bluuebunny/crossref_metadata_2025 huggingface dataset:
Gate SiO2 Film Integrity on Ultra-Pure Argon Anneal (100) Silicon Surface
Authors: Teramoto Akinobu , Li Xiang , Kuroda Rihito , Suwa Tomoyuki , Sugawa Shigetoshi , Ohmi Tadahiro
Published: October 2011

The atomically flat surface is obtained by the ultra-pure argon ambient at relatively low temperature less than 900 °C, and it can be maintained by using the N2 ambient with light shielding cleaning and the radical oxidation. The crystal originated particles (COPs) on the wafer is also decreased by the argon annealing at 900 °C. The charge to break down (Qbd) of the radical gate oxide on the atomically flat silicon surface was evaluated. For the early period in the annealing treatment, the initial failure of Qbd which is often observed on the conventional flat surface disappears, however, the intrinsic lifetime is still the same as the conventional one. And then, the intrinsic lifetime is improved by completing atomically flat treatment. After roughening the atomically flat silicon surface, the Qbd characteristics of gate oxides on the Cz wafer is the same as that on the epitaxial wafer which does not have COP.
A Hysteresis-Free High-k Dielectric and Contact Resistance Considerations for Graphene Field Effect Transistors
Authors: Vaziri Sam , Östling Mikael , Lemme Max C.
Published: October 2011

We demonstrate a high-k atomic layer deposition process for graphene field effect transistors which suppresses hysteresis in ambient air measurements. Furthermore, the mobility of the GFETs only degrades by a factor of about two compared to uncovered devices. We further introduce a model that shows the influence of graphene-metal contact resistance at the source and drain on parameter extraction like mobility and transconductance.
Elastic Relaxation Evaluation in SiGe/Si Hetero-Epitaxial Structures
Authors: Gonzalez Mireia B. , Naka Nobuyuki , Hikavyy Andriy , Eneman Geert , Loo Roger , Simoen Eddy , Claeys Cor
Published: October 2011

In this paper, the impact of downscaling the geometry on the stress levels of SiGe/Si hetero-epitaxial structures is investigated by two different experimental techniques, i.e., Raman spectroscopy and High-Resolution X-ray diffraction analysis. The experimental results are complemented by finite element stress simulations. It is shown that the lowest stress levels are obtained for window sizes lower than 5 um wide, and moreover, for a larger epitaxial thickness. As is discussed, this dependence is connected with elastic relaxation at the edges of the SiGe epilayers.
(Invited) Direct Observation of Electronic States in Gate Stack Structures: XPS under Device Operation
Authors: Yamashita Yoshiyuki , Yoshikawa Hideki , Chikyo Toyohiro , Kobayashi Keisuke
Published: October 2011

Although gate stack structures with high-k materials have been extensively investigated, there are some issues to be solved for the formation of high quality gate stack structures. In the present study, we employed hard x-ray photoelectron spectroscopy in operating devices. This method allows us to investigate bias dependent electronic states while keeping device structures intact. Using this method we have investigated electronic states and potential distribution in a Pt gate metal/high-k gate stack structure under device operation. We have found that potential gradient was formed at the Pt/HfO2 interface by analyzing the shifts of the core levels as a function of the applied bias voltage. Angle resolved photoelectron spectroscopy revealed that SiO2 layer was formed at the Pt/HfO2 interface. The formation of the SiO2 layer at the interface might concern the Fermi level pinning, which is observed in metal/high-k gate stack structures.
In Situ HCl Etching of InP in Shallow-Trench-Isolated Structures
Authors: Orzali Tommaso , Wang Gang , Waldron Niamh , Merckling Clement , Richard Olivier , Bender Hugo , Wang Wei-E , Caymax Matty
Published: October 2011

CMOS scaling for sub-12 nm nodes will need high-mobility channel semiconductors such as III-V materials to be integrated on large diameter Si substrates. A way to overcome lattice mismatch is to confine defects resulting from strain relaxation on the sidewalls of trenches made by etch-back of Si in standard Shallow-Trench-Isolation (STI) structures. The surface of the InP layers, grown as buffer material in these trenches by selective epitaxy, is planarized by means of CMP, after which it needs to be recessed to allow for the deposition of the III-V channel stack. We have developed an in-situ HCl etching process allowing a close control of the recess depth down to a few nm and leaving a clean and planar InP surface well suited for subsequent III-V epitaxial growth. The process development was carried out in a commercial Aixtron Crius MOCVD reactor on standard SiO2 STI patterned 200 mm Si (001) wafers.
Different Properties of Erbium Silicides on Si(100) and Si(551) Orientation Surfaces
Authors: Tanaka Hiroaki , Teramoto Akinobu , Kuroda Rihito , Nakao Yukihisa , Suwa Tomoyuki , Kawase Kazumasa , Sugawa Shigetoshi , Ohmi Tadahiro
Published: October 2011

The electrical and physical properties of ErSix on n-type Si(100) and Si(551) surfaces are reported. The Schottky barrier heights (SBHs) depend on the Si substrate orientation. On a Si(100) surface, a low electron SBH around 0.3 eV is obtained and the obtained SBH is larger than 0.4 eV on a Si(551) surface, while this difference is caused by the quantity of Si atoms in ErSix and on Si(100) this is less than on Si(551). These silicidation reactions are very important to develop the future high current drivability devices using any surface orientation.
(Invited) Integration and Scalability of ALD-Based Mixed Phase Nanometer-Scale Barrier Layers for Extendable Metal Interconnects
Authors: Eisenbraun Eric
Published: October 2011

