bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-Temperature Performance Limitations of Lithium-Ion Batteries
Authors: Gering Kevin L.
Published: November 2006

This work considers root causes for diminished performance of Li-ion cells at cold conditions, and provides suggestions toward improving low-temperature performance through modified electrolyte compositions. This evaluation considers concentration polarization, lithium desolvation, and potential electrolyte phase transformations from solid surface-driven Gibbs Adsorption processes. A new lumped parameter, denoted as Li-STEP, is used to describe the contribution of lithium desolvation to interfacial phenomena. Additionally, supporting insights are provided from test data for 18650 Li-ion cells and Li-ion button cells. The analyses suggest that at lower temperatures, poor transport properties of an EC-based electrolyte promote high concentration polarization, yielding localized enriched and depleted electrolyte regions that cause higher cell impedance and that can shift local thermodynamics to favor phase formation of EC-rich solid phases. Analysis of Li-STEP for an EC-based electrolyte suggests the lithium desolvation process accounts for roughly half of the activation energy required for lithium transport through interfacial regions.
Ionic Transport and Interfacial Stability of Sulfonate-Modified Fumed Silicas as Nanocomposite Electrolytes
Authors: Fedkiw Peter S. , Zhang Xiang-Wu
Published: November 2006

Degussa A200 and R711 fumed silica surfaces were modified by attaching lithium sulfonate groups through alkyl or oligomer chains, respectively, in an attempt to form single-ion conducting fumed silicas: A200-lithium propanesulfonate (A200-LiPS), R711-poly(lithium vinylsulfonate) (R711-pLiVS), and R711-poly(lithium 2-acrylamido-2-methyl-1-propanesulfonate) (R711-pLiAMPS). Conductivity, lithium transference number, and Li/electrolyte interfacial stability measurements were conducted on nanocomposite electrolytes prepared by dispersing the conducting fumed silicas into solvents consisting of oligomeric polyethylene glycol dimethyl ether (PEGdm), polyethylene oxide (PEO), or PEGdm/PEO blends. Among the three sulfonate-modified fumed silicas, the highest conductivity was always obtained using R711-pLiAMPS. Adding lithium salts to the solvent, such as lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(perfluoroethylenesulfonyl)imide (LiBETI), lithium bis(oxalato)borate (LiBOB), and lithium phosphate (Li3PO4), increases room-temperature conductivity and interfacial stability while maintaining relatively high lithium transference numbers.
Electrochemical Corrosion of the Ti-xAl-yFe Alloys Fabricated by Direct Metal Deposition in Hanks Solution
Authors: Pimenova Natalia , Starr Thomas
Published: November 2006

A problem addressed of toxicity of vanadium in the Ti-6Al-4V used as biomedical implant has been. Combinatorial library of the new type of titanium alloys composed of non-toxic elements, such as Ti, Al, and Fe with lower modulus of elasticity and greater corrosion resistance has been fabricated by direct metal deposition technique. The resistance to electrochemical corrosion in Hanks solution of each titanium based alloy was tested cyclic voltammetry and polarization method.
Influence of Hydrogen Charging on the Formation of Nanostructural Titanium Surface by Electrochemical Treatment
Authors: Ou Keng-Liang , Chen C. S. , Cheng C. L. , Lee B. H. , Lin C. T. , Chan C. C.
Published: November 2006

The influences of nanophases (titanium hydride compounds) on the formation of nanostructural titanium oxide by electrochemical treatment was investigated by XPS, GIXRD, TEM, and SEM. Nanostructural TiO2 was formed after anodization with cathodic pretreatments. The nano-TiH2 is formed by cathodic pretreatments. The nano-TiH2 is directly dissolved after anodization. Furthermore, the nanoporosities formed by dissolution of nano-TiH2 were changed to TiO2. The nano-TiH2 plays an important role in forming nanoporous TiO2 layer. The anodization with cathodic pretreatment not only produces nano- titanium hydride layer, but also results in formation of nanostructured titanium oxide. It is believed that bioactive titanium implant with oxidation and nanostructure can be enhanced and integrated bone interface contact.
Electrically-Assisted Formation and Desorption of Dodecyl Phosphate Self-Assembled Monolayers on Indium Tin Oxide Surfaces
Authors: Voros Janos , Tang Clarence S. , Antoni Mathieu , Schönbächler Isabelle , Keller Beat , Textor Marcus
Published: November 2006

Molecularly homogenous and hydrophobic surfaces play an important role in a number of technological applications such as tribology and protein/cellular adhesion. Self-assembled monolayers of dodecyl phosphates (DDPO4) have previously been demonstrated to spontaneously form on titanium oxide, producing surfaces with excellent hydrophobic properties. In this paper, we report on the adsorption of DDPO4 onto a transparent electronic material, indium tin oxide (ITO), under both open circuit and applied potential conditions. We have used two complementary surface characterization techniques: variable angle scanning ellipsometry and contact angle measurements to investigate the adsorption of DDPO4 on an ITO surface. Under open circuit condition, both methods consistently confirmed the formation of DDPO4 monolayers on the ITO surface. The presence of an electrical field increased the amount of DDPO4 adsorbed on the ITO surface. An applied anodic electrical stimulus of 1800 mV resulted in an exponential loss of the monolayer as confirmed by X-ray photoelectron spectroscopy and electrochemical optical waveguide lightmode spectroscopy (EC- OWLS). This electrically stimulated selective adsorption/desorption of DDPO4 opens up new ways to tailor the physico-chemical properties of surfaces.
Thin Film Silicon Solar Cells on ZnO/SnO2/Glass Substrate
Authors: Lee Yoo Jin , Shin Jin Koog , Lim Koeng Su
Published: November 2006

