bluuebunny/crossref_metadata_2025 huggingface dataset:
Iridium and Lead Doped Ruthenium Oxide Catalysts for Oxygen Evolution
Authors: Valdez Thomas I. , Billings Keith J. , Sakamoto Jeff , Mansfeld Florian , Narayanan S. R.
Published: September 2009

The performances of ruthenium oxide-based oxygen evolution catalysts fabricated by various techniques have been studied. A thermal processing technique has been identified that can produce viable iridium and lead-doped ruthenium oxide catalyst. The best oxygen evolution performance was obtained with an iridium-doped ruthenium oxide catalyst with nine molar percent iridium. The cell voltage of the Ir(9)-d-RuO2 catalyst at an applied current density of 200 mA/cm2 was 1.45 volts at 70 oC. The oxygen evolution Tafel slope for doped ruthenium oxide catalysts are in the range of 40 to 55 mV/decade, a minimum of 10 mV/decade lower than what was found for ruthenium oxide.
Theoretical Description of the Nafion/Platinum Interface by DFT Calculations
Authors: Pacheco Robson , Rocco Ana Maria
Published: September 2009

In the present work, the Nafion/Pt interface is simulated utilising molecular model systems in DFT calculations. Results indicate the formation of intermediate structures (represented as R-SO3PtnH and R-SO2PtnOH), which can contribute to the stabilisation of the membrane/catalyst interface in fuel cells. The systems exhibit energy density (E/n) and bond lengths dependent on the size of the platinum clusters.
Influence of H2- or Co-Phthalocyanine Impregnation of Pt/C and Pd/C Catalysts on Formic Acid Electro-Oxidation
Authors: Chenitz Régis , Dodelet Jean-Pol
Published: September 2009

H2- and Co-phthalocyanines were impregnated on commercial Pt/C and Pd/C catalysts to determine whether this improved their catalytic activity toward formic acid oxidation. Heat-treatments of these phthalocyanine-impregnated catalysts were also performed in Ar atmosphere for 30 min at different temperatures (300, 600, and 950{degree sign}C). The adsorption of phthalocyanine at the surface of Pd/C decreases the activity of this catalyst, but improves that of Pt/C. The greatest improvement in activity was obtained with Co-phthalocyanine impregnated on Pt/C without heat-treatment, whereby the rate of dehydrogenation of formic acid at low potential was drastically increased and thus moved Pt activity closer to that of Pd. Pyrolysis of these phthalocyanine-impregnated catalysts did not improve their activity.
The Electrocatalytic Oxidation of Sodium Borohydride at Palladium and Gold Electrodes for an Application to the Direct Borohydride Fuel Cell
Authors: Simões Mario , Baranton Steve , Coutanceau Christophe , Lamy Claude , Léger Jean-Michel
Published: September 2009

Carbon supported palladium, gold and platinum nanoparticles were synthesized by microemulsion method in order to compare their catalytic activity for the electrooxidation of borohydride in alkaline medium. Two different pathways can be considered for this oxidation reaction: the direct oxidation of BH4- into BO2- and its indirect oxidation via hydrogen evolution. The electrochemical analysis of the polarisation curves recorded at different electrode rotation rates at Pd/C and Au/C in NaOH + NaBH4 electrolyte indicated that the electrooxidation process mainly occured following the direct pathway on both catalysts with 6 to 7 moles of exchanged electrons per mole of borohydride. On the other hand, on Pt/C catalyst, the oxidation reaction occurs with a strong hydrogen evolution. Furthermore, the kinetics parameters pointed out a ten times higher intrinsic catalytic activity of Pd/C compared to Au/C for borohydride oxidation reaction (bor).
Fuel-Cell Performance of Multiply-Crosslinked Polymer Electrolyte Membranes Prepared by Two-Step Radiation Technique
Authors: Yamaki Tetsuya , Sawada Shin-ichi , Asano Masaharu , Maekawa Yasunari , Yoshida Masaru , Gubler Lorenz , Alkan-Guersel Selmiye , Scherer Guenther G.
Published: September 2009

A multiply-crosslinked polymer electrolyte membrane was prepared by the radiation-induced co-grafting of styrene and a bis(vinyl phenyl)ethane (BVPE) crosslinker into a radiation-crosslinked polytetrafluoroethylene (cPTFE) film. We then investigated its fuel-cell performance at 60 and 80ºC in terms of the effect of radiation and chemical crosslinking. At 60ºC, all the membranes initially exhibited similar performance, but only the cPTFE-based membranes were durable at 80ºC, indicating the necessity of radiation crosslinking in the PTFE main chains. Importantly, cell performance of the multiply-crosslinked membrane was found high enough to reach that of a Nafion112 membrane. This is probably because the BVPE crosslinks in the graft component improved the membrane-electrode interface in addition to membrane durability. After severe OCV hold tests at 80 and 95ºC, the performance deteriorated, while no significant change was observed in ohmic resistivity. Accordingly, our membranes seemed so chemically stable that an influence on overall performance loss could be negligible.
Two-Phase Behavior and Compression Effect in a PEFC Gas Diffusion Medium
Authors: Mukherjee Partha P. , Wang Chao-Yang , Schulz Volker P. , Kang Qinjun , Becker Jurgen , Wiegmann Andreas
Published: September 2009

