bluuebunny/crossref_metadata_2025 huggingface dataset:
Organic Mask Removal Assessment for 32nm Fully Depleted SOI Technology with TiN-metal Gate on HfO2
Authors: Lachal Laurent , Chiaroni Julien , Lajoinie Emile , Louveau Olivier , Ritton Frederic , Lavios Pascal , Finet Jean-Marc , Biranceau Pierre , Arnoux André , Sauvagnargues Eric , Bailloux Olivier , Medico Gino , Tallaron Christiane , Humbert Franck , Rochat Névine , Martinez Eugenie
Published: October 2008

To pursue the device capability improvement, new materials have to be introduced in the gate stack. TiN metal gate on HfO2 is one of the solutions to replace existing gate. Thus, manufacturing processes, such as resist stripping, have to be adapted to these new materials as current processes can not be compatible. HfO2 compatibility was first studied by ellipsometry and ATR measurements, showing that Downstream type plasma (DS) with He-H2 or H2-N2 gas mix for dry processes, and Hydrozone ™ (HZ) for wet processes were fully compatible. Then TiN compatibility was investigated by WDXRF and XPS. Results indicate that the same processes as for HfO2 are compatible with TiN. Finally, effectiveness study proved that DS He-H2 or H2-N2 plasmas were similar to O2 plasma. To fully remove the polymers, HZ processes or derivatives have to be performed after plasmas.
Al2O3/ZrO2/Al2O3 High-k Dielectric Stacks on Germanium Substrates Grown by Atomic Layer Deposition at High and Low Temperatures
Authors: Bethge Ole , Abermann Stephan , Henkel Christoph , Bertagnolli Emmerich
Published: October 2008

Al2O3/ZrO2/Al2O3 high-k dielectric stacks have been grown on Germanium substrates by Atomic Layer Deposition (ALD) at temperatures of 150 oC and 200 {degree sign}C from trimethylaluminum (TMA)/water(H2O) and tetrakis-(dimethylamino)zirconium (Zr(NEt2)4)/H2O precursors. The stacks are investigated and compared in terms of Ge-substrate preparation by wet chemical etching (HCl, HF, HI and HBr) and their applicability in "metal oxide semiconductor" (MOS) devices. As a result, we show that in general the deposition of the stacks at lower temperatures (150 oC) leads to lower leakage currents in the range of about one order of magnitude and better interface C-V characteristics. The deposition on GeOx-free substrates obtained by HBr-etching yields to much higher breakdown voltage of the high-k oxide.
Comparison between Direct-Contact HfO2/Ge and HfO2/GeO2/Ge Stack Structures: Physical and Electrical Properties
Authors: Abe Yasuhiro , Miyata Noriyuki , Yasuda Tetsuji
Published: October 2008

We studied the physical and electrical properties of direct-contact HfO2/Ge and HfO2/GeO2/Ge structures, and demonstrated the superiority of a direct-contact HfO2/Ge structure in the leakage current and EOT. The HfO2/Ge structure was thermally stable up to 700åC, whereas the interface GeO2 layer was decomposed by 400åC-annealing for the HfO2/GeO2/Ge structure, and the decomposed products diffused into the HfO2 film. Good leakage-current characteristics were obtained in the HfO2/Ge structure with reduced Ge diffusion. Moreover, we found that the HfO2/Ge structure effectively thinned EOT. We identified the existence of an electrostatic interface dipole with a voltage of ~0.8 V (negative charges on HfO2 and positive on Ge sides). However, a dipole similar to that in the HfO2/Ge structure was induced for the HfO2/GeO2/Ge structure after 400åC-annealing. We therefore suggested that a direct-contact HfO2/Ge interface was formed due to thermal decomposition of the interfacial GeO2 layer caused by the annealing.
Identifying Performance-Critical Defects in the High-k/Metal Gate Stacks
Authors: Bersuker Gennadi , Hen D. , Price J. , Neugroschel A. , Tseng Hsing-Huang , Jammy Raj
Published: October 2008

We review results on the performance and reliability of the high-k/metal gate stack transistors and discuss physical properties of the defects affecting these characteristics. Analysis of the reported data identifies process-related defects in either the high-k film or interfacial SiO2 layer that are responsible for the observed degradation phenomena, thus opening the way for process improvements to effectively mitigate their effect.
Interface Properties Improvement of Ge/Al2O3 and Ge/GeO2/Al2O3 Gate Stacks using Molecular Beam Deposition
Authors: Bellenger Florence , Merckling Clement , Penaud Julien , Houssa Michel , Caymax Matty , Meuris Marc , De Meyer Kristin , Heyns Marc M.
Published: October 2008

Physical and electrical properties of Ge/Al2O3/Pt and Ge/GeO2/Al2O3/Pt gate stacks using molecular beam deposition were proposed in this work. In spite of a straight deposition of Al2O3 on Ge substrate, XPS and TEM analysis revealed the formation of a thin interfacial layer coming from the intermixing between Ge sub-oxides and the high-ĸ dielectric. Electrical measurements showed a high density of interface states (3x1012eV-1.cm-2) mainly due to the presence of this interlayer. Performing a FGA in 10% H2/90% N2 on such structures leads to a significant reduction of DIT and leakage current density. Moreover, growing an in-situ GeO2 layer on Ge before high-ĸ deposition allowed us to reduce the interface states and to reach a very low DIT-value of 1~2x1011eV-1.cm-2 for Ge/GeO2/Al2O3 gate stacks after FGA, providing the efficient passivation of Ge/GeO2 interface. It has also been demonstrated that Al2O3 was a good capping layer, preventing from Ge/GeO2 interfacial degradation under high temperature treatment.
Physical Characterization of the Metal/High-k Layer Interaction upon Annealing
Authors: Conard Thierry , Franquet Alexis , Vandervorst Wifried , Reading Michael , Van den Berg Jaap , Van Elschocht Sven , Schram Tom , Adelmann Christoph , De Gendt Stefan
Published: October 2008