The sub-22nm CMOS device regime represents the introduction of significant challenges to conventional copper-based interconnect fabrication. In particular, the scalability of PVD-based copper barrier and seed methodologies for future interconnects is not assured. Alternative material and processing strategies based on directly-platable barriers formed by atomic layer deposition-based processing techniques hold promise to enable continued performance extendibility of copper interconnects. This paper will discuss a number of approaches under consideration, and will describe the mechanisms that allow these approaches to achieve performance targets for sub-22nm interconnects.
(Invited) Plasma Enhanced Atomic Layer Deposited Ruthenium for MIMCAP Applications
Authors: Swerts Johan , Salimullah M.M. , Popovici M. , Kim M.-S. , Pawlak M.A. , Delabie Annelies , Schaekers M. , Tomida K. , Kaczer B. , Opsomer K. , Vrancken C. , Debusschere I , Altimime L. , Kittl J.A. , Van Elshocht Sven
Published: October 2011

A comparative study of the growth behavior of nm-thin ruthenium layers by plasma enhanced atomic layer deposition using two ruthenium precursors is discussed. For bis(ethylcyclopentadienyl)-ruthenium or Ru(EtCp)2, we have found a large incubation time on titanium nitride when using N2/NH3 plasma. With N2/H2 plasma the incubation was significantly reduced. For (methylcyclopentadienyl-pyrrolyl)ruthenium or MCPRu, no incubation was observed for either plasmas. The measured growth per cycle was ~ 0.02 nm for Ru(EtCp)2 whereas ~ 0.04 nm for MCPRu. The top surface of the PE-ALD Ru films can be oxidized without surface roughening by applying a low pressure O2 anneal, while O3 exposure leads to roughening due to etching and re-deposition downstream of etched Ru. Awareness of the impact of oxidizing ambients on Ru is essential for successful integration of Ru layers as electrode in metal-insulator-metal capacitors.
(Invited) ALD and AVD Grown Perovskite-type Dielectrics for Metal-Insulator-Metal Applications
Authors: Wenger Christian , Lukosius Mindaugas , Blomberg Tom , Abrutis Adulfas , Baumann Peter , Ruhl Guenther
Published: October 2011

Atomic Vapor Deposition (AVD) and Atomic Layer Deposition (ALD) techniques were successfully applied for the depositions of perovskite type dielectrics, namely, Sr-Ta-O, Ti-Ta-O, Sr-Ti-O, Ba-Hf-O, Nb-Ta-O and Ce-Al-O. Thin films were investigated as alternative dielectrics for Metal-Insulator-Insulator (MIM) capacitors. Structural and electrical properties are investigated after depositing the metal oxides on 200 mm TiN/Si (100) substrates within the temperature range of 225-400 ºC. Electrical properties, investigated after sputtering Au top electrodes, revealed that the main characteristics are different for each dielectric. The highest dielectric constants were achieved for crystalline SrTiO3 (k=95), crystalline CeAlO3 (k = 60) and amorphous Ti-Ta-O (k = 50) films. However, Sr-Ta-O based MIM capacitors showed the lowest leakage current densities as well as the smallest capacitancevoltage linearity coefficients.
Picosun SUNALE ALD Systems for High Quality Nanocoatings - Bridging the Gap between R&D and Industrial Production
Authors: Toivola Minna , Lehto Tero , Li Wei-Min , Pilvi Tero , Soininen Pekka J.
Published: October 2011

Atomic layer deposition (ALD) is a chemical vapor processing method with which highly conformal, uniform, defect and pinhole free ultrathin films can be coated even on the most challenging nanoscale architectures such as high aspect ratio trenches, through silicon vias and highly tortuous through-porous networks. ALD is already widely in use in e.g. electronics, optics and sensor industries but it is rapidly gaining foothold also inside the renewable energy and clean and sustainable technology community. Picosun is Finnish, globally operating ALD equipment manufacturer whose exclusive, pioneering expertise in the field reaches back to the invention of the ALD technology itself and whose ALD systems are used by high profile industries and top level research organizations across four continents.
Atomic Layer Deposition of Antimony Telluride Thin Films Using (Me3Si)2Te with SbCl3 as Precursors
Authors: Gu Diefeng , Nminibapiel David , Baumgart Helmut , Robinson Hans , Kochergin Vladimir
Published: October 2011

Atomic Layer Deposition (ALD) growth of antimony telluride (Sb2Te3) thin films has been investigated. We fabricated antimony telluride layers as a function of ALD deposition temperature in order to establish the ALD process window using (Me3Si)2Te with SbCl3 as chemical precursors. The initial ALD nucleation of antimony telluride was found to follow the Vollmer-Weber island growth model. We found a strong dependence of the nucleation process on the chemical nature of substrate. Substrates covered with silicon dioxide interfaces worked significantly better compared to bare Si substrates for Sb2Te3 ALD film deposition. We present SEM and AFM analysis of the resulting surface morphology of Sb2Te3, which is strongly influenced by the deposition temperature and recommend an ALD temperature window with optimized substrate surface coverage and improved Sb2Te3 surface texture.
Remote Plasma Atomic Layer Deposition of Thin Films of Electrochemically Active LiCoO2
Authors: Donders Merijn E. , Knoops Harm C. , Kessels W.M.M. , Notten Peter H.
Published: October 2011