A key performance limitation in the polymer electrolyte fuel cell (PEFC), manifested in terms of mass transport loss, originates from liquid water transport and resulting flooding phenomena in the constituent components. A key contributor to the mass transport loss is the cathode gas diffusion layer (GDL) due to the blockage of available pore space by liquid water thus rendering hindered oxygen transport to the active reaction sites in the electrode. The GDL, therefore, plays an important role in the overall water management in the PEFC. The underlying pore-morphology and the wetting characteristics have significant influence on the flooding dynamics in the GDL. Another important factor is the role of cell compression on the GDL microstructural change and hence the underlying two-phase behavior. In this article, we present the development of a pore-scale modeling formalism coupled with realistic microstructural delineation and reduced order compression model to study the structure-wettability influence and the effect of compression on two-phase behavior in the PEFC GDL.
In-Plane Mass-Transport Studies of GDL Variation Using the Segmented Cell Approach
Authors: Wood David L. , Mukundan Rangachary , Borup Rodney
Published: September 2009

The effects of cathode GDL variation on segmented cell performance were investigated using polarization analysis, AC impedance, and cyclic voltammetry. Three different SGL SIGRACET® materials were used with markedly different PTFE treatments operating under 100%/100% and 50%/50% (anode/cathode) relative humidity (RH) conditions. The total cell performance varied little under both wet and dry operating conditions for three different GDL types, but performance differences were observed for individual segments based on polarization and AC impedance data. When the different GDL types were arranged in a mixed configuration, an improvement over the base case GDL 24BC of 11% and 8% in current density at 0.6 V was seen for wet and dry conditions, respectively. When the three different GDL types were compared for ECSA loss after 300 operating hours, the GDL 24BC5 exhibited the largest decline, which was attributed to increased Pt particle agglomeration. The cell with the mixed configuration showed an ECSA decline comparable to GDL 24BC and GDL 24DI. Therefore, it was demonstrated that moderate performance improvements can be realized by varying the in-plane GDL type in relation to its flow-field position without sacrificing durability.
Effective Thermal Conductivity of Gas Diffusion Layer in Through-Plane Direction
Authors: Kawase Motoaki , Inagaki Tatsuya , Kawashima Shota , Miura Kouichi
Published: September 2009

Temperature remarkably influences the water behavior in the PEMFC. However, the temperature inside the PEMFC has not been well understood. A lot of heat comparable to the electric power is emitted out of the cell. The PEM temperature is determined by the effective thermal conductivity through the layers and the temperature gradient created in the through-plane direction for emitting the heat. By measuring the PEM temperature with thin thermocouples and thick membrane, the effective thermal conductivity was estimated. It strongly depended on the cell binding pressure. Binding the cell improves the contact between carbon paper and carbon current collector as well as compresses carbon paper, leading to rise in the apparent effective thermal conductivity in the through-plane direction. The interfacial resistance to heat transfer was found 39 % of the overall resistance.
Experimental Measurement of Relative Permeability Functions for Fuel Cell GDL Materials
Authors: Hussaini Irfan , Wang Chao-Yang
Published: September 2009

Gas diffusion layer in PEM fuel cells plays a pivotal role in water management. Modeling of liquid water transport through the GDL relies on knowledge of relative permeability functions in the in-plane and through-plane directions. In the present work, air and water relative permeabilities are experimentally determined as functions of saturation for typical GDL materials such as Toray-060, -090, -120 carbon paper and E-Tek carbon cloth materials in their plain, untreated forms. Saturation is measured using an ex-situ gravimetric method. Absolute and relative permeability functions in the two directions of interest are presented. Significant departure from the generally assumed cubic function of saturation is observed.
The Impact of Impurities on Long-Term PEMFC Performance
Authors: Garzon Fernando , Lopes Thiago , Rockward Tommy , Sansiñena Jose-Maria , Kienitz Brian , Mukundan Rangachary
Published: September 2009

Electrochemical experimentation and modeling indicates that impurities degrade fuel cell performance by a variety of mechanisms. Electrokinetics may be inhibited by catalytic site poisoning from sulfur compounds and CO and by decreased local proton activity and mobility caused by the presence of foreign salt cations or ammonia. Cation impurity profiles vary with current density, valence and may change local conductivity and water concentrations in the ionomer. Nitrogen oxides and ammonia species may be electrochemically active under fuel cell operating conditions. The primary impurity removal mechanisms are electrooxidation and water fluxes through the fuel cell.
Mechanistic Investigations of NO2 Impact on ORR in PEM Fuel Cells: a Coupled Experimental and Multi-scale Modeling Approach
Authors: Lemaire Olivier , Barthe Benoit , Rouillon Ludovic , Franco Alejandro A.
Published: September 2009

While present studies dealing with the impact of pollutants on fuel cell performance mainly concern anode side, this work focuses on the impact of one of the main pollutant in air: nitrogen dioxide (NO2). Based on new experimental results and our multi-scale modeling approach, this paper presents new progresses on the understanding of the interaction of NO2 with fuel cells. The parametrical study reveals that the effect of NO2 is always characterized by a rapid decrease of performance followed by a stabilization phase. The performance recovery after the pollution phase depends strongly on the temperature and on the current density. The experimental "potential wave" phenomenon observed was explained on the basis of our modeling approach which highlights the importance of accounting for the competitive adsorption of the Oxygen Reduction Reaction (ORR) and NO2 intermediates, as well as the surface reactivity between the different adsorbates.
Electrode and Catalyst Durability Requirements in Automotive PEM Applications: Technology Status of a Recent MEA Design and Next Generation Challenges
Authors: Haas Herwig R. , Davis Michael T.
Published: September 2009

The functionality of fuel cell vehicles is continuously being improved by several automakers and efforts are being made to demonstrate performance, durability, efficiency and freeze start capability comparable to conventional vehicles. Recent results demonstrating acceptable operational performance, efficiency, freeze start capability and durability are shown and discussed. The main barrier preventing fuel cells from being competitive with conventional ICE is the high cost of the stack and system. For the stack, the key cost driver is catalyst loading. Requirements for future catalysts will be presented, demonstrating the challenges and technology gaps following from a reduction of catalyst loadings as well as the use of PtCo based catalysts.
Influence of Formic Acid Impurity on Proton Exchange Membrane Fuel Cell Performance
Authors: Zhang Xiaoyu , Galindo Hugo , Grace Hector , Baker Phillip , Wang Xiaofeng , Pasaogullari Ugur , Suib Steven L. , Molter Trent
Published: September 2009