Hydrogenated amorphous and microcrystalline silicon thin film solar cells were fabricated on ZnO/SnO2:F/glass structured substrate by transformer coupled plasma chemical vapor deposition(TCP-CVD) techniques. Asahi U-type glass (SnO2:F coated glass) widely used as a substrate for amorphous silicon thin film solar cells has a critical problem to be reduced in H2 plasma. In this research, we investigated the effects of ZnO thin films used as a reduction barrier on the characteristics of solar cells by varing the thickness of ZnO films on Asahi U-type glass. The I-V characteristics of Al/n/i/p/ZnO/SnO2/glass structured (called the 'superstrate' configuration) solar cells were measured at AM1.5, 100 mW/cm2 and Voc (open circuit voltage), Jsc (short cuicuit current density), FF (fill factor), Eff (efficiency) of these cells were calculated.
Iron Cross-Contamination Dynamics at Elevated Temperatures in Oxygen Gas Flow
Authors: Rapoport Igor , Taylor Patrick , Orschel Benno , Kirscht Fritz , Kearns Joel
Published: November 2006

One major source of metals contamination during high temperature processing are metals pre-deposited on the wafers surface before thermal treatment and metals cross- contamination from other wafers and/or furnace components. This study investigates the mechanism of metals transfer via gas phase vs. temperature and oxygen gas flow conditions. We also investigated the cross-contamination from Silicon Carbide (SiC) components at elevated temperatures. Cross-contamination from SiC can be explained as (a) metal diffusion from the direct contact area between silicon wafer and SiC (MDD - Metals Direct Diffusion) and (b) metal desorption from the SiC surface and re-adsorption on the silicon wafer surface from the gas phase (MAG - Metals Adsorption from Gas Phase). Both MDD and MAG contamination components are driven by SiC surface metal contamination. Using high resolution Surface Photo- Voltage (SPV) iron mapping we investigated the character of iron cross-contamination. Iron diffusion and desorption activation energies were experimentally determined.
Studies of Cu Atomic Layer Replacement, Formed by Underpotential Deposits, to Form Pt Nanofilms Using Electrochemical Atomic Layer Epitaxy
Authors: Stickney John L. , Kim Youn-Geun , Kim Jay Y.
Published: November 2006

In this paper, the development of a surface limited redox replacement reaction (SLR3) for the deposition of Pt is discussed. In the present study, a Au(111) substrate was cleaned using Ar ion bombardment to form a well ordered (1x1) LEED pattern, after annealing. This surface was then transferred from the UHV surface analysis chamber to an antechamber containing an electrochemical cell. A monolayer of Cu was deposited on the Au substrate from a CuSO4 solution, at an underpotential. The Au substrate, with Cu UPD, was then immersed in a Pt(IV) solution at open circuit, spontaneously replacing the Cu UPD with Pt. The resulting Pt atomic layer coated Au substrate was then transferred back to the analysis chamber, and the surface characterized using LEED and Auger electron spectroscopy (AES). This paper describes the first attempt by this group to grow Pt films by metal EC-ALE.
Electrodeposition of Co/Cu Multilayered Thin films and Microposts
Authors: Podlaha Elizabeth J. , Moldovan Monica , Young Dave , Li Yutong
Published: November 2006

Multilayer Co/Cu thin films were galvanostatically deposited onto n-type (100) silicon wafers with a 20 nm Cu seed layer. Both a regular square-wave pulse and a pulse train method were examined. The current-in-plane (CIP) giant magnetoresistance (GMR) that resulted when the cobalt layers were pulsed in a pulse train fashion together with a single copper layer pulse, showed a maximum in the GMR value with duty cycle. X-ray lithography and electrodeposition were combined to deposit an array of CoCu/Cu multilayer microposts into deep recesses for novel GMR architectures. The GMR was measured with the current perpendicular to the plane of the multilayers (CPP) in a single micropost with a height of 500 μm and a cross section of 183×183 μm.
Preparation and Characterization of Tungsten Carbides as Alkaline Fuel Cell Catalysts
Authors: Shen Peikang , Xie Fangyan , Meng Hui
Published: November 2006

The applications of transition metal carbides as catalysts had received a great deal of interest since the discovery of their catalytic activities. In the present study, nano W2C powders with high surface area were synthesized by the microwave irradiation method. X-ray diffraction measurement confirmed the product is crystalline tungsten carbide, which could be pure W2C or the mixture of W2C and WC. TEM results showed that tungsten carbide powders are uniformly dispersed with the particle size around 10 nanometers. Electrochemical characterization proved that both W2C and the mixture could catalyze the reduction of O2. It was further testified that small amount of methanol in the solution did not influence the reduction of O2 when the mixture was used. Because of its cheap price and abundant reserves, the advantages are obvious using tungsten carbide as catalysts in fuel cells instead of the precious metal catalysts.
Alkaline Direct Methanol Fuel Cell
Authors: Sarangapani Srinivasan , Luczak Frank , Enayetullah Mohammad , Vitella Tom , Osenar Paul
Published: November 2006