One of the remaining challenges in the field of portable electronics is the miniaturization of lithium-ion batteries without decreasing their storage capacity. To tackle this challenge and to effectively integrate battery technology in even a wider variety of applications, it is essential to produce high quality thin films for all-solid-state batteries. A remote plasma ALD process for the positive electrode material LiCoO2 was developed using the combination of CoCp2 as the cobalt precursor, LiOtBu as the lithium precursor and O2 plasma as the oxidant source. The thin films were deposited at a temperature of 325 °C with a virtually linear growth rate of 0.06 nm/cycle. After annealing the samples at 700 °C for 6 minutes the high temperature phase LiCoO2 was obtained, as demonstrated by XRD and Raman spectroscopy measurements. Electrochemical charge/discharge cycling showed good electrochemical activity with a promising storage capacity.
Structure-Performance Relationship Study of Alkaline Polymer Electrolytes
Authors: Pan Jing , Chen Chen , Zhuang Lin , Lu Juntao
Published: October 2011

The ionic conductivity and mechanical performance are two challenging subjects of the present study of alkaline polymer electrolytes (APEs). In this paper, we report our recent progress in the structural design of APE. On the one side, by designing the self-crosslinking structure, we have achieved APEs with exceptional stabilities in both the mechanical strength and the ionic conductivity, which enables the operation of APE at 90oC. On the other side, by introducing hydrophobic side chains, we have established efficiently-connected ionic channels in the APE and thus significantly increase the ionic conductivity, which is comparable to that of Nafion at 80oC.
Study of Water Removal in a PEMFC Using Computational Fluid Dynamics (CFD)
Authors: Castañeda Sergio , Sánchez Carlos
Published: October 2011

VOF model was used to simulate the water removal in the fuel cell gaseous flow channel for the characteristics of the studied device in our laboratory, at high current densities operating conditions. The effect of the air flow speed entering to the channel, the width of the emerging water pore, the hydrophobicity of the diffusion layer and the closeness of the pores in it were evaluated. It was found that water removal is favored by high inlet air speed, wide pore size, a hydrophobic diffusion layer and closer pores.
An Analytical Model of a Novel, Microfluidic PEM Fuel Cell Device
Authors: Barrasso Dana , Besser Ronald S.
Published: October 2011

The proton exchange membrane fuel cell has not met its potential as an alternative electrical energy source, due in part to the high cost of its platinum catalyst. Sputtered platinum films have been suggested as alternatives to conventional ionomer dispersion catalyst layers. Although sputtered platinum fuel cells exhibit high performance per mass of catalyst, they have lower power densities than conventional fuel cells. The emerging technology of Nafion etching presents opportunities to create innovative fuel cell architectures. A novel microfluidic fuel cell device is proposed that combines these technologies. An analytical model was developed to predict the performance of conventional, sputtered, and microfluidic fuel cells. Based on the simulations, the power density of the microfluidic device is on par with conventional fuel cells, while its mass-specific power is comparable to that of the sputtered platinum fuel cells, suggesting that the microfluidic device may increase performance while maintaining low catalyst loading.
Focusing Research by Developing Performance Related Selection Criteria for PEMFC Contaminants
Authors: St-Pierre Jean , Angelo Michael , Zhai Yunfeng
Published: October 2011

A multitude of contaminants are present in atmospheric air. A large proportion of these contaminants have unknown effects on fuel cell performance. An assessment of the overall performance impact of all suspected contaminants is a costly and time consuming task. Thus, a method is required to select the most relevant contaminants. A two tier down selection approach is presented. Six qualitative criteria were used to create a shorter list of 19 contaminants (first tier). Two quantitative criteria were developed based on the cell performance response to further down select contaminants for detailed studies (second tier). First tier contaminants were injected into fuel cells. Performance data were used to provide a preliminary evaluation of the second tier down selection criteria.
Investigation of Carbon Fiber Gas Diffusion Layers by Means of Synchrotron X-ray Tomography
Authors: Tötzke Christian , Manke Ingo , Hartnig Christoph , Kuhn Robert , Riesemeier Heinrich , Banhart John
Published: October 2011

The 3-dimensional spatial distribution of liquid water in different gas diffusion layer (GDL) materials was analyzed using synchrotron X-ray tomography. The capability of the method was demonstrated by virtually separating the GDL components in order to facilitate individual analysis of fiber material, liquid water and gas filled pore spaces. The influence of hydrophobic surface treatment on the water distribution in the GDL was illustrated by analyzing three GDL materials with different degrees of hydrophobicity. In the least hydrophobic sample, liquid water tends to form larger clusters which stretch out about several hundred µm inside the porous GDL. In contrast, only small water clusters were found in the strongly hydrophobic material with high Polytetrafluoroethylene (PTFE)-content as the liquid is partially pressed out of the GDL. Additionally, the influence of fiber orientation on the water distribution in the felt material was demonstrated.
Detachment of Liquid-Water Droplets from Gas-Diffusion Layers
Authors: Das Prodip K. , Grippin Adam , Weber Adam Z.
Published: October 2011

A critical issue for optimal water management in proton-exchange-membrane fuel cells at lower temperatures is the removal of liquid water from the cell. This pathway is intimately linked with the phenomena of liquid-water droplet removal from surface of the gas-diffusion layer and into the flow channel. Thus, a good understanding of liquid-water transport and droplet growth and detachment from the gas-diffusion layer is critical. In this study, liquid-water droplet growth and detachment on the gas-diffusion layer surfaces are investigated experimentally to improve the understating of water transport through and removal from gas-diffusion layers. An experiment using a sliding-angle measurement is designed and used to quantify and directly measure the adhesion force for liquid-water droplets, and to understand the droplets' growth and detachment from the gas-diffusion layers.
Effect of Titanium Powder Loading in Microporous Layer on a Polymer Electrolyte Unitized Reversible Fuel Cell
Authors: Ito Hiroshi , Maeda Tetsuhiko , Nakano Akihiro , Hwang Chul Min , Ishida Masayoshi , Kato Atsushi , Yoshida Tetsuya
Published: October 2011