The effect of trace amounts of formic acid (HCOOH) on proton exchange membrane fuel cell (PEMFC) performance is reported. Experimental approaches including long term stability test, cyclic voltammetry (CV) scans and electrochemical impedance spectroscopy (EIS) were used to evaluate and characterize the contamination. The results show that trace amounts of HCOOH can cause degradation in fuel cell performance and significantly contaminate the electrodes. Furthermore, fully recovery from the contamination could not be achieved only by reverting to pure hydrogen while operating the fuel cell. Mechanisms of contamination of the electrodes and performance degradation of the PEMFC are also postulated.
Innovative Membranes for PEMFC with Mixed Sulfonic and Phosphonic Acid Functionality
Authors: Donzel Nicolas , Ruiz Elodie , Jones Deborah J. , Rozière Jacques
Published: September 2009

The properties of a new ether-linked polybenzimidazole (PBI) that can be directly sulfonated in solution have been associated with those of a polymeric phosphonic acid, with the aim of inducing proton conductivity at both lower (-SO3H groups) and higher (-PO3H2 functions) temperatures. Conductivity was determined up to 120 {degree sign}C and at relative humidity values between 25 and 95% on dense interpenetrating network type membranes having 5-10 phosphonic acid groups/sulfonated PBI repeat unit. At 120 {degree sign}C, the mixed functionality (-SO3H/-PO3H2) membrane has higher conductivity than the sulfonic or phosphonic acid functionalised membranes alone at relative humidity values below 80%, and the dependence of its conductivity at this temperature on RH is significantly lower than that of the sulfonated PBI membranes alone.
Investigation of a Double Layer Membrane for Direct Methanol Fuel Cell Applications
Authors: Hasani-Sadrabadi Mohammad M. , Dashtimoghadam Erfan , Majedi Fatemeh
Published: September 2009

In the current research, a double-layer polyelectrolyte membrane based on chitosan and Nafion® 112 was fabricated and assessed for applicability in direct methanol fuel cells. It was found that in the presence of crosslinked chitosan as the barrier layer, proton conductivity and methanol permeability reach to 0.082 S.cm−1 and 5.14×10−7 cm2.s−1, respectively. Moreover, the obtained proton exchange membrane exhibited selectivity value of approximately 176300 in comparison with corresponding values of 40500 and 28500 for Nafion® 117 and Nafion® 112, respectively. Activation energy measurements revealed a value of 8.6 kJ.mol-1for proton transportation process. The obtained results indicate this type of double-layer proton-conducting membrane could be considered as potential polyelectrolytes for direct methanol fuel cell applications.
Spatially Resolved Impedance Spectroscopy on Direct Methanol Fuel Cells Considering Fuel Concentration Oscillations in Gas Channels
Authors: Sanders Tilman P. , Baumhöfer Thorsten , Sauer Dirk Uwe , Schröder Alexander , Wippermann Klaus
Published: September 2009

Impedance spectroscopy is usually carried out by exiting the whole fuel cell or even the whole fuel cell stack. The alternating excitation current or voltage, which is imposed on the cell leads to alternating fuel consumption of the cell. This alternating consumption accumulates in the fuel channels and can lead to significant fuel concentration oscillations in the gas channels of the flow fields. This results in significant chemical excitation of the parts of the fuel cell which are further away from the fuel inlet. Due to the accumulation of this chemical excitation along the gas channel, the measured impedance of these parts of the fuel cell does not characterize the local state of the MEA. This has been reported and experimentally verified in the literature. Since the local state is of interest for the investigation of spatially resolved phenomena, a new measurement technique has been developed.
Preparation of Fluorine Doped Zinc Tin Oxide Coating Layer on SUS 316 Bipolar Plates by ECR-MOCVD for PEMFC
Authors: Lee Joong-Kee , Park Ji Hun , Chang Wonyoung , Byun Dongjin
Published: September 2009

Fluorine-doped zinc tin oxide (ZnSnOx:F) films on SUS316 are prepared by electron cyclotron resonance-metal organic chemical vapor deposition (ECR-MOCVD) in order to achieve the corrosion-resistant and low contact resistance bipolar plates for polymer electrolyte membrane (PEM) fuel cells. The prepared ZnSnOx:F films coated on SUS316 substrate are characterized by X-ray diffraction (XRD), auger electron microscopy (AES) and field emission-scanning electron microscopy (FE-SEM). To simulate the aggressive PEMFC environment, all of the electrochemical experiments are conducted in 1M H2SO4 + 2ppm HF solution at 70oC. The fluorine doping appears to be one of the critical process parameters on the formation of the corrosion-protective layer for PEMFC bipolar plates, as well as affecting the electrical properties of the films.
Influence of Gas Diffusion Layers with Microporous Layer on the Performance of Polymer Electrolyte Fuel Cells
Authors: Kitahara Tatsumi , Konomi Toshiaki , Nakajima Hironori
Published: September 2009