The replacement of poly-silicon by metallic compounds in the gate stack leads to the search of metals with suitable work function. However, it is observed that thermal budget has a large influence on the effective work functions of several metals. In this paper, we investigated the possible modification of the chemical states by physical analysis techniques (XPS, XRR, MEIS, TOF-SIMS) by studying the chemistry of the high-k oxide/metal interface. We show that in the case of the TiN/TaN/HfO2/SiO2/Si stack, several modifications occur upon 1000oC N2 annealing: Increase of the nitrogen content of the TaN, interdiffusion of the Ti and TaN, and formation of Ta2O5 at the TaN/HfO2 interface.
Effects of Low Temperature O2 Treatment on the Electrical Characteristics of Amorphous LaAlO3 Films by Atomic Layer Deposition
Authors: Liu Yiqun , Kim Hoon , Wang Jun-Jieh , Li Huazhi , Gordon Roy G.
Published: October 2008

Amorphous LaAlO3 films were deposited on hydrogen-terminated silicon substrates by atomic layer deposition (ALD) at 300 oC. The precursors were lanthanum tris(N,N'-diisopropylformamidinate), trimethylaluminum (TMA) and water. Capacitance-voltage measurements made on ALD MoN/LaAlO3/Si stacks showed humps especially at low frequencies. They were effectively removed by O2 treatment at 300 o C without affecting the dielectric constant (κ~15). The O2 treatment can be carried out either after deposition of a LaAlO3 film, or after each ALD cycle. The O2 treatment also lowered the leakage current from 80 mA cm-2 to 1 mA cm-2 for EOT = 1.3 nm. This indicates that oxygen vacancies are the main defects in as-deposited LaAlO3. Oxygen treated LaAlO3 is one of the best candidates for future high-κ dielectric material due to its low leakage, low defect density and abrupt interface with silicon.
Impact of High Pressure O2 Annealing on Amorphous LaLuO3/Ge MIS Capacitors
Authors: Tabata Toshiyuki , Lee Choong Hyun , Kita Koji , Toriumi Akira
Published: October 2008

Amorphous LaLuO3/Ge MIS capacitors were fabricated and dielectric properties were investigated. LaLuO3 has a high dielectric constant (k~23) and an amorphous structure after annealed at 600oC. Its energy band-gap is reasonably large (5.5~5.8 eV). The C-V characteristics annealed in a small amount of O2 ambient were quite good and showed a high saturated capacitance thanks to a negligible interface layer formation. Furthermore, it has been demonstrated that the hysteresis in C-V curves was reduced by high pressure O2 annealing. Although an optimization of the trade-off between EOT increase and hysteresis reduction will be the next challenge for LaLuO3 on Ge, the high pressure O2 annealing will make a strong combination with amorphous LaLuO3.
Capacitance-Voltage (CV) Characterization of GaAs-Oxide Interfaces
Authors: Brammertz Guy , Lin H.C. , Martens Koen , Mercier David , Merckling Clement , Penaud Julien , Adelmann Christoph , Sioncke Sonja , Wang Wei-E , Caymax Matty , Meuris Marc , Heyns Marc M.
Published: October 2008

We will shortly review the basic physics of charge carrier trapping and emission from trapping states within the bandgap of a semiconductor in order to show that high temperature CV-measurements are necessary for GaAs MOS characterization. The mid-gap trapping states in GaAs have characteristic emission times of the order of 1000 seconds, which makes them extremely complicated to measure at room temperature. Higher substrate temperatures fasten these emission times, which makes measurements of the mid-gap traps possible with standard CV-measurements. CV-characterizations of GaAs/Al2O3, GaAs/Gd2O3, GaAs/HfO2 and In0.15Ga0.85As/Al2O3 interfaces show the existence of four interface state peaks, independent of the gate oxide deposited: a hole trap peak close to the valence band, a hole trap peak close to mid-gap energies, an electron trap peak close to mid-gap energies and an electron trap peak close to the conduction band.
Modeling the Effects of the Cathode Micro-Porous Layer on the Performance of a PEM Fuel Cell
Authors: Wang Xuhai , Nguyen Trung V.
Published: October 2008

In this study, a model was developed to evaluate the role of the micro-porous layer (MPL) and the effects of its properties on the liquid water saturation levels in the cathode porous media and the performance of a proton exchange membrane (PEM) fuel cell. The results validated that the fuel cell performance was improved by adding an MPL between the macro-porous gas diffusion layer (GDL) and the catalyst layer (CL) in the cathode side. The MPL, due to its high hydrophobicity, increases the liquid water pressure in the cathode to the levels much higher than those in the anode resulting in an increased back-transport rate of liquid water from the cathode to the anode. The more hydrophobic the MPL is, the higher liquid pressure increases, and, consequently, the higher driving force is created across the membrane to drive water from the cathode to the anode.
Lattice-Boltzmann Simulations of Multiphase Flows in PEM Fuel Cell GDLs and Micro-channels
Authors: Mukherjee Shiladitya , Cole James Vernon , Jain Kunal , Gidwani Ashok
Published: October 2008

