bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal Matrix Nanocomposites as Thin Films and Microstructures from Basic Electrolytes
Authors: Podlaha Elizabeth J. , Fitzgerald Jill , Lozano-Morales Alonso
Published: November 2006

The electrodeposition of Cu-gamma-Al2O3 nanocomposites as thin films and into recessed electrodes prepared with x-ray lithography was examined in ammonia-citrate electrolytes. Partial current density, current efficiency and deposit particle concentration were determined with a rotating disk electrode. At pH 8 the presence of particles resulted in an enhancement of the Cu reaction rate, while at pH 10 the reaction rate appeared inhibited. The amount of particles in the deposit and current efficiency was larger for pH 8 than pH 10, rendering the pH 8 solution a more promising electrolyte to electrodeposit 500 micron deep recesses for MEMS composite components.
Quasi-Solid Dye Sensitized Solar Cells with Ionic Liquid-Type Gel Electrolytes
Authors: Hayase Shuzi , Kato Takehito , Okazaki Akio , Ogomi Yuhei , Kado Takashi T. , Tanaka Shuhei , Beppu Takayuki
Published: November 2006

Solidification of dye sensitized solar cells (DSC) is carried out in two methods. One is a method to use soft gels containing less than 10 % of chemically crosslinkable gelators. The soft gel is characterized with the latent property. The other is a method to use hard gels containing 100 % of surface modified TiO2 nano-particles as gelators. In both cases, electrolytes are solidified without decreasing photovoltaic performances even after solidification by fabricating ion-paths in the solidified electrolytes associated with self-organization of long alkyl groups.
Colloidal Quantum Dot-Based Infrared Photodiodes
Authors: Xu Jian , Cui Dehu , Paradee Gary , Xu Shengyong , Gerhold Michael
Published: November 2006

We report in this paper our studies on the photoconductivity and photovoltaic effects of colloidal PbSe nanocrystal quantum dots (NQDs) which were embedded in conductive polymer matrices to form hybrid polymer/NQD infrared photodiodes. The generation of photocarriers in PbSe NQDs and their transport in NQD-polymer composites were described by a simplified band diagram picture of the device. Both photocurrent and photovoltage outputs were measured from the NQD-incorporated photodiode upon the illumination of near-infrared (NIR) light, whereas the net polymer-based devices do not exhibit any photoresponsivity. The intensity dependence of the photocurrent indicates the pseudomonomolecular recombination kinetics in the NQD-polymer composite. The measured photocurrent spectrum is consistent with the absorption characteristic of PbSe NQDs. Further enhancement of the photodiode efficiency can be achieved by engineering the nanocrystal surface to reduce the potential barriers due to the ligant capping molecules.
Luminescent Properties of ZnS:Eu2+ Nanocrystals
Authors: Sharma Gaytri , Han Sang-Do , Khatkar S.P , Taxak V.B , Rhee Young Woo
Published: November 2006

Europium-activated ZnS nanocrystals were synthesized by a low temperature tartaric acid assisted sol-gel method. The emission peak of Eu2+ due to the 4f65d1 →4f 7 transitions at 480nm was observed in the emission spectra on excitation at 260nm. Scanning electron microscopy (SEM) investigations were carried out to understand surface morphological features and the particle size of the nanocrystals. The uniformity of phase of Eu2+ doped ZnS nanocrystals was checked by X-ray diffraction (XRD) technique. In addition, the dependence of the luminescence intensity on Eu2+ concentrations of the nanocrystals has also been discussed. The particle size of the nanocrystals was found to be 28nm.
Voltammetry of Benzenepolycarboxylic Acids at the Solid Electrodes
Authors: Kvaratskhelia Elene -. , Kvaratskhelia R.
Published: November 2006

The study of voltammetry of the four benzenepolycarboxylic acids: trimellitic, trimesic, pyromellitic and mellitic acids at the Pt, Cu, Ta, Cu-Hg electrodes in aqueous and mixed area (the water-ethanol and water-pyridine mixtures) shows that these acids in all cases form the hydrogen ions discharge process waves. With the aid of the suggested by authors method the values of the degrees of dissociation of investigated acids were calculated. With the aid of obtained voltammetric data the values of dissociation constants of acids were estimated.
Highly Active Ruthenium Based Catalysts for Oxygen Reduction Reaction
Authors: Popov Branko N. , Liu Lingyun
Published: November 2006

Novel Ru-based chelate catalysts were prepared by heat-treating carbon supported metal chelate compounds at 800 {degree sign}C. The catalytic active sites of ruthenium chelate catalysts were optimized by optimizing the chemical composition and the synthesis conditions. RRDE studies indicated that oxygen reduction activation overvoltage and Tafel slope of optimized ruthenium chelate catalysts prepared with the Ru/N ratio of 1:20 and heat treatment temperature of 800 {degree sign}C are the same as commercial Pt/C catalyst with the Pt loading of 20µg/cm2.
Tantalum Nitride and Oxynitride for New Cathode of Polymer Electrolyte Fuel Cell
Authors: Ishihara Akimitsu , Doi Shotaro , Liu Q. Y. , Mitsushima Shigenori , Kamiya Nobuyuki , Ota Ken-Ichiro
Published: November 2006