The influence of microporous layer (MPL) design parameters for gas diffusion layers (GDLs) on the performance of polymer electrolyte fuel cells (PEFCs) was clarified. The appropriate MPL design parameters vary depending on the humidification conditions of the supplied gases. Under high humidification, a decrease in the MPL pore diameter is effective for the prevention of flooding and the enhancement of the PEFC performance. However, when the pore diameter becomes too small, the PEFC performance tends to decrease. Reducing the MPL thickness penetrated into the substrate improves in-plane permeability, and enhances the ability of the MPL to avoid flooding. Under low humidification, a decrease in the MPL pore diameter is effective to prevent drying-out of the MEA. Increasing the MPL thickness is also effective for maintaining the humidity of the MEA. However, when the MPL thickness becomes too large, oxygen transport to the electrode through the MPL is reduced, lowering the PEFC performance.
Effects of Surface Irregularities and Interfacial Cracks on Polymer Electrolyte Fuel Cell Performance
Authors: Manahan Michael P. , Kim Soowhan , Kumbur Emin C. , Mench Matthew M.
Published: September 2009

The present study seeks to investigate the impact of surface irregularities and cracks at the catalyst layer (CL) and micro-porous layer (MPL) interface on the mass and electronic transport of polymer electrolyte fuel cells (PEFCs). Two different CLs were compared, i.e. one with negligible cracking and the other with high cracking (~6% active area reduction), under a combination of various operating conditions, including high/low relative humidity, and the presence of nitrogen/helium inert gases in the cathode inlet stream. A limiting current density analysis indicated that the cracked CL demonstrated a small increase in the Fickian diffusion of the reactants across the cathode electrode compared to the negligible-cracked CL case. Furthermore, the results from a relative humidity analysis showed that the protonic resistance in the CL might dominate the moderate current density region (0.15 A/cm2<current density<0.45 A/cm2). Finally, comparison of the cell performance for cracked and negligible-cracked CL cases suggests that the cracks may act as water pooling sites, which in turn, may enhance the performance in the high current density region (current density>0.45 A/cm2) due to the decreased water surface coverage and/or enhanced water removal.
Influence of Carbon Cloth GDLs on Electrochemical Performance of PEMFCs
Authors: Dotelli Giovanni , Omati Luca , Gallo Stampino Paola
Published: September 2009

Gas diffusion layer (GDL), a key component of PEMFCs, is usually made of carbon cloth or paper, treated with different hydrophobic agents, and coated with a micro-porous layer (MPL). A set of GDLs having different textile properties, produced by an Italian Company (Seal S.p.A.), and coated with the same MPL, was investigated. The samples were tested with the same Catalyst Coated Membrane (Nafion® 112 with Pt load 0.5/0.5 mg cm-2), considering different operating conditions such as flow rate and cathode humidity. The cell testing was run at 60{degree sign}C and for each configuration steady-state polarization curves were obtained. In order to evaluate the role of different GDLs AC impedance spectroscopy of the running cell was also performed.
Stainless Steel In-situ Corrosion Testing in a PEFC Multisinglecell
Authors: Auvinen Sonja , Tingelöf Thomas , Ihonen Jari K. , Siivinen Jarmo , Johansson Max
Published: September 2009

The corrosion and contact resistances of different coated and uncoated stainless steel grades were studied with a multisinglecell. MEAs and exhaust water were analyzed for accumulated iron after several long steady-state measurements. The interfacial contact resistances were measured before and after each test. Low contact resistance was achieved with the coated samples. There was large variation in the corrosion results due to differences in the coating quality.
Alternative Support Materials for Fuel Cell Catalysts
Authors: Ettingshausen Frank , Weidner André , Zils Susanne , Wolz André , Suffner Jens , Michel Marc , Roth Christina
Published: September 2009

One major issue still impeding the rapid market introduction of low-temperature polymer electrolyte membrane fuel cells (PEMFC) is the catalyst's poor long-term stability. In particular in the harsh conditions at the cathode side corrosion of the standard carbon support takes place, and high platinum loadings even speed up this process. Recent research focuses on novel, non-carbon support materials, using either electron-conductive oxides or conductive polymers. In this paper the synthesis and characterization of TiO2-supported Pt, niobium-doped TiO2-supported Pt, Sb-doped tin oxide as well as polyaniline-supported Pt as novel cathode catalysts for PEMFC are presented.
Development of Novel Metal Oxide Supported Pt catalysts for Polymer Electrolyte Membrane and Unitized Regenerative Fuel Cells Applications
Authors: Huang Sheng-Yang , Ganesan Prabhu , Zhang Peng , Popov Branko
Published: September 2009

TiO2-supported Pt electrocatalyst was synthesized as a possible alternate cathode catalyst for PEM fuel cell. The Pt/TiO2 catalyst exhibited good fuel cell performance (1.24 A cm-2 at 0.6 V) due to the low mass transport limitations in the cathode catalyst layer. The Accelerated Stress Test (AST) results indicated ultrahigh stability for the Pt/TiO2 electrocatalyst. The strong metal support interaction (SMSI) and corrosion-resistance of TiO2 support enhanced the stability of Pt catalyst.
Synthesis of Ta-oxide Based Nano-sized Cathode Catalyst on Highly Ordered Meso-porous Carbon for PEM Fuel Cells
Authors: Shoyama Masashi , Tomimura Tetsuya , Okubo Yasuhiro , Nambu Hironobu , Lin Meng-Liang , Hara Kenji , Fukuoka Atsushi , Ishihara Akimitsu , Ota Ken-ichiro
Published: September 2009

new preparation process of nano-sized Ta-based cathode catalyst on highly ordered mesoporous carbon (MPC) for polymer electrolyte fuel cell has been investigated. The TaON/MPC hybrid catalyst showed high surface area (~1,200m2/g) and high onset potential for the oxygen reduction reaction (EORR~0.85V vs. RHE).
Pt/Modified MWNT as Electrocatalysts for High Temperature PEM Fuel Cells
Authors: Daletou Maria , Paloukis Fotios , Stefopoulos Andreas
Published: September 2009

