electron microscopy was applied to the determination of the c lattice parameter of LiCoO2. [0001] orientation which showed a sufficient number of high-order Laue zone (HOLZ) lines was found to be suitable to the work. The ratio of the distances between {0551} HOLZ line family and the interceptions of {2641} family at [0001] orientation was able to allow the c to be determined. The accuracy of the technique was high enough to assess the homogeneity of the material and to investigate the change of the c lattice parameter with variation of lithium content in the material.
On the Mg Trapping Mechanism in Electrodes Comprising Chevrel Phases
Authors: Mitelman Ariel , Levi Elena , Lancry Eli , Aurbach Doron
Published: September 2007

Chevrel phases (CPs), MxMo6T8 (M - metal, T = S, Se), may be used as unique cathode materials for rechargeable Mg batteries because of the high mobility of multivalent cations. However, the electrochemical behavior is strongly affected by the host composition. For the selenide, the intercalation process is completely reversible, while partial Mg trapping occurs upon its extraction from the sulfide at room temperature. These peculiarities of the electrochemical behavior were understood based on the analysis of the crystal structure of intercalation compounds, MgXMo6T8 (T = S, Se) determined by a combination of ab initio calculations and experimental methods (high resolution neutron and powder X-ray diffractions).
Online Estimation of the State of Charge of a Lithium Ion Cell
Authors: Santhanagopalan Shriram , White Ralph E.
Published: September 2007

A procedure to predict the state of charge of a lithium ion cell using experimental data (cell potential vs time), as it becomes available, is presented. The procedure is based on the physics of the system and provides a realistic estimate of the state of charge of the cell as a function of time, for a given set of properties of the electrodes. An electrochemical cell model is used to obtain an Extended Kalman filter (EKF) for estimating the state of charge (SOC) of a lithium ion cell in which the negative electrode is the limiting electrode. The method could also be used for a cell in which the positive electrode is limiting.
Corrosion of Aluminum Current Collectors of Cycle-Life Tested Li-Ion Batteries
Authors: Cohen-Hyams Tzipi , Go John , Devine Thomas M.
Published: September 2007

The aluminum current collectors from six ATD cells that were commercially fabricated and cycle-life (charge/discharge) tested at 25ºC were microscopically inspected for evidence of corrosion. The results clearly show that aluminum covered with porous cathodes of LiNi0.8Co0.15Al0.5O2 of cycle-life ATD cells cycled at 25{degree sign}C is susceptible to significant underdeposit corrosion in LiPF6-containing battery electrolytes. Aluminum current collectors of uncycled ATD cells contain mechanical pits formed during the attachment of the cathode, but with cycling at 25{degree sign}C there is an increase in percentage pit area, in the number of pits, in pit-size-distribution, and in pit depth, which is a strong evidence of corrosion of Al current collectors of ATD cells. The formation of corrosion pits, corrosion of mechanical pits, and the non negligible amount of aluminum that was found in the electrolytes (~2700 ppm) of cycle-life tested ATD cells explain the significant contribution of corrosion to the power fade and capacity fade and the possibility of mechanical degradation of the cathode as well.
Oxygen-Induced Corrosion of Copper Plating Substrates in Acid Sulphate Electrolytes
Authors: Breathnach M. , Ahmed Shafaat , Sharna R , Burke L. D. , Buckley D. N.
Published: September 2007