Tantalum (oxy)nitrides (TaOxNy) have been investigated as a new cathode of polymer electrolyte fuel cells without platinum. TaOxNy films were prepared by radio frequency magnetron sputtering under Ar + O2 + N2 atmosphere with heating the substrate, and the effect of heat treatment on the catalytic activity for oxygen reduction reaction (ORR) and the properties of TaOxNy films were examined. The solubility of Ta in 0.1 mol dm-3 sulfuric acid at 30oC under atmospheric condition was about 2×10-7 mol dm-3, indicating that TaOxNy had high chemical stability. The ORR current density on TaOxNy deposited at 800oC was about 20 times larger than that on TaOxNy deposited at 50oC. Both the degree of crystallinity and the relative nitrogen content increased with increasing the heat treatment temperature.
New Strategies to Activation and Assembling of Catalytic Metal Nanoparticles through Modification with Polyoxometallate Monolayers
Authors: Kulesza Paweł J. , Marassi Roberto , Karnicka Katarzyna , Wlodarczyk Renata , Miecznikowski Krzysztof , Chojak Małgorzata , Kolary Aneta
Published: November 2006

The modification of Pt nanoparticles of ca. 8 nm diameter by adsorbing monolayers of phosphododecatungstic acid (H3PW12O40) on their surfaces tends to activate them towards efficient electrocatalytic reduction of oxygen in acid medium. The modification steps were be performed either before or after introduction of catalytic nanoparticles onto the glassy carbon substrates. Formation of a stable colloidal suspension of phosphotungstate protected Pt-nanoparticles as a source of activated catalytic centers was required in the first case; whereas, in the second case, bare Pt nanoparticles had been deposited on glassy carbon before they were subsequently modified with ultra-thin films of H3PW12O40. Rotating disk voltammetry was used to probe the electroreduction of dioxygen in 0.5 mol dm-3 H2SO4. In addition to the usual reactivity towards the oxygen reduction, H3PW12O40 could act as both effective mediator (e.g. for the reduction of the hydrogen peroxide intermediate) and the source of mobile protons at the interface.
PEM Fuel Cells: Materials Issues
Authors: McBreen James , Balasubramanian Mahalingam , Yoon Won-Sub , Chung Kyung Yoon , Lee Hung Sui , Yang Xiao-Qing , Atanasoski Radoslav , Schmoeckel Alison , Vermstrom G. D. , Debe Mark K.
Published: November 2006

This paper discusses the materials issues that have to be resolved before polymer electrolyte membrane fuel cells (PEMFC) become commercial in automobiles. The main materials issues are (1) a membrane that can operate at higher temperatures and lower relative humidity, (2) improved onboard hydrogen storage, (3) a hydrogen fuel infrastructure and (4) lower cost electrocatalysts. The paper discusses in detail x-ray absorption spectroscopy (XAS) and related electrochemical studies of novel binary and ternary alloy electrocatalysts from 3M Company.
Pore Size Effect on Improvement of Surface Proton Conductivity for Three-Dimensionally Ordered Macroporous Silica Membrane
Authors: Kanamura Kiyoshi , Munakata Hirokazu , Ochiai Sho
Published: November 2006

A proton conducting porous silica matrix for composite membranes was prepared by introducing of sulfonic acid groups onto the silica surface. The proton conductivity of the silica membrane itself was increased in more than two orders of magnitude after the surface sulfonation. In the cases of the composite membranes between proton conductive polymer and silica matrix, the conductivity was also enhanced. Especially, considerably high enhancement on proton conductivity was observed in the composite membrane. Such an improvement on the proton conductivity was more enhanced by using the sulfonated silica matrix with smaller pore size.
New Composite, Gel-Type Proton Membranes
Authors: Scrosati Bruno , Navarra Maria Assunta , Fernicola Alessandra , Panero Stefania
Published: November 2006

This paper reviews the properties of a new microporous, composite proton conducting gel membrane, formed by swelling with aqueous acid solutions suitable polymer matrices matrices containing a dispersed ceramic fillers. The data reported show that these membranes have a high and stable conductivity, a proton transport not critically influenced by the relative humidity level and a projected very low cost. Tests in a hydrogen-air laboratory cell also demonstrate that the membranes are basically suitable for application in polymer electrolyte fuel cells.
Investigation of the Lateral Water Distribution in a Proton Exchange Membrane in Fuel Cell Operation by 3D-MRI
Authors: Tsushima Shohji , Nanjo Takanori , Nishida Kousuke , Hirai Shuichiro
Published: November 2006

Lateral distribution of water content in a proton exchange membrane in an operating fuel cell was measured by using three- dimensional magnetic resonance imaging (3D-MRI), which clearly visualized not also lateral water distribution in the membrane but also condensed water in flow channels in the cell. Both a parallel flow and a serpentine flow were investigated in a variety of current density. In the parallel flow, the membrane near the gas inlet shows lower water content compared to those near the gas outlet. It was also shown that with increase of current density, overall water content in the membrane decreased, presumably due to dehydration of the membrane triggered by electro-osmotic effect. In the serpentine flow, dehydration area across the membrane from the flow inlet to the outlet was found. These MRI observations indicate that condensed water droplets strongly affect overall flow behaviors in the operating fuel cell.
Surface Electrochemistry of Composite Materials for High-Temperature PEM Fuel Cells
Authors: Lvov Serguei , Chalkova Elena , Fedkin Mark , Komarneni Sridhar , Wesolowski David
Published: November 2006

Since the surface properties of solid oxides, such as zeta potential, surface charge density, and stoichiometry of surface complexes reflect the interfacial behavior of solid oxide particles, detailed surface studies can help to predict the performance of a particular oxide material in the composite membranes for high-temperature proton exchange membrane (PEM) fuel cells. Some electrochemical parameters of the electrical double layer (EDL) on the solid oxide surface were discussed in relation to ionic conductivity and water retention of solid oxide/Nafion composite membranes. The zeta potential values measured at the TiO2/water interface at elevated temperatures helped to explain some advantages of these composite membranes in PEM fuel cell operation at low relative humidity.
Direct Methanol Fuel Cells: What's New Since Ten Years?
Authors: Leger Jean-Michel , Coutanceau Christophe , Lamy C.
Published: November 2006