A new approach towards the development of electrocatalytic layers for use in high temperature PEM fuel cells is reported. Modified carbon nanotubes (CNTs) were used as the support. The aim was to achieve a uniform distribution of polar groups, which can interact with phosphoric acid, on the surface of the modified carbon support. MWNTs were selected due to their unique properties and were surface modified introducing pyridine based groups on the side walls. The different supports were thoroughly characterized by means of relevant techniques. Platinum was deposited on the new carbon supports resulting in the newly synthesized catalysts. Initial measurements of the catalytic activity towards oxygen reduction were performed in order to evaluate the potential use of these materials as catalytic layers in HT PEMFCs.
Performance of a Direct Borohydride Fuel Cell Stack
Authors: Towne Silas , Carella Michael , Mustain William , Viswanathan Vilayanur , Rieke Peter , Pasaogullari Ugur , Singh Prabhakar
Published: September 2009

In this work, we study the performance of a 10 cell DBFC stack. A peak power density of 410 mW/cm2 was obtained at 80oC. Here, a 40 wt% Pt/C cathode and 10 wt% MmNi3.3Al0.2Mn0.6Co1.0 AB5-type anode catalysts have been used. The cathode fuel is 15 wt % H2O2 in 1M sulfuric acid. The anode fuel is 10 wt% NaBH4 in 20 wt % NaOH. Mitigating H2 evolution at the anode and O2 evolution at the cathode are also investigated.
Evaluation of Acoustic Emission Technique for PEMFC Diagnosis
Authors: Legros Benoit , Nogueira Ricardo , Thivel Pierre-Xavier , Bultel Yann
Published: September 2009

This study evaluates the acoustic emission (AE) technique for the detection of membrane dehydration in proton exchange membrane fuel cells during operation. AE measurements were firstly carried out during dehydration of Nafion® samples (ex-situ study). As AE was shown to be sensitive enough to detect structural changes taking place at the last stages of dehydration, in-situ study was performed on PEM single cell during current interruption. AE activity occurs only on specific running conditions and consequently gives promises of further interesting applications.
High Temperature Operation of a Solid Polymer Electrolyte Fuel Cell Stack Based on a New Ionomer Membrane
Authors: Aricò Antonino Salvatore , Di Blasi Alessandra , Brunaccini Giovanni , Sergi Francesco , Antonucci Vincenzo , Asher Peter , Buche Silvain , Fongalland D. , Hards Graham A. , Sharman Jonathan , Bayer Armin , Heinz Gerhard , Zuber Ralf , Gebert Matthias , Corasaniti Martina , Ghielmi Alessandro , Jones Deborah J.
Published: September 2009

Polymer electrolyte fuel cell stacks assembled with Johnson Matthey Fuel Cells and SolviCore MEAs based on the AquivionTM short-side chain, chemically stabilized perfluorosulfonic acid membrane were investigated in the framework of the Autobrane EU project. Electrochemical experiments in fuel cell short stacks were performed under automotive conditions at pressures of 1-1.5 bar abs. over a wide temperature range, up to 130 {degree sign}C, with varying levels of humidity (down to 18% R.H.). The stacks using the first set of large area MEAs showed elevated performance in the temperature range from ambient to 100 {degree sign}C (cell power density in the range of 600-700 mWcm-2) with a moderate decrease above 100 {degree sign}C. The performances and electrical efficiencies achieved at 110 {degree sign}C (cell power density of about 400 mWcm-2 at an average cell voltage of about 0.6 V) are promising for automotive applications. Further optimization of stack components to maximize the high temperature performance is currently underway.
Combined Cooling Heating and Power (CCHP) Generation in a Fuel Cell-Heat Pump Hybrid System
Authors: Suslu Osman S.
Published: September 2009

Fuel cells enable clean and silent electric power production in smaller units with efficiencies reached only in MW-facilities by central power plants. The waste heat of the fuel cell can easily be utilized for residential heating. Membrane steam reformers purify hydrogen without cooling the reactor's effluent; only permeated hydrogen has to be cooled down prior to the electro-oxidation at the fuel cell's anode. Both the absorption and compression heat pumps may be utilized for utilizing waste heat and electricity of the fuel cell in heating and cooling applications. The following work contains scenarios for different coefficient of heating performance for both types of heat pumps. According to the net electric efficiency of the fuel cell and the coefficient of performance of the heat pumps, an overall coefficient of performance of the CCHP system is obtained. Such a CCHP system can contribute to a reduction of CO2 emissions in residential heating.
Synthesis of Multicomponent Sulfide Phosphors from Uniform Precursors Prepared by Solution Methods
Authors: Petrykin Valery , Ohara Keishiro , Suzuki Yoshihito , Tezuka Satoko , Kakihana Masato
Published: September 2009

An innovative approach for direct synthesis of high purity BaAl2S4:Eu and Ba2SiS4:Eu phosphor materials using solution-based methods was developed for the first time. The synthesis strategy involves preparation of high homogeneity oxide precursors by a solution based method followed by the sulfurization-reduction in CS2 atmosphere. Analysis of chemicals composition of individual particles by SEM-EDX confirms substantially higher uniformity of the materials prepared by solution based synthesis compared to the samples obtained by conventional method.
Emission Quench of ZnS-AgInS2 Semiconductor Nanocrystals and Its Application to Biosensors
Authors: Uematsu Taro , Taniguchi Shohei , Doi Toshihiro , Torimoto Tsukasa , Kuwabata Susumu
Published: September 2009