Polymer electrolyte membrane based direct methanol fuel cells (PEM-DMFC) have a complicated system design, and their fuel efficiency is limited by methanol cross-over through the proton exchange membrane. In addition, the methanol oxidation kinetics as well as oxygen reduction kinetics are quite slow in the acid electrolyte system. In contrast to acid DMFCs, it is known that electro-oxidation (and oxygen electro-reduction) reactions are improved in basic media. Alkaline DMFCs, unlike their acid counterparts, do not require MEAs, presently the most costly and complex stack component. It is however unknown if alkaline DMFC could be used as PEM alternatives for portable power applications. The technical challenge then, is to develop AFC stacks that can be used to fabricate compact low-power (20 W) systems that have sufficient resilience to carbonate build-up inherent in alkaline cells. In addition to carbon dioxide from ambient air, the methanol fuel is an additional source of electrolyte carbonation (CO2 generated in situ). For portable power applications, one way to circumvent this issue is to replenish the spent alkaline electrolyte on a regular maintenance schedule. This paper reports the results of some preliminary work carried out to investigate the viability of alkaline DMFC for portable power application.
Internal Polymer Electrolyte Membrane Fuel Cell/Energy Storage Hybrid Power Systems
Authors: Wang Chunsheng , D'Souza Steven R. , Ma Jianxin
Published: November 2006

Novel internal PEM fuel cell/energy storage hybrid power systems were fabricated to improve the pulse power output of the system by incorporating supercapacitor element (Ru2O•xH2O) and battery element (CeZrO2) into the catalyst layer of fuel cells. The continual power output of the internal PEM fuel cell/energy storage hybrid power system is similar to the conventional PEM fuel cell. However, the peak power output of the hybrid system was much higher than that of the conventional system.
CdS:Mn Thin Film Synthesis Using Pulse Electrodeposition Technique
Authors: Jain Kiran , Karar N. , Chandra H. , Rashmi Rashmi
Published: November 2006

Mn doped CdS thin films were prepared by unipolar pulse electrodeposition technique. XRD, Optical transmission and photoluminescence measurements were used for characteration of the films. XRD results showed presence of hexagonal phase for CdS:Mn samples. A photoluminescence emission near 580 nm was observed, which is correlated to Mn incorporation in the CdS lattice
Time-Resolved Kinetics of Electrode Reactions
Authors: Gileadi Eliezer
Published: November 2006

Tribute is given to the personality and the work of Dr. S. Srinivasan. A discussion of the different time scales at which electrode processes take place, and the consequence of this on the interpretation of the mechanism of electrode reactions are discussed. One of the tenets of the Marcus theory of electron transfer is the Born-Oppenheimer approximation, namely the fact that electron transfer if extremely fast compared to the movement of nuclei. The consequence of this principle is discussed for complex electrode reactions. of primarily two types: (a) the formation of unstable intermediates, which are assumed to be stabilized by adsorption (b) metal deposition and dissolution. In both cases electron transfer would lead to the formation of highly unstable intermediates. Thus, although the final state can be quite stable, a mechanism involving electron transfer is not likely to be followed.
Zirconium Nitride and Oxynitride for New Cathode of Polymer Electrolyte Fuel Cell
Authors: Doi Shotaro , Liu Yan , Ishihara Akimitsu , Mitsushima Shigenori , Kamiya Nobuyuki , Ota Ken-Ichiro
Published: November 2006

Zirconium compounds (ZrOxNy) have been investigated as a new cathode of polymer electrolyte fuel cells without platinum. The electrocatalysts of ZrOxNy were prepared by the radio frequency magnetron sputtering method under Ar + O2 + N2 atmosphere with heating the sputtered material. The effect of the heat treatment on the catalytic activity for the oxygen reduction reaction (ORR) and the properties of ZrOxNy has been examined. The solubility of ZrOxNy was less than 5×10-8 mol dm-3 in 0.1 mol dm-3 sulfuric acid at 30 oC under atmospheric condition. This indicated that ZrOxNy had a high chemical stability in acidic media. The ORR current density on ZrOxNy which was heated at 800 oC was about 30 times larger than that on ZrOxNy deposited at 50 oC. The higher heat treatment caused the change of crystalline structure and the increase of the crystallinity of ZrOxNy.
Non-Noble Metal Catalyst for Oxygen Reduction Reaction in Acidic Medium
Authors: Popov Branko N. , Kumaraguru Swaminatha , Subramanian Nalini P. , Colon Mercado Hector
Published: November 2006

Cobalt based non noble metal catalysts were prepared from heat treated cobalt ethylene diamine complexes adsorbed on carbon. The effect of surface oxygen groups on carbon was studied. Surface oxygen groups on carbon were introduced with HNO3 oxidation. Quinone groups introduced by nitric acid treatment, in addition to increasing the dispersion of the chelate complexes, play a role in forming the active site for oxygen reduction.
Electrocatalyst Materials for PEM Fuel Cells Based on Substituted Heteropoly Acids
Authors: Herring Andrew M. , Stanis Ronald J. , Ferrell Jack , Kuo Mei Chen , Turner John A. , Limoges Bradford
Published: November 2006

Very small amounts of various vanadium or iron substituted Heteropoly acids (HPA) are strongly adsorbed on to commercial XC-72R based carbon gas diffusion electrodes. The electrochemical activity of these adsorbed HPA for both the hydrogen oxidation reaction and the oxygen reduction reaction is investigated as non-platinum electro-catalysts and it is shown that these materials have a moderate activity at the extremely low doping levels achieved. On the cathode rearrangement of the precursor HPA induced by moderate heating (vanadium) or cycling the fuel cell in the absence of oxygen (iron) occurs to give a more active electro-catalyst. The HPA studied are also proposed for use in CO tolerant anodes and as mixed electronic/protonic conductors in platinized fuel cell electrodes.
Synthesis and Characterization of NanostructuredPtW Alloy for Oxygen Reduction in PEMFCs
Authors: Xiong Liufeng , Kreidler Eric , He Ting
Published: November 2006

