bluuebunny/crossref_metadata_2025 huggingface dataset:
Ice Formation and Distribution in the Catalyst Layer During Freeze-Start Process - CRYO- SEM Investigation
Authors: Li Jing , Lee Stephen , Roberts Joy
Published: September 2007

Ice distribution in the catalyst layer (CL) and gas distribution layer (GDL) of PEM fuel cells under isothermal constant voltage (ICV) operation at subzero temperature was determined using CRYO-FESEM. The analysis method was designed to ensure that the entire experiment was carried out under subzero ({degree sign}C) conditions so that the water is always kept in a frozen state without thawing. Under a moderately wet shutdown, the porosity of the cathode CL decreased from an initial, dry porosity of 65% to 15.9% for the purge only sample and to 8.2% for a sample at a full ICV state. At the full ICV state, the gas was not able to reach the active sites and the reaction ceased. Two distinct regions with different porosities in the CL were observed at the half ICV state, which indicates that ice in the CL melted at the beginning of the ICV operation.
A Model Study for Oxygen Reduction Reaction and Durability of Pt/C Catalyst in Triple-Phase Boundary of PEFCs
Authors: Hirai Tomoaki , Kinumoto Taro , Katakura Katsumi , Iriyama Yasutoshi , Uchimoto Yoshiharu , Ogumi Zempachi
Published: September 2007

We developed a novel solid-state electrochemical cell for modeling triple-phase boundary of polymer electrolyte fuel cells and investigated oxygen reduction reaction (ORR) activity and durability of Pt/C catalysts using the cell. ORR current was depended on relative humidity as well as the thickness of coated Nafion layer on the model electrode. We also conducted the theoretical calculation and clarified that ORR current in the model TPB region is not restricted by oxygen diffusion but by an ohmic drop due to proton migration in the coated Nafion layer on the model electrode. Durability test of Pt/C catalysts in the model TPB region was carried out under oxygen atmosphere. After the test, aggregation and somewhat larger Pt particles were observed on the model electrode at which electrode potential would reach to be open circuit potential, i.e., low overpotential region, under oxygen atmosphere.
DOE Fuel Cell Program: Durability Technical Targets and Testing Protocols
Authors: Garland Nancy , Benjamin Thomas , Kopasz John
Published: September 2007

Fuel cells, especially those for transportation applications, must operate over a wide range of operating and cycling conditions. The desired operating range encompasses temperatures from well below the freezing point to well above the boiling point of water, relative humidity from ambient to saturated, and half-cell potentials from 0 to >1.5 V. Furthermore, the anode may be exposed to both hydrogen and air during different parts of the driving and start/stop cycles. Transportation fuel cell operation is greatly exacerbated by the transient and cyclic nature of the operating conditions. The cell/stack conditions cycle, sometimes quite rapidly, between high and low voltage, temperature, humidity, and gas composition. The cycling results in physical and chemical changes to components, sometimes with catastrophic results. This document describes DOE durability targets and the status of current fuel cell technology as well as accelerated stress test (AST) protocols to assess the performance and durability of PEM fuel cell components.
Observation of Membrane Degradation by In-Situ and Ex-Situ Electron Paramagnetic Resonance
Authors: Vogel Barbara , Aleksandrova Elena , Mitov Svetlin , Krafft Michael , Dreizler Andreas , Kerres Jochen , Hein Martin , Roduner Emil
Published: September 2007

The degradation of fuel cell membranes was investigated with perflourinated and with polyaromatic materials. Since radical mechanisms are thought to be responsible for damaging the components in a working fuel cell, •OH radicals were generated by cleavage of hydrogen peroxide by UV light, by heat, and using Fenton's reagent. Aiming at the development of accelerated ageing tests for membranes, measurements of radical species were performed by electron paramagnetic resonance ex-situ with monomer and polymer solutions and with membranes, and in-situ on catalyst coated membranes. No signals indicating •OH attack on Nafion were detected, in contrast to all polyaromatic membrane materials. Nevertheless, in-situ spin trap measurements with Nafion reveal strong signals which formally belong to trapped H atoms but are not related to degradation. Relative to the Faraday electrons from the electrochemical reaction they appear on a ppm level.
Hydrogen Peroxide Generation at the Pt/Recast-Nafion Film Interface at Different Temperatures and Relative Humidities.
Authors: Chlistunoff Jerzy , Pivovar Bryan
Published: September 2007

The oxygen reduction reaction (ORR) at the interface between platinum and recast Nafion with 1100 equivalent weight was studied using voltammetry utilizing interdigitated microelectrode arrays (IDAs). At high relative humidity (RH) (60-100%), peroxide generation was found to decrease with scan rate. The opposite behavior was observed at low RH (10%), with a more complex response at an intermediate RH (35%). Peroxide generation was found to significantly increase with temperature at 60% RH, but the effect of temperature was not as well defined at other humidities. The effects of humidity, scan rate and temperature on peroxide generation are explained by the occurrence of two phenomena. At high humidity, peroxide generation results mainly from the blocking of Pt surface by the hydrophobic component of Nafion, in agreement with previously postulated interfacial restructuring of ionomer (1-3). While at low humidity, peroxide generation originates predominantly from dehydration of the hydrophilic component of Nafion at the interface
Tracking Crystallinity Changes in PFSA Polymers During Ex-Situ Peroxide Degradation
Authors: Aieta Niccolo V. , Leisch Jennifer E. , Santos Monica M. , Yandrasits Michael , Hamrock Steven , Herring Andrew M.
Published: September 2007