The lattice Boltzmann (LB) method is employed to simulate single and multiphase flow through porous gas-diffusion-layer (GDL) of a Proton Exchange Membrane Fuel Cell (PEMFC). The porous layer is composed of layers of fibers. The structure is reconstructed numerically and validated by other published data on porosity and pore-size distributions. The in-plane gas-permeability is greater than the through-plane values and has greater sensitivity to fiber orientations. The permeability decreases as the GDL is compressed. When liquid is introduced, multiple droplets emerge from the other side of the GDL through surface pores. On hydrophobic GDL, the liquid advancing inside the GDL is in the form of several interconnected streams leading to surface openings. As the hydrophobicity is increased the liquid break-through occurs at lower saturation.
A-3D-Modeling and Experimental Validation of a High Temperature PBI based PEMFC
Authors: Ubong Etim U. , Shi Zhongying , Wang Xia
Published: October 2008

This paper is to investigate the performance of a high temperature proton exchange membrane fuel cell. Both experimental work and numerical simulation are conducted. The high temperature proton exchange membrane (HT-PEM) is based on polybenzimidazole (PBI) doped with phosphoric acid. A single cell with triple serpentine flow channels was operated at steady state at various levels of temperature, pressure and air stoichiometry. A three dimensional model based on COMSOL Multiphysics software was used to simulate the cell performance and polarization curves were used to validate the experimental values. The theoretical model accurately predicts the experimental results. A sound knowledge of the impact of various variables, at various levels of the cell operation is necessary for unraveling the parametric influence and can prove extremely useful for optimizing the cell operation.
Bimetallic Palladium-Base Metal Nanoparticle Oxygen Reduction Electrocatalysts
Authors: Wang Xiaoping , Kariuki Nancy , Niyogi Suhas , Smith Matt C. , Myers Deborah J. , Hofmann Timo , Zhang Yufeng , Bär Marcus , Heske Clemens
Published: October 2008

Bimetallic palladium-base metal nanoparticle catalysts are being investigated as alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells. We report here our results on the palladium-copper, palladium-nickel, and palladium-iron systems. We are studying the effect of synthetic procedure, palladium to base metal ratio, heat treatment temperature, and heat treatment atmosphere on the ORR activity as well as on the valence band structure of these systems. Palladium-copper nanoparticle catalysts synthesized by the colloidal technique with a composition of 75 mol% copper are the most active investigated thus far. This catalyst shows an ORR activity which is approximately 75% that of platinum (per gram of platinum-group metal). The corresponding valence band structure is strongly modified compared to that of Pd and Cu alone and resembles that of Pt, which is believed to be the reason for its superior performance among the other investigated platinum-free alternatives.
Template Synthesis of Mesoporous Ru- and RuSe-based Catalysts for Proton Exchange Membrane Fuel Cells
Authors: Garsuch Arnd , Michaud Xavier , O'Neill Catherine , Li Ping , Dahn Jeff
Published: October 2008

Mesoporous Ru- and RuSe-based catalysts for proton exchange membrane fuel cells were prepared using an amorphous silica gel as a template. Impregnation with sucrose (carbon source), ruthenium(III)-chloride and selenium dioxide was employed to infiltrate the catalyst precursors in the mesopores of the template. After carbonization in argon and reduction in hydrogen atmosphere, the catalyst materials were liberated by dissolving the template framework with hydrofluoric acid. Nitrogen adsorption, X-ray diffraction and transmission electron microscopy were used in order to investigate the structural properties of the prepared catalyst samples. The catalytic activity towards the reduction of oxygen was tested using the rotating-ring-disk-electrode technique. It was observed that RuSe-containing carbon samples possess a higher catalytic activity for oxygen reduction than Ru-containing carbon samples.
Synthesis of Electrocatalytic Carbides
Authors: Rees Eric J. , Essaki Kenji , Brady Connor , Burstein G. T.
Published: October 2008

Microwave-induction heating has been used to synthesise tungsten and tantalum carbides, from precursor mixtures of the metal oxides and graphitic carbon. The electrocatalytic tungsten carbide is considered to be a possible alternative to platinum-based materials, on fuel cell anodes. It is shown that the phase composition of the products of microwave heating is similar to that produced by conventional furnace heating. However the more rapid microwave technique leads to the production of smaller nanoparticles, and concomitantly higher electrocatalytic activity. A number of admixants have been investigated for the carbide synthesis, including iron, nickel, potassium chloride, and manganese. These additives had various significant influences on the syntheses. When an admixant exhibited an effect on the furnace-synthesized carbide products, a similar effect was found following microwave-syntheses. In particular, KCl promoted the reduction of tungsten oxide to the metal and carbide phases, and nickel led to grain coarsening of the product.
Analyses of Oxygen Reduction Reaction at Pt-Based Electrocatalysts
Authors: Watanabe Masahiro , Wakisaka Mitsuru , Yano Hiroshi , Uchida H.
Published: October 2008

We first reported that enhanced activities in oxygen reduction reaction (ORR) are obtained at Pt skin-layer formed on the surfaces of alloyed Pt with non-precious metals such as Fe, Co, Ni, etc. and also that a positive core level shift in Pt4f7/2 was observed at the Pt skins, due to the modification of the Pt electronic structures. It was also found that such an enhancement is induced without changing the activation energy but the corresponding frequency factor value Z from that of pure Pt. The enhancement mechanism is discussed with the experimental data obtained by using electrochemical-XPS system on adsorbed O-containing species at the Pt skin-layers in comparison with pure Pt. The enhancement, or increased Z values, can be correlated to the increase in Oads formed by dissociative adsorption of O2, resulting in the enhanced activity.
The Chemistry of Fuel Cell Membrane Chemical Degradation
Authors: Coms Frank D.
Published: October 2008

