bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionic Liquid Composite Polymer Electrolyte Membranes for the Unhumidified Intermediate Temperature Fuel Cell
Authors: Lee Je Seung , Nohira Toshiyuki , Hagiwara R.
Published: November 2006

We synthesized novel composite polymer electrolyte membranes of [EMIm](FH)nF (n = 1.3 and 2.3) ionic liquids and measured their physical and electrochemical properties. The ionic conductivities of composite membrane (P(VdF-co-HFP):s-DFBP-HFDP: [EMIm](FH)2.3F = 1:0.3:1.75 in weight ratio) were up to 11.3 and 34.7 mS cm-1 at 25 and 130{degree sign}C, respectively. We also studied the fuel cell performance using these composite membranes at intermediate temperature without humidification. The OCV observed for the cell using [EMIm](FH)2.3F composite electrolyte was ~1.0 V at 130{degree sign}C and stable during the measurement conducted for over 5 h. The maximum power density of 14.8 mW cm-2 was observed at 37.2 mA cm-2 at 120{degree sign}C. From the high thermal stability and high ionic conductivity, the fluorohydrogenate ionic liquid composite membranes seem to be promising candidate electrolytes for unhumidified PEMFCs at intermediate temperature.
Optimized DMFC Performance Comparison for Modified and Unmodified Nafion Membranes
Authors: Pintauro Peter N. , Lin Jun , Trivisonno Angelo , Wycisk Ryszard
Published: November 2006

The effects of methanol flow rate, methanol feed concentration, and membrane thickness on the performance of modified Nafion membranes (Nafion-FEP blends and stretched recast Nafion) and unmodified (commercial) Nafion 117 and 112 in a direct methanol fuel cell were examined. That flow rate which produced the highest power density at 0.4 V (60oC and 500 sccm air) for each membrane at a methanol feed concentration of 0.5, 1.0 and 3.0 M was identified. Experimental results indicate that flow rate adjustments, with or without cathode air backpressure, cannot be used to compensate for a high methanol crossover membrane (i.e., lower power densities were obtained for Nafion 112 and 117 due to their poor methanol barrier property). Under optimum flow rate conditions, stretched recast Nafion membranes worked best at all methanol feed concentrations, with a power density at 0.4 V ranging from 65-80 mW/cm2 (for ambient pressure air).
Proton Conductive Composite Materials with Co-continuous Phases Using Silane Functionalized and Crosslinkable PVDF Polymers
Authors: Lvov Serguei , Chung Mike , Komarneni Sridhar , Chalkova Elena
Published: November 2006

A new composite membrane material, based on the combination of inorganic proton conductors with a chain-end and side chain functionalized PVDF-based polymer has been developed. The approach involves synthesis of this polymer serving as an effective interfacial agent, to bind and to assemble the inorganic particles into a continuous medium, synthesis of inorganic particles, dispersion of inorganic particles and film casting followed by curing with a coupling agent to form crosslinking sites in 3-D polymer network. A composite membrane containing 60% of three-dimensional phase of zirconium hydrogen phosphate and 40% of PVDF fluoropolymer with silane terminal and side chain groups was fabricated. It demonstrates a high proton conductivity in water at elevated temperature, minimal dependence on the availability of free water, and bonding compatibility between the polymer and inorganic surfaces via inorganic crosslinkers.
Synthesis, Ionic Conductivity, and Thermal Properties of Hyperbranched Polymer with Phosphonic Acid Groups at Terminals for High Temperature Fuel Cell
Authors: Itoh Takahito , Aihara Yuichi
Published: November 2006

Two different molecular weight hyperbranched polymers (HBP-PA (L) and HBP-PA(H)) with phoshonic acid groups at the chain ends were successfully synthesized. The ionic conductivities of the low molecular weight HBP-PA(L) and the high molecular weight HBP-PA(H) were found to be 1.3x10-4 and 6.4x10-5 S/cm, respectively, at 135 oC under dry condition, and showed the VTF type temperature dependence. And also, both polymers were thermally stable up to 300 oC, and they had suitable thermal stability as an electrolyte in the polymer electrolyte fuel cell operating under dry condition.
Corrosion and ORR activity of Pt alloy electrocatalysts during voltammetric pretreatment
Authors: Strasser Peter , Hahn Nathan T. , Koh Shirlaine
Published: November 2006

This paper addresses the impact of voltammetric pretreatment of Pt alloy electrocatalyst for the oxygen reduction reaction on the emergence of stable voltammetric profiles and sustained activity characteristics in de-aerated and oxygen-saturated acidic electrolytes. The evolution of metal-corrosion related features during sweep voltammetry and cyclic voltammetry (CV) is monitored for Pt50Co50 and Cu-rich Pt-Cu alloy electrocatalysts a t various extents of CV pretreatment. While the Co-containing catalyst requires essentially only one slow anodic CV to attain a stable profile, Cu containing alloys are found to require more extensive pretreatment until reproducible surface areas and activities are obtained. The study underscores the need for customized pretreatment protocols for optimal Pt alloy activity testing.
Acid Stability and Oxygen Reduction Activity of Magnetron-Sputtered Pt1-xTax (0 < x < 1) Films
Authors: Bonakdarpour Arman , Lobel Robert , Dahn Jeff R. , Sheng Shuran , Monchesky Ted
Published: November 2006