Nanostructured PtW alloys on carbon support have been synthesized by various approaches. The morphology and particle size of the prepared alloy catalysts were characterized by high resolution electron transmission microscopy (HRTEM), high angle annular dark field-scanning transmission electron microscopy (HAAF-STEM), and X-ray diffraction (XRD). The electrocatalytic activity of PtW alloys were examined by rotation disk electrode (RDE) technique. The results have shown that the particle size and morphology of PtW electrocatalysts greatly depend on the synthetic approaches. Well alloyed PtW phase and uniform size distribution are important to achieve high activity for oxygen reduction reaction (ORR). The prepared, carbon supported PtW alloys are twice more active than commercial Pt/C for ORR in acid electrolyte, and will be the potential candidate as cathode electrocatalyst for PEMFCs.
Enhancing the Performance of Low Pt Loading Prepared by Dual Ion-Beam Assisted Deposition in PEM Fuel Cells
Authors: Mukerjee S. , Saha Madhu S. , Gulla Andrea , Allen Robert
Published: November 2006

Ultra-low Pt and Pt based alloy/mix (Pt-Co and Pt-Cr) electrodes were prepared by dual ion-beam assisted deposition (Dual IBAD) method. Activity enhancement, based on normalization with electrochemical surface area and mass activity is reported relative to a commercial gas diffusion electrode containing carbon supported Pt electrocatalysts. Mass specific power density of 0.297 gPt/kW is reported with 250 Aå IBAD deposit at 0.65 V. Based on the morphological differences, which enable such enhanced activities and the mass manufacturability of this electrode system; we report a significant new development in terms of materials for PEMFC application.
In Situ X-Ray Absorption Spectroscopy Studies of Water Activation on Novel Electrocatalysts for Oxygen Reduction Reaction in Acid Electrolyte
Authors: Mukerjee S. , Ramaker David , Gatewood Daniel , Ziegelbauer J. M.
Published: November 2006

The novel oxygen reduction reaction electrocatalyst RhxSy was probed in situ via a new X-ray Absorption Spectroscopy technique to elucidate the specific sites and modes of water activation. The material was modeled by traditional XANES and EXAFS analysis techniques, and shown to be a mixture of at least two phases: Rh3S4 and Rh17S15. The Δμ technique was performed on the RhxSy catalyst by taking a difference of the normalized XANES spectra in respect to the cleanest adsorbate free potential. Theoretical XANES were generated using the FEFF 8.0 code with molecular models of the Rh3S4 structure at different levels and geometries of O(H) adsorption. Fitting of the theory to the experimental data has revealed that the RhxSy electrocatalyst proceeds through water activation by first adsorbing OH and O in a 1-fold configuration at lower potentials, and is eventually completely covered by n-fold O at potentials greater than 0.80 V.
Platinum-Iridium Alloys as Oxygen Reduction Electrocatalysts for Polymer Electrolyte Fuel Cells
Authors: Ioroi Tsutomu , Yasuda Kazuaki
Published: November 2006

Platinum-iridium (Pt-Ir) alloy electrocatalysts for polymer electrolyte fuel cell (PEFC) cathodes were prepared, and the physical and electrochemical properties were examined. A variety of unsupported Pt-Ir alloy catalysts was prepared in hot KOH solution, and the structure of the alloy was a uniform solid solution phase between Pt and Ir. Evaluation of the activity for the oxygen reduction reaction (ORR) was performed by the rotating disk electrode (RDE) method in 0.1 M HClO4 solution. The ORR kinetic analysis by the RDE showed that alloying Pt with Ir, especially with 5-20 wt.% Ir, enhanced the catalytic activity for the ORR by a factor of more than 1.5 at 0.8 V vs. RHE.
Molecular Flexibility in the Short-Side-Chain Perfluorosulfonic Acid Membrane
Authors: Paddison Stephen J. , Elliott James
Published: November 2006

We present a comparative theoretical study of the differences in rotational degrees of freedom of the various C−C, C−O, C−S, and S−O bonds in oligomeric sequences of the short-side-chain (SSC) perfluorosulfonic acid (PFSA) membrane for the purposes of understanding the flexibility of pendant side chain and the ability of the sulfonic acid group to aggregate in the polymer. Potential energy profiles were determined at the B3LYP/6-31G** level in the CF3CF(-O(CF2)2SO3H)-(CF2)7-CF(-O(CF2)2SO3H)CF3 two pendant side chain fragment of the PFSA polymer. The rotational barrier of the CF2−CF2 bonds along the backbone was found to be nearly 7.0 kcal/mol and is the energy difference between the staggered trans and planar cis conformations. Furthermore, the calculations revealed that the stiffest portion of the side chain is near its attachment to the backbone, with the CF−O and O−CF2 barriers of 9.1 and 8.0 kcal/mol, respectively. The most flexible portion of the side chain is the carbon-sulfur bond with a barrier of only 2.1 kcal/mol.
Electro-osmotic Pumping of Methanol/Water Mixtures for Direct Methanol Fuel Cell Applications
Authors: Kim Daejoong , Posner Jonathan , Santiago Juan
Published: November 2006

We present experimental investigations of porous glass electroosmotic pumping of methanol/water mixture to study the feasibility of electroosmotic pump applications for direct methanol fuel cells. We first measure electroosmotic mobility of deionized water and pure methanol and evaluate pump pressure, flow rate, and current.
Investigation of Fuel Modification to Reduce Crossover in Direct Methanol Fuel Cells
Authors: Lam Alfred , Wilkinson David P. , Zhang Jiujun
Published: November 2006