Direct Methanol Fuel Cell (DMFC) is often considered as a promising electrochemical generator for various applications, including microsources. Unfortunately, serious limitations still remain and need to be solved before developments of such devices. Challenges concern the various components of DMFC: both anodic and cathodic reactions need more suitable electrodes in addition to the difficulty to conceive suitable electrolytic membranes. These different points are discussed in this paper focusing on the results published during the last ten years.
Spectroscopic Studies of Heteropoly Acid-doped 3M Perfluorinated Sulfonic Acid Polymer Membranes
Authors: Herring Andrew M. , Meng Fanqin , Frey Matthew , Hamrock Steve , Turner John , Dec Steve , Williamson Don
Published: November 2006

3M PFSA ionomer membranes were doped with heteropoly acids (HPA) and the ionomer/HPA interaction characterized by attenuated total reflection FTIR, pulse field gradient spin echo NMR and small-angle X-ray scattering. The HPA doping was achieved by casting a mixed solution containing both components. Three Keggin-type HPAs were used in this work: 12- phosphotungstic acid, 12-silicotungstic acid, and 12- zincotungstic acid, at doping concentrations of 1 and 5wt %, respectively. FTIR spectra of the composite membranes clearly show the presence of the HPA and evidence for different interactions under different hydration states. Proton diffusion coefficients were determined by PFGSE NMR under dry and 100 % RH from room temperature to 130 {degree sign}C. SAXS patterns of the control PFSA and the HPA-doped PFSA membranes were recorded under dry and wet conditions. Scattering behavior for different samples and conditions are remarkably different, consistent with the incorporation of HPA and the swelling of the ionomer clusters under hydration.
On the Passivation of 349TM Stainless Steel in Simulated PEMFC Cathode Environment
Authors: Wang Heli , Turner John A.
Published: November 2006

Austenite stainless steel 349TM has been tested in a simulated polymer electrolyte membrane fuel cell (PEMFC) cathode environment, and a stable passive film was formed within 15 minutes of polarization. X-ray photoelectron spectroscopy (XPS) has been utilized to investigate these surface films on the steel. The surface oxide film formed in air (air-formed film) composed of iron oxides and chromium oxide, with a Fe-rich outer layer and a Cr-rich inner layer. Neither of them was a dominating species in the air-formed film. On the other hand, the passive film formed in the simulated PEMFC cathode environment was dominated by Cr-oxide. The thickness of the films was estimated to be 2.4 nm for air-formed film, and 3.0 nm for the passive film. The difference in morphology between fresh and passived steels was identified by means of atomic force microscopy (AFM).
Mixed-Feed Direct Methanol Fuel Cell: Materials and Design Solutions
Authors: Barton Scott C. , Deng Weihua , Gallaway Joshua W. , Levendovsky S. , Olson T. S. , Atanassov Plamen , Sorkin M. , Kaufman A. , Gibbard H. Frank
Published: November 2006

Technological challenges related to the development of mixed reactant direct methanol fuel cells (DMFCs) are addressed. Promising cathode catalysts were tested and their performance was compared to the traditional Pt catalyst. A novel hydrophilic barrier layer was applied to the PtRu anode in order to improve its performance by limiting oxygen diffusion to the anode catalyst layer. This strategy is shown to be effective despite increased ohmic resistance associated with the barrier layer.
Findings of the Fuel Cell Workshop
Authors: Fuller T. , Meyers J.
Published: November 2006

The National Science Foundation and the Electrochemical Society sponsored a workshop on low-temperature fuel cells. The objectives were to bring together an interdisciplinary group of scientists and engineers to define basic science needs addressing challenges for low-temperature fuel cells. The specific objectives were to 1) identify gaps in low-temperature fuel-cell technologies, 2) describe technical approaches to meet these critical research needs, and 3) establish an agenda for basic research in low-temperature fuel cells necessary to advance knowledge across several disciplines. The intent is that these findings will be widely disseminated and have broad impact on the development of a hydrogen economy, technologies to meet future energy needs, and educational initiatives.
Verification of Generated Water in a Super-cooled State Below Freezing Point in PEFC
Authors: Ishikawa Yuji , Morita Tohru , Nakata Keiichi , Yoshida Kazuhiko , Shiozawa Masahiro
Published: November 2006

When a fuel cell is operated below freezing point, generated water is frozen inside the fuel cell leading to a drop in performance. This is one of the most important problems that must be solved with regards to PEFC. Until now, however, few papers were published that discuss where the generated water freezes in the fuel cell. This research, therefore, was carried out for the purpose of clarifying the phenomenon of water freezing below freezing point. In order to achieve this, we observed the water generated on the surface of the catalyst layer simultaneously with visible and infrared images. The results revealed surprisingly that water generated below freezing point was in a liquid state at the time of generation and maintained a super-cooled state. It is generally known that a large rise in temperature is experienced when water in a super-cooled state starts to freeze.
Transient Model for MEA Hydration During Fuel Cell Operation
Authors: Bradean Radu , Boulianne Robert , Grewal Karamjit , Ayotte Dana , Haas Herwig
Published: November 2006