Unitized reversible fuel cells (URFC) combine the functionality of a fuel cell and electrolyzer in one unitized device. For a URFC with proton exchange membrane, a titanium (Ti)-felt is applied to the gas diffusion layer (GDL) substrate at the oxygen electrode, and additionally titanium (Ti)-powders are loaded in the GDL substrate. The Ti-powder loading in the Ti-felt substrate yields hydrophobic meso-pores. The influence of this treatment is small for the electrolysis performance. In contrast, the change of pore-size distribution brings a significant improvement of fuel cell performance under fully humidification conditions. This fact indicates that the hydrophobic meso-pores in the GDL play an important role for mass transport.
The Effect of MPL Permeability on Water Fluxes in PEM Fuel Cells: Experimental Verification
Authors: Baghalha Morteza
Published: October 2011

The distribution of water fluxes is strongly influenced by the properties of the media adjacent to the cathode catalyst layer (CCL), viz. polymer electrolyte membrane (PEM) and gas diffusion media (GDM). We propose a model that is applied under varying humidification of the cathode feed gas, with water removal in liquid and vapor form. The model warrants the definition of a critical current density up to which water removal out of the CCL could proceed completely via vapor diffusion to the cathode side. Above the critical current density, excessive water generation leads to the build-up of an excess liquid pressure in the CCL, which drives hydraulic fluxes to PEM and GDM sides. Experimental data from literature were analyzed and found to be in good agreement with predictions of the model. This analysis reveals that the effective liquid water permeability of commercial GDMs (that includes an MPL) lies within the same order of magnitude of the liquid water permeability of the PEM.
The Effect of Uniform Particle Size Distribution on Pt Stability
Authors: Trogadas Panagiotis , Fuller Thomas F.
Published: October 2011

The present study aims to address the effect of the uniformity of particle size distribution on Pt stability. A theoretical model based on the chemical reactions of Pt oxidation and precipitation in the membrane is presented. The incorporation of a particle size distribution function and a population balance allows the investigation of different initial particle size distributions. Initial results demonstrate the change of platinum ions concentration across the electrode and membrane and reveal the shift of particle size distribution towards larger diameters under potential hold and potential cycling simulations.
Membrane and Catalyst Performance Targets for Automotive Fuel Cells by FCCJ Membrane, Catalyst, MEA WG
Authors: Ohma Atsushi , Shinohara Kazuhiko , Iiyama Akihiro , Yoshida Toshihiko , Daimaru Akimasa
Published: October 2011

The Fuel Cell Commercialization Conference of Japan (FCCJ) revised in 2011 a part of the target performance, durability, and cost of fuel cells for transportation application based on the latest technical data and knowledge obtained from the vehicle tests in the public thoroughfare and the simple systems to be expected in the commercialization stage. FCCJ also updated a methodology for testing membrane-electrode assemblies (MEAs) and its materials: electrolyte membranes and electrocatalysts. This revision is intended to assist the development of materials for industry, university, and research institutes from practicality, simplicity, and convenience points of view. The purpose of this paper is to describe the revised targets and the updated evaluation methods with the background technical information related to fuel cell vehicles (FCVs).
Comparative Study of the Degradation of Different Carbon Supported Pt Fuel Cell Catalysts
Authors: Hartl Katrin , Hanzlik Marianne , Arenz Matthias
Published: October 2011

Before characterizing fuel cell catalysts in time and cost intensive MEA or fuel cell stack tests, it is advantageous to evaluate catalysts in fast and inexpensive electrochemical half-cell tests. Recently, we developed a new methodology for accelerated degradation tests in electrochemical half-cells, IL-TEM, which enables the comparison of the surface area loss of the catalysts, determined by RDE, with the change in local structure, e.g. the detachment of individual particles from the high surface area carbon support, determined by TEM. In this presentation we demonstrate by IL-TEM that relative small differences in the synthesis of the catalyst can have a pronounced effect in the observed degradation mechanism.
Effect of Graphitic Content on Carbon Supported Catalyst Performance
Authors: Patel Anant , Artyushkova Kateryna , Atanassov Plamen , Harvey David B. , Dutta Monica , Colbow Vesna , Wessel Silvia
Published: October 2011

The effect of graphitic content on carbon supported platinum catalysts was investigated in order to investigate its influence on catalyst performance. Four catalysts of varying surface areas and graphitic content were analyzed using XPS, HREELS, and tested using RDE experiments. The catalysts were also heat treated at 150oC and 100%RH as means to uniformly age them. The heat treated samples were analyzed using the same methods to determine what changes had occurred due to this aging process. When compared to the BOL catalysts, heat treated catalysts displayed increased graphitic carbon and platinum metalic content, however they also showed depressed catalytic activity. The primary cause is still under investigation, though it is believed to be related to loss of amorphous carbon content.
Electrochemical and Morphological Studies of Ceramic Carbon Electrodes for Fuel Cell Systems
Authors: Eastcott Jennie I. , Powell Jeffery A. , Vreugdenhil Andrew J. , Easton E. Bradley
Published: October 2011