The corrosion of thin films of copper due to the presence of oxygen in CuSO4/H2SO4 electrolytes was investigated. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images showed noticeable corrosion in aerated 0.1 mol dm-3 H2SO4 electrolytes after times as short as 4 min while no significant corrosion occurred in de-aerated electrolyte. Etching was most evident at the grain boundaries but intra- granular etching was also noticeable. In CuSO4/H2SO4, corrosion was slower at higher concentrations of CuSO4. A corrosion rate equivalent to 26 μA cm 2 was estimated by monitoring the concentration of copper in the 0.1 mol dm-3 H2SO4 electrolyte using atomic absorption spectrometry (AAS). Galvanostatic corrosion at 26 μA cm-2 showed somewhat different morphology. An oxygen reduction current of ~0.8 mA cm-2 was measured in aerated 0.1 mol dm-3 H2SO4. The measured rate of corrosion of copper due to oxygen is thus ~30 times that expected from the oxygen reduction current. The mechanism responsible for this enhanced oxygen reaction rate has not been determined. It is concluded that holding the potential at the equilibrium Cu/Cu2+ value in experiments such as in- situ AFM is not a practical solution to the problem of copper substrate corrosion.
Leveling of Microvias by Electroplating for Wafer Level Packaging
Authors: Luehn Ole , Celis Jean-Pierre , Van Hoof Chris , Baert Kris , Ruythooren Wouter
Published: September 2007

The filling of microvias with diameters between 30 and 100 µm and aspect ratios up to 2.5 in silicon wafers, was investigated to determine the performance of copper electroplating. An electrolyte with a low leveler concentration was only suitable for filling microvias with aspect ratios below 1. An increase of the leveler concentration enabled the filling of microvias with higher aspect ratios. The fill-up evolution shows a bottom-up plating behavior. Electrochemical measurements show that for conditions prevailing at the bottom of the via, the electrodeposition rate is enhanced while for conditions prevailing at the top, it is inhibited. This difference originates from a concentration gradient of leveler inside the via and different convection conditions inside and outside the via.
Nickel Mouldable Electrodes: Mott-Schottky Analysis of Ni(OH)2 Deposited Layers on Nickel Powder-Epoxy Resin Composite Electrodes.
Authors: Bastos Juan , Barbosa Mirta R. , Gregori Juan , García-Jareño José Juan J. , Vicente Francisco
Published: September 2007

Electrochemical impedance of Ni(OH)2 layers generated on composite Ni-epoxy resin material in basic media are analysed. The formation of α- is favoured in comparison of the β-Ni(OH)2 due to the surface morphology of the composite. The calculated number of charge carrier across Ni(OH)2 from Mott-Schottky analysis of EIS simultaneously depends on the surface morphology of the composite substrate as well as on the method of deposit.
Electrodeposition of CoNiMo Magnetic Nanowires
Authors: Esteves Marcos C. , Sumodjo Paulo , Podlaha Elizabeth
Published: September 2007

CoNi and CoNiMo nanowires were electrodeposited using commercial alumina templates and a pH 7 glycine-ammonia electrolyte. The resulting magnetic properties and composition were compared with thin film counterparts. The nanowires had larger coercivity and more crystallinity than the thin. The presence of molybdenum had no significant influence over the coercivity and remanence in the nanowires, unlike thin films.
Water Soluble Binder for LiFePO4/Polymer/ Carbon HQ technology
Authors: Zaghib K. , Charest Patrick , Dontigny Martin , Petitclerc Michel , Guerfi Abdelbast
Published: September 2007

A new water soluble elastomer was evaluated as a binder with LiFePO4 -VGCF cathode material in Li-ion batteries and different carbon origin anodes. The electrochemical characteristics of this cathode and anodes were compared to that with PvdF-based cathode binder. The elastomer-based cathode and anodes show high flexibility with good adhesion. The electrochemical performance was also evaluated and compared to PvdF-based cathodes at 25å and 60{degree sign}C. A lower irreversible capacity loss was obtained with the elastomer- based cathode and graphite-based anode , The Li-ion gel electrolyte developed by Hydro-Québec shows high stable cycle life but lower power density at rates less than 5C compared to liquid electrolytes
Investigation of the local structure in LiCo1-2yNiyMnyO2 (0.25{less than or equal to}y{less than or equal to}0.5) cathode materials for Li-ion batteries
Authors: Abdel-Ghany Ashraf , Zaghib K. , Mauger Alain , Massot Michel , Gendron Francois , Ramana Chintalapalle V. , Julien C.
Published: September 2007