Several fuel cell products have transient requirements in which the operating conditions strongly vary in time. These transients can significantly affect fuel cell performance, freeze start, durability and reliability. It has been previously shown at Ballard Power Systems that maintaining an optimum MEA water content during transients, the fuel cell operating capability is significantly increased. To design better operating strategies for transient fuel cell operation, a model is developed to predict the MEA water content as a function of time. The model results are compared to the measurements of MEA water content at different times during several types of transient fuel cell operation.
Water Management and Mass Transport Studies in Free Convection Proton-Exchange Membrane Fuel Cells
Authors: Modroukas Dean , Modi Vijay , Frechette Luc , Barton Scott C.
Published: November 2006

This investigation addresses water management and mass transport phenomena for low temperature (<40{degree sign}C), free convection PEM fuel cells that have been studied using novel microfabricated structures. Tailored mass transfer media (TMTM) were fabricated using microelectromechanical systems (MEMS) techniques applied to low resistivity silicon. These structures were tailored with discrete wetting/non-wetting features to effectively manage liquid water distribution within the cell and simultaneously provide unobstructed gas transport to/from the catalyst layer. The TMTM were based on a micromachined hydrophobic silicon mesh comprised of 140μm square pores with discrete sets of zones engineered to be hydrophilic using a carbon-polyethylene oxide treatment. These structures were tested with and without treatments in a single-cell test fixture for temperature from 25{degree sign} to 40{degree sign}C operating on ambient air. For all test conditions, the treated versus untreated structure performance showed limiting current increases that ranged from 32% to 88%.
Water Removal from Proton Exchange Membrane Fuel Cells via Electroosmotic Pumping
Authors: Buie Cullen R. , Posner Jonathan , Fabian Tibor , Cha Suk-Won , Kim Daejoong , Prinz Fritz , Eaton John , Santiago Juan
Published: November 2006

We have developed proton exchange membrane fuel cells (PEMFCs) with integrated planar electroosmotic (EO) pumping structures that actively remove liquid water from cathode flow channels. EO pumps have no moving parts, scale appropriately with fuel cells, can operate across a wide range of conditions, and consume a small fraction of fuel cell power. We demonstrate and quantify the efficacy of EO water pumping using controlled experiments in a single channel cathode flow structure. Our results show that, under certain operating conditions, removing water from the cathode using integrated EO pumping structures improves fuel cell performance and stability.
Optimized Catalyst Layer Structure for PEM Fuel Cells
Authors: Nguyen Trung V. , Natarajan Dilip , Jain Rajeev
Published: November 2006

The optimal operating conditions for PEM fuel cells for high durability and performance are near water saturated conditions. Under these conditions liquid water exists in the catalyst layers of the anode and cathode. When the accumulation of water is excessive it can lead to electrode flooding, which reduces the performance of the fuel cells, by flooding the gas pores needed for active gas transport and forming an additional liquid water film barrier over the active sites. Consequently, to reduce the effect of electrode flooding of the catalyst layers the structure of the catalyst layer must be modified to enable fast gas and liquid water transport. Furthermore, this must be achieved without resulting in any significant loss in the ionic and electronic conductivity of the catalyst layer. This work presents two approaches developed to achieve this goal. The first approach explores the concept of creating a four phase (electronic, ionic, gas and liquid) simultaneously. The second approach explores the concept of first creating a three-phase (electronic, ionic and gas) structure and then modifying the gas structure to provide simultaneous but separate gas and liquid transport paths. The results show the second approach to be more optimal.
Synthesis of Highly Porous Catalytic Layers for Polymer Electrolyte Fuel Cell Based on Carbon Aerogels
Authors: Marie Julien F. , Berthon-Fabry Sandrine , Achard Patrick , Chatenet Marian , Chainet Eric , Pirard René , Cornet Nathalie
Published: November 2006

Recent studies of the PEMFC catalytic layer electrocatalyst support showed that high surface area carbon blacks cannot be used efficiently (1) because they have necessarily small primary pores that yield high diffusion limitation for the oxygen reduction reaction (ORR). In the present paper, we first synthesized and characterized carbon aerogels which exhibit high surface area, high porous volume and adjustable pore-size distribution. In that way, they enable to decouple between surface area and porosity, while they are also promising electrocatalyst supports (2). Second, we elaborated new catalytic layers made from 2 different carbon aerogels with 2 different Nafion loadings. Finally, we characterized the structure of such catalytic layers, and evaluated their activity towards the oxygen reduction reaction (ORR). Finally, an appropriate catalyst support should display large pore-size and high surface area in order to reduce the PEMFC cathode platinum loadings without loosing activity, following the reduction of oxygen diffusion limitation.
A Novel Photographic Printing Process for the Preparation of Pt Nano-Particles for Fuel Cell Applications
Authors: Jiang Juan , Hall Timothy , Tsagalas Loukas , Hill Davide , Miller Albert
Published: November 2006

A novel photographic printing process has been applied to the preparation of catalysts for application to fuel cells. This method is suitable for high volume manufacturing and is also compatible with integrated circuit fabrication for potential use in micro fuel cells. Pt nano-particles have been deposited by photo-printing onto Toray carbon paper and Nafion membranes. TEM images of the deposits revealed that Pt particles of less than 5 nm were deposited and they formed spherical clusters of up to 300 nm. These spherical clusters were more uniformly distributed on the surface of the Nafion membrane rather than on the carbon paper, as shown in SEM images. Electrochemical characterization by Cyclic Voltammetry (CV) showed that the mass specific methanol oxidation current density could be as high as 197 mA/mg.
Comparison of Maxwell-Stefan and CFD Approximation Equations for PEMFC Applications
Authors: Martinez Michael J. , Shimpalee Sirivatch , Van Zee John W.
Published: November 2006