Pt1-xTax (0 ≤ x ≤ 1) thin film libraries were prepared using combinatorial DC magnetron sputtering on a variety of substrates. The bulk composition of the films obtained by electron microprobe before and after treatment in 0.5 M H2SO4 at 80ºC, showed no detectable dissolution of Ta at any x in Pt1- xTax. X-ray photoelectron spectroscopy (XPS) of acid-treated samples revealed that for regions with high Ta content (x > 0.5), full oxidation of surface Ta had occurred. The samples, when used as oxygen reduction electrocatalysts, also showed corrosion stability; however, addition of Ta lowered the activity towards ORR significantly for x > 0.1 in Pt1-xTax.
Fe-Based Catalyst for Oxygen Reduction: Functionalization of Carbon Black and Importance of the Microporosity
Authors: Lefevre Michel , Jaouen Frédéric , Dodelet Jean-Pol , Li Xiuhua H. , Chen Ke , Hay Allan
Published: November 2006

Fe/N/C catalysts for the reduction of oxygen under the acidic conditions prevailing in PEM fuel cells have been prepared on two carbon black supports functionalized with N-bearing groups. Once loaded with 2000 ppm Fe, the functionalized carbons were pyrolyzed at 950ºC in Ar or NH3. The best catalysts were obtained under NH3. In addition to being a nitrogen precursor, NH3 also etches the carbon support increasing its microporosity. In NH3, the functionalities are rapidly etched away from the carbon support, but this once-functionalized carbon now reacts faster with NH3 than the pristine carbon. Therefore, the optimum microporosity necessary to produce the maximum catalytic activity is reached after a shorter pyrolysis time on the functionalized carbon supports than on the pristine carbons. However, the maximum catalytic activity for the oxygen reduction reaction (ORR) is the same for the once functionalized carbon as for the pristine one.
Improvement of Heat-Treated Fe/N/C-Based Catalysts for Oxygen Reduction in PEM Fuel Cells By Using New Carbon Black Powders as Catalyst Supports
Authors: Ruggeri Stéphane , Dodelet Jean-Pol
Published: November 2006

Several new developmental carbon blacks were prepared at the Sid Richardson Carbon Black Corporation by injecting ammonia, methane or water vapor in the carbon black furnace during their fabrication. These new carbon powders were then used to obtain Fe/N/C catalysts for oxygen reduction reaction (ORR) in the acidic conditions prevailing in PEM fuel cells. The best catalysts were obtained when ammonia and methane were injected in the carbon black furnace during its production. The results are interpreted in terms of structural changes induced in the carbon blacks during their fabrication. These changes influence their subsequent reaction rate with NH3 when the structurally modified carbon black supports, loaded with 0.2 wt% Fe, are heat-treated at 950 degrees Celcius in pure ammonia to obtain the catalysts. This etching reaction produces up to ten times more catalytic sites with these modified carbon blacks than with their respective regular forms.
A Pyrochlore-Type Oxide Electrocatalyst for DMFC
Authors: Shimizu Youichi , Takase Satoko , Otsubo Takamasa
Published: November 2006

Electrocatalytic properties of various pyrochlore-type oxides synthesized by a co-precipitation method were systematically investigated for methanol oxidation for the electrocatalyst of the direct methanol fuel cell (DMFC). The best anode performance was achieved with the electrode containing Pb1.75Bi0.25Ir2O7-Z or Pb2Ir1.9Pb0.1O7-Z. They also showed high anodic performance per surface area of the catalysts. The Ir4+ state on the surface of the electrocatalyst should be important role for MeOH oxidation.
64-Electrode PEM Fuel Cell Studies of CO-Tolerant Hydrogen Oxidation Catalysts
Authors: Stevens David , Rouleau Joshua , Mar Richard , Atanasoski Radoslav , Schmoeckel Alison , Debe Mark K. , Dahn Jeff R.
Published: November 2006

The hydrogen oxidation catalytic performance of a ternary composition spread (Pt1-xRux)1-yMoy sample has been determined in a 64-electrode proton exchange membrane fuel cell. Linear gradients of the three elements were sputter deposited onto 3M's nano-structured thin film support through a shadow mask to produce 64 different, electrically isolated, catalyst compositions. CO stripping voltammetry showed that pre-adsorbed CO was removed at lower potentials as the ruthenium content increased. The presence of Mo generated a redox couple, broadened the CO stripping peak and reduced its intensity. In the presence of CO in reformate, the hydrogen oxidation overpotential decreased as the ruthenium content increased, in agreement with previous experimental studies reported in the literature on Pt1-xRux binary alloys. At intermediate ruthenium content, the overpotential could be further reduced through the incorporation of some molybdenum. At high Ru/Mo content, the hydrogen oxidation overpotential was high, presumably due to the resultant low Pt content.
Water Transport in Gas Diffusion Layers of PEMFCs
Authors: Litster Shawn , Bazylak Aimy , Sinton David , Djilali Ned
Published: November 2006

We present an ex-situ analysis of water transport in the carbon paper gas diffusion layers for PEM fuel cells. We employ florescent imaging that allows us to distinguish liquid water from air through an optical microscope by seeding the water with fluorescent molecules. We were able to infer the vertical location of water and create three-dimensional reconstructions of the water surface by correlating surface height with image intensity. Our study investigated water phase movement in an uncompressed GDL as well as the additional effect of the localized compression that a fuel cell's bipolar plate introduces. The visualizations indicate that localized compression promotes regions of increased wettability. We put forth that the increased wettability results from fractured carbon fibers and the degradation of the PTFE coating.
Role of Binders in High Temperature PEMFC Electrode
Authors: Park Jung O. , Hong Suk-Gi , Kim Taeyoung , Kwon Kyungjung , Suh Sanghyuk , Cho Myungdong , Yoo Duckyoung
Published: November 2006