X-ray scattering is used to determine levels of crystallinity in both 3M® ionomer and Nafion®, both perfluorosulfonic acid (PFSA) based polymers. Weight loss and measured fluoride ion release both suggest breakdown of the polymer. X-ray scattering as well as mechanical measurements suggest that the crystalline domain size and spacing are unaffected by this degradation.
Study of Membrane Ionic Losses in a PEM Fuel Cell Using Dimensional Analysis
Authors: Chanda Sreedhar , Wang Xia
Published: September 2007

The ionic resistance of the membrane of a polymer electrolyte fuel cell (PEMFC) is often considered to be analogous to electrical resistance. However, experimental data show that the membrane resistance depends on more variables than typical electrical resistance and the dependencies are not fully understood yet. Presently, several empirical relations are used to relate membrane's ionic resistance to its dependent variables - usually the absolute temperature and water content. In this paper, the Buckingham PI theorem is used to determine dimensionless parameters governing the membrane ionic losses in a PEMFC. The generated parameters are compared to experimental results.
Temperature Effects on PEM Fuel Cells Pt/C Catalyst Degradation
Authors: Bi Wu , Fuller T.
Published: September 2007

Operating proton exchange membrane (PEM) fuel cells at relatively high temperatures provides benefits that include greater tolerance to CO, easier management of water and improved efficiency of heat rejection. However, the degradation of fuel cell components is accelerated at higher cell temperatures resulting in shortened cell lifetimes. In this study, we investigated temperature effects on cathode Pt/C catalyst durability. Cathode degradation was accelerated using square-wave potential cycling between 0.87 V and 1.2 V (vs. reference hydrogen electrode). More rapid Pt/C degradation was observed at higher temperatures, resulting in lower performance, loss of Pt catalyst electrochemically active surface area, and deposition of Pt in the membrane. Each has been quantified at 40, 60 and 80 C. More durable catalysts with improved microstructures are needed to meet the future fuel cell commercial applications, and alternative accelerated tests for higher temperatures are required.
An Electrochemical STM Study of Coarsening and Corrosion of Platinum Films
Authors: Xu Qingmin , Kreidler Eric , Wipf David , He Ting
Published: September 2007

In-situ electrochemical scanning tunneling microscopy is used to study the coarsening of platinum crystals under potentiostating and the dissolution and coarsening of platinum crystals through potential cycling. A rapid coarsening of platinum crystals was observed for potentiostating in the double-layer region. It is suggested that the coarsening is a variant of Ostwald ripening dominated by surface-diffusion transport. In addition, potential cycling not only causes surface platinum dissolution as a result of the platinum redox reaction but also platinum crystal ripening. Details of the platinum surface restructuring are described and the possible influences of these phenomena on fuel cell operation are discussed.
Carbon-Supported Pd-Co Alloy Electrocatalysts for Methanol Tolerant Oxygen Reduction
Authors: Wang Wenming , Yang Hui , Cao Jianyu Cao , Huang Qinghong , Zou Zhiqing , Xia Baojia
Published: September 2007

Carbon-supported Pd-Co bimetallic nanoparticle electrocatalysts of different Pd/Co atomic ratios were prepared by a modified polyol reduction. An activity comparison of the oxygen reduction reaction (ORR) on Pd-Co alloy catalysts with the same Pd loading, the same fcc disordered structure and a similar particle size has been made. Both composition and structure of Pd-Co alloys have a significant influence on the ORR. The change in the ORR activity with different Pd/Co compositions is correlated to their structural parameter. The maximum ORR activity for Pd2Co/C catalyst heat-treated at 500 oC is attributed to an optimal alloy composition and to a favorable Pd-Pd mean interatomic distance caused by alloy formation. Moreover, the Pd-Co alloy catalyst exhibited much higher ORR activity than the Pt/C catalyst in the presence of methanol, thus it may function as a methanol-tolerant ORR catalyst in a direct methanol fuel cell.
Vapor Feed Direct Methanol Fuel Cell with Flowing Electrolyte
Authors: Brushett Fikile , Mitchell Michael , Jayashree Ranga , Zhou Wei-Ping , Kenis Paul
Published: September 2007

This paper reports on the design and characterization of a vapor feed direct methanol fuel cell with flowing acidic electrolyte. A vapor fuel feed has the advantage of reducing methanol crossover and facilitating the removal of CO2. We observed a maximum power density when using 10 M liquid methanol as the source for the vapor fuel feed. At this concentration, an optimal balance appears to exist between the desired increase in the rate of methanol oxidation and the undesired increase in the rate of methanol crossover, which both result from increasing the methanol concentration. Performance studies show that the system is kinetically limited by the oxidation of methanol.
Lessons Learned from Phosphoric Acid Electrolyte Fuel Cell Development Pertinent to PEMFCs
Authors: Kunz Harold R.
Published: September 2007

The recent high level of activity on proton exchange membrane (PEM) fuel cells has brought into the fuel cell community many new participants who are unaware of the vast phosphoric acid (PAFC) research results that are available and pertinent to PEM fuel cells. This report provides a summary of some of the PAFC information related to cathode catalyst activity, cathode performance decay, and electrolyte migration.
Cyclic Current Profile Performance of Proton Exchange Membrane Fuel Cells in Stationary Applications
Authors: Barbosa Romeli , Gatto Irene , Squadrito Gaetano , Orozco Germán , Arriaga Luis G. , Ornelas Ruben , Antonucci Vincenzo , Passalacqua Enza
Published: September 2007