This work examines the accuracy of using the approximated multi-component (AMC) with a correction term as used in common Computational Fluid Dynamics (CFD) techniques. This comparison is important because the structure of CFD programs does not permit the direct use of the more commonly used Maxwell-Stefan form of multicomponent equations. A comparison of species concentration in a polymer electrolyte fuel cell (PEMFC) computed by using the Maxwell-Stefan and the corrected AMC models is presented. It is shown that the corrected form of the AMC model can produce accurate results as compared to the Maxwell-Stefan model.
Design and Development of a Novel Flow Field for PEM Fuel Cells to Obtain Uniform Flow Distribution
Authors: Debe Mark K. , Herdtle Thomas
Published: November 2006

A new flow field design concept was discovered, based on the close coupling of the flow field geometry and gas transport through the MEA diffusion current collector component's in- plane permeability. The new flow field offers significant gain in uniformity of reactant distributions within PEM fuel cells. Computational fluid dynamic simulations of the two dimensional gas flow velocities over the MEA active areas are used to demonstrate the improvement in mass flow uniformity with the new design compared to more conventional flow field types. A math analysis based on Darcy's law applied to the new flow field design concept provided the basis for a quantitative estimate of how the effect depended on geometry, and further improvements to be made which compensate for down-the-channel consumption of reactants for any given stoichiometry. Experimental tests with version 1.0 of the new flow field design are discussed.
Durability and Degradation in High-Temperature Polymer Electrolyte Fuel Cells
Authors: Schmidt Thomas J.
Published: November 2006

This work summarizes the major degradation modes observed in polymer electrolyte fuel cells with a strong emphasis on the modes observed in high temperature PEFCs based on PBI H3PO4 membranes. Some aspects are discussed in more detail, e.g., carbon corrosion, phosphoric acid evaporation rates, and the impact of high cathode potentials. Finally, a still ongoing durability test of a Celtec® P Series 1000 MEA is discussed in the light of cathode degradation. The MEA itself currently is running for more than 18,000 hours at constant current density. The overall degradation rate is only 6µV/h at the operation point of 0.2 A/cm². At this current density, the main part (55%) of the degradation is due to increased mass transport overpotentials and by reduced oxygen reduction kinetics (30%). The remaining 15% can be ascribed to a slight increase in ohmic cell resistance. The underlying processes leading to the different types of degradation are discussed.
Characterization of Support Corrosion in PEM Fuel Cell: Improved Durability of Carbon Nanotube Based Electrode
Authors: Yan Yushan , Wang Xin , Li Wenzhen , Chen Zhongwei , Waje Mahesh M.
Published: November 2006

Electrochemical surface oxidation of Vulcan XC-72 and multiwalled carbon nanotube (MWNT) was compared following potentiostatic treatments up to 168 hrs under condition simulating PEMFC cathode environment. The subsequent electrochemical characterization at different time intervals suggests that MWNT is electrochemically more stable than Vulcan XC-72 with less surface oxide formation and 30% lower corrosion current under the investigated condition. As a result of high corrosion resistance, MWNT shows smaller loss of Pt surface area and higher catalytic activity when used as fuel cell catalyst support.
Durability Aspects of Nanostructured Thin Film Catalysts for PEM Fuel Cells
Authors: Debe Mark K. , Schmoeckel Alison , Hendricks Susan , Vernstrom George , Haugen Greg , Atanasoski Radoslav
Published: November 2006

Various durability properties of a nanostructured thin film based catalyst system (3M's NSTF) which does not contain carbon or additional ionomer, are compared with conventional carbon supported dispersed Pt catalysts. The NSTF catalysts are shown to have mass losses by TGA at 170oC that are two orders of magnitude less. The NSTF whisker support material in combination with the large-grained polycrystalline thin film catalysts that encapsulate the whiskers give significantly greater durability under normal fuel cell operating conditions and also under accelerated high voltage conditions, whether scanning between 0.6 and 1.2 volts at 20mV/sec under H2/N2, or under steady state conditions of 1.5 volts. At 1.5 volts, NSTF catalysts lose no surface area, specific activity or fuel cell performance over periods as long as 3 hours, whereas the Pt/C based electrodes lose both large amounts of surface area, activity and performance in just 30 minutes at 1.5 volts.
Consumption of Pt Catalyst under Electrolysis and Fuel Cell Operation
Authors: Kawahara Shuya , Mitsushima Shigenori , Ota Ken-Ichiro , Kamiya Nobuyuki
Published: November 2006

The relationship between the charge transfer of Pt dissolution reaction and the consumption has been investigated to clarify the dissolution mechanisms. It was determined using both the symmetric and asymmetric waves of potential. The charge of Pt oxidation was always larger than that of reduction. The difference of the oxidation and the reduction charges should be caused by the dissolution of Pt. From the relationship between the difference of the charges and the amount of the consumption, the electron number of Pt dissolution reaction was ca. 4. Therefore, the dissolution mechanism under the symmetric wave and asymmetric waves of the slow anodic / the fast cathodic sweep would be Pt → Pt4+ + 4e-. Pt consumption under asymmetric waves of the fast anodic / the slow cathodic sweep was enhanced, and this reaction would be PtO2 + 4H+ + 2e- → Pt2+ + 2H2O. The dissolved Pt2+ was detected with the RRDE measurement.
Impact of Sulfur Dioxide on the Performance of PEMFC Cathodes
Authors: Pietron Jeremy J. , Swider-Lyons Karen
Published: November 2006