The direct methanol fuel cell (DMFC) has the potential to replace battery technology for micro & small portable applications and may be used in larger applications if key technological barriers can be overcome. Presently, fuel crossover through the electrolyte is a major limitation on the performance and fuel utilization efficiency. Different approaches to reduce crossover have been examined, including new membranes, membrane modification, variation of operating conditions, and novel electrode design. The investigation of methanol crossover through fuel modification represents an important new approach to the reduction of crossover in a DMFC. In this study, systems of acetic acid/water/methanol & propionoic acid/water/methanol have been found to reduce methanol crossover through Nafion® 117 membranes, carbon fibre diffusion layers, diffusion electrodes and membrane electrode assemblies.
Influence of Ionomer Loading on the Performance of Pt-Ru and Pt-Fe Electrodes Used in DMFCs
Authors: Arico Antonino S. S. , Baglio Vincenzo , Stassi Alessandro , D'Urso Claudia , Antonucci Vincenzo , Di Blasi Alessandra
Published: November 2006

High surface area carbon supported bimetallic Pt-Fe and Pt-Ru alloy catalysts have been investigated for the oxygen electro- reduction and methanol oxidation , respectively, in low temperature direct methanol fuel cells (30-60 {degree sign}C). The cathode electrocatalyst was prepared by using a combination of colloidal and incipient wetness methods. For both anode and cathode catalysts, carbon supported bimetallic nanoparticles with particle size of 2-3 nm were obtained. These materials were studied in terms of structure, morphology and composition by using XRD, XRF and TEM techniques. The oxygen reduction and methanol oxidation processes were in-situ investigated in a DMFC device. For the oxygen reduction, the electrochemical data obtained with the Pt-Fe/C catalyst were compared to those obtained in the presence of a Pt/C catalyst characterised by the same concentration of active phase on carbon and similar particle size. An enhancement of the DMFC single cell performance was recorded with the Pt-Fe/C catalyst. It was observed that the ionomer loading play a significant role in determining the performance of the DMFC. The highest power density was recorded with electrodes containing 25% Nafion loading (~90 mW cm-2 at 60 {degree sign}C).
Investigation of Ruthenium Dissolution in Advanced Membrane Electrode Assemblies for Direct Methanol Based Fuel Cell Stacks
Authors: Valdez Thomas I. , Firdosy Samad , Koel Bruce , Narayanan S. R.
Published: November 2006

The mechanism of ruthenium dissolution in Direct Methanol Fuel Cell (DMFC) Membrane-Electrode-Assemblies (MEAs) was investigated by preparing various MEAs and subjecting them to continuous operation for a period of 250 hours. All of the MEAs exhibited voltage decay. The voltage decay for MEAs operating at 40 oC, 0.5 M methanol was in the range of 6 to 48 mV at an applied current of 50-mA/cm2 and 67 to 150 mV at an applied current of 100-mA/cm2. The technique of anode polarization was used to determine the source of degradation and revealed that anode performance in these MEAs was constant and that the cathode was more sensitive to duration operation. EDAX analysis was performed on each cell to determine if ruthenium had dissolved from the anode and precipitated onto the cathode, no ruthenium was found on the MEA. This paper discusses stack properties that can promote ruthenium dissolution in DMFC MEAs.
Electrical Properties of Hydrous Ruthenium Dioxide in Direct Methanol Fuel Cells
Authors: Wang Yang , Zheng Jim P.
Published: November 2006

The electrical properties of hydrous ruthenium oxide (RuO2.xH2O) have been investigated in a modified direct methanol fuel cell (DMFC). The configuration of the modified DMFC involves a RuO2.xH2O layer sandwiched between anode catalyst layer and membrane. The experiments on polarization curves and electrochemical impedance spectra of the modified DMFC have been carried out to obtain the ionic resistance and capacitance of the RuO2.xH2O layer. Further numerical simulation study based on an electrical circuit model indicates that the RuO2.xH2O layer in the modified DMFC is equivalent to a resistive-capacitive transmission line and functions similar to a capacitor in parallel with the anode electrode. The improvement in the dynamic response of the modified DMFC has been experimentally confirmed in square current pulse operating condition. Finally, a novel monolithic hybrid DMFC has been proposed and discussed.
Low Temperature Membrane Properties
Authors: Onishi Lisa , Newman John
Published: November 2006

Nafion properties at low and subzero temperatures were experimentally measured. Membrane water content was measured by setting water activity = 1 and varying air pressure from 0 and 0.96 atm at 30{degree sign}C. Water content in mol SO3-/mol H2O =14 and 22 was found when air pressure = 0 and 0.94 atm, respectively. Schroeder's paradox did not exist in the absence of air. The state of water was shown to depend on the cooling rate, where melting and freezing peaks were lower for a 10{degree sign}C/min cooling rate than for a 1{degree sign}C/min cooling rate. The freezing peaks were -27 and -16{degree sign}C for 10 and 1{degree sign}C/min cooling scan rates. Membrane conductivity was measured from 0 to 80{degree sign}C for 100% RH vapor-equilibrated and 0 and 95{degree sign}C for liquid-equilibrated Nafion. The liquid-equilibrated conductivity had an activation energy of 10.2 kJ/mol.
Impact of Freezing on Nafion: Protection Using Acid Electrolyte
Authors: Leddy Johna , Dunwoody Drew
Published: November 2006