In the present work cyclic current profile performance of proton exchange membrane fuel cells in stationary application is shown. The studies were carried out in a H2/air PEMFC 32 cm2 geometric area using SGL carbon material. The electrodes were prepared using a solution with 30% Pt/C (ETEK) catalyst and 33% by weight of Nafion® deposited on the diffusion layer (ETEK LT 1200w) by spray technique. The catalyst loading of both electrodes was 0.26 mg Pt-cm-2. Membrane Electrode Assembly was aged for 11700 cycles and characterized for a full set of performance and component parameters after each around 4000 cycles where diagnosis procedures were executed. The diagnosis consists in polarization curve, H2 crossover rate and electrochemical active surface (ECA) area by CV.
Measurement of Current Distributions in a PEM Fuel Cell with Interdigitated Flow Field
Authors: Zhang Guangsheng , Ma Bin , Shang Dehua , Guo Liejin , Sun Hong , Liu Hongtan
Published: September 2007

Current distributions in a PEM fuel cell with interdigitated flow fields were measured with the current distribution measurement gasket technique. The measurement results show that interdigitated flow field indeed improves the uniformity of current distribution in PEM fuel cells, especially when reactant gases are insufficient, which is attributed to stronger mass transfer of forced convection. Current distribution at high gas humidification temperatures demonstrates the good water removal capability of the interdigitated flow field.
Metal Silicide Nanowires
Authors: Chen Lih J. , Wu Wen-Wei , Hsu H.C. , Chen S.Y. , Chueh Y.L. , Chou L.-J. , Lu K.C. , Tu K.N.
Published: September 2007

Recent progresses on the growth and characterization of metal silicide nanowires are highlighted. Four examples are given: 1. point contact reactions between Ni and Si nanowires and reactive epitaxial growth of axial nano NiSi/Si, 2. growth of high-density titanium silicide nanowires in a single direction on a silicon surface, 3. synthesis and characterization of metallic TaSi2 nanowires and 4. self-assembled growth of NiSi2 and α-FeSi2 nanowires by nitride mediated epitaxy.
Gold-Ga2O3 Co-Shell Nanowires
Authors: Hsieh Chin-Hua , Chou L.-J.
Published: September 2007

A simple thermal annealing process was carried out to produce the innovative heterostructure of gold-Ga2O3 co-shell nanowires. By changing the growth temperature and the size of the gold catalyst, it is easy to control the growth of pure Ga2O3 or gold- Ga2O3 co-shell nanowires. The twin boundary induced gold-Ga2O3 co-shell nanowires, including the gold-peapodded and gold-Ga2O3 core-shell nanowires, were first fabricated by the reaction of the gold, gallium metal and silica. The morphologies, crystal structures and microstructures were investigated by field-emission scanning electron microscope (FESEM, JSM-6500F), X-ray spectrometer (SHINMADZU) and field-emission transmission electron microscope (FETEM, JEM-3000F), respectively. Furthermore, the novel 1-D gold-Ga2O3 co-shell nanowires, reported in present study, shows the potential application for the next generation optoelectronic devices in semiconductor industry.
High Performance ZnO Thin Film Transistors Fabricated on Both Glass and Flexible Substrates
Authors: Liu Chien Cheng , Chen Yu Sheng , Wu Meng Lun , Huang JianJang
Published: September 2007

ZnO-based thin film transistors (TFTs) fabricated on both glass and flexible substrates are investigated. The ZnO thin film mentioned in this entire work is deposited by RF magnetron sputtering with the presence of O2 at low deposition rate and low temperature. For TFT on glass, the IDS is as high as 1 mA when biased at the saturation region VDS = 10-20 V and VGS = 5 V without any post thermal anneal. The Ion/Ioff ratio is . We believe the results are among the best ZnO TFTs ever obtained. For TFT on plastic, all the patterns are defined by standard photolithography. The IDS - VDS and IDS - VGS curves along with optical transmission of the whole structure are presented in this paper.
Properties of the State-of-the-Art Bulk and Homoepitaxial Films of III-V Nitride Semiconductors
Authors: Freitas Jaime A.
Published: September 2007

Understanding the nature of defects and their role on the properties of wideband gap material system it is essential to obtain the necessary material control to reach the full realization of their technological potential. A combination of defect sensitive techniques have been successfully employed to evaluate the crystalline quality, and to detect and identify point, extended defects, and impurities in thick freestanding GaN, bulk AlN, and homoepitaxial layers. The sharpness and line-shapes of X-Ray diffraction and Raman scattering phonon lines of AlN and GaN were used as figures of merit to evaluate the crystalline quality and homogeneity of the bulk and epitaxial layers. Systematic luminescence studies of AlN and GaN, grown by different techniques, and homoepitaxial films show evidence of the pervasive nature of some defects.
Resistive Non-Volatile Memory Effect Enhanced by a Ferroelectric Buffer Layer on Semiconductive Pr0.7Ca0.3MnO3 Film
Authors: Xing Zhongwen , Wu Naijuan , Ignatiev Alex
Published: September 2007

The novel electric-pulse-induced resistance (EPIR) switching effect has been obtained in metal electrode- Pr0.7Ca0.3MnO3 (PCMO)-metal electrode capacitor-like film structures. The EPIR effect encompasses the reversible change of resistance of PCMO under the application of short, low voltage pulses. This reversible resistance switching at room temperature is very attractive for today's computing technology with its wide applications as a resistance random access memory (RRAM) due to its nonvolatility, fast write/read/erase speed, low power-consumption and high radiation-hardness. In this work, a nano-meter thick ferroelectric Pb0.7Zr0.3TiO3(PZT) layer was inserted between the top electrode and PCMO film as a buffer layer in the EPIR device. Such a resistive memory device is comprised of a PCMO epitaxial layer on a c-oriented YBCO bottom electrode layer and a PZT ferroelectric buffer layer grown on top of the PCMO layer with an Ag top electrode. Compared with the Ag/PCMO/YBCO devices, the insertion of the PZT buffer into the Ag/PCMO interface is found to make the EPIR ratio increase greatly and the threshold pulse voltage necessary to switching the resistive device decrease significantly. Since Pr1-xCaxMnO3 is a unique compound oxide, showing semiconductive behavior over the whole composition (x) range, this is attributed to the resistive change of the depletion region at the Ag/PCMO interface including the PZY buffer, in which ferroelectric polarizations play a crucial role in the enhanced EPIR switching effect.
Device Challenges for Making a p-Side Down HVPE-Grown n-InGaN/p-GaN Single Heterostructure LED
Authors: Reed Meredith , Readinger Eric D. , Shen P. , Wraback Michael , Syrkin Alexander , Usikov Alexander , Dmitriev Vladimir
Published: September 2007