Rotating disk electrode (RDE) methods are used to quantify the poisoning of the oxygen reduction reaction (ORR) at Pt catalysts for PEMFCs by SO2. With the addition of 50 ppm of SO2, the Pt loses 17% of its mass activity, however its Tafel slope remains unchanged. With 200 ppm SO2, the catalyst activity drops by 52% and its Tafel slope changes from 129 to 186 mV dec-1 at potentials <0.83 V. Levich-Koutecky analysis shows significant deviation from mass-transport controlled kinetics at high concentrations (200 ppm) of SO2, even at high overpotentials, demonstrating poisoning of the Platinum/Vulcan Carbon (Pt/VC) catalysts. The analyses show that SO2 poisoning of Pt at higher potentials (> 0.85 V) is mainly due to blocking of Pt sites by adsorbed SO2, and is more severe at lower potentials (< 0.83 V) due to stronger adsorption that alters the electronic state of the Pt.
Hydrogen Sulfide Kinetics on PEM Fuel Cell Electrodes
Authors: Weidner J. W. , Sethuraman Vijay A. , Balasubramanian Sivagaminathan , Wise Leslie
Published: November 2006

A concise mechanism for the poisoning kinetics of hydrogen sulfide (H2S) on composite solid polymer electrolyte Pt (SPE- Pt) electrode is presented. The simplified version of the mechanism is validated experimentally by charge balances and theoretically by a model, which predicts the oxidation current as a function of the applied potential. H2S dissociatively adsorbs onto SPE-Pt electrode as linear and bridge bonded sulfur (S) species and, under favorable potentials, undergoes electro-oxidation to sulfur and then to sulfur dioxide (SO2). A fraction of the adsorbed S species remains as 'hard-to-oxidize' adsorbents and causes irreversible loss of catalytic activity. Deactivation of bridge sites due to sulfur poisoning occurs first followed by the loss of linear sites.
Stability and Dissolution of the Platinum Single Crystal Surfaces in Perchloric Acid
Authors: Komanicky Vladimir , Chang Kee-Chul , Menzel Andreas , You Hoydoo , Wang Xiaoping , Myers Deborah , Markovic Nenad
Published: November 2006

Stability and dissolution of platinum single crystal surfaces were investigated with atomic force microscopy and inductively coupled plasma mass spectroscopy. Both macroscopically flat low- index surfaces of (111), (100), and (110), and (111)-(100) nanofaceted surfaces [Komanicky et al., J. Phys. Chem. B, 2005, 109, 23543.] were investigated. A clear difference was observed between the large low-index surfaces and the nanofaceted surfaces. In the low-index surfaces, the platinum oxide formation passivates the surfaces, resulting in a lower overall dissolution rates at higher potentials. On the other hand, the nanofaceted surface dissolve faster at a higher potential indicating the edges and corners are the main sources of dissolution. The differences in the dissolution behaviors between (111), (100), and (110) surfaces will also be discussed.
Effect of Relative Humidity on Membrane Durability in PEM Fuel Cells
Authors: Liu Wen , Cleghorn S.
Published: November 2006

A series of steady state life tests were conducted in order to better understand the influence of relative humidity on membrane durability in PEM fuel cells. It was discovered that under-saturated outlet conditions resulted in much longer membrane life and lower fluoride release rate from the membrane, as compared with over-saturated outlet conditions. Under such favorable conditions, ePTFE reinforced GORE-SELECT® membranes using perfluorinated sulfonic acid (PFSA) ionomer have demonstrated over 5,000 hours life at 95 ºC cell temperature, and over 2,500 hours life at 110 ºC. The impact of concentration of metal ions was studied by life testing MEAs containing membranes with different levels of Fe2+. It was hypothesized that under-saturated outlet conditions may prevent contaminants such as metal ions from entering the membrane, therefore, resulting in less chemical attack of the ionomer, and leading to longer membrane life.
Factors Impacting Chemical Degradation Of Perfluorinated Sulfonic Acid Ionomers
Authors: Liu Han , Gasteiger H. A. , Laconti Anthony , Zhang Jingxin
Published: November 2006

Several factors impacting chemical degradation of perfluorinated sulfonic acid ionomers are identified in this paper. Based on the results from this study, gas crossover is the fundamental mechanism that leads to PFSA membrane chemical degradation. H2, O2 and a catalytic surface are required to generate H2O2/radicals. The effect of electrochemically generated Pt oxide/hydroxide, Vulcan® XC-72R, Pt/C is clarified. Two major degradation pathways, H2O2 Pathway and Direct Radical Generation Pathway, are proposed. The impact of iron contamination and H2O2 concentration is also discussed. It was shown that a H2O2 flow cell is a better approach for membrane/MEA evaluation than conventional beaker based Fenton's tests (i.e., batch-like tests).
H2O2 Formation Mechanism in PEMFC
Authors: Mittal Vishal , Kunz Russell , Fenton James
Published: November 2006

The membrane degradation in a polymer electrolyte membrane fuel cell (PEMFC) has been believed to occur due to formation of H2O2 and its decomposition to radicals (·OH, ·HO2) in the presence of bivalent metal cations, which can be present as impurities in the membrane. This mechanism is mainly based on the study of H2O2 formation in the oxygen reduction reaction using rotating ring disc electrodes and ex-situ membrane degradation tests in Fenton's reagent. Whether the mechanism is consistent with the one in an operating fuel cell was investigated. Results indicate that H2O2 may be formed in the fuel cell in small amounts, but it is not the main source of harmful radicals and the membrane degradation. H2 and O2 seem to react directly on the catalyst in the electrode to form radical species, which degrade the membrane without formation of H2O2.
Methodology to Understand the Degradation Mechanism of Nafion Membrane in PEM Fuel Cells
Authors: Kim Jungik , Waller Laura , Barbastathis George , Shao-Horn Yang
Published: November 2006