A detailed thermochemical and kinetic analysis of PFSA ionomers and the reactive oxygen species formed in an operating fuel cell is reported. The analysis reveals that hydroxyl radical is the only oxygen species capable of abstracting a hydrogen atom from carboxylic acid intermediates, thereby propagating the PFSA main chain unzipping process. Two chemically specific, main chain scission mechanisms are proposed. The first involves formation of sulfonyl radicals under dry conditions and the second invokes the action of hydrogen atoms formed from hydrogen gas and hydroxyl radical. The thermochemical analysis provides a strong basis from which to rationalize the results from a broad range of in-situ and ex-situ fuel cell degradation studies.
Development Status of High-Temperature PBI-based Membrane Electrode Assemblies
Authors: Schmidt Thomas J. , Baurmeister Jochen
Published: October 2008

This paper describes some detailed information on the development and properties of high temperature polybenzimidazole based Celtec MEAs. Specifically, insight is given on anode behavior for the oxidation of CO containing reformates as well as on the development of corrosion stable cathodes.
One Dimensional Analysis of Subzero Start-Up for Polymer Electrolyte Fuel Cells
Authors: Chen Jixin , Wang Yun , Mukherjee Partha P.
Published: October 2008

This paper investigates interaction of the electrochemical kinetics, oxygen transport and solid water formation within polymer electrolyte fuel cell (PEFC) electrode during cold start. Followed by the analysis of Wang [1], we simplify the one-dimensional model of electrode processes, which allows solving the profiles of important quantities and directly relating the ice impact mechanisms to surface overpotential. The key parameters that govern these profiles are evaluated in the range of the relevant factors for a typical fuel cell. We also decouple the mechanisms of solid water impacts and compare their importance. This study is valuable for studying the characteristics of cold-start for PEFCs.
Water Movement During Freezing in a Polymer-Electrolyte-Membrane Fuel Cell
Authors: Balliet Ryan J. , Thomas-Alyea Karen E. , Newman John
Published: October 2008

A two-dimensional, transient model of the full-cell sandwich has been developed in order to predict water redistribution during the freezing process. Critical factors affecting the magnitude and direction of water movement are found to be the location of the cell within the stack, the permeability of the porous media of the cell, and the high thermal conductivity of the rib relative to the gas channel.
Electroosmotic Drag Coefficient of Proton Exchange Membrane as a Function of Relative Humidity
Authors: Braff William , Mittelsteadt Cortney K.
Published: October 2008

A novel technique for measuring the electroosmotic drag coefficient (EODC) of proton exchange membranes using a non flow through, or "dead-ended" hydrogen pump is presented here over a full range of non-condensing humidification. This experiment is conducted in situ under "fuel cell like" conditions, so the transport phenomena observed are directly applicable to an operating fuel cell without any extrapolation. Experiments were conducted on 50 μm and 500 μm Nafion® 1100 EW membranes. The measurements consistently demonstrated that for low to medium humidification, the EODC observed is below unity. This observation confirms that the vehicular proton transport mechanism cannot be the sole source of proton transport at low relative humidity, leading one to conclude that the Grotthus "hopping" mechanism is active even at low levels of humidification.
Transients of Water Distribution and Transport in PEFCs
Authors: Hussaini Irfan , Wang Chao-Yang
Published: October 2008

Response of PEM fuel cells to a step-change in load is investigated experimentally in this work. Voltage undershoot, a characteristic feature of such transient response, is shown to be due to transients of water distribution in membrane phase occurring at sub-second time scales. Use of humidified reactants as a means to control magnitude of voltage undershoot has been demonstrated. Constant stoichiometry operation under certain current-step conditions is found to result in reactant starvation, potentially leading to cell shut down. Further, response under step decrease in current density has been explored to determine existence of hysteresis. Under sufficiently humidified conditions, response under forward and reverse step changes are found to be symmetric, but under low RH conditions, voltage undershoot is found to be twice as large as the overshoot.
Fast test for the durability of PEM fuel cell catalysts
Authors: Shao Yuyan , Kou Rong , Wang Jun , Kwak Ja Hun , Viswanathan Vish , Wang Yong , Liu Jun , Lin Yuehe
Published: October 2008

ETek Pt/C catalyst was used as standard materials to develop a new test protocol for fast screening durable catalyst for PEM fuel cells. Potential step (Pstep) method with the upper potential of 1.4V and the potential-static (Pstat) holding at 1.4 V or 1.2V are used to degrade the catalyst. The degradation in the electrochemical surface area (ESA) for Pt/C under Pstep conditions is greatly accelerated as compared with that under other conditions. The durability of Pt/Vulcan and Pt/CNT were studied using the new protocol with the electrochemical stressing of Pstep(1.4V/0.6V), which provided the same results as those tested using conventional protocols: Pt/CNT is more durable than Pt/Vulcan. This confirms that the new protocol works well in screening catalyst in terms of durability. The new protocol can differentiate the durability of electrocatalysts by shortening the test time to several hours.
A Comparative Study of Co-PPy-MWCNTs Prepared differently as a Non-noble Catalyst for Fuel Cells
Authors: Li Haixia , Li Hengyi , Cheng Xuan
Published: October 2008

The cobalt-polypyrrole (Co-PPy) composites adsorbed on the multiwall-carbon nanotubes (MWCNTs) were prepared by three methods. The structural, chemical and electrochemical properties of Co-PPy-MWCNTs samples were characterized by using XRD, SEM/EDX, element analysis, TG, FTIR, XPS, and cyclic voltammetry (CV). The results revealed that the Co-PPy was deposited on the MWCNTs surface and the ratios of Co/N for the three samples prepared differently varied. The conductivities and electrochemical catalytic activities of Co-PPy-MWCNTs samples were also affected by the different interactions between Co and PPy presented when using three preparation methods.
Characterization of Ag-Mn-base Nanostructured Catalysts
Authors: Kostowskyj Michael A. , Kirk Donald W. , Thorpe Steven J.
Published: October 2008