Ceramic carbon electrodes were prepared via polymerization of silane materials containing sulfonic acid groups in the presence of Pt/Vulcan XC72. Cyclic voltammetry and electrochemical impedance spectroscopy were used to investigate the effects of sulfonic acid functionalities on platinum utilization and proton conductivity, as well as CCE microstructure. It has been determined that incorporation of small amounts of sulfonated silane to the CCE structure can lead to a profound enhancement of proton conductivity despite decreases in BET surface area. Retention of surface area was achieved through combination of sulfonated and unsulfonated organosilane precursors. These composite samples show improved performance during fuel cell testing than for CCEs prepared using unsulfonated precursors.
High Performance Membrane Electrode Assembly Fabricated by Ultrasonic Spray Technique
Authors: Huang Xinyu , Rigdon William A. , Neutzler Jay , Larrabee Diana , Sightler Joshua
Published: October 2011

The core of a polymer electrolyte membrane fuel cell stacks are membrane electrode assemblies (MEAs). Manufacturing processes for MEA have significant impact on their performance and durability. The authors report an ultrasonic atomization and spraying technique to deposit catalyst layer directly onto the membrane to realize membrane electrode assemblies. Electrochemical test of as-fabricated MEAs indicated very good performance and reasonable stability. The Platinum yield of the fabrication process was found to be around 89%.
Effect of Fe Content on Pt-Fe/C Bimetallic Catalyst Performance by Pulse-Microwave Assisted Chemical Reduction
Authors: Zheng Jun-Sheng , Wang Xi-Zhao , Fu Rong , Yang Dai-Jun , Lv Hong , Ma Jian-Xin
Published: October 2011

Pt-Fe/C bimetallic catalyst for proton exchange membrane fuel cells (PEMFCs) was prepared by a pulse-microwave assisted chemical reduction synthesis (PMWSCR) process. The microstructure and morphology of the as-prepared catalysts were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The electrocatalytic performance was measured by cyclic voltammetry and constant potential polarization method. The results indicate that the PMWSCR is an efficient method for preparing bimetallic catalyst, and the Pt-Fe atomic ratio are of great important on the size and dispersion of Pt nanoparticles, crystal structure, and catalytic performance. When the atomic ratio of Pt/Fe is 1, the metal nanoparticles are uniform and highly dispersed on the surface of carbon support with an average size of 1.8 nm. The electrochemical measurements show that the electrochemical surface area of the catalyst is 61.9 m2•g-1 when the atomic ratio of Pt/Fe is 1, and the catalyst exhibits the superior performance as the cathode catalyst with a power density of 3.3 W•cm-2•mg-1.
Pt Monolayer on Electrodeposited Pd Nanostructures-Advanced Cathode Catalysts for PEM Fuel Cells
Authors: Bliznakov Stoyan , Vukmirovic Miomir , Yang Lijun , Sutter Eli , Adzic Radoslav R.
Published: October 2011

The Pt monolayer-shell Pd nanowires/nanorods-core (PtML/PdNW(PdNR)) electrocatalysts, supported on carbon nanoparticles are notable for their very high activity and stable performance towards the oxygen reduction reaction (ORR). In the present work Pd nanostructures are electrochemically deposited on oxidized carbon (COX) surface and the impact of the deposition parameters on the deposits morphology is studied. The electrochemical deposition of Pd nanowires is demonstrated for the first time, and a viable mechanism for the growth of Pd nanostructures is proposed. The one-dimensional growth of the Pd nanowires is ascribed to the hydrogen-underpotential-mediated layer-by-layer deposition of Pd. In addition, the surface structure of deposited nanowires is composed predominantly of {111}-oriented facets that facilitate the enhanced ORR activity and stability of the PtML/PdNW/COX electrocatalysts. The Pt mass and specific activities of these electrocatalysts, as well as their stable performance under potential cycling conditions, are significantly higher than those of the commercial Pt/C electrocatalysts, and highlight their great potential for resolving the remaining obstacles to commercializing PEMFCs.
The Effect of Synthesis Methods on the Electrochemical Activity and Durability of Carbon Supported Platinum Nanoparticles as Electrocatalysts for PEMFC
Authors: Darab Mahdi , Thomassen Magnus , Sunde Svein
Published: October 2011

4 samples from 10 % to 30% platinum loading with the same carbon support (all Vulcan XC-72) has been synthesized and characterized to be used as electrocatalysts for PEM fuel cells. Adsorption polyol proved to be the most promising synthesis technique among others applied. Conventional and modified polyol methods and impregnation were also utilized to synthesize Pt/C samples. Transmission Electron Microscopy has been used to produce electron microscopic images of the Pt nanoparticles dispersed inside the carbon structure. Furthermore electrochemical characterizations including regular CVs and CO stripping voltammetry were applied to understand and determine the electrochemical performance, while CO stripping voltammetry as an extremely strong tool to detect aggregates in the catalysts samples has been used to examine the presence of agglomerations. In-situ electrochemical studies also have been performed on the electrocatalysts inside a PEM fuel cell system. Cyclic voltammetry, current potential curves (polarization curves) have been used to study the electrochemical performance of the synthesized catalysts. In this regard, the catalysts have been utilized to produce MEAs using a spray technique and different pressing steps and the MEAs were mounted inside the fuel cell test station. At the end to obtain a strong idea on how durable the synthesized catalysts - made by different synthesis techniques- are, the samples underwent a degradation protocol consisting of 100 cycles between certain potentials and all in-situ tests would be repeating to have the data before and after the degradation.
Characterization of Durable Nanostructured Thin Film Catalysts Tested under Transient Conditions Using Analytical Aberration-Corrected Electron Microscopy
Authors: Cullen David A. , More Karen L. , Reeves K. Shawn , Vernstrom George D. , Atanasoska Liliana L. , Haugen Gregory M. , Atanasoski Radoslav
Published: October 2011