Understanding the water uptake phenomena of Nafion® membrane is very important in terms of the performance and durability of PEM fuel cells. In this paper, AFM, fluorescence, and laser interferometry were used to characterize the water uptake phenomena of Nafion®. The results of AFM revealed that the phase contrast between hydrophilic and hydrophobic domains of Nafion® increased with the water content of Nafion® surface. Overall water uptake capability of used and fresh Nafion® samples was compared using fluorescence technique. Finally, a laser interferometry technique was introduced as an in-situ monitoring tool to measure temperature and water content of the membrane during fuel cell operation.
New Approach for Detection of Different Critical Stack Operating Conditions for Large Volume Fuel Cell Applications
Authors: Ramschak Erich , Peinecke Volker , Prenninger Peter , Baumgartner Wolfgang , Schaffer Thomas , Hacker Viktor
Published: November 2006

In comparison to state of the art fuel cell stack monitoring techniques, where for reliability and durability reasons either single cell or cell-block voltages are monitored separately, the new approach derives information about critical cell & stack status from the stack sum voltage only. Since the wiring and instrumentation effort as well as the cost are therefore strongly reduced, this new technology has its advantages at high volume applications like FC vehicle fleets or it can be used as a quality management (QM) instrument during the assembly process of stacks. In this new approach, the fuel cell response (stack voltage) is analysed in comparison to a particular low frequency signal, which is superimposed on the stack current. Critical cell operation occurs, if e.g. a too low air stoichiometry causes a rather sharp voltage drop at a particular cell current. If in such case the current is superimposed by a signal with a specific frequency pattern, then the system response (stack voltage) will be harmonically distorted. Particularly, this means that even if just one single cell is in a critical status, it will cause frequency distortion and occurrence of harmonics in the stack sum voltage. The fractions of harmonics are analyzed in the frequency domain and are compared to the originally superposed frequency pattern, which provides the information that one or some cells are operating in a critical mode.
Freeze/Thaw Effects in PEM Fuel Cells
Authors: Mukundan R. , Kim Yu Seung , Garzon F. H. , Pivovar Bryan
Published: November 2006

When polymer electrolyte membrane (PEM) fuel cells are exposed to sub-freezing temperatures, the water present in the various components can freeze resulting in ice formation. In this study we examine the effect of freeze/thaw cycling on fully humidified fuel cells frozen to various sub-freezing temperatures. The cells showed negligible performance degradation when cycled up to 40 times to as low as -40C. However, the cells started to fail with an associated increase in the high frequency cell resistance within 10 freeze/thaw cycles down to -80C. In this paper we also report the conductivity and state of water of the Nafion® membrane at sub-freezing temperatures. A change in activation energy associated with the freezing of water in the ionomer was observed at high relative humidities. This change in activation energy and associated phase transition was avoided at low relative humidities or when the water is replaced with a non-freezing solvent.
Substrate Preparation for Nanowire Fabrication by Selective Metalization of Patterned Silane Monolayers
Authors: Nelson Kyle A. , Cosby Sam , Blood Jon , Lee Michael , Wheeler Dean R. , Davis Robert , Woolley Adam , Linford Matthew , Harb John
Published: November 2006

In this Proceedings we show surface passivation for chemically templated growth on patterned surfaces. Our ultimate goal is to chemically pattern insulating substrates at nanometer dimensions and to grow metal lines by electroless deposition in the patterned regions. We investigate a series of monofunctional silanes of the general formula ClSi(CH3)2(CH2)n- 1CH3 as possible passivating agents for preventing adsorption of an aminosilane, Pd nanoparticles, and Cu metal by electroless deposition. The thin film made from the n = 12 silane shows excellent resistance to an aminosilane. Good resistance is also demonstrated by silane films with larger n to Pd nanoparticle deposition. Finally, it is shown that overall resistance to Cu deposition improves as n increases. Sufficient selectivity is present in these films to allow features of nanometer dimensions to be created on chemically templated surfaces. Capping the surface with ClSi(CH3)3 further improves surface passivation.
Electrodepositon in Nano Structured Templates Using Novel Cathode Preparation
Authors: Lee Jaeheon , Bartley Kenneth L. , Palusinski Olgierd
Published: November 2006

Porous membranes are being developed as template platforms for potential nano device applications. Specifically, polycarbonate (PC), aluminum oxide (alumina) and polyethylene terephthalate (PET) membranes are being studied. Often physical vapor deposition (PVD) is used on one side of the membrane to act as a cathode for electrodeposition of a metal or conducting polymer. However, this is time consuming and the temperature required for PVD may affect the template material and cause delamination due to different coefficients of thermal expansion between the metal and membrane. Nickel and silver particles suspended in organic solvents are commercially available that can replace PVD. They offer the advantages of ease of use, fast drying times, and low cost. In addition, thermal problems caused by PVD are eliminated. Successful deposition of copper into PC and alumina nanopores is verified through SEM imaging and electrical conductivity tests.
Deposition and STM Study of Nanocrystal Platinum on Highly Oriented Pyrolytic Graphite
Authors: Zhou Xiangyang , Zhang Fuxiang , Srivastava Rajiv
Published: November 2006