In this paper, we demonstrate the electrical and optical properties of hydride vapor phase epitaxy (HVPE)-deposited single heterostructure (SH) n-InGaN/p-GaN LED structures. We also discuss the device challenges associated with fabrication, as well as potential solutions for these problems.
Enhancement of the Light Emissions from Ag Doped ZnO Thin Films by Post-Annealing Process in Air
Authors: Jeong Eun-Kyung , Kim Dae-Hyun , Kim In-Soo , Choi Se-Young
Published: September 2007

The structural, electrical and emission properties of Ag doped ZnO (SZO) thin films were investigated. All of the films were deposited with different Ag content of targets by e-beam evaporator. As-deposited SZO films were p-type and they showed weak peak intensity in XRD patterns and it was not observed any distinguishable emission peak from PL spectra at room temperature. After annealing at the temperature range between 350~650{degree sign}C, the crystalline quality of the films enhanced and the (101) peak became dominant with increasing annealing temperature and Ag content. The UV emission near 378nm and the broad visible emission near 528nm observed. The ratio of the intensity of the UV emission to that of visible emission increased as the Ag content increased. The SZO thin film can be a promising candidate for p-type ZnO and the UV light emitting material.
MBE-Grown Ultra-shallow AlN/GaN HFET Technology
Authors: Xing Huili G. , Deen David , Cao Yu , Zimmermann Tom , Fay Patrick , Jena Debdeep
Published: September 2007

Due to large polarization effects, two-dimensional electron gas (2DEG) concentrations higher than 1x1013 cm-2 can be produced at the AlN/GaN heterojunction with AlN barriers as thin as 2 nm. This ultra-shallow channel together with the wide bandgap of AlN (6.2 eV) makes AlN/GaN heterojunction field effect transistors (HFET) extremely attractive for high frequency (>100 GHz) high power applications. At Notre Dame, these structures have been grown using molecular beam epitaxy and the record transport properties among III-V nitrides are achieved: a sheet resistance of ~ 170 ohm/square for a single heterostructure at room temperature. HFETs have been fabricated with optical lithographically defined gates. At present the device dc characteristics show a maximum drain current of 800 mA/mm and transconductance of 180 mS/mm for 3 μm long gate. This clearly demonstrates its value toward high speed devices. The development as well as challenges of this technology will be discussed here.
A Study on Thermal Formation and Electrochemical Reduction of Copper Oxide using Difference Viewer Imaging Technique
Authors: Huang Ruoshuang , Lin Chang-Jian , Lillard R. Scott , Isaacs Hugh S.
Published: September 2007

Thermal oxidation of copper oxides and their electrochemical reduction in solutions were studied on coarse grained polycrystalline copper using in situ difference viewer imaging technique (DVIT). The oxidation and reduction rates were closely contingent upon grain orientation. Red, green, and blue (RGB) pixel intensities from images of oxide film interference colors were used to assess oxide thickness. The oxide thickness was correlated with the orientations of grains. The reduction of air formed oxides in pH 10 borate solutions exhibited different stages during cathodic potentiodynamic polarization. An initial pre-peak shoulder in the polarization curve was probably due to the reduction of Cu (II), followed by a major peak reflecting Cu(I) reduction; using the DVIT this reduction could be seen to be due to non- uniform nucleation which was followed by reduction of oxide remnants; finally, as hydrogen evolution began, there was a metallic brightening of the surface attributed to the sintering of copper crystallites formed during oxide reduction when underpotential adsorbed oxygen was reduced.
Passivity Breakdown and the Evolution of Localized Corrosion Damage on Type 316L Stainless Steel
Authors: Yang Shoufeng , Macdonald Digby D.
Published: September 2007

Passivity breakdown on Type 316L stainless steel in the presence of C1¯ and NO¯3 species has been studied and the data are interpreted in terms of the Point Defect Model. Linear relationships between the breakdown potential (Vc) and log ([C1¯]) and log ([C1¯]/[NO¯3]), as predicted by the PDM are found experimentally. The interfacial reaction, in which a cation is ejected from the barrier layer to form the surface vacancy pair, is found to be a charge transfer process with the transition state being located close to the final state on the reaction coordinate. The dependence of Vc on potential scan rate yields the critical, areal concentration of condensed cation vacancies (ξ) at the metal/barrier layer interface that is in good agreement with that calculated theoretically based on the structure of Cr2O3, of which the barrier layer is postulated to comprise.
The Effect of Borate on Cerium Film Formation
Authors: Aldykiewicz Antonio J. , Davenport A. J. , Isaacs Hugh S.
Published: September 2007