Electrodes with different binders were prepared to test the role of binders in performance of the cell that operated at the temperature of 150{degree sign}C. The electrodes that used PTFE as binder resulted in the Tafel slopes over 100 mV/decade. By using polyurethane-PEAA binder, the Tafel slope was reduced to 87 mV/decade, and the reduction in the Tafel slope caused an increase in cell performance. The analysis of I-V characteristics that were obtained from cells operated at 150{degree sign}C is discussed.
A High Performance Pt-Free Anode for Intermediate-Temperature Fuel Cells
Authors: Heo Pilwon , Nagao Masahiro , Sano Mitsuru , Hibino Takashi
Published: November 2006

Proton exchange membrane fuel cells (PEMFCs) are among the most promising power sources for vehicular and residential applications because of their clean and efficient energy conversion. However, these fuel cells require expensive Pt- based electrodes, which raise the cost of fuel-cell systems considerably. Here, we propose an approach to solving this problem by combining a molybdenum carbide (Mo2C) catalyst with an In3+-doped SnP2O7 electrolyte. The resulting fuel cell can operate in the temperature range of 150 to 300ºC, providing the high catalytic activity of Mo2C for electrochemical hydrogen oxidation, which is comparable to that of a Pt anode catalyst. Another important advantage of this fuel cell is that the Mo2C anode catalyst showed perfect tolerance to 10%CO.
The Effect of Dynamic and Steady State Voltage Excursions on the Stability of Carbon Supported Pt and PtCo Catalysts
Authors: Ball Sarah C. , Hudson Sarah L. , Theobald Brian , Thompsett David
Published: November 2006

To improve the stability of Pt-based catalysts to meet the targets set for automotive fuel cell operation, a detailed understanding of the mechanisms of corrosion and Pt particle stability is required. The stability of Pt and PtCo on both high-area and low-area carbon supports has been studied using both dynamic and steady state voltage excursion measurements. At 1.2V steady state, the catalysation of carbon did not significantly increase the rate of carbon corrosion. However, corrosion rates of the low area carbon was 1/20th that of the high-area carbon. Under dynamic cycling, the stability of small Pt particles was found to be poor due to dissolution/sintering on the high-area carbon, however the PtCo alloy particles were found to be very stable on both the high-area and low-area carbons. In addition, it has been found that Pt oxide/reduction can catalyse carbon corrosion with both high and low-area carbons.
Dissolution of Ru from PtRu Electrocatalysts and its Consequences in DMFCs
Authors: Gancs Lajos , Hakim Nazih , Hult Brian , Mukerjee Sanjeev
Published: November 2006

Rapid and irreversible performance loss could be observed for a single cell DMFC using a PtRu anode electrocatalyst when it was operated under non-optimized conditions. Post-mortem cyclic voltammetry and EDAX data reveal that the anode electrode became depleted in Ru, and the dissolved Ru crossed through the PE membrane and then deposited onto the Pt cathode electrode. Comparative elemental compositional as well as CO and MeOH electrooxidation performance analysis was performed with commercial PtRu black samples having the same 50:50 atomic ratio but different degree of alloying. The data suggests that the latter physical property is crucial in maintaining the anodic activity for prolonged time. On the other hand, dissolved Ru species present in the micromolar concentration range in liquid electrolyte are shown to have severe detrimental impacts on ORR kinetics on a Pt thin-film RDE (having a surface roughness factor of ca. 6).
Impact of Sulfur Dioxide on the Performance of the PEMFC Cathodes
Authors: Garsany Yannick , Baturina Olga A. , Pietron Jeremy , Swider-Lyons Karen
Published: November 2006

Rotating ring disk (RRDE) methods are used to quantify the poisoning of the oxygen reduction reaction (ORR) at Pt/VC catalysts by adsorbed sulfur species. Coulometric analysis indicates that only S(0) is adsorbed on the Pt/VC surface. RRDE measurements show that the ORR activity decreases significantly as the sulfur coverage increases. Sulur coverage {greater than or equal to} 0.37, drastically changes both the activity and the reaction pathway of the ORR on the Pt/VC catalyst from a 4-electron to 2-electron process reaction. At high current densities, the Tafel slopes of the sulfur-poisoned electrodes increase, and the electrodes are no longer efficient for the ORR, as evident by the loss 95% mass activity with initial sulfur coverage of only 0.14. The decrease in activity due to the adsorbed sulfur is accompanied by an enhanced formation of hydrogen peroxide (up to 70% for initial sulfur coverage {greater than or equal to} 0.37).
CO-Air Bleed Interaction and Performance Degradation Study in Proton Exchange Membrane Fuel Cells
Authors: Du Bin , Pollard Richard , Elter John F.
Published: November 2006

Optimum air bleed level was selected based on both voltage decay rate and fluoride release rate from the endurance tests. Reverse water-gas shift reaction was found to be negligible for a standard proton exchange membrane fuel cell with a Pt-Ru anode. The effect of transient high CO was investigated. It was found that a fuel cell suffered a recoverable voltage loss without long term adversary effect when it was exposed to transient high CO (20 to 200 ppm) for a short period of time. However, fuel cells suffered a permanent loss in CO mitigation capability when they were exposed to high CO for hours. This was attributed to the formation of RuOx as a result of high anode overpotential.
Degradation Investigation of PEMFC by Scanning Electron Microscopy and Direct Gas Mass Spectroscopy
Authors: Fujii Yoshinobu , Tsushima Shohji , Teranishi Kazuhiro , Kawata Kentarou , Nanjo Takanori , Hirai Shuichiro
Published: November 2006