Nafion (DuPont) is a microstructured ion exchange polymer with high water content. Water volume fraction estimates for as-received and proton exchanged Nafion films range from 28 to 43% by volume. The ionic conductivity and anion exclusion of Nafion are often ascribed to the highly cationic, water-filled microdomains of the polymer. A question arises: if Nafion is frozen, will the microdomains be disrupted with subsequent loss of structural integrity and its associated anion exclusion, selectivity, and conductivity? Here, a preliminary assessment of the impact of freezing recast Nafion 1100 films is reported.
Platform for Rapid Prototyping of PEM Fuel Cell Designs with Enhanced Cold-Start Performance and Durability
Authors: Gupta Nikunj , York Cynthia , Needham John , Hagans Patrick
Published: November 2006

In this paper recent results will be presented on the cold- start performance and performance decay of a polymer electrolyte membrane fuel cell utilizing a novel single cell insulated platform. The cell will be shown to replicate closely the start-up performance of a stack center cell thus greatly reducing the time and expense required to examine initial cold-start performance and start-up procedures of new cell configurations.
Mathematical Analysis of Membrane Water Content Utilizing Three-Dimensional Fuel Cell Modeling
Authors: Fraser Simon D. , Monsberger Michael , Hacker Viktor
Published: November 2006

A mathematical model of a polymer electrolyte membrane fuel cell is applied with an analysis of the membrane water balance. The model is a so-called 'along the channel model' and is based on a custom developed three-dimensional computational fluid dynamics code. A special emphasis was put on developing a consistent representation of the membrane layer with the gas diffusion electrodes attached to either side. Water production in the cathode electrode active layer is considered along with membrane water transport mechanisms due to electro-osmosis and concentration gradients as well as the exchange of water with the gas streams flowing in the anode and cathode electrode gas channels. An in-depth analysis of the interdependencies between membrane water content and local cell performance is enabled by computing a simultaneous solution of the different fuel cell model domains. A parametric study is applied to investigate the variation of governing cell properties with different cell currents.
Modeling the Effect of Microporous Layer in PEM Fuel Cells
Authors: Nguyen Trung V. , Jain Rajeev
Published: November 2006

The performance of a PEM fuel cell is limited by the slow kinetics of the oxygen reduction reaction occurring at the cathode of the PEM fuel cell. The oxygen reduction reaction requires large overpotential approximately 10-20 times as compared to the hydrogen oxidation reaction at the anode. The performance is aggravated by the accumulation of the liquid water produced at the cathode by the oxygen reduction reaction. The liquid water masks the active catalyst sites and acts as a barrier to the transport of reactants in the catalyst layer and gas diffusion layer to the active sites. The instantaneous removal of water is vital to improve the performance of the PEM fuel cell. With the introduction of a hydrophobic microporous layer between the catalyst layer and the gas diffusion layer, the performance is significantly improved by effective removal of water from the catalyst layer. This paper studies the function of microporous layer in effective water management at the cathode of the PEM fuel cell using a one dimensional steady state model.
Capillary Pressure Properties of Gas Diffusion Materials Used in PEM Fuel Cells
Authors: Ohn Heebong , Nguyen Trung V. , Jacobson David , Hussey D. , Arid Muhammad
Published: November 2006

Capillary pressure curve is used to account for the mass transport limitation in the porous gas diffusion layer (GDL) in modeling two-phase phenomena in conventional distributors. Various assumptions and approximations on capillary pressure curve have been made to develop models. To date the capillary pressure curve in gas diffusion medium in PEM fuel cell does not seem to have been obtained. In this study, volume displacement technique and neutron imaging technique that can obtain capillary pressure curve in gas diffusion material is described. An experimental data of capillary pressure curve of porous material used in PEM fuel cell will help two-phase models of PEM fuel cell to be more accurate in their predictions of fuel cell behaviors.
Microfabricated Fuel Cell with Composite Glass/Nafion Proton Exchange Membrane
Authors: Kohl Paul A. , Li Jun , Moore Christopher , Bhusari Dhananjay , Prakash Shruti
Published: November 2006

The performance of microfabricated fuel cells with Nafion- coated glass composite membranes was investigated. The performance and durability of the fuel cells with silica glass membranes were improved by casting a thin-film of Nafion on the anode side of the thin, phosphosilicate glass membrane. Nafion increased the strength of the glass membrane and provided a better chemical environment for the air-cathode. The use of a two-layer anode catalyst improved the anode performance by increasing the catalyst loading while maintaining catalyst porosity for proton transport.
The Effect of N2 Dilution on CO Poisoning in a Proton Exchange Membrane Fuel Cell
Authors: Wang Wentao , Van Zee John W. , Lee W. K.
Published: November 2006

Data are reported to examine the N2 dilution effect on CO poisoning. These data indicate, as expected, that the effect of CO poisoning is more pronounced when H2 is diluted at constant CO concentration. The unusual observation is that the extent of poisoning (as measured by the anode polarization) is also more pronounced as H2 is diluted with N2 even though the ratio of CO/H2 is held constant. It is shown that the presence of N2 not only dilutes H2 but also makes the adsorbed CO more difficult to desorb from the surface of the anode catalyst.
Measurement of Fuel Cell Flowfields Using Particle Image Velocimetry
Authors: Sharp Kendra V. , Yoon Sang Youl , Ross Jacob , Mench Matthew
Published: November 2006