This work investigated the synthesis and characterization of a Ag-Mn bifunctional catalyst for the oxygen reduction reaction at the cathode of a fuel cell system. A template-base electroless deposition method was developed to deposit Ag as a model system and then to co-deposit Ag-Mn and synthesize the nanowire catalysts. Scanning electron microscopy showed that Mn altered the growth mechanism of the pure Ag deposit. Scanning transmission electron microscopy confirmed that small amounts of Mn co-deposited with Ag using the novel procedure developed. Current work is ongoing to determine the chemical form and amount of Mn present in the nanowires.
Enhancing the Performance of Non-noble Metal Catalysts for the Reduction of O2 in PEM Fuel Cells: is the Adsorption of Iron the Limiting Factor for Increasing the Site Density of the Catalysts?
Authors: Herranz Juan , Lefe`vre Michel , Dodelet Jean-Pol
Published: October 2008

The adsorption of iron II acetate over two microporous carbon blacks of different surface properties was studied in order to determine if this factor limits the activity of Fe/N/C catalysts for ORR made with these carbon supports. Whereas one of these carbons only had oxygen-derived functionalities over its surface, the other one contained both oxygen and nitrogen bearing functionalities. Their points of zero charge (PZC) were first determined to be 3.9 and 8.8, respectively. Adsorption curves showing the evolution of the metallic uptake with the pH revealed that both carbon supports are able to adsorb 100% of the positive Fe ions in solution at pH>4, and this up to 0.8 wt% Fe. Therefore, the adsorption of iron is not the factor responsible for the limited site density of Fe/N/C catalysts having a Fe content {less than or equal to} 0.8 wt% loaded either by adsorption or by wet-impregnation of the carbon supports.
Platinum-free Anionic Fuel Cells for Automotive Applications
Authors: Tanaka Hirohisa , Asazawa Koichiro , Sakamoto Tomokazu , Kato Takeshi , Kai Mitsuru , Yamaguchi Susumu , Yamada Koji , Fujikawa Hirotoshi
Published: October 2008

In order to overcome the barriers against the FCVs, a platinum-free anionic fuel cell has been developed. The platinum-free fuel cell, by using liquid hydrazine hydrate (N2H4·H2O) for fuel, comprises cobalt or nickel for the anode and cobalt for the cathode, can demonstrate a high performance, and achieves zero CO2 emissions. For vehicle application, a detoxification method, which repeatedly fixes and releases hydrazine hydrate, has also been developed. In this paper, the fuel cell performance using nickel, cobalt and platinum as an anode catalyst was compared. It was shown clearly that nickel and cobalt have the superior catalytic activity to platinum. The influence of fuel concentration and KOH addition is also discussed. This new fuel cell technology can conquer the conventional subject, and is expected to spread widely. Moreover, this technology was exhibited and attracted attention in Environmental Showcase of G8 Hokkaido Toyako Summit held in July, 2008.
Galvanostatic Pulse Plating of PtRu Nanoparticles for Direct Methanol Fuel Cells
Authors: Hsieh Yu-Chi , Lu Yung-Jean , Wu Pu-Wei , Chang Yun-Min , Chiu Yu-Fan
Published: October 2008

A galvanostatic pulse electrodeposition technique of preparing nanoparticulate PtRu electrocatalyst for direct methanol fuel cells has been demonstrated. After extensive cyclic voltammetric analysis, we determined the optimized parameters for the methanol oxidation to be current on-time on 50 ms, current off-time of 400 ms, current density of 50 mA/cm2, and total charge of 8.0 C/cm2. In addition, the catalyst loading was measured at 68 μg/cm2, resulting in a mass activity of 213 mA/Pt.mg. The composition for the nanoparticles was confirmed as Pt65Ru35. High-magnification images on the specimen indicated fine particles in 4-20 nm with uniform distributions.
Improved Durability of Iron Promoted Non-Precious Metal Catalysts for Hydrogen Generation through Bio-ethanol Reforming
Authors: Huang Lihong , Xie Jian , Chen Rongrong , Chu Deryn , Hsu Andew
Published: October 2008

Nickel-based catalysts with iron promotion were prepared by impregnation, tested in auto-thermal reforming (ATR) of ethanol for hydrogen production. The reaction results show a remarkable improved durability in catalytic activity as well as selectivity to hydrogen in ATR is obtained: Over the 10 wt.% iron-loading nickel catalyst, conversion of ethanol at 99.61 % and selectivity of hydrogen around 115 % are kept at 600 C during a 30-hour test, while that of iron-free sample decreases sharply from 85.10 % to 19.71 % on hydrogen selectivity within a 26-hour test. The improved durability is attributed to the synergistic effect of the NiAl2O4-FeAl2O4 mixed crystals that are more resistant to sintering and oxidation in the oxidative atmosphere of ATR.
Thermal Behavior of an Air Cooled PEM Fuel Cell Stack
Authors: Tolj Ivan , Abdallah Mayssa , Barbir Frano
Published: October 2008