We present a durability test of polymer electrolyte membrane fuel cell (PEMFC) under load cycle operation. Polarization curves of the fuel cell was deteriorated by load cycle, although cross-sectional analysis by scanning electron microscopy (SEM) indicated no identical degradation on the membrane electrode assembly (MEA). In-line direct gas mass spectroscopy (DGMS) analysis successfully detected intermittent peaks of carbon dioxide (CO2) emission in exhausted gas from the cathode, indicating carbon corrosion proceeding during load cycle in the fuel cell.
Performance Characteristics of a Polymer Electrolyte Fuel Cell with the Anodic Supply Mode
Authors: Lee Yongtaek , Jang Yong Hee , Jung Taehun , Chung Jin Taek , Kim Yongchan
Published: November 2006

The transport phenomena inside the PEFC varied according to the anodic supply mode. In the dead-end mode, without having any discharged gas, the impurities could remain inside the cell. Moreover, the externally supplied water and diffused water from the cathode can be accumulated in the channel, which blocks the flow path. The flow-through mode can prevent the problem by letting the excess hydrogen flow through the anode free into the atmosphere, but the waste of fuel is inevitable. The anodic recirculation may help the removal of the accumulated water with additional power consumption for the recirculation pump. In this study, the performance characteristics of a PEFC were investigated according to the anodic supply mode. The anodic supply mode tested in this study included the dead-end, the flow-through, and the recirculation mode. The efficiency of the system in accordance with the anodic supplied mode was also estimated.
PEM Fuel Cell Durability With Transportation Transient Operation
Authors: Borup Rod , Davey John , Garzon Fernando , Wood David , Welch Paul , More Karren
Published: November 2006

PEM fuel cell durability testing is performed with tests conducted using steady-state conditions, with dynamic conditions using power cycling simulating a vehicle drive cycle and by accelerated testing methods. The long-term performance characteristics of MEAs, Electrocatalysts and Gas Diffusion Layers (GDLs) and their impact on PEMFC durability are evaluated in terms of their associated degradation mechanisms. Testing simulating automotive drive cycles show a greater rate of particle growth than do tests in which the cell potential is held constant. The loss of electroactive Pt surface area is shown to be due primarily to the growth in platinum particle size; particle growth appears to have multiple growth mechanisms. Cathode particle size growth is dependent on temperature, relative humidity and potential. Cell performance degradation due to mass transport limitations correlates with changing hydrophobicity of GDL materials.
Temperature-Driven Water Transport in Polymer Electrolyte Fuel Cells
Authors: Zaffou Rachid , Kunz Harold R. , Fenton James M.
Published: November 2006

Water transport induced by heat flow across polymer electrolyte fuel cell (PEFC) membranes has been studied under well-controlled thermal conditions. The investigation showed that water can be transferred across a membrane electrode assembly (MEA) that is subjected to a through-plane temperature differential. Thermo-osmotic water transport is a membrane-controlled phenomenon. The thermally driven water flux was found to be relatively large even for small temperature differences (~1oC). A physical model of thermo-osmosis is proposed. Comparison between the proposed model results and the experimental data shows good agreement.
Water Management at the Cathode of a Planar Air-Breathing Fuel Cell with an Electroosmotic Pump
Authors: Fabian Tibor , O'Hayre Ryan , Litster Shawn , Prinz Fritz B. , Santiago Juan G. G.
Published: November 2006

Water management is a significant challenge in portable fuel cells and particularly in fuel cells with air-breathing cathodes. Liquid water condensation and accumulation at the cathode surface is unavoidable in a passive design operated over a wide range of ambient and load conditions. Excessive flooding of the open cathode can lead to a dramatic reduction of fuel cell power. We report a novel water management design based on a hydrophilic and electrically conductive wick in conjunction with an electroosmotic (EO) pump. A prototype air- breathing fuel cell with the proposed water management design successfully functioned under severe flooding conditions, including ambient temperature 10ºC and relative humidity 80 %, for up to 6 h without any observable cathode flooding or loss of performance.
What is Learned Beyond the Scale of Single Cells?
Authors: Büchi Felix N. , Freunberger Stefan A. , Santis Marco
Published: November 2006

Often the properties of a single cell are considered as representative for a complete polymer electrolyte fuel cell stack or even a fuel cell system. In some cases this comes close, however, in many real cases differences on several scales become important. Cell interaction phenomena in fuel cell stacks that arise from inequalities between adjacent cells are investigated in detail experimentally. For that, a specialized 2-cell stack with advanced localized diagnostics was developed. The results show that inequalities propagate by electrical coupling, inhomogeneous cell polarization and inducing in-plane current in the common bipolar plate. The effects of the different loss-mechanisms are analyzed and quantified.
Microfluidic Tools for Assessing the Multiphase Properties of Water in PEMFC Gas Diffusion Electrodes
Authors: Fairweather Joseph , Cheung Perry , Schwartz Daniel T. , St-Pierre Jean
Published: November 2006

The microfluidic Tempe cell, a new tool for measuring multiphase flow parameters, is presented. The cell is suitable for acquiring the saturation-dependent capillary pressure, Pc(S), and relative permeability, kr(S), for thin porous PEMFC electrodes. A laser-drilled porous Teflon sample for the validation of capillary pressure measurement is also presented.
Nanoscale Current Imaging of the Conducting Channels in PEM Fuel Cells
Authors: Buratto Steven , Bussian David , O'Dea James R. , Metiu Horia
Published: November 2006