Photoluminescence of semiconductor nanocrystals is quenched by redox molecules. The quench reactions have been studied in terms of potential, electric charge and the resulting electron transfer reaction. Regarding CdTe nanocrystals, it was studied in detail how charges of CdTe and redox species, and ion strength influence the quench of PL. Recently, with ever-increasing demand for low-toxic semiconductor nanocrystals, we succeeded in synthesizing ZnS-AgInS2 solid solution nanocrystals (ZAIS) having a high quantum yield (~ 50 %). Quenching was also observed for ZAIS nanocrystals, and some quenchers showed different quench ability between their redox states. Furthermore, the combination of redox-responsive quenching with an enzymatic reaction allows fabrication of optical biosensor which increases their PL intensity with the addition of glucose.
Luminescence of Octahedrally Coordinated Eu2+ in Rb2MP2O7 (M = Ca, Sr)
Authors: Srivastava A. M. , Comanzol Holly , Camardello Sam , Aycibin Murat , Happek Uwe
Published: September 2009

In a recent paper [1] we have investigated the peculiar luminescence of divalent europium in Cs2CaP2O7 and Cs2SrP2O7 which is characterized by both an extremely large Stokes shift and a high quenching temperature. Here we report on the Eu2+ luminescence in Rb2CaP2O7 and Rb2SrP2O7. Again we find a large Stokes shift, combined, however, with a much smaller quenching temperature [Fig. 1] than in the Cs compounds. In order to determine whether the emission must be attributed to excitonic or to an extreme case of standard d-f luminescence, we combine standard optical measurements with photoionization studies.
Structure and Luminescence of Rare Earth-doped Silicon Oxides Studied Through XANES and XEOL
Authors: Roschuk Tyler , Wilson Patrick , Li Jing , Dunn Kayne , Wojcik Jacek , Crowe Iain , Gwilliam Russell , Halsall Matthew , Knights Andrew , Mascher Peter
Published: September 2009

Luminescent Si-based materials are of significant interest due to their potential applications in the fields of photonics and solid state lighting. The use of rare earth dopants incorporated into Si-based materials allows the attainment of specific wavelengths of emission for color tunability. Details of the RE luminescence and even the ability to obtain luminescence are strongly dependent on the composition and structure of the Si-based host material. Through the use of X-ray absorption spectroscopy details of the atomic bonding environment of the films has been obtained. X-ray excited optical luminescence, measured after excitation at the absorption edges of the constituent atoms within these materials, reveals that excitation of the rare earth ions occurs primarily at energies related to oxygen states.
A New Yellow Phosphor La3Si6N11:Ce3+ for White LEDs
Authors: Kijima Naoto , Seto Takatoshi , Hirosaki Naoto
Published: September 2009

La3Si6N11:Ce was synthesized from the mixture of nitrides and oxides as raw materials at 1580 - 2000 ° under nitrogen atmosphere of 0.92 MPa. It was found that La3Si6N11:Ce emits yellow light at the excitation wavelength of 455 nm. When a small amount of oxygen was included in the raw materials, LaSi3N5:Ce tended to form more than La3Si6N11:Ce. Thermal quenching of the yellow emission of La3Si6N11:Ce was smaller than that of the conventional yellow phosphor, (Y,Gd)3Al5O12:Ce. It was clarified that La3Si6N11:Ce is suitable for a white LED constituting of a blue LED and a yellow phosphor.
Luminescence and X-ray Diffraction Studies of Rare Earth Doped Silica Sol-Gel Glass
Authors: Hoffman Kurt R. , Alazar Henok , Boye Dan , Silversmith Ann
Published: September 2009

We present recent work exploring the effects of aluminum co-doping on the luminescent properties of rare earth ions in sol-gel glasses. Using x-ray diffraction techniques we have identified the formation of aluminum rich nano-crystals in silica glass annealed to high temperatures. We discuss implications of these results in understanding the impact aluminum co-doping has on rare earth luminescence in sol-gel glass.
On the Luminescence of Ce3+ in LnI3 (Ln = Lu3+, Y3+, Gd33+)
Authors: Camardello Sam , Comanzol Holly , Srivastava A. M. , Aycibin Murat , Happek Uwe
Published: September 2009

The remarkable feature of the Ce3+ luminescence in the isostructural LnI3 [Ln3+ = Lu3+, Y3+, Gd3+] family of materials pertains to the experimental observation that the energy of the emitted photon increases with decreasing ionic radii of the host lattice. To understand this variation, the optical properties of the Ce3+ ion in YF3 is evaluated and compared with those reported for LuI3 and GdI3. It is shown that the crystal field splitting and the centroid shift of the Ce3+ 5d1 electronic configuration in these iodides are of the same order of magnitude. The lowest energy Ce3+ 4f1→ 5d1 transition in the three iodides is practically uninfluenced by the ionic radii of the host lattice cation, which the Ce3+ ion substitutionally replaces. The increase in energy of the emitted photon with decreasing ionic radii of the host lattice is due to the increasing Stokes shift of the Ce3+ luminescence in the sequence LuI3 -YI3 - GdI3.
Evaluation of Laser Potentialities from Concentration Quenching Analysis in Yb3+-Doped Cubic Crystals
Authors: Boulon Georges , Guyot Yannick , Yoshikawa Akira
Published: September 2009

We present an evaluation of laser potentialities of Yb3+-doped solid-state laser cubic crystals from concentration dependences of the 2F5/2 experimental decay time. We shall analyze few oxi- de and fluoride crystals of 4N (99.99) purity for commercializa- tion which can be extended today to laser ceramics of the same composition. Experimental results will be related for two crys- tals: Yb3+-doped YAG garnet and Yb3+-doped KY3F10 fluoride.
Theory of Semiconductor Quantum Dot Lasers
Authors: Asryan Levon V.
Published: September 2009