Layered LiCo1-2yNiyMnyO2 materials were synthesized with high homogeneity and crystallinity using the wet-chemical method assisted by oxalic acid as polymeric agent. The long-range and local structural properties are investigated with experiments including X-ray diffraction, Fourier transform infrared, Raman scattering, and electron paramagnetic resonance spectroscopy. The evolution of the structure is discussed as a function of the cobalt content, which confers layer-like behavior on the framework. Studies of the lithium extraction from the host lattices are also reported.
Magnetic Properties of LiNi0.33Mn0.33Co0.33 as Positive Electrode for Li-Ion Batteries
Authors: Abdel-Ghany Ashraf , Mauger Alain , Gendron Francois , Zaghib K. , Julien C.
Published: September 2007

In this work, we studied the magnetic properties of LiNi0.33Mn0.33Co0.33O2 synthesized by wet chemistry via oxalate route. Measurements included the temperature dependence of the magnetic susceptibility, χm (T) and magnetization M(H). The influence of the synthesis conditions on the magnetic and electronic properties is presented and discussed. Analysis of magnetic data allows the determination of the cationic disorder, i.e. the concentration of Ni2+ ions in the 3a lithium sites.
Gathering Kinetic Data of Electrochemical Phase Formation Processes Through Analysis of Experimental Current Transients. Overview and New Approaches
Authors: Palomar-Pardavé Manuel , Romero-Romo Mario , Ramírez-Silva María Teresa , Mostany Jorge L. , Scharifker Benjamin R.
Published: September 2007

In this work potentiostatic current transients recording during the electrochemical phase formation processes of different systems namely: condensation of amphipilic molecules, synthesis of conducting polymers, anodic films formation and metal deposition are presented and analyzed. It is shown that, notwithstanding their different nature, all these processes can be analyzed following a similar methodology which has been already developed to explained nucleation and growth of metallic centers. Moreover since in some cases the surfaces of the new growing phase present catalytic activity, a concomitant or parallel process may occur, this case is also analyzed.
A novel phosphatase upregulated inAkp3knockout mice
Authors: Narisawa Sonoko , Hoylaerts Marc F. , Doctor Kutbuddin S. , Fukuda Michiko N. , Alpers David H. , Millán José Luis
Published: September 2007

Reexamination of the Akp3−/−mouse intestine showed that, despite the lack of intestinal alkaline phosphatase (IAP), the Akp3−/−gut still had considerable alkaline phosphatase (AP) activity in the duodenum and ileum. This activity is due to the expression of a novel murine Akp6 gene that encodes an IAP isozyme expressed in the gut in a global manner ( gIAP) as opposed to duodenum-specific IAP ( dIAP) isozyme encoded by the Akp3 gene. Phylogenetically, gIAP is similar to the rat IAP I isozyme. Kinetically, gIAP displays a 5.7-fold reduction in catalytic rate constant ( kcat) and a 30% drop in Km, leading to a 4-fold reduction kcat/ Kmcompared with dIAP, and these changes in enzymatic properties can all be attributed to a crucial R317Q substitution. Western and Northern blot analyses document the expression of Akp6 in the gut, from the duodenum to the ileum, and it is upregulated in the jejunum and ileum of Akp3−/−mice. Developmentally, Akp3 expression is turned on during postnatal days 13–15 and exclusively in the duodenum, whereas Akp6 and Akp5 are expressed from birth throughout the gut with enhanced expression at weaning. Posttranslational modifications of gIAP have a pronounced effect on its catalytic properties. Given the low catalytic efficiency of gIAP, its upregulation during fat feeding, its sequence similarity with rat IAP I, and the fact that rat IAP I has been implicated in the upregulation of surfactant-like particles during fat intake, it appears likely that gIAP may have a role in mediating the accelerated fatty acid intake observed in Akp3−/−mice fed a high-fat diet.
Reactive oxygen species are messengers in maintenance of human and guinea pig gallbladder tonic contraction
Authors: Cong Ping , Xiao Zuo-Liang , Biancani Piero , Behar Jose
Published: September 2007