Thermal behavior of a 1 kW, air cooled PEM fuel cell stack was analyzed and simulated. Operation of the stack under various scenarios was simulated such as start-up from room temperature, steady state at full and half load and sudden changes of load (from full to half load and reverse), under constant or variable flow rate of the cooling air. In variable power load operation, the stack temperature is not constant. One interesting finding of this analysis is that liquid water occurs at the outlet whenever the stack temperature falls below 60{degree sign}C, although the nominal operating conditions were selected such that there is no liquid water at the outlet at steady state operation. The results also indicate that this particular stack has insufficient heat exchange area with cooling air resulting in relatively large cooling air flow rates and low temperatures.
Investigation of Stress and Water Distribution in Membrane Electrode Assembly (MEA) During Fuel Cell Operation
Authors: Kusoglu Ahmet , Karlsson Anette , Santare Michael , Cleghorn Simon , Johnson William B.
Published: October 2008

Investigation into the durability of fuel cells is a challenging issue due to the large number of parameters affecting membrane electrode assembly (MEA) integrity. The mechanical stresses induced in the membrane due to swelling associated with water absorption play an important role in the long-term failure of the MEA. Thus, the stresses and the water distribution in the MEA are coupled. To better understand the relationship between mechanical stresses and water absorption, we introduce a numerical model to simultaneously determine the swelling-induced stresses and the water distribution in the MEA under various cell operating conditions. Preliminary results suggest that open-circuit voltage (OCV) operations lead to the most severe environment for the mechanical response, whereas under current load, the stresses and the permanent deformation are on average lower and localized at the cathode side of the MEA. The results suggest that the mechanical behavior of the MEA must be taken into account in the investigations of MEA degradation to establish a complete understanding on the failure mechanisms and durability.
Nonisothermal Through-Plane Transport Model of PEMFC with Local VLE Assumption
Authors: Kawase Motoaki , Inagaki Tatsuya , Miura Kouichi
Published: October 2008

A nonisothermal model of the proton exchange membrane (PEM) fuel cell is developed with taking the through-plane heat and water transport into consideration. Local vapor-liquid equilibrium of water in the gas diffusion layer (GDL) is assumed. The steam pressure is determined only by temperature in the presence of condensed water. Only 1 oC temperature rise in GDL creates a steam flux corresponding to water generation at the current density of 0.74 A/cm2. Using stacked four PEM sheets, between which 20 μm thick thermocouples were inserted, the PEM temperature was measured in a cell having carbon paper GDLs, operated at 80 oC with hydrogen and oxygen supplied. About 1 oC rise in the PEM temperature was observed at a current density of 0.6 A/cm2. The effective thermal conductivity of the GDL was estimated from the experimental results. The temperature rise calculated by the one-dimensional numerical simulation well represents the experimental results.
Carbon-supported Pd-Pt Alloy Nanoparticles for Methanol Tolerant Oxygen Reduction
Authors: Wang Wenming M. , Li Zhilin L. , Zou Zhiqing , Yang Hui , Feng Songlin
Published: October 2008

We report one-step synthesis of Pd-rich carbon-supported Pd-Pt alloy electrocatalysts of different Pd/Pt atomic ratios with and without the addition of trisodium citrate as the complexing agent and stabilizer. An activity comparison of the oxygen reduction reaction (ORR) on the Pd-Pt/C catalysts with the same fcc structure and a similar particle size has been investigated. The Pd3Pt1/C catalyst exhibits the highest ORR activity among all the alloy catalysts prepared with the addition of trisodium citrate and a comparative ORR activity with the Pt/C. However, the Pd3Pt1/C catalyst prepared without the addition of trisodium citrate shows an enhanced ORR activity in comparison with the Pt/C. All the bimetallic catalysts exhibited much higher methanol tolerance during the ORR than the Pt/C catalyst. The high methanol tolerance of the Pd-Pt/C alloy catalysts during the ORR may be ascribed to a composition effect and to the formation of Pd-based alloys.
Pt-decorated Au Nanoparticles: Highly Active Catalyst for Formic Acid Oxidation
Authors: Noel Kristian , Wang Xin
Published: October 2008

Highly active Pt-decorated Au nanoparticles on carbon support was successfully synthesized based on successive reduction strategy. The electrocatalytic activity of this decorated structure toward formic acid oxidation unexpectedly increases despite the low amount of Pt being used. The enhancement is attributed to the less Pt ensemble sites that the decorated structure possesses (ensemble effect) and the increase in the Pt atom reactivity on Au nanocrystal (electronic effect).
The Impact of Trace Carbon Monoxide / Toluene Mixtures on PEMFC Performance
Authors: Dorn Susanne , Bender Guido , Bethune Keith , Angelo Michael , Rocheleau Rick
Published: October 2008

The impact of fuel impurities toluene (C7H8) and carbon monoxide (CO) on the performance of polymer electrolyte membrane fuel cells (PEMFCs) was investigated. Single and mixed impurities were injected into the fuel cell via the anode feed stream. Experiments were accompanied by gas chromatography analysis to determine the conversion and reaction processes occurring during contaminant exposure. Impurity injections of 2 and 20 ppm C7H8 caused an insignificant overpotential change of 2 and 8 mV respectively. An almost complete conversion of C7H8 to methylcyclohexane (C7H14) was observed. Impurity injections of 2 ppm CO caused a significant overpotential change of 247 mV. At steady state conditions more than 60% of the injected CO was converted to CO2 in the fuel cell. When the impurities were injected into the anode feed stream as a mixture the overpotential change was 100 mV greater than the sum of the overpotential changes the single impurities caused .Hydrogenation of C7H8 to C7H14 was observed but in contrast to the single C7H8 impurity experiment it stopped when a certain CO coverage was reached. The strong adsorption of CO caused a competition between the hydrogen reduction reaction and the hydrogenation of C7H8 for the available reaction sites.
A New Ionomer Based on Novel PolyPOM Materials
Authors: Herring Andrew M. , Horan James L, , Kuo Mei-Chen , Dec Steven F. , Frey Matthew H. , Genupur Anitha , Ren Lucy , Yandrasits Mike A. , Hamrock Stephen J.
Published: October 2008