Operating characteristics of quantum dot (QD) lasers are discussed. Carrier-density-dependent internal loss sets an upper limit for operating temperatures and considerably reduces the characteristic temperature. Such a loss also constrains the shallowest potential well depth and the smallest tolerable size of a QD at which the lasing can be attained. In a laser with a single layer of QDs, this loss can strongly limit the output power and cause a rollover of the light-current curve (LCC). Excited-state-mediated capture of carriers from the waveguide into the QD ground-state places a fundamental limitation on ground-state lasing - the output power saturates at high injection currents. The saturation power is controlled by the transition time between the excited- and ground-state in a QD; the longest, cut-off time exists, beyond which no ground-state lasing is possible. Spatial hole burning causes the multimode generation, reduces the total optical power and contributes to nonlinearity of the LCC.
One Material, Multiple Faces - Nanostructured Bismuth
Authors: Park Hongsik , Han Dongil , Kim Jin Ho , Hsu Chih-Hsun , Shin Hyunjung , Xu Jimmy
Published: September 2009

One-dimensional (1D) bismuth and bismuth sulfide nanowires have been successfully fabricated. The diameter of bismuth nanowires was precisely controlled from 66 to 25 nm using atomic layer deposition (ALD) and IR absorption characteristics were investigated. Bismuth sulfide (Bi2S3) nanowires were synthesized by biomolecule-assisted synthesis, which resulted in high crystallinity and good uniformity, with diameters of (50 {plus minus} 10) nm and lengths of (1.9 {plus minus} 0.2) µm. Their morphology was controlled by changing the sulfur sources. To assess their electrical properties, we fabricated nanowire transistors with a back-gate structure. The as-grown nanowires are found to be n-type semiconductors and the on-off ratio of the transistors is about 102 with a silicon dioxide layer of 50 nm thickness as the gate insulator.
Temperature Dependence of the Photoluminescence Intensity in Si3+xN4:H Films with Amorphous Si Nanoclusters: Evidence for Two Processes Involved in the Nonradiative Relaxation of Photoexcitations
Authors: Volodin Vladimir , Stuchinsky Victor A. , Korchagina Taisiya , Popov Aleksandr , Vergnat Michel
Published: September 2009

The temperature dependence of the photoluminescence intensity in Si3+xN4:H films grown on Si substrates in a PECVD process held at temperatures 100 and 380oC was analyzed versus the film stoichiomery. The film stoichiometry parameter x was varied in the range x = 0.08 to 3.7 via varying the NH3/SiH4 flow ratio (0.5 to 5). According to Raman scattering data, the films contained amorphous Si nanoclusters, whose sizes increased with x and substrate temperature. For the first time, the involvement of two different processes in the nonradiative relaxation of excitations optically generated in the system under study has been demonstrated. These processes were tentatively identified as the thermal dissociation of nanocluster-bound excitons and their nondissociative migration to nonradiative sites in neighboring Si nanoclusters. The activation energies and the frequency factors of the two processes were shown to be consistent with the quantum confinement model for the amorphous Si nanocluster related photoluminescence.
Regularization Algorithm for DOS Spectrum Deconvolution From C(V) and Q(V) Dependencies of Si Nanowire-Based MOS Structure
Authors: Ligatchev Valeri , Chin Sai Kong
Published: September 2009

Based on Tikhonov's regularization approach, we developed regularization algorithm (RA) for deconvolution electron spectrum N(E) from data of capacitance - gate voltage [C(V)] and charge-gate voltage [Q(V)] characteristics of nanowire-based FETs. Our RA solves one-dimensional ill-posed Fredholm integral equation(s) of the second kind employing analytical properties of Fourier integral transform. The N(E) functions for CB states deconvoluted from C(V) characteristics exhibit good quantitative agreement with DOS spectrum, obtained earlier [S.-K. Chin, V. Ligatchev, IEEE Electron Device Letters, 30, 395 (2009)] by Schrodinger-Poisson simulations for FETs with cylindrical Si NW cores and radii of 10 nm at temperatures 38 K.
CARBonCHIP: Carbon Nanotubes Technology on Silicon Integrated Circuits; Some Key Results
Authors: Rapposelli Paolo , Capraro Bernard , Dijon Jean , Groeseneken Guido , Cott Daire , Pinson Jean , Joyeux Xavier , Amadou Julien , Van Noyen Jasper , Sels Bert
Published: September 2009

CARBonCHIP ("Carbon Nanotubes Technology on Silicon Integrated Circuits") has been a three year EU FP6 STReP collaborative project aimed to determine whether carbon nanotubes are a viable material to be used in the manufacture of interconnected transistors for future electronic devices beyond the 22 nm node. The research activities performed within the CARBonCHIP consortium primarily focused on the back end of line leading to the ability to now selectively grow dense bundles of vertical CNTs (10E12 CNTs cm-2) inside small diameter vias (140 nm) with repeatable yield. The final project deliverable, summarised in this paper, has been the generation of a materials based roadmap indicating further development of CNTs as a viable building block in nanoelectronics IC devices to extend Moore's Law beyond the year 2020. As this is a public report, only information which has been published or disseminated at a public level is being documented.
Fabrication and Characterizations of Nanorod Light Emitting Diode Arrays Using Nanosphere Lithography
Authors: Ke Min-Yung , Wang Cheng-Yin , Chen Liang-Yi , Chen Hung-Hsien , Chiang Hung-Li , Cheng Yun-Wei , Hsieh Min-Yan , Chen Cheng-Pin , Huang JianJang
Published: September 2009

In this paper, by sping-coating a mono layer of nanospheres (nanoparticles) on top of the sample, the technology of nanosphere lithography is developed and applied to GaN based LED epi-structures. By etching the p-type GaN further through the active region, p-i-n nanorods are exposed all over the mesa area. By inserting a spacer layer in between rods, nanrod LED arrays can be realized without shorting the p-type contact to n-GaN. The electrical and optical properties of the InGaN/GaN-based nano-devices are investigated at room temperatures.
UV Photodetectors with Lateral Self-assembled ZnO Nanowires Grown at Low Temperature
Authors: Yang Po-Yu , Lee I-Che , Chang Chia-Tsung , Lin Kao-Chao , Wang Jyh-Liang , Cheng Kuo-Jui , Lin Chun-Chuan , Cheng Huang-Chung
Published: September 2009