The stability of Ru0.1Ir0.9 oxidation evolution reaction (OER) catalysts deposited on Pt-coated nanostructured thin films (NSTFs) has been investigated by aberration-corrected electron microscopy. Accelerated stress tests showed that the OER catalysts significantly improved the durability of the Pt under cell reversal conditions. High-resolution images of the end-of-life NSTFs showed significant Ir loss from the whisker surfaces, while no Pt loss was observed. The retention of the Pt indicated that the OER catalysts had protected the catalyst-coated whisker surfaces from degradation.
Electrochemical Preparation of Pt-Based Catalyst on Carbon Paper Treated by Sn Sensitization and Pd Activation
Authors: Ahn Sang Hyun , Choi Insoo , Kwon Oh Joong , Lim Taeho , Kim Jae Jeong
Published: October 2011

CoRuPt/Pd and CoPtRu/Pd catalysts were prepared on a carbon paper with Sn sensitization, Pd activation, Co electrodeposition and galvanic displacement. Sn-Pd treatment on carbon paper was conducted to enhance its hydrophilic property related to nucleation of following Co electrodeposition process. The Co particles were formed on Sn-Pd treated carbon paper with varying deposition potential and time. Then, Pt and Ru galvanic displacement were performed to obtain CoRuPt/Pd and CoPtRu/Pd catalysts. Following electrochemical measurement indicated that the CoRuPt - 1 catalyst which had 1.02 of Pt/Ru surface molar ratio showed peak potential of 741 mV (vs. RHE) for methanol oxidation and 637 mV (vs. RHE) for carbon monoxide stripping, respectively. These values were 80 and 8 mV lower than those of a PtRu/C commercial catalyst.
Mesoporous Carbon as Support for PtRu Catalyst Electrochemical and Fuel Cell Characterization
Authors: Viva Federico A. , Bruno Mariano M. , Corti Horacio R.
Published: October 2011

With the aim to increase dispersion and minimize the size of metal nanoparticles, a mesoporous carbon was used as catalyst support. Mesoporous carbon with controlled pore size was prepared by carbonization of a resorcinol-formaldehyde polymer. PtRu (1:1 ratio) nanoparticles were deposited onto the carbon support by reduction with NaBH4. The obtained catalyst morphology and composition was determined by TEM, PXRD and EDS analysis. Electrochemical active surface area of the catalyst was determined by CO stripping. Electrocatalytic activity for methanol oxidation was assessed by cyclic voltammetry and chronoamperometry. Membrane electrode assembly (MEA) was prepared using the PtRu over mesoporous carbon catalyst on the anode. Polarization curves from a single cell fuel cell were obtained using 1M methanol solution on the anode and O2 on the cathode. Electrochemical measurements and fuel cell test showed a better performance when compared to a commercial catalyst.
Investigation on the Stability of Pt/C and Pt-RuOx/C Catalysts
Authors: Rufino Élen C. , Purgato Fabiana L. , Olivi Paulo
Published: October 2011

Electrode electroactivity depends directly on its nature, morphology, and structure. These parameters, in turn, are related to the preparation method, which will influence the cell performance and electrode stability. Thermal decomposition of polymeric precursors is among the several proposed methods for catalyst preparation. In this work, the effect of modifications to this method during the synthesis of Pt-RuOx/C electrocatalysts on the composition and electrochemically active surface area of electrode catalysts were monitored. To this end, the prepared electrodes were subjected to a large number of potential scans and to constant potential for a prolonged time period in sulfuric acid 0.5 mol L-1 and methanol 0.1 mol L-1 solution
High Performance Plasma Sputtered Fuel Cell Electrodes with Ultra Low Catalytic Metal Loadings
Authors: Coutanceau Christophe , Brault Pascal , Caillard Amaël , Mougenot Mathieu , Baranton Stève , Ennadjaoui Aboubakr , Cavarroc Marjorie
Published: October 2011

Ultra-low Pt content PEMFC electrodes have been manufactured using magnetron co-sputtering of carbon and platinum on a commercial E-Tek uncatalyzed gas diffusion layer in plasma fuel cell deposition devices. Pt loadings lower than 0.01 mg cm-2 have been realized. The Pt catalyst is dispersed as small clusters with size less than 2 nm over a depth of 500 nm. PEMFC test with symmetric electrodes loaded with 0.01 mg cm-2 led to maximum reproducible power densities as high as 0.4 Wcm-2 with Nafion 212. Replacement of platinum by palladium using plasma sputtering methods was also realized by preparing MEAs composed of 0.01 mgPd cm-2 for the anode and 0.01 mgPd cm-2 + 0.001 mgPt cm-2 for the cathode and Nafion 212 membrane. Power density as high as 250 mW cm-2 were achieved at 80°C, which corresponds to a specific power density of 250 kW gPt-1.
High Surface Area Tungsten Carbide with Novel Architecture and High Electrochemical Stability
Authors: Bernard d'Arbigny Julien , Taillades Gilles , Rozière Jacques , Jones Deborah , Marrony Mathieu
Published: October 2011