Cerium cations were found to inhibit corrosion of Aluminun alloys by the formation of a tetravalent cerium oxide film. The film forms by the oxidation of cerium in solution followed by precipitation under alkaline conditions. The process can be accelerated or facilitated by catalyzing the oxidation reaction, e.g., by the addition of hydrogen peroxide in solution. In this work a trivalent film was found to precipitate under similar conditions by the addition of borate to the solution. The addition of borate appears to stifle the oxidation of cerium in solution. The result is most likely the precipitation of an insoluble cerium compound followed by physical deposition.
Dissolution Characteristics of Al2Cu and Al-4Cu Thin Films
Authors: Missert N. A. , Isaacs Hugh S. , Copeland Guild , Ingham Bridget , Huang Ruoshuang , Vasiljevic Natasa
Published: September 2007

Although Cu redistribution during dissolution of Al-Cu alloys is thought to have an important influence on susceptibility to localized corrosion, the details of the redistribution process in different environments are still not clear. This work uses in-situ x-ray absorption spectroscopy to follow the oxidation state of Cu in intermetallic Al2Cu and Al-4%Cu thin films during dissolution under potential control, in pH 10 borate and near-neutral Cl- environments. The oxidation state of Cu is observed to change only following significant dissolution of Al at potentials well above open circuit. In borate, formation of Cu (I) and Cu (II) occurs at potentials below the equilibrium potential for Cu/Cu2O, suggesting that the surface Cu is electrically isolated from the matrix. At higher potentials and longer exposure times, Cu ions went into solution, but subsequent re-plating of Cu on the surface was not observed.
Simple Fabrication of a Silver Epoxy Coated Microelectrode for SECM Imaging in Small Volumes
Authors: Diaz-Ballote L. F. , Wipf David O.
Published: September 2007

This work describes a simple and practical way to fabricate a dual Pt-microelectrode/silver quasi-reference electrode, (ME/AgQRE). These dual electrodes are particularly useful in small volume electrochemical experiments and scanning electrochemical microscope (SECM) applications. The ME/AgQRE consists of a silver ring, formed with a conductive silver epoxy around a glass support, which insulates a Pt-microwire, which acts as a disk microelectrode. The performance of the ME/AgQRE was evaluated using cyclic voltammetry and sample volumes as small as one microliter. These results were also compared with voltammograms performed in solutions of about 50 mL with a standard reference electrode (Ag/AgCl) as well as a with silver wire quasi-references electrode. In addition, the ME/AgQRE was used to acquire SECM images of a 25 μm-diameter Pt substrate, immersed in a solution containing 2 mM KI in 0.1 M NaCl. Approach curves and line scans (in feedback mode) showed significant advantages of these electrodes.
The Influence of Potential and Temperature on the Kinetics of Oxygen Reduction on Alloy 22 in Neutral Chloride Solutions.
Authors: Zagidulin Dmitrij , Jakupi Pellumb , Sherar Brent , Noel Jamie J. , Shoesmith David W.
Published: September 2007

The passive film on Alloy 22, and its influence on the kinetics of oxygen reduction, has been studied in neutral 5 mol dm-3 NaCl at temperatures from 30oC to 90oC using Electrochemical Impedance Spectroscopy, X-Ray Photoelectron Spectroscopy and Cyclic Voltammetry. The impedance is very dependent on potential but only slightly dependent on temperature. Passivity is maximized, and oxygen reduction most suppressed, over the potential range -0.2 V to 0.2 V. At higher potentials the passive film resistance decreases markedly, leading to catalysis of oxygen reduction in the range 40oC to 60oC. At higher temperatures catalysis is lost.
An Improved Borohydride-H2O2 Laboratory Fuel Cell
Authors: Santos Diogo M. , Condeco Jose A. , Franco Marta W. , Sequeira Cesar A.
Published: September 2007

A new direct borohydride fuel cell (DBFC) which uses sodium borohydride and hydrogen peroxide as reactants is described. Cell performance is measured in a laboratorial cell constructed and modified according to the tested parameters: electrolyte concentration, membrane type and configuration, fuel and oxidant concentrations. Platinum electrodes were selected from a wide range of electrocatalytic materials and used throughout the work both for borohydride oxidation and peroxide reduction. A short-circuit current density of 92 mA cm-2 and a maximum power density of 56 mW cm-2 at 25 ºC were attained when the improved cell was used. Suggestions for future work are presented.
Morphology of the Surface of the Polycrystalline and Single-Crystal SiC Treated with pure NF3 Plasma and Analysis of Chemical Reaction of SiC with NF3
Authors: Takatsugu Kanatani , Tetsuro Tojo , Masamichi Tanaka , Minoru Inaba , Akimasa Tasaka
Published: September 2007

SiC is a promising semiconductor material for use in high temperature and high power electronic device applications. In the semiconductor industry in Japan, a large amount of NF3 is now used as a dry etchant and a cleaner gas for CVD chambers. NF3 is chosen as a fluorine radical source, because it efficiently decomposes to from free radicals, and all possible reaction products are volatile.
Mass Transport Effects of a Current Collector Coated on the Entire Cathode Surface of a Micro Tubular Solid Oxide Fuel Cell
Authors: Serincan M. F. , McPhee William A. , Sammes Nigel M.
Published: September 2007

Micro tubular Solid Oxide Fuel Cells (SOFC's) are advantageous in terms of power density, with a goal in this program to achieve 18kW/L by using 100 μm diameter anode supported SOFC's. In this study a silver cathode current collector, which covers the entire cathode surface of a micro tubular SOFC, is modeled, thereby predicting the reactant concentration distribution over the porous current collector and estimating the concentration losses. The main advantage of this design is in utilizing the whole surface of the cathode for current collection, which results in a uniform distribution of electric field inside the electrode, as well as a uniform distribution of reaction rate and ohmic heating. In addition, the temperature field has peripheral uniformity, thus thermal distortions along the tube are eliminated.
Discharge Characteristics of Polypyrrole/Silver Vanadium Oxide Composite Used for Lithium Primary Batteries
Authors: Lee Jong-Won , Anguchamy Yogesh , Popov Branko N.
Published: September 2007