The electrochemically active area of a proton exchange membrane fuel cell (PEMFC) is investigated using conductive probe atomic force microscopy (CP-AFM). A platinum coated AFM tip is used as a nanoscale cathode in an operating PEMFC. We present results that show highly inhomogeneous distributions of conductive surface domains at several length scales. At length scales on the order of the aqueous domains of the membrane, ~50 nm, we observe single channel electrochemistry.
Diagnostics of Cathode Flooding in a Segmented PEMFC with Local Reference Electrodes
Authors: Siroma Zyun , Takahashi Junji , Yasuda Kazuaki , Tanimoto Kazumi , Inaba Minoru , Tasaka Akimasa
Published: November 2006

A fourfold-segmented PEMFC with four reference electrodes was created to measure current distribution, local polarization of the anode and cathode, and local impedance. When sufficient amounts of fully humidified gases were fed to the anode and cathode, cathode flooding was observed. When the feeding of the anode gas was reduced, reaction downstream of the anode was hindered, which seemed to be caused by anode flooding, instead of starvation due to consumption of the gas.
Simple Model for the Water Phase Distribution in the Gas Diffusion Layer of a PEMFC Cathode
Authors: Martinez Michael J. , Shimpalee Sirivatch , Van Zee John
Published: November 2006

A simple, two phase model that incorporates pore size distribution (PSD) data from gas diffusion layers (GDL) is described. The model is used to predict water phase distribution and explain differences in performance when different GDLs are used under the same conditions. Experiments show that, under high humidity conditions, the cell with GDL A has higher performance as compared to the cell with GDL B. The model was tested with these two GDLs. Results shows that higher liquid saturation levels are produced when GDL B is used as compared to GDL A. Also, under high humidity conditions the model was able to predict a significantly higher performance when GDL A is used as compared to GDL B.
Numerical Investigation of Water Transport in the PEMFC Components
Authors: Gurau Vladimir , Mann J. Adin , Zawodzinski T. A.
Published: November 2006

There are two competing mechanisms of water transfer between the ionomer-phase distributed in the catalyst layer and the catalyst layer pores; these are: (i) sorption/desorption and (ii) water dragged by the protons engaged in the electrochemical reaction (the secondary current). The level at which water accumulates in GDLs is determined by the saturation equilibrium at the GDL-channel interface. The level at which water accumulates in the catalyst layer is determined by the GDL permeability and the saturation equilibrium at the GDL- catalyst layer interface. In the cathode flow domain mass is overall produced by (i) mass of protons crossing the double- layer and (ii) mass of water transferred between the ionomer- phase distributed in the catalyst layer and the catalyst layer pores; for this reason the homogeneous multi-phase models based on the two-phase mixture model are inadequate to describe two- phase phenomena in PEMFCs. We propose a multi-phase, multi- fluid model that captures these phenomena.
A Multi-Scale Approach for the Simulation of Polymer Electrolyte Membrane Fuel Cells
Authors: Yoneda Masakazu , Tago Yukari , Suzuki Koshiro , Takimoto Masato , Sukemura Shunichi
Published: November 2006

A framework of multi-scale simulation of Polymer Electrolyte Membrane Fuel Cells and some of its sample calculations are exhibited. The macroscopic simulators, which are based on the continuum model, are well established and show high predictability, at least qualitatively. To acquire higher quantitative precision, they need to be supplemented by the insights of microscopic phenomena, which are difficult to observe. Microscopic simulators, which are based on discrete methods, are developed for this purpose, along with the macroscopic ones. This multi-scale simulator is expected to contribute to the design of practical PEMFCs.
Stack Models and Designs for Improving Fuel Cell Startup From Freezing Temperatures
Authors: Bradean Radu , Haas Herwig , Eggen Kjell , Richards Chris , Vrba Tomas
Published: November 2006

Fuel cell startup from freezing temperatures is a requirement for automotive applications as many countries experience cold climate. It has been shown at Ballard Power Systems that an optimum MEA water content is necessary at startup in order to achieve fast freeze startup with no performance loss. In this paper we present stack models and designs for obtaining an appropriate MEA water content at startup by maximizing water migration from MEA to plate channels due to temperature gradients during natural cooling. Using this concept no external power is needed after fuel cell shut down from wet operation to achieve the intended MEA water content at startup. Experimental results for the MEA water content along the stack after shut down and natural cooling and for the stack performance during startup from freezing temperatures are presented for the new stack design.
Toward Electroosmotic Flow-Driven Air Pumps for Miniaturized PEM Fuel Cells
Authors: Kim Daejoong , Buie Cullen , Santiago Juan G. G.
Published: November 2006

We propose an air displacement scheme using AC electroosmotic pumping and experimentally investigate its feasibility. An electroosmotic pump under a low frequency AC electric field is used to displace volumes of a pump working electrolyte. This working electrolyte is pumped into a space enclosed by a flexible membrane, and the movement of the membrane displaces air to a fuel cell. We demonstrate operation of a forced convection fuel cell using this technique. In this preliminary demonstration, the pump power consumption exceeds the fuel cell power generation. We are currently working to reduce the pump- to-fuel cell power ratio to 0.4 or less, by optimizing solvent chemistry, pump geometry, and pump forcing functions.
Spiral-Wound PEM Fuel Cells for Portable Applications
Authors: Kimble Michael C. , Blakley Thomas J. , Jayne Karen D.
Published: November 2006