Because the parasitic load on most fuel cell systems is dominated by pressure losses across the flow fields, understanding the dynamics in a flow channel has garnered significant recent attention. The current work is aimed at enabling advanced design of reactant flow channels by elucidating the details of the velocity fields within various reactant flow channel geometries. Gas-phase measurement is critical to ensuring that the results are valid for real fuel cell systems, and for application of this technique to the study of flow channels with two-phase obstruction phenomena. In the current research, gas-phase velocity fields have been measured using particle image velocimetry (PIV) in representative geometries, including a straight channel (for technique validation) and a 180å switchback with channel-to-land ratio of 1:1. The accuracy of the measurement depends on the ability of the seed particles to follow the flow. Numerical simulations have been performed to develop a criterion for identifying appropriate seed particles. The research presented is a first step towards measuring velocity fields in novel flow reactant channels in operational cells.
Durable PEM Fuel Cell Electrode Materials: Requirements and Benchmarking Methodologies
Authors: Makharia Rohit , Kocha Shyam , Yu Paul , Sweikart Mary Ann , Gu Wenbin , Wagner Frederick , Gasteiger H. A.
Published: November 2006

This paper discusses methodologies to evaluate durability of catalyst and carbon-support materials used in Polymer Electrolyte Membrane (PEM) fuel cells under relevant automotive accelerated test conditions. Durability of carbon-supported Pt and Pt-alloy catalyst is evaluated under an accelerated voltage- cycling protocol, developed by analyzing idle-to-peak power load-transients of various automotive drive-cycles. Results indicate that Pt catalysts on conventional carbon supports (Pt/C) are unlikely to meet automotive durability target; however, given no loss in specific-activity over time, Pt- alloys are likely to be successful. Shutdown/startup of fuel cell stack and local fuel starvation are recognized as an accelerating mechanism for carbon-support corrosion. Conventional and corrosion-resistant supports are evaluated under an accelerated protocol (1.2V vs. RHE). Corrosion of these currently used supports induces unacceptable mass- transport related performance loss at high current densities. Implementation of corrosion-resistant supports in high- performance electrodes, combined with controlled system strategies, will most likely lead to automotive carbon support durability targets being met.
Electrochemical Oxidation Resistance of Carbonaceous Materials
Authors: Dowlapalli Madhusudhana R. , Atanassov Plamen , Xie Jian , Rice Gordon
Published: November 2006

Carbon blacks are used in low temperature fuel cells as electrocatalyst supports to ensure electronic conductivity between the electrocatalyst and the current collector. They provide path for even gas distribution, for gas access to the electrocatalyst, and for the removal of products (gases and liquids). Principal objective of this study is to investigate the corrosive behavior of carbon blacks in conditions, which are typical for electrochemical systems like fuel cells, batteries, and electrolyzers. Carbon corrosion prevention is the basis of oxidation resistance of these materials. Physical and chemical changes during oxidation of these carbon blacks are being reviewed along with methodology for studying their corrosion in low-temperature fuel cell environment. Emphasis is being laid upon the need of proper methods of evaluation of the oxidation resistance of these carbon blacks. The ultimate goal of this work is to formulate oxidation-resistant carbon blacks, and to develop suitable technologies for their synthesis or modification.
Coarsening of Pt Nanoparticles in Proton Exchange Membrane Fuel Cells upon Potential Cycling
Authors: Shao-Horn Yang , Ferreira Paulo , la O' G.J. , Morgan Dane , Gasteiger H. A. , Makharia Rohit
Published: November 2006

Two different Pt/C samples (Pt/Vulcan and Pt/C-high-surface- area) were subject to potential cycling between 0.6V and 1.0V vs. reversible hydrogen electrode, where significant platinum area loss was found. Both cycled MEA cathode samples were examined and compared in detail by glancing angle X-ray powder Diffraction and transmission electron microscopy (TEM) to reveal processes responsible for observed platinum loss. TEM data and analyses of pristine and cycled Pt/C catalyst and cross-sectional MEA cathode samples unambiguously confirmed that coarsening of platinum particles occurred via two different processes as reported recently1: i) Ostwald ripening on carbon at the nanometer- scale; and ii) diffusion of soluble platinum species in the ionomer phase at the micrometer-scale, chemical reduction of these species by cross-over H2 molecules and precipitation of platinum particles in the cathode ionomer phase.
Polymer Electrolyte Membrane Degradation Mechanisms in Fuel Cells - Findings Over the Past 30 Years and Comparison with Electrolyzers
Authors: Laconti Anthony , Liu Han , Mittelsteadt Cortney , McDonald Robert
Published: November 2006

This paper summarizes some of the progress that has been made over the past 30 years in identifying chemical and mechanical degradation mechanisms in proton-exchange membrane fuel cells (PEMFCs), as well as approaches in refining stack operating conditions, cell hardware configurations and membrane- electrode assembly (MEA) stabilization to mitigate degradation and extend life. New analytical methods have been brought to bear to understand the relationships between PEM degradation and fuel cell operating conditions, especially low relative humidity, elevated temperatures, and frequent open-circuit periods. PEM/MEA degradation similar to that observed in PEMFC may also occur under certain accelerating conditions for proton-exchange membrane water electrolyzers (PEMELCs) that typically operate for 30 to 100 thousand hours without incident when properly hydrated, thermally managed and mechanically supported. A comparison is made of common hardware and operational factors for PEMELCs and PEMFCs that can lead to PEM/MEA degradation.
Strategies for Mitigation of PFSA Polymer Degradation in PEM Fuel Cells
Authors: Escobedo Gonzalo , Raiford Kimberly , Nagarajan Gowri S. , Schwiebert Kathryn E.
Published: November 2006