A new cathode material based on polypyrrole (PPy) and silver vanadium oxide (SVO) was developed for lithium primary batteries in implantable cardioverter defibrillators. The composite electrodes with 7.0 to 12.5 wt% PPy yielded a higher discharge capacity and a better pulse discharge capability when compared to the pristine SVO electrode. The pulse discharge and ac-impedance studies indicated that PPy forms an effective conductive network on the SVO surface and thereby reduces the particle-to-particle contact resistance and facilitates the interfacial charge transfer kinetics.
Aqueous Voltammetry of 1-Bromopyrrolidin-2,5-Dione
Authors: ul Haque Inam , Akram Wajiha , Aslam Nishat , Sadaf Shamaila , Bano Kiran
Published: September 2007

Whereas reductive voltammetry of 1-bromopyrrolidin-2,5-dione (N-Bromosuccinimide), or SBr has been extensively studied in non-aqueous systems, relatively few papers have dealt with its electro-reduction in aqueous solutions. This paper describes voltammetry of 1-bromopyrrolidin-2,5-dione at platinum electrode in aqueous nitrate solution.
Electrocatalytic Reduction of Nitrite in Presence of Mo(VI)/Mo(IV) or Fe(III)/Fe(II) Redox Couples
Authors: Vicente Francisco , Tamarit Ramón , Giménez-Romero David , Garzón María José J. , García-Jareño José Juan J. , Agrisuelas Jerónimo
Published: September 2007

Polarographic results obtained in MoO22+/NO2- systems confirm that Mo(V) is an active state in the Mo-Fe cubane complexes for reducing the nitrite ions. However, parallel results support the idea that the nitrite coordination of Fe(II) and Fe (III) sites also play an essential role in their electrocatalytic effect on nitrite reduction. The fact that the height of the catalytic waves increases linearly with nitrite concentration makes it of analytical interest too, and both Mo(VI)/Mo(IV) and Fe(III)/Fe(II) redox couples become electrochemical systems of great interest to understand the enzymatic behaviour of some Mo-enzymes, such as the nitrite and nitrate reductases where the participation of the electrochemical reaction of water is emphasised.
Highly Thermal-Stable Amorphous TaSi2Cx Thin Films
Authors: Lin Ting-Yi , Cheng Huai-Yu , Chin Tsung-Shune , Fang Jau-Shiung
Published: September 2007

Structural changes at high temperature of amorphous TaSi2Cx films deposited on Si(100) were evaluated. Increased carbon content remarkably raises crystallization temperature, thus TaSi2Cx films (x > 16 at %) sustain amorphous phase at 800 oC for at least 30 minutes. A preliminary evaluation of such films as a diffusion-barrier of Cu metallization in a sandwich scheme Si(100)/TaSi2Cx(20 nm)/Cu showed the stability of 750 oC (x= 19 at%) or 800 oC (x= 22 at%) for at least 5 minutes without a sharp increase in sheet-resistance nor the formation of Cu3Si. Since Ta, Si and C are compatible with IC processing, these films are readily applicable as diffusion barriers in Cu metallization.
Nanofabrication Process for Highly Ordered Porous Materials by the Liquid Phase Deposition Methods
Authors: Deki Shigehito , Nakata Akiyoshi , Miyake Takuya , Ooka Sachiyo , Mizuhata Minoru
Published: September 2007

We have studied a novel technique for the direct synthesis of two-dimensional metal oxide films with highly ordered periodic structure. TiO2 films with highly nano-ordered architectures were directly deposited on substrates at room temperature by the liquid phase infiltration (LPI) method. 2D arrays of several kinds of metal oxide rods with diameters ranging from ca. 100 to 1000 nm are fabricated by filling the holes in a Si wafer. We summarized the various kinds of ordered structured metal oxide thin film with this method and the other techniques which have been reported that a novel soft solution process for the direct synthesis of large-area well-crystallized oxides with 1D-3D ordered periodic structure has been developed based on the LPI method. Metal oxide thin films were deposited directly into the nano-space, and thus the nano-space was completely infiltrated with metal oxide. The LPI process provides a direct fabrication route for metal oxide films with highly ordered structures, enabling nanoscale modification of optical properties of photonic crystals.
Graphite Foams for Lithium-Ion Battery Current Collectors
Authors: Dudney Nancy J. , Tiegs Terry N. , Kiggans James O. , Jang Young-Il , Klett James W.
Published: September 2007

Graphite open-cell foams, with their very high electronic and thermal conductivities, may serve as high surface area and corrosion resistant current collectors for lithium-ion batteries. As a proof of principle, cathodes were prepared by sintering carbon-coated LiFePO4 particles into the porous graphite foams. Cycling these cathodes in a liquid electrolyte cell showed promising performance even for materials and coatings that have not been optimized. The specific capacity is not limited by the foam structure, but by the cycling performance of the coated LiFePO4 particles. Upon extended cycling for more than 100 deep cycles, no loss of capacity is observed for rates of C/2 or less. The uncoated graphite foams will slowly intercalate lithium reversibly at potentials less than 0.2 volts versus lithium.
Application of In Situ Techniques for Investigations in Lithium-Ion Battery Materials
Authors: Vetter Jens , Hardwick Laurence J. , Würsig Andreas , Holzapfel Michael , Schneider Oliver D. , Ufheil Joachim , Novák Petr
Published: September 2007