Tungsten carbide microspheres comprising an outer shell and a compact kernel have been synthesized by a simple hydrothermal method and exhibit very high surface area promoting a high dispersion of platinum nanoparticles. Tungsten bronze formation in surface of these WC microspheres was clearly identified by combination of electrochemical characterization and XPS measurements. The presence of a tungsten bronze layer at the surface of a WC core leads to a higher electrochemically active surface area (EAS) stability compared to that of the usual Pt/C electrocatalysts used for PEMFC.
RuO2•xH2O-TiO2 as Catalyst Support for PEM Fuel Cells
Authors: Lo Chih-Ping , Wang Guanxiong , Kumar Amod , Ramani Vijay
Published: October 2011

Electrocatalytic activities of Pt supported on RuO2•xH2O-TiO2 and anhydrous RuO2-TiO2 were examined. The electrochemically active surface area (ECSA) of Pt/RuO2•xH2O-TiO2 was found to be less than that of Pt/RuO2-TiO2 (3.2m2/g vs. 16.9m2/g), which suggested that RuO2•xH2O interfered with Pt electrocatalytic activity/accessibility. Pt catalytic activity was recovered when Pt/hydrous RuO2-TiO2 was calcined at 450°C, which led to the conversion of hydrous RuO2-TiO2 to anhydrous RuO2-TiO2 as observed from XRD patterns. The BET surface areas of hydrous RuO2-TiO2 and anhydrous RuO2-TiO2 did not change. Converging evidence from CV, XRD and BET analyses confirmed that hydrous RuO2 exhibited lower Pt catalytic activity/accessibility.
Comparative Studies of Oxygen Reduction Reaction and Ethanol Oxidation Reaction on PtSn/C and PtNi/C Catalysts
Authors: D'Villa-Silva Melina , Simões Fernando Carmona , De Souza Rodrigo F. , Da Silva Júlio César M. , Santos Mauro C.
Published: October 2011

In this work were used Sn and Ni as second metals with Pt to study both the electrochemical oxidation of ethanol using "in situ" ATR-FTIR and the oxygen reduction reaction which is assessed using a rotating ring disk electrode technique (RRDE). The onset potential of ethanol oxidation is 0.3 V for PtSn/C, and 0.4 V for PtNi/C. Acetic acid is the main product formed using PtSn/C while using PtNi/C CO2 is the main product. The current densities for ORR using PtSn/C were similar to those ones using PtNi/C in all potential regions, including the region of limit diffusion current. However, the peroxide production was smaller for PtNi/C than PtSn/C between -0.1 to -0.5 V. For PtNi/C, the reaction proceeds through the transfer of 3.7 electrons, while for PtSn/C about 3.8 electrons.
Ethanol Electrooxidation on PtSnNi/C Nanoparticles Prepared in Water-In-Oil Microemulsion
Authors: Cantillo Nelly M. , Solla-Gullón Jose , Herrero Enrique , Sánchez Carlos
Published: October 2011

The objective of this study is to investigate the catalytic activity of Pt/C, PtSn/C and PtSnNi/C towards ethanol electrooxidation. Water-in-oil microemulsion method has been used since it has been identified as one of the most powerful technique of catalyst preparation; it allows easily varying and controlling the atomic composition of the catalyst. The nanoparticles obtained were characterized by TEM and EDX techniques, showing a well dispersed material on the carbon support with a narrow distribution of sizes. Cyclic voltammetry and chronoamperometry measurements were carried out in acidic medium in the absence and in the presence of ethanol. The water-in-oil microemulsion method was found to be suitable for making active PtSn/C and PtSnNi/C electrocatalysts for ethanol oxidation. The addition of nickel enhances the catalytic activity of PtSn/C electrocatalysts by decreasing onset potential and increasing current density, therefore PtSnNi electrocatalysts represent a promising alternative towards improving ethanol oxidation process.
Synthesis and Evaluation of Low Platinum-Content Pt-CeOx/MWCNT Cathodes for the ORR in the Absence and Presence of Ethanol in Acid Media
Authors: Rodríguez Varela F.J. , Gaona Coronado A.A. , Loyola J.C. , Escalante-García J.I. , Bartolo Pérez P.
Published: October 2011

We present in this work the electrochemical activity for the oxygen reduction reaction (ORR) of a 20% Pt-CeOx/MWCNT electrocatalyst with low-platinum content, synthesized by the microwave-assisted polyol method. The cathode shows a high mass specific catalytic activity in acid media as well as remarkable inertness in the presence of ethanol. EDAX analysis indicates that the weight percent content of platinum in the composite cathode was 3.9 wt %. Meanwhile, XPS characterization of ceria reveals a material with mixed Ce+3 and Ce+4 oxidation states, with a predominant Ce2O3 phase. The catalytic activity for the ORR and enhanced tolerance properties of Pt-CeOx/MWCNT to ethanol are ascribed to the presence of the Ce3+ state in the composite cathode.
An In Situ Probe for Investigating PEM Degradation Kinetics and Degradation Mitigation
Authors: Prabhakaran Venkateshkumar , Arges Christopher G. , Ramani Vijay
Published: October 2011

This study has demonstrated that a fluorescent molecular probe (6-carboxy fluorescein) can be used for in-situ, real-time monitoring of the formation of reactive oxygen species (ROS) that are responsible for chemical degradation of the PEM (polymer electrolyte membrane) during fuel cell operation. An example of the method's utility for assessing mitigation of PEM degradation was successfully shown by incorporating a FRS, CeO2 nanoparticles, into the PEM. This work discusses the requirements for the use of a molecular probe for in-situ monitoring of ROS and its compatibility with components found in the fuel cell.
Proton Conductivity of Polymer Electrolyte Membranes during Transient Hydration and Dehydration Cycles
Authors: Rigdon William A. , Huang Xinyu , Hussey Daniel S. , Jacobson David L.
Published: October 2011