In this paper, a self-assembled lateral growth of ZnO nanowire (NW) photodetector has been successfully synthesized by an aqueous solution method at low temperature (85oC). The growth of ZnO NWs on a silicon substrate with a ZnO seeding layer exhibits single-phase wurtzite ZnO crystal structure, and grows along the c-axis direction. Furthermore, we have demonstrated the current-voltage characteristics and photoresponse of the ZnO NWs with and without UV (325 nm) illumination. Therefore, this low-temperature and simple fabrication process is a viable processing technique to selectively grow lateral ZnO NWs on a flat substrate of any material, with potential applications in flexible NW devices.
Towards Refractive Index Modulation in TiO2 by Means of Electrochemical Anodization
Authors: Liu S. K. , Lin C.C. , Lin Jing Chie , Lee S.L. , Couteau C. , Lerondel Gilles
Published: September 2009

In order to demonstrate the feasibility of porous TiO2 multi-layers we address the possibility of color tuning of single thin films by means of varying the electrochemical anodization conditions (voltage and time). Ellipsometric data analysis using Bruggeman effective medium approximation confirms the interferometric nature of the sample color.
High-operating Current ZnO Based Thin Film Transistors with a Bi-layer ZnO/GZO Channel
Authors: Liu Kuang Chung , Chiang Hung Li , Hsiao Shih-Hua , Su Liang Yu , Peng Lung Han , Huang JianJang
Published: September 2009

A high-operating current ZnO based thin film transistor on glass substrate is demonstrated by inserting a thin but high-carrier density Ga-doped ZnO (GZO) layer in between two ZnO layers. The device shows a drain-source current 3.4mA at VGS=5V and VDS=14V, which is significantly higher than that of the conventional one. The improvement of the current level is due to the insertion of the GZO layer, which serves as a source to supply additional carriers to the channel layer. Also, the threshold voltage of the device becomes smaller, but remains in the enhancement mode. This result shows our proposed structure has the advantage of adjusting threshold voltages.
On the Driving Force of Shockley Stacking Fault Motion in 4H-SiC
Authors: Caldwell Joshua D. , Stahlbush Robert , Ancona Mario , Glembocki Orest J. , Hobart Karl
Published: September 2009

Determining the primary driving force for Shockley stacking fault (SF) expansion within 4H-SiC has been of intense interest due to the deleterious effects of these defects upon the electrical characteristics of bipolar SiC devices. Previoulsy reported models have focused on determining the reasons for the perceived improved thermodynamic stability of the SFs, which are planes of SiC with the 3C-SiC polytype, with respect to the 4H-SiC host lattice. However, annealing and high temperature device operation experiments have clearly shown that SFs are not the thermodynamically preferred state of 4H-SiC in the absence of excess injected carriers. Here, we introduce and discuss a possible mechanism governing SF expansion and contraction that is consistent with previously reported experimental observations and present further experimental and simulation results that support this model.
Deposition of 4H-SiC on C-plane Sapphire with C60
Authors: Li JianChao , Batoni Paolo , Tsu Raphael
Published: September 2009

We report the growth of heteroepitaxial of 4H-SiC on (0001) sapphire substrate at 1000-1100oC using C60 and silicon solid sources molecular beam epitaxy (MBE). The difference between the use of substrate nitridation and AlN buffer layer is striking. The former resulted in peeling while the latter offered stable films of 4H-SiC when the thickness of AlN exceeded several tens of nm. X-Ray diffraction, atomic force microscope (AFM), Fourier transform infrared spectroscopy (FTIR) and photoluminescence (PL) were employed for the positive identification and characterization of the grown 4H-SiC.
Nanostructured Surface Morphology of ZnO Grown On A-plane GaN
Authors: Chen C. W. , Pan C. J. , Tsao F. C. , Liu Y. L. , Chi G. C. , Chang C. Y. , Hsueh T. H.
Published: September 2009

ZnO nanostructures were grown on a-plane GaN templates by chemical vapor deposition (CVD) without employing a catalyst. The a-plane GaN templates were pre-deposited on an r-plane sapphire substrate by metal-organic CVD. For the 800{degree sign}C-grown sample, a ZnO layer with a thickness of 0.1 μm was formed by grains with a size of about 40 nm. For the 900oC-grown sample, ZnO nanowires were grown in angles off-related to the GaN basal plane with a ZnO layer between wires and template formed by grains with a size of about 300 nm. X-ray diffraction spectra showed that the ZnO layer was grown with a heteroepitaxial relationship of (110)ZnO||(110)GaN. The growth mechanism on a-plane GaN was the Volmer-Weber mode and differed from the Stranski-Krastanow mode observed for growth on c-plane GaN. This difference results from the higher interfacial free-energy on the a-plane between ZnO and GaN than that on the c-plane orientation.
Suppression of Leakage Current of AlGaN/GaN HEMTs by HF Treatment
Authors: Choi Young-Hwan , Lim Jiyong , Kim Young-Shil , Kim Min-Ki , Seok Ogyun , Han Min-Koo
Published: September 2009

A new treatment using HF etchant for the suppression of leakage current of AlGaN/GaN High-Electron Mobility-Transistors (HEMTs) is proposed and verified. The proposed treatment is applied between ohmic contact and Schottky contact formation. The AlGaN/GaN HEMT treated by HF etchant suppresses the leakage current by 1-2 orders compared with that of conventional device without any sacrifice of forward DC characteristics. The decrease of leakage current may be due to the improved interface between Schottky metal and the treated buffer region.