Lighter weight and compact fuel cells are desired for low power levels less than 50 watts. Often, PEM fuel cells in this category are smaller versions of the larger planar fuel cells maintaining similar components. However, for low power level systems, the currents are often on the order of a few amps and thus do not require bipolar plates, but can instead rely on edge-tab current collection. A cylindrically designed PEM fuel cell can help reduce the stack mass and volume for small portable systems. A membrane and electrode assembly envelope is wrapped around a mandrel core for supplying hydrogen while ambient air diffuses from the ends. Metallic screen current collectors and carbon-free electrocatalysts allow the cell to operate in both fuel cell and electrolyzer modes. A benefit of this reversible cylindrical fuel cell is that it minimizes the number of components thus helping to maximize the energy density for portable power applications.
Two-Phase Flow in Small Channels and the Implications for PEM Fuel Cell Operation
Authors: Allen Jeffrey
Published: November 2006

A significant challenge in designing robust PEM fuel cells is managing the flux of water from the humidified reactant streams and the electrochemical reaction. The problem of water management is especially challenging under cold conditions because of the reduced water carrying capacity of the reactant streams as well as the potential for water freezing within the fuel cell assembly which can lead to degradation of the bulk materials and surface treatments of the various fuel cell components. Effective water management begins in the gas flow channels where the product water is removed from the cell. Because of the small length scales associated with the gas flow channels, capillary forces are important to the behavior of liquid surfaces in the channel. This implies that the cross- sectional geometry and surface chemistry of the gas flow channels are important to the behavior of liquid surfaces in the channel and, subsequently, to the behavior of two-phase flow. Recent research efforts have focused on investigating the role of capillarity on the behavior of two-phase flow in systems where capillary forces are important The results of this research are dramatic. The presence of corners in a small channel can result in a completely different pressure drop and flow morphology from that found in circular cross sections. In addition, a change in the channel wall wetting (hydrophilic or hydrophobic) can also result in unique pressure drops and flow morphologies.
Performance Analysis of Air-Breathing Fuel Cells
Authors: Litster Shawn , Djilali Ned
Published: November 2006

We present a theoretical analysis of an air-breathing PEM fuel cell that has a non-planar microstructure and we compare its performance to a fuel cell with the traditional planar architecture. Previous theoretical and experimental studies demonstrate that air-breathing fuel cells exhibit unique performance characteristics due to membrane dehydration. To enhance predictions of fuel cell performance during membrane dry-out, our model features a membrane conductivity correlation that is applicable for low humidity and a finite- thickness model of the cathode catalyst layer that resolves ion conduction. Our analysis predicts a volumetric power density for the non-planar architecture that is 100% greater than that for the planar arrangement. The non-planar fuel cell's higher power density results from the greater active area per unit volume and the humidity retention in the cathode's gas diffusion layer.
Effect of Anisotropy of Gas Diffusion Layers on Two-Phase Heat and Mass Transport in Polymer Electrolyte Fuel Cells
Authors: Pasaogullari Ugur , Mukherjee Partha P. , Wang Chao-Yang , Chen Ken S.
Published: November 2006

A non-isothermal, two-phase model is applied to a two- dimensional model of GDL to study the heat and mass transport in the in-plane direction (i.e. channel-to-land) and in the through-plane direction (i.e. catalyst layer-to-channel). For the first time, the anisotropy in the GDL thermal conductivity is taken into account, and found to be an important factor governing the temperature distribution in the GDL. The maximum temperature difference in the GDL is found to be a strong function of the GDL anisotropy. A temperature difference of up to 5ºC is predicted, and a significant effect of temperature distribution on the water transport and distribution is observed. In addition, the latent heat effects due to condensation/evaporation of water on the temperature and water distributions are also analyzed and found to strongly affect the two-phase transport.
Oscillations in the Gas Channels - The Forgotten Player in Impedance Spectroscopy in Polymer Electrolyte Fuel Cells B. Modeling the Wave
Authors: Kramer Denis , Schneider Ingo A. , Wokaun Alexander , Scherer Günther G.
Published: November 2006

A two-dimensional, steady-state impedance model is presented, rigorously derived from continuum mechanics and conservation laws. The model will reflect unique features of the local impedance response of air-fed PEFCs. Oxygen concentration oscillations originatingfrom the modulated ac current are not confined to the GDL by allowing for a non-zero amplitude at the GDL-channel interface. Therefore, the propagation of oxygen concentration oscillations within the cathodic gas flow becomes possible. To describe the oscillating oxygen concentration field within air-fed PEFC channels during impedance spectroscopy measurements, the fluid dynamics within the channel is approximated by a laminar flow profile. For the sake of simplicity, electrode reactions are assumed to obey Tafel's law. The concentration wave within the channels will be characterized, and the bearings on measurable impedances will be analyzed.
Nanostructured Materials for Direct Methanol Fuel Cells
Authors: Hwang Bing-Joe , Loka Subramanyam Sarma , Chen Ching-Hsiang , Wang Guo-Rung , Liu Din-Goa , Lee Jyh-Fu
Published: November 2006

Nanostructured materials including carbon supports, electrocatalysts (anode and cathode), and membranes have been developed that are suitable for direct methanol fuel cells (DMFCs) applications. We discuss various approaches taken towards developing the nanostructured materials for DMFCs.
Impact of Functionalization of Nanoparticles on the Barrier Properties of Ionomernanocomposite Membranes for DMFC
Authors: Karthikeyan Chedarampet S. , Nunes Suzana P. , Prado Luis , Schulte Karl
Published: November 2006