Platinum nano-particles were deposited from 0.01 M hexaxhloroplatinate acid solutions on high oriented pyrolytic graphite substrates using a cyclic potential sweeping method. The particles were examined using scanning tunneling microscopy (STM). The Pt particles deposited on the highly oriented pyrolytic graphite from a 0.01 M hexaxhloroplatinate acid without supporting solute were about 5 nm in size with a small variance. It was found that these Pt nano-particles were ellipsoidal without apparent crystalline facet but with a high density of surface defects. The Pt particles deposited on the highly oriented pyrolytic graphite from a 0.01 M hexaxhloroplatinate acid with H2SO4 as supporting solute were about 10-100 nm in size with a much greater variance.
Eletrodepositon of CoNiMo Magnetic Thin Films from a Chloride Bath in the Presence of Citrate or Glycine
Authors: Esteves Marcos C. , Sumodjo Paulo
Published: November 2006

CoNiMo magnetic films were galvanostatically electrodeposited from chloride baths containing either citrate or glycine as additive. The composition, microstructure, morphology and magnetic properties of the deposits were analyzed and related with the different bath compositions used and the applied current. Baths containing citrate and/or at low pH are not suitable conditions to produce magnetic films with reasonable good properties to be used in magnetic devices. Generally, use of glycine in the bath and pH 7 yielded better films. Deposits prepared from glycine containing baths were amorphous, whilst the ones deposited from citrate containing baths presented two diffraction peaks. Crystallite size calculated by Scherrer formula laid around 11 nm. High magnetic saturation values were achieved: around 1.2 T. Additionally, coercivities as low as 50 Oe were obtained for films prepared using baths containing glycine. Films electrodeposited with the citrate containing baths showed higher coercivity: 125 Oe.
Electrodeposition of Magnetic CoPd Thin Films. Influence of Plating Condition
Authors: Takata Fernanda M. , Sumodjo Paulo , Esteves Marcos C.
Published: November 2006

Electrodeposition of magnetic CoPd thin films from a chloride bath containing glycine was investigated. The effect of applied current density (CD), bath composition, solution pH on film composition and current efficiency (CE) are discussed. Alloy composition, is dependent on bath composition and not on the pH of the solution. CEs are higher when the CD is between 25 and 50 mA cm-2. XRD data show that CoPd alloys are amorphous. For CD greater than or equal to 50 mA cm-2 the films show a typical cauliflower morphology whereas a smooth surface film is obtained for CD < 50 mA cm-2. Cracks and holes are observed with low CDs, with increasing solution pH. Magnetic measurements show that the films are easily magnetized when the applied field is longitudinal. Magnetic saturation (Ms) is dependent on the alloy composition. Coercivities were obtained in the range of 84 - 555 Oe were not attributed to any plating variable.
Cesium Recovery from Tank Waste Using the CsHg Alloying Reaction in Hydrophobic Room-Temperature Ionic Liquids:	A Green Chemistry Approach
Authors: Tsuda Tetsuya , Hussey Charles , Luo Huimin , Dai Sheng
Published: November 2006

The effects of residual moisture and oxygen on the electrochemical processing step for the recovery of Cs(I) extracted into the hydrophobic ionic liquids, tri-1- butylmethylammonium bis((trifluoro-methyl)sulfonyl)imide (Bu3MeN+Tf2N-) or N-methyl-N-propyl-piperidinium bis ((trifluoromethyl)sulfonyl)imide (MePrPip+Tf2N-) containing the ionophore, calix[4]arene-bis(t-octylbenzo-crown-6) from simulated aqueous tank waste was investigated in the presence of residual water and oxygen. The electrochemical reduction of ionophore-bound Cs(I) at Hg electrodes is surprisingly tolerant of small amounts of water, but greatly affected by oxygen. However, sparging with dry N2 lowers the residual water and oxygen content of the extraction solvent to the level where the reduction of Cs(I) at Hg is possible. Thus, the entire treatment cycle for tank waste can be carried out in an open cell, provided that the cell is sparged with dry N2. MePrPip+Tf2N- + BOBCalixC6 was a better extraction solvent than Bu3MeN+Tf2N- + BOBCalixC6, but the former solvent was unstable toward metallic Cs and Cs(Hg)x alloy.
Studies Related to Recovery of Gold from a Spent Thiosulfate-Sulfite Electrolyte Using an Electrolytic Cell
Authors: Sobri Shafreeza , Roy S. , Kalman E. , Nagyp P. , Lakatos M.
Published: November 2006

Interest has grown in developing non-toxic electrolytes for gold electrodeposition to replace the conventional cyanide- based bath for long term sustainability of gold electroplating. One such alternative electrolyte is a solution containing thiosulphate and sulphite, which has been developed specially for microelectronics applications. However, at the end of the electrodeposition process, the spent electrolyte contains a significant amount of gold. This study has been initiated to investigate the feasibility of gold recovery from a spent thiosulphate-sulphite electrolyte.
Electrocodeposition of Silver Particles with Tin for Fabrication of Lead-Free Solder Bumps
Authors: Barkey Dale P. , Wu B. , Keigler Arthur , Liu Zhenqui
Published: November 2006

Solders based on tin-lead alloys are used extensively in semiconductor packaging. Electrodeposition is a favored solder- application process in flip-chip packaging because it provides superior thickness control and is easily scaled down to small pitch sizes. However, industrial processing and consumer use of lead-bearing products is a recognized public-health hazard, and the international trend toward regulation is driving demand for lead-free alternatives such as the Sn/Ag eutectic. Direct alloy deposition and stack deposition have been used to produce Sn/Ag bumps. Electrocodeposition, in which metallic or dielectric particles suspended in the plating bath are incorporated into a metal electrodeposit is potentially more economical. In this study, electrocodeposition of silver particles with tin was used to generate Sn/Ag composites and alloys.