The tonic contraction of human and guinea pig gallbladder (GB) is dependent on basal levels of PGE2 and thromboxane A2 (TxA2). The pathway involved in the genesis of these prostaglandins has not been elucidated. We aimed to examine the source of reactive oxygen species (ROS) and whether they contribute to the genesis of GB tonic contraction by generating basal prostaglandin levels. Tonic contraction was studied in human and guinea pig GB muscle strips treated with ROS scavengers (Tiron and catalase), apocynin (an inhibitor of NADPH oxidase), and NOX-1 small interference RNA (siRNA). The subunits of NADPH oxidase and their functional roles were determined with specific antibodies in GB muscle cells. ROS scavengers reduced the GB tonic contraction and H2O2 and PGE2 levels. Apocynin also inhibited the tonic contraction. Antibodies against subunits of NADPH oxidase present in GB muscle cells lowered H2O2 and PGE2 levels. NOX-1 siRNA transfection reduced the tonic contraction, NOX-1 expression, and levels of H2O2 and PGE2. Tiron and apocynin inhibited the expected increase in tension and H2O2 levels induced by stretching of muscle strips. H2O2 increased the levels of PGE2 and TxA2 by increasing platelet-activating factor-like lipids that phosphorylate p38 and cPLA2 sequentially. H2O2 generated by NADPH oxidase participates in a signal transduction pathway that maintains the GB tonic contraction by activating PAF, p38, and cPLA2 to generate prostaglandins.
A1Adenosine Receptor Activation Promotes Angiogenesis and Release of VEGF From Monocytes
Authors: Clark Adam N. , Youkey Rebecca , Liu Xiaoping , Jia Liguo , Blatt Rebecca , Day Yuan-Ji , Sullivan Gail W. , Linden Joel , Tucker Amy L.
Published: September 2007

Adenosine is a proangiogenic purine nucleoside released from ischemic and hypoxic tissues. Of the 4 adenosine receptor (AR) subtypes (A1, A2A, A2B, and A3), the A2and A3have been previously linked to the modulation of angiogenesis. We used the chicken chorioallantoic membrane (CAM) model to determine whether A1AR activation affects angiogenesis. We cloned and pharmacologically characterized chicken AR subtypes to evaluate the selectivity of various agonists and antagonists. Application of the A1AR-selective agonist N6-cyclopentyladenosine (CPA; 100 nmol/L) to the CAM resulted in a 40% increase in blood vessel number (P<0.01), which was blocked by the A1AR-selective antagonist C8-(N-methylisopropyl)-amino-N6-(5′-endohydroxy)-endonorbornan-2-yl-9-methyladenine (WRC-0571; 1 μmol/L). Selective A2AAR agonists did not stimulate angiogenesis in the CAM. In an ex vivo rat aortic ring model of angiogenesis that includes cocultured endothelial cells, fibroblasts, and smooth muscle cells, 50 nmol/L CPA did not directly stimulate capillary formation; however, medium from human mononuclear cells pretreated with CPA, but not vehicle, increased capillary formation by 48% (P<0.05). This effect was blocked by WRC-0571 (1.5 μmol/L) or anti-VEGF antibody (1 μg/mL). CPA (5 nmol/L) stimulated a 1.7-fold increase in VEGF release from the mononuclear cells. This is the first study to show that A1AR activation induces angiogenesis. Stimulation of A2ARs on endothelial cells results in proliferation and tube formation, and A2and A3ARs on inflammatory cells modulate release of angiogenic factors. We conclude that adenosine promotes a coordinated angiogenic response through its interactions with multiple receptors on multiple cell types.