Ionomer nanocomposite membranes based on sulfonated poly (ether ether ketone) were prepared using nanofillers of different shapes such as layered laponite, cylindrical MCM-41, and spherical aerosil, and were characterized for direct methanol fuel cells. Prior to the preparation of the nanocomposite membranes, the nanofillers were modified using imidazole glycidoxypropyl triethoxysilane (IGPTES). The effect of surface modification of the inorganic nanofillers on the methanol permeability and proton conductivity is studied and discussed in this report. We found that nanocomposite membranes containing functionalized nanofillers displayed lower methanol permeabilities compared to the non-functionalized fillers at the same time retaining the proton conductivity. The effect of surface modification was more pronounced for aerosil membranes, which showed a drastic decrease in permeability and an increase in proton conductivity. However, membrane with modified MCM-41 is the suitable and promising candidate for direct methanol fuel cells as it displayed the best permeability and conductivity values.
Utilization and Transport in Mediated Enzyme Electrodes with Multiscale Supports
Authors: Calabrese Barton Scott , Sun Yuhao , Chandra Bhupesh , Hone James
Published: November 2006

We report the electrochemical performance of a redox polymer-mediated glucose anode catalyzed by glucose oxidase and supported on a multiscale carbon material. The support is comprised of carbon paper upon which is grown multiwall nanotubes by chemical vapor deposition combined with ohmic heating of the carbon paper. The material possessed 100-fold higher surface area, and electrochemical performance increased 10-fold, compared to bare carbon paper. Maximum performance is limited by a balance between catalyst activation and reactant transport in the void volume between carbon paper fibers.
CVD Delta-Doped Boron Surface Layers for Ultra-Shallow Junction Formation
Authors: Sarubbi Francesco , Nanver Lis K. , Scholtes Tom L.
Published: November 2006

A new doping technique is presented that uses a pure boron atmospheric/low-pressure chemical vapor deposition (AP/LPCVD) in a commercially available epitaxial reactor to form less than 2-nm-thick δ-doped boron-silicide (BxSi) layers on the silicon surface. For long exposure B segregates at the surface to form a very slow growing amorphous layer of pure B (α-B). The electrical properties of the as-deposited α- B/BxSi stack have been studied by fabricating and measuring diodes where the B depositions are formed directly in the diode contact windows for different exposure times. It is demonstrated that the presented doping technique can be used to form high-quality δ-doped p+n junctions. Moreover, the formed α-B/BxSi layer is an attractive source of high-concentration B dopants for thermal annealing processes that does not induce any transient-enhanced diffusion (TED) effects.
Understanding Ion Implantation Defects in Germanium
Authors: Peaker Anthony R. , Markevich Vladimir , Slotte J , Rummukainen M , Capan I , Pivac B , Gwilliam R , Jeynes C , Dobaczewski L
Published: November 2006

The recent interest in germanium as an alternative channel material for PMOS has revealed major differences from silicon in relation to ion implantation. In this paper we describe some initial results of a fundamental study into defect creation and removal in ion implanted germanium. In this stage of the work we have used silicon and germanium implants into germanium and into germanium rich silicon-germanium. The defect evolution in these samples is compared with electron and neutron irradiated material using annealing studies in conjunction with deep level transient spectroscopy, positron annihilation and Rutherford back scattering. It is proposed that both vacancy and interstitial clustering are important mechanisms in implanted germanium and the likely significance of this is discussed.
Ultra-Shallow Junctions Formed by Co-Implantation and Sub-Melt Laser Annealing
Authors: Felch Susan B. , Falepin Annelies , Severi Simone , Augendre Emmanuel , Noda Taiji , Parihar Vijay , Nouri Faran , Hoffmann Tom , Pawlak Bartek , Eyben Pierre , Vandervorst Wilfried , Thirupapuliyur Sunderraj , Schreutelkamp Robert , Collart Erik , Graoui Houda
Published: November 2006

This paper presents the benefits of both co-implantation of diffusion-retarding species and ultra-fast annealing techniques as studied on blanket and device wafers. F and C co-implantation with B+ for PMOS and P+ for NMOS combined with conventional spike annealing produce reduced junction depths and improved dopant activation and profile abruptness, as measured on blanket wafers and compared to similar implants without the co-implanted species. Device wafers show that the overlap capacitance is reduced, consistent with the shallower junction depths and reduced lateral diffusion. The improved dopant activation manifests itself in reduced series resistance and improved Ion values. Depending on the implant conditions, either the gate/extension overlap capacitance or the series resistance can be improved when sub-melt laser annealing is used instead of conventional spike anneal. For both approaches, scanning spreading resistance microscopy (SSRM) measurements confirm the shallow junction depths and reduced lateral diffusion.
Resist Stripping Process on Germanium : a Basic Post-Implant Study
Authors: Lachal Laurent , Chiaroni Julien , Le Royer Cyrille , Ritton Frederic , Manfredonia Raphael , Perrin Fabrice
Published: November 2006