Some examples for the application of various in situ techniques in the investigation of lithium-ion battery materials are given. The effect of crystallite size on lithium insertion behavior of anatase TiO2 is shown by in situ Raman microscopy. In TiO2 with a crystallite size of 10-20 nm, an extended solid solution domain is found compared to samples with ca. 80 nm crystallite size. Graphite exfoliation is investigated by in situ Raman mapping and differential electrochemical mass spectrometry (DEMS). Inhomogeneities within single graphite particles are found with Raman mapping. CO2 formation at Li(Ni,Co,Al)O2 electrodes is monitored with DEMS and in situ ATR-SNIFTIRS. CO2 evolution is measured at elevated temperatures by DEMS, but formation of CO2, dissolved in the electrolyte, is also detected at room temperature by ATR-SNIFTIRS.
Synthesis and Electrochemical Characterization of Spinel Lithium Titanium Cxide as Anode Material for Lithium Secondary Battery by sol-gel Method
Authors: Oh Mi-Hyun , Kim Han-Joo , Kim Young J. J. , Kim K J. , Park Soo-Gil
Published: September 2007

Anode material lithium titanium oxide (Li4Ti5O12) for lithium- ion batteries was prepared by novel sol-gel method and by high energy ball milling (HEBM). Li4Ti5O12 based spinel-framework structures are of great interest material for lithium-ion batteries. X-ray diffraction (XRD) data show that powders grown with a spinel structure have been obtained at 850{degree sign}C for 5h. Scanning electron microscopy (SEM) analysis, show that uniformly distributed Li4Ti5O12 particles with grain sizes of 100nm are abtained. Lithium cells, consisting of Li4Ti5O12 as working electrode, lithium foil as both counter and reference electrodes showed the 280 mAh/g in the range of 0.0 ~ 3.0 V. Furthermore, the crystalline structure of Li4Ti5O12 didn't transform during the lithium intercalation and deintercalation process.
LiFePO4 High Electrochemical Performance at 60{degree sign}C with Purity Controlled by SQUID Magnetometry
Authors: Zaghib K. , Ravet Nathalie , Mauger Alain , Gauthier Michel , Goodenough John B. , Julien C.
Published: September 2007

The local structure and magnetic properties of a series of carbon-coated LiFePO4 particles prepared under different conditions are analyzed with XRD, FTIR, and SQUID magnetometry for comparison. While nano-sized ferromagnetic particles (γ Fe2O3 clusters) are detected by magnetic measurements in samples grown from iron(II) oxalate, such ferromagnetic clusters do not exist in the optimised samples grown from FePO4 (H2O)2. FTIR analyses show that carbon does not penetrate significantly inside the LiFePO4 particles despite the fact that it has been very efficient in reduction of Fe3+ to prevent gamma-Fe2O3 clustering, thus pointing to a gas-phase reduction process. The impact of the carbon coating on the electrochemical properties is also reported. No iron dissolution was observed after 200 charge-discharge cycles at 60{degree sign}C for cells containing Li foil, Li4Ti5O12, or graphite as negative electrodes.
Comparison of Thermal-Electrochemical Model Predictions with Experimental Data of Lithium-Ion Batteries
Authors: Kumaresan Karthikeyan , Sikha Godfrey , White Ralph E.
Published: September 2007

A set of parameters (and their concentration and temperature dependences) has been obtained for a lithium-ion battery composed of a MCMB anode, LiCoO2 cathode in 1M LiPF6 in a mixture of ethylene carbonate (EC), propylene carbonate (PC), ethyl-methyl carbonate (EMC) and di-ethyl carbonate (DEC) electrolyte. The parameter set was obtained by comparing the model simulations to the experimental discharge profiles obtained at various temperatures and rates. The concentration and temperature dependence of the extracted parameters were correlated through empirical expressions. These correlations can be used to predict the discharge process of a lithium-ion battery for different charge/discharge rates and temperatures.
Challenges and Opportunities for Electrochemical Processing in Microelectronics
Authors: Ritzdorf Tom
Published: September 2007

Electrochemical deposition processes have become increasingly accepted in mainstream semiconductor and microelectronic processing over the last four decades. The most commonly discussed process is copper deposition for damascene interconnect manufacturing, but plating has also been used extensively for depositing metal layers in thin film recording heads, depositing solder alloys for flip chip bumps and for depositing gold conductors in III-V semiconductor devices. There are many other opportunities to utilize electrochemical processes in microelectronic manufacturing. This overview discusses some of the current development direction of processes currently in use, as well as some opportunities for implementing additional electrochemical processes in semiconductor processing.
Controlling Whisker Formation in Tin-Based Solders Using Electrically Mediated Electrodeposition
Authors: Garich Holly , McCrabb Heather , Taylor E. Jennings , Inman Maria
Published: September 2007

The global trend to eliminate lead from electronic devices is driven by legislative and marketing pressures based on environmental, health and social concerns on the cumulative effects of lead in waste streams. Tin and tin-rich alloys are the forerunning replacements for tin-lead solders. However, pure tin electrodeposits have a tendency to form tin whiskers that may cause short-circuiting, metal vapor arcing and failure of the component. The major cause of whisker growth is thought to be compressive stress in pure tin deposits after DC plating. Faraday Technology, Inc. has developed an electrically mediated electrochemical process for depositing lead-free solders, based on non-steady state electric fields to control the deposition process and consequently the physical properties of the deposit. Results of electrically mediated tin deposits are presented and compared to DC deposits in terms of grain size, internal stress type/magnitude and surface roughness.
Porous Gold Structures Built on Silicon Substrates
Authors: Brito Neto Jose Geraldo A. , Kondo Kentaro , Hayase Masanori
Published: September 2007