The heteropoly acids (HPAs) are a class of inorganic oxides that have some of the highest solid state proton conductivities known at room temperature. At elevated temperatures proton diffusion coefficients in these crystalline materials increase, but, not all the protons are mobile resulting in a decrease of the observed proton conductivity. The proton conductivity in these materials is heavily dependant on the hydration state of the HPA. In order to develop new PEMs based on the HPAs for elevated temperature, dry operation, it will be necessary to both immobilize the HPA and ensure that all of the protons are mobile all of the time. If both these objectives can be obtained a new class of PEMs will be developed that could facilitate the use of PEM fuel cells in automotive applications. We have created a new class of PEM by polymerizing HPA monomers with appropriate co-monomers to produce films with unique proton conducting properties.
Water Uptake and Conductivity of Cross-linked SPEEK Membranes
Authors: Linkous Clovis A. , Rhoden Stephen L. , Linkous William G. , Pearman Benjamin P. , Mohajeri Nahid
Published: October 2008

Water uptake is an important attribute of all membrane electrolytes, as it is related to mechanical strength, creep, and dimensional stability. Thus some means of controlling water uptake by a hydrophilic sulfonic acid polymer is desirable. This is particularly important for SPEEK, which at high degrees of sulfonation (i.e., low equivalent weight) has demonstrated substantial water uptake, on order of 10's of water molecules per sulfonic acid unit. We have attempted to control water uptake in SPEEK membranes by performing cross-linking reactions on the finished polymer. Water-soluble SPEEK (85% degree of sulfonation, or 418 g/eq EW), 1,4-benzenedimethanol, and various transition metal chloride catalysts were cast together to form a membrane that was heated at 200 oC for 10 min. The resulting insoluble membrane was shown to have conductivity comparable to an uncross-linked SPEEK membrane over a range of relative humidities.
Degradation of Pt Catalyst Layer in PEFCs During Load Cycling under Pressurized Condition
Authors: Asano Koichi , Mugikura Yoshiriho , Watanabe Takao
Published: October 2008

The degradation of the Pt catalyst layer of polymer electrolyte fuel cells was studied for pressurized conditions. The cell performance loss under pressurized conditions was observed to be smaller than that under normal pressure conditions. A clear loss of Pt was observed at the cathode at the point of contact with the electrolyte and a Pt band was conspicuously formed in the membrane under pressurized conditions. Thus, a serious degradation was found to occur in the Pt catalyst layer under pressurized conditions.
Investigation of the Behavior of Liquid Water for Its Transport Process into the GDL
Authors: Yoneda Masakazu , Takimoto Masato , Ejiri Eiji , Koshizuka Sheiichi
Published: October 2008

The behavior of liquid water transport process into the GDL is investigated by direct numerical simulation as well as experiment using X-ray computed tomography. As a result, it is possible that liquid water adjacent to the MPL is transported as mist which can pass through the small-pores by Brownian motion. Furthermore, the effect of the MPL on a PEFC performance under both dry-out and flooding condition could be elucidated by a hypothesis about the water transport mechanism involving the Kelvin effect inside the hydrophobic mesopore inside it.
Operating Characteristics 5W Class DMFC Stack for Mobile Devices
Authors: Park Young-Chul , Peck DongHyun , Jung Doo-Hwan , Kim SangKyung , Lim Seong-Yop , Lee Bong-Do , Jang Jae-Hyuk , Lee Dokyol
Published: October 2008

We have developed very small direct methanol fuel cell stack for mobile devices. The stack was designed with the total size of 48 mm × 50 mm × 17 mm (volume: ~ 40.8 cc) and it consisted of 6 cells and each cell has an active area of 13.7 cm2. The maximum power output of the stack is 7.63W (1.81V @ 4.22A) and the nominal power output of the stack was 5.49W (2.4V @ 2.29A) at 2.4V (0.4 V/cell). In this work, we studied starting characteristics of 5W class small DMFC stack and effects of methanol/air stoichiometry on the stack performance at constant current.
Effect of Potential on Sulfur-Poisoning of Pt/C Catalyst
Authors: Imamura Daichi
Published: October 2008

The Pt/C catalyst of polymer electrolyte membrane fuel cell (PEMFC) was poisoned by 5 ppm of hydrogen sulfide for 5 hours at potentials of 0V, 0.3V, 0.6V and 0.9V vs. RHE, and the catalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) analysis. Only diffraction peaks of Pt, carbon and ionomer were observed in all samples, and the crystallite size of Pt was about the same after poisoning. In the XPS and XAFS analyses, accumulation of sulfur species on Pt/C catalyst and oxidation of Pt were observed in the samples poisoned at 0.3V and 0.6V.
Evaluation of the Microstructure and the Elementary Steps from the Impedance of DMFC Anode
Authors: Fukunaga Hiroshi , Kabaya Y. , Tatatsuka T , Yamada K.
Published: October 2008

The microstructure and the elementary steps of the direct methanol fuel cell (DMFC) anode are investigated using an advanced equivalent circuit. A serial circuit of two parallel circuits of resistance and capacitance, which is in parallel with a Faradaic impedance, is introduced to simulate the anodic reaction. Three processes with different anode polarization dependencies are clearly reproduced by the simulation using this equivalent circuit, and they are considered to be interfacial resistance representing the transport of ions through the electrode pores, electrooxidation reaction of the anode, and another process parallel to the reaction intermediate. The anode polarization dependence of the interfacial resistance and the change in the distortion was better explained by the modified equivalent circuit than by the conventional equivalent circuit using a constant phase element (CPE) with unfixed exponent. The relationship of the interfacial resistance with catalyst loading or electrode thickness was clarified using this equivalent circuit.
MEA Fabrication and Fuel Cell Performance of Sulfonated Poly(Arylene Ether) with Cross-linkable End Group
Authors: Lee Kwan Soo , Kim Yu Seung , Pivovar Bryan , Lee Jae-Suk
Published: October 2008