Germanium and Germanium-On-Insulator (GeOI) MOSFETs with high-k gate dielectrics have received recent attention for the advanced technology nodes, because of the better carrier transport properties in Ge compared to Si. For Ge or GeOI CMOS, it is mandatory to determine Ge dedicated resist stripping processes, because of the Germanium non-compatibility with actual cleaning solutions. An initial compatibility study shows a passivation effect on germanium during dry step for high N2/ (O2+N2) plasma ratio. For the post active area etching, dry stripping performed on patterned Poly-Ge-On-Insulator (PolyGeOI) wafers shows good compatibility. The lateral Ge consumption due to the water rinse step is minimized by dry process, indicating a plasma passivation effect. Post implant stripping is especially difficult because the Si typical solutions are highly aggressive for Ge, and also because of the resist graphitization. Using a ramping temperature process, a good resist removal efficiency has been achieved.
Iridium Silicide: a Promising Electrode for Metallic Source/Drain in Decananometer MOSFETs
Authors: Larrieu Guilhem , Dubois Emmanuel , Wallart Xavier , Katcki Jerzy
Published: November 2006

A detailed study of the formation of iridium like silicide obtained on ultra high vacuum annealing and on rapid thermal annealing is proposed using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electrical characterizations. Using XPS analysis, the stochiometry of silicidation (IrSi, IrSi1.6) is identified. A very uniform IrSi layer obtained at low temperature gave a lower Schottky barrier height than a PtSi silicide. Lastly, the IrSix phase, obtained at 900{degree sign}C, proposed a very poor film quality.
Influence of Alloying Elements on the Formation and Stability of NiSi
Authors: Detavernier Christophe , Deduytsche Davy , Jordan-Sweet Jean , Cabral Cyril , Lavoie Christian
Published: November 2006

We demonstrate that the addition of alloying elements can substantially affect the formation and morphological stability of nickel silicide. A comprehensive study of phase formation was performed on 24 Ni alloys with varying alloying element concentrations. Using time resolved x-ray diffraction (XRD), we follow the formation of the silicide phases in real time during rapid thermal annealing. Simultaneous in situ resistance and light scattering measurements complement the XRD technique and show the onset of thermal degradation for the monosilicide films.
Evolution of Structural and Electrical Properties of Plasma Nitrided Silicon Oxynitrides During the Formation Process
Authors: Storbeck Olaf
Published: November 2006

In this work the formation of silicon oxynitrides by decoupled plasma nitridation of thin RTO grown silicon oxide films, varying in thickness, and composition was investigated. Non- destructive Cocos measurement techniques were used after each processing step as base oxidation, plasma nitridation and different post nitridation anneals. It was found, that the base oxide thickness strongly influences the interaction of the plasma species with the solid state material, and thereby impacts severely the film properties. A effective model describing the effect of plasma nitridation process on the dielectric material is proposed.
Stress Characterization of Polycrystalline Silicon for Advanced CMOS Technologies
Authors: Chen Yuanning , Mercer Doug , Kohli Puneet
Published: November 2006

As advanced integrated circuit manufacturing moves through the 65nm technology node, we find that polycrystalline silicon (Poly-Si) films can be engineered to modulate the strain in the underlying channel for improved NMOS transistor performance in addition to fulfilling this primary function as the CMOS gate electrodes. In this paper, we study how the deposition conditions for Poly-Si films change the intrinsic stress. The effect of subsequent processing steps, such as ion implantation and rapid thermal annealing (RTA), on the Poly-Si stress are also measured. Poly-Si films deposited with different conditions are characterized by secondary ion mass spectrometry (SIMS) and sheet resistance. The results show that the compressive stress of columnar Poly-Si films deposited using disilane as the precursor has been reduced by 50% compared with films deposited using silane for the precursor. The stress measurement results confirm that the implant energy modifies the poly-Si film stress: the higher the energy, the lower the compressive stress. The SIMS and sheet resistance data indicate that the deposition conditions can affect the final Poly-Si dopant activation.
Feasibility of Dipole Based Work Function Tuning for Sub-1nm EOT Metal Gated High-K Stacks
Authors: Misra Veena , Jha Rashmi , Chen Bei , Lee Jaehoon , Lee Bongmook
Published: November 2006

Band edge work functions and hence low VTS are still a difficult challenge for most metal gated high-K dielectric stacks due to uncontrolled reaction layers which result in dipoles and impact the band bending in the substrate. One example of this unwanted dipole formation is the reported oxygen vacancy at the metal-HfO2 interface which acts to reduce the effective work function of PMOS metals [1]. Furthermore, the composition and thicknesses of all layers in the gatestack and the process history also influence the final value of the effective work function.
Damascene Metal Gate Technology for Gentle Integration of Crystalline High-K-Gate Dielectrics
Authors: Endres Ralf , Stefanov Yordan , Schwalke Udo
Published: November 2006

This paper presents the first successful attempt to integrate crystalline high-K gate dielectrics into a virtually damage free damascene metal gate process. Process details as well as initial electrical characterization results on fully functional gate Gd2O3 dielectric MOSFETs with equivalent oxide thickness (EOT) down to 1nm are discussed.
Thermal/Chemical Stability of ALD Ru-TaN Thin Films for Gate Electrode Applications
Authors: Tungare Mihir , Kumar Sumit , Li Min , Eisenbraun Eric
Published: November 2006

A low temperature atomic layer deposition (ALD) nanolaminate process was developed for the growth of Ru-TaN thin films with a controllable Ru:Ta elemental ratio. XPS analyses of the deposited films suggest the presence of Ru-Ta bonding along with the formation of Ta2O5. Ru-rich films with a resistivity of ~150μΩ-cm and a RMS roughness of 0.78nm were found to possess a work function of 4.94eV{plus minus}0.17eV after RTA. These multicomponent films showed superior thermal and chemical stabilities when compared to pure Ru and TaN films grown under similar processing conditions and subjected to similar thermal treatments, and may be suitable for emerging CMOS gate applications.