In this work, we describe the synthesis of porous Au structures by galvanic displacement reaction using porous Si as template material. Two metal ions were used as Au precursors: tetrachloroaurate(III) and bis(ethylenediamine)Au(III). Fluoride was employed to etch the Si oxides that form as a result of the displacement reaction. The porous Si layer employed as template displays an array of parallel cylindrical pores with diameters near 100 nm. The porous metal layer that forms with tetrachloroaurate(III) is an agglomerate of spherical particles with ca. 100 nm diameters. On the other hand, metallization with bis(ethylenediamine)Au(III) preserves the honeycomb morphology of the original porous Si layer.
Electronic, Structural and Magnetic Properties of Nanocrystalline Li1+xMn2-xO4 Spinels
Authors: Dygas Jozef R. , Kopec Monika , Krok Franciszek , Gendron Francois , Mauger Alain , Julien C.
Published: September 2007

A series of spinels Li1+xMn2-xO4 (0{less than or equal to}x{less than or equal to}0.33) was prepared by the wet chemistry technique using succinic acid as a chelating agent. Precursors were decomposed at 400{degree sign}C and formation of the spinel structure was completed upon annealing in air at about 750{degree sign}C. SEM revealed well crystallized grains of average size about 70 nm, in agreement with crystallite size calculated from broadening of the X-ray reflections. Impedance spectra measured with sputtered gold electrodes were analyzed by the least- squares fitting of a complex function representing conductivity and dielectric properties of the spinels. Temperature dependence of the electrical parameters confirmed that charge carriers are small polarons. In the case of LiMn2O4, effects of charge ordering on conductivity and dielectric relaxation were studied. Magnetization measurements on a SQUID and electron spin resonance spectra provided information about magnetic ordering and impurities.
Electrochemical Lithium and Sodium Reactions with Carbon Microspheres Obtained by Polycondensation
Authors: Alcantara Ricardo , Lavela Pedro , Ortiz Gregorio , Tirado Jose L.
Published: September 2007

Lithium insertion in carbon microspheres takes place by irreversible attachment to the border of graphene layers and/or in the vicinity of hydrogen-carbon bonds, reversible intercalation between disorderly-stacked graphene layers, and lithium adsorption on the pore surfaces. As compared with lithium, the lower stability of the passivating films and sodium-carbon compounds usually leads a poorer reversible insertion of sodium. Surface modification of carbon microspheres with citric acid improves reversible insertion by the loss of porosity (up to ca. 300 mAhg-1 for sodium insertion). Impregnation with tin oxide leads to higher insertion capacities penalized by a poorer retention.
The Kinetics of Sub-Fluorinated Carbon Fluoride Cathodes for Lithium Batteries
Authors: Yazami Rachid , Ozawa Yasunori , Miao Shu , Hamwi Andre , Whitacre Jay , Smart Marshall , West W. , Bugga Ratnakumar
Published: September 2007

We have developed a new family of sub-fluorinated carbon fluoride materials, CFx (x<1) that show a good tradeoff between energy density and power density, together with excellent low temperature (down to -60{degree sign}C) performances in lithium primary batteries application. The starting carbon materials consist of synthetic graphite and carbon multi-wall nanotubes. The outstanding CFx electrode kinetics may be related to its unique nano-composite crystal structure having intimately mixed fluorinated and unfluorinated carbon domains, as evidenced by x-ray diffractometry and electron microscopy studies.
Correlating the Oxygen Redox Chemistry and Oxygen Nonstoichiometry at La1-xSrxMnO3 plus or minus delta SOFC Cathodes
Authors: Fournier Joseph L. , Birss Viola
Published: September 2007

This work uses the Wagner Factor as a qualitative means of explaining the effects that perturbing the oxygen content in La1-xSrxMnO3{plus minus}δ (LSM) cathodes has on their O2 redox activity and as well as the emergence of pseudo-capacitive characteristics under low pO2 atmospheres. The Wagner Factor correlates the rate constant of the O2 redox reaction in mixed conducting perovskites (kchem, Dchem) to changes in the oxide's oxygen concentration. The emergence of an oxygen under- stoichiometric (3-δ) state under low O2 partial pressures and/or at high cathodic overpotentials is believed to lead to the observed electrochemical capacitive behavior.
Interface Modifications of Carbon-based Supercapacitor Electrodes
Authors: Simon P. , Largeot Celine , Dugas Romain , Balducci Andrea , Taberna Pierre-Louis , Chmiola John , Portet Cristelle , Yushin Gleb , Gogotsi Yury
Published: September 2007

This paper deals with the performance improvement of supercapacitor electrodes by designing specific properties at the inner and outer electrode interfaces.
Charge Carrier Tunneling Across the Passive Film on Platinum
Authors: Bao Jianer , Macdonald Digby D.
Published: September 2007

The reduction of oxygen on platinum in 0.1M KOH has been studied at ambient temperature using a rotating ring disk electrode and two Tafel slopes are observed. The structural and electronic properties of this film were investigated over an extended temperature range (25oC to 220oC) using the rate of hydrogen oxidation as an experimental probe in a pressurized, controlled hydrodynamic flow channel. By combining Quantum Mechanical Tunneling theory and the Point Defect Model, a new method was devised for determining the thickness of the extremely thin oxide film on platinum. This QMT-PDM method yields a temperature-invariant tunneling constant (which defines the blocking character of the oxide film to charge transfer) as 0.57x108cm-1 and yields a barrier height of 0.31eV. Finally, the barrier oxide layer on platinum is postulated to comprise a columnar, nano crystalline structure with tetragonal unit cells oriented with the c-axis perpendicular to the metal surface.