This paper describes approaches to reduce susceptibility of perfluorosulfonic acid membranes such as Nafion® to degradation through chemical attack by oxygen-based radicals and physical degradation as a result of mechanical stress. These approaches include the incorporation of a continuous reinforcing layer and modification of the polymer to stabilize it against attack by peroxide radicals.
Applying the Lessons Learned from PAFC to PEM Fuel Cells
Authors: Fuller T. , Perry Mike , Reiser Carl
Published: November 2006

As PEM fuel cells advance it is useful to compare and contrast the experiences from phosphoric acid fuel cells. Early in the development of PEM Fuel cells, the poor membrane durability seen in the GEMINI program prevented PEM technology from being selected for follow-on space programs. However, the subsequent development of Nafion® greatly improved membrane durability, and the focus moved from durability to improving power density and cost. It is only recently that attention has returned to durability. Here we will discuss the major degradation challenges of PEM fuel cells, and more specifically compare the experiences of PAFC with that of PEM fuel cells. Phosphoric acid fuel cells have been available commercially for over a decade with about 250 units accumulating more than 7 million hours of operation in the field. How relevant is the field data to PEM fuel cells and what can we learn from this experience?
Carbon Corrosion Induced by Partial Hydrogen Coverage
Authors: Fuller T. , Gray Gary
Published: November 2006

A two-dimension model of carbon corrosion induced by the partial coverage of hydrogen on the anode is presented. In proton exchange fuel cells, this degradation mode is caused principally by two mechanisms: 1) blockage of hydrogen from a portion of the anode under steady-state conditions, and 2) transitioning between the off state and a normal operating state. Whereas, corrosion of anode supports because of insufficient fuel is well known, corrosion of the cathode supports under these conditions is less well understood and likely a larger contributor of degradation than commonly expected. Under certain conditions the overpotential in the cell may reach values greater than 1.5 V.
Flow Control in a Fuel Cell Flow Field for Improved Performance and Reliability
Authors: Blanco Mauricio , Wilkinson David P. , Yan Givon , Wang Haijiang , Zhao Henbing
Published: November 2006

In this paper, a new approach of changing the flow field active area with changing operating conditions is analyzed and discussed. In order to change the active area, two special cathode plates with interdigitated and serpentine flow fields were designed and tested. Each flow field is divided into six separate sections, which are connected to valves (open or closed manually). Reducing the active area in the low power region increases the effective current density (hence lower voltage) and increases the effective reactant flow and associated pressure drop. However, the absolute current and flow do not change from the normal situation for the full active area. Thus, improved fuel cell stack performance stability is achieved without increasing the parasitic load significantly. In addition, other direct benefits of this new approach for future fuel cell designs could include improved cell-to-cell reactant distribution, reduced low current density failure modes, and overall system advantages.
Accelerated Life Tests for Fuel Cells
Authors: Heneka Markus J. , Ivers-Tiffée Ellen
Published: November 2006

In reliability engineering, accelerated life testing (ALT) is a well known tool for rapid lifetime evaluation. As fuel cells are potential long-life devices, the method may be of particular importance in this field. The aim of this contribution is to give an introduction to the basic concepts of ALT and to discuss chances and challenges of the technique. In addition, first experimental results on the application of ALT to Solid Oxide Fuel Cells (SOFC) are presented.
Outstanding Student/Post-doc Presentation Award Recipient: 1-D Transient Model of Shutdown to a Frozen State in a Polymer Electrolyte Fuel Cell
Authors: Mench Matthew , He Suhao
Published: November 2006

To better understand, control, and mitigate degradation during freezing of a polymer electrolyte fuel cell (PEFC), a 1-D transient model has been formulated, based on theories of porous media flow and soil frost heave. The model is essentially a modified hybrid of Harlan's hydraulic model and Miller's rigid ice model with additional improvements for suitable application to PEFCs. Methods to derive the unfrozen water versus temperature characteristic curves for PEFC components are also given. Through the formulated model, it is predicted that ice lens will occur most likely around the catalyst layer, either between catalyst layer and diffusion media, or between catalyst layer and Nafion® membrane. Lens formation under lands is unlikely due to high overburden pressure. This can explain the punches observed in carbon paper after freeze-thaw tests. Another phenomenon, the delamination between Nafion® and catalyst layer, can be explained by the formation of ice lens from water expelled from Nafion® during freezing. The Nafion® thickness and initial water content have direct effects on the damage in this mode.
Durability Evaluation of Direct Methanol Fuel Cells
Authors: Jiang Rongzhong , Chu Deryn
Published: November 2006

Two types of direct methanol fuel cells (DMFC) were evaluated under constant voltage discharge for long term operation. One type is a DMFC single cell, tested for 2600 hours at 0.45V and 70 oC; and the other is an air-breathing DMFC bi-cell, tested for 5000 hours at 0.6V and room temperature (20 oC). A concept of cumulative capacity and cumulative energy is proposed to quantitatively analyze the long term discharge data. The single cell, which has run for a shorter time, shows higher cumulative energy (78 Wh•cm-2•cell-1) than that of the bi-cell (47 Wh•cm- 2•cell-1). A phenomenon of delamination between the interface of electrode and electrolyte membrane was observed after long term operation. Hot-pressing the electrode was tried to fix the problem of delamination. The single cell after hot-pressing was tested again for 2800 hours under the same operating conditions. By summing the two discharges, a total cumulative energy of 154 Wh•cm-2•cell-1 is achieved.