Partially fluorinated poly(arylene ether) copolymer having reactive functional group are used to fabricate the MEA to improve the interfacial adhesion between membrane and electrode. The optimum MEA processing procedure was studied using different hot pressing temperature and crosslinking. Good interfacial adhesion between hydrocarbon membrane and Nafion bonded electrode produced excellent fuel cell performance which was comparable to the MEA using Nafion 212.
Improvement of Anode Oxidation Reaction of a Fuel Cell using Ammonium Formate with Pt-Pd Catalysts
Authors: Aoki Hidemitsu , Nitta Tomohiro , Kuwabata Susumu , Kimura Chiharu , Sugino Takashi
Published: October 2008

We attempt to develop high-performance and safe fuel cells using ammonium formate (HCOONH4) as a solid (powder) fuel. The ammonium formate with high deliquescence can be easily supplied as a fuel through a porous film in high humidity. This solid fuel has the potential to realize safe portability compared with liquid fuels such as methanol from the viewpoint of toxicity and flammability. We have found that oxidation of ammonium formate can be improved by the addition of Palladium (Pd) catalysts to Pt catalysts. There is a high potential for the use of ammonium formate as a solid (powder) fuel for polymer electrolyte membrane (PEM) fuel cells.
Deposition of Pt Nanoparticles on Oxygen Plasma Treated Carbon Nanotubes by Atomic Layer Deposition
Authors: Hsueh Yang-Chih , Hu Chia-Te , Wang Chih-Chieh , Liu Chueh , Perng Tsong-Pyng
Published: October 2008

Platinum nanoparticles were formed on oxygen plasma treated carbon nanotubes by atomic layer deposition (ALD). The treatment time of oxygen plasma generated by a microwave plasma enhanced chemical deposition system varied at 5 s to 20 s under a power of 600 W. The reaction cycle number was controlled at 50-125 and the length of pulse time for Pt precursor, O2 and N2 were set at 1 s, 5 s and 20 s, respectively. It was observed that formation of uniform and well distributed Pt nanoparticles was achieved. Furthermore, the growth rate of Pt nanoparticles could be controlled by altering the reaction cycle number and oxygen plasma treatment time. X-ray photoelectron spectroscopic analysis indicated that oxygen plasma could graft oxygen-containing functional groups to the CNTs surface, to act as the nucleation sites for growth of Pt nanoparticles.
Local Temperature in the MEA and Performance in the PEMFC
Authors: Ko Dongsoo , Moon Cheoreon , Yang Jangsik , Jeong Jihwan , Choi Gyungmim , Kim Duckjool
Published: October 2008

In this study, local temperature in a membrane electrode assembly (MEA) and performance of a proton exchange membrane fuel cell (PEMFC) are investigated by numerical studies and experiments. The performance of a lab-scale PEMFC is measured with the load changes for three different cell temperatures (40°, 50°, and 60°) at a relative humidity of 100%. In order to observe the local temperature in the MEA and analyze the performance of the PEMFC, the numerical studies using the CFD module of STAR-CD, which are based on experimental data, are conducted. The results show that the cell condition at a cell temperature of 50° gives the highest performance and the maximum temperature in the MEA dramatically increases with increasing cell temperature and current density. These results might be used to design the PEMFC system and channel flow-field.
Sulfur Dioxide Contamination in PEMFCs: Degradation and Recovery of Performance
Authors: Zhai Yunfeng , Bender Guido , Dorn Susanne , Angelo Michael , Bethune Keith , Rocheleau Rick
Published: October 2008

In this paper, we report on the effects of 1, 2, and 10 ppm SO2 injected into the cathode feed stream of a PEMFC that was operated at a constant current of 0.6 A/cm2. All experiments showed significant performance degradation before concentration dependent steady state poisoning conditions were reached. The poisoning process was identified as a 2-step process, indicated by an inflection of the voltage degradation. Cell voltage recovery by neat H2/air operation was incomplete, but independent on contaminant concentration. Subsequent CV stripping indicated that sulfur species remained on the catalyst surface during the self-induced recovery. The CV scans also showed features which developed due to SO2 exposure that were reported for Pt/Pt systems in sulfuric acid solution.
The Effect of Concentration on the Galvanostatic Pulse Deposition of PtRu
Authors: Chiu Yu-Fan , Chang Li-Chung , Wu Pu-Wei , Hsieh Yu-Chi
Published: October 2008

Fabrication of PtRu nanoparticles was conducted by a galvanostatic pulse electrodeposition technique. We studied various deposition parameters including current on-time and off-time, current density, as well as concentrations for the Pt and Ru precursors in the plating bath in order to determine the optimized process condition for the highest methanol oxidation ability. Cyclic voltammetric profiles were obtained in electrolytes of 0.5 M H2SO4, and mixture of 0.5 M H2SO4 and 1.0 M CH3OH to determine characteristics in the hydrogen absorption/desorption and peak currents in the anodic/cathodic scans. We observed that a shorter current off-time resulted in better catalytic abilities when the Pt precursor concentration was increased. Partial dissolution of Ru in the as-deposited PtRu nanoparticles during the current off-time might be responsible.