Most modeling work of the polymer electrolyte membrane fuel cell (PEMFC) assumes an equilibrium relationship between membrane water content and proton conductivity. However, evidence is provided which shows that deviations from the equilibrium relationship exist during the transient hydration and dehydration cycles. Although Nafion® membranes follow a nearly symmetric water uptake and loss, dry membranes gain conductivity much faster than they absorb water while wet membranes lose conductivity at about the same rate they desorb water. This asymmetric behavior should be accounted for when predicting the transitional behavior of PEMFCs.
Radicals in Fuel Cell Membranes: Mechanisms of Formation and Ionomer Attack
Authors: Gubler Lorenz , Dockheer Sindy M. , Koppenol Willem H.
Published: October 2011

Radical intermediates formed during polymer electrolyte fuel cell (PEFC) operation cause degradation of the proton exchange membrane. Generation and decay of the radicals HO•, H•, and HOO• in the membrane was simulated based on a kinetic framework with H2O2 as precursor. The degradation of the PFSA membrane was assumed to proceed via end-group attack. Two chemical environments were considered, a fuel cell test and an ex situ Fenton test. It was found that the reaction pathways and corresponding radical concentrations differ considerably. In particular, no H• is formed in a Fenton test due to the absence of H2. The influence of the concentration of Fe-ion impurities and end-groups on the radical concentration and rate of ionomer attack was studied. The calculated fluoride emission rate shows fairly good agreement with experimental results reported in the literature.
Sub-Tg Macromolecular Motions in Phosphoric Acid Doped Polybenzimidazole Membranes for High Temperature Fuel Cell Applications
Authors: Nalawade Amol , Abukmail Ahmed , Hassan Mohammad K. , Mauritz Kenneth A.
Published: October 2011

Broadband dielectric spectroscopy was used to identify sub-Tg macromolecular motions for undoped and phosphoric acid - doped polybenzimidazole (PBI) films. Loss permittivity vs. frequency spectra showed three secondary relaxation processes labeled beta, gamma and delta in order of decreasing temperature for undoped PBI. As acid content in the membrane increased, peak broadening was observed for all relaxations while the peak positions shift closer to each other. The loss and storage permittivity vs. frequency curves for PBI membranes are displaced upwards with increased acid content which reflects increasingly greater polarizability due to increasingly greater populations of polar phosphoric acid groups. The high storage permittivity values observed for acid doped samples in the low frequency regime could be due to membrane | electrode interfacial polarization relaxation. The Kramers-Krönig integral transform was used to calculate pure loss permittivity relaxation peaks from experimental dc-free storage permittivity curves to eliminate obscuring dc conductivity contribution.
Evaluation of the Durability of Polymer Electrolyte Membranes in Fuel Cells Containing Pt/C and Pt-Co/C Catalysts under Accelerated Testing
Authors: Rodgers Marianne P. , Bonville Leonard J. , Slattery Darlene K.
Published: October 2011

A major degradation source in proton exchange membrane fuel cells results from radical attack of the membrane. Radicals form on the electrodes and at the platinum band in the membrane. Platinum alloys have enhanced durability in fuel cells and it is hypothesized that the higher durability of PtCo/C electrodes will translate into less Pt band formation and therefore higher membrane durability. To investigate the effect of Pt/C vs. PtCo/C on membrane durability, CCMs were prepared with either Pt/C or PtCo/C in their electrodes and accelerated degradation studies were carried out. Use of PtCo/C rather than Pt/C in the electrode resulted in much lower CCM degradation. It is postulated that the use of PtCo/C reduces Pt band formation in the membrane, resulting in decreased membrane degradation. This postulation is supported by the presence of a platinum band in the CCM containing Pt/C, but not in the one containing PtCo/C after testing.
Recoverable Performance Loss due to Membrane Chemical Degradation in PEM Fuel Cells
Authors: Zhang Jingxin , Litteer Brian , Coms Frank , Makharia Rohit R.
Published: October 2011

Recoverable voltage loss was observed for a PEM fuel cell due to membrane chemical degradation under open circuit voltage (OCV) conditions. The anion analysis of the fuel cell effluent water, collected during both the OCV hold and voltage recovery stages, indicates that sulfate release rate is much higher during recovery than that during the OCV hold. The surge in sulfate anion release occurs simultaneously with the recovery of fuel cell voltage. It was found that the reversible voltage loss, and concurrent sulfate release rate during voltage recovery, is lower for Ce-mitigated NRE211 membrane compared to as-received membrane. The recoverable voltage loss is proposed to be mainly due to the sulfate anion generated by membrane chemical degradation adsorbing onto the platinum catalyst surface.
R and D for Improvement on Polymer Electrolyte Membrane and Ionomer Dispersion
Authors: Iizuka Yuto , Inoue Yuichi , Kato Akihiro , Honda Masatoshi , Miyake Naoto , Yoshimura Takashi , Ino Tadashi , Kondo Masahiro
Published: October 2011

Experimental membrane AKE-4 and ionomer dispersion SS400, which are based equivalent weight (EW) 450 ionomer, were prepared. AKE-4 and SS400 combination was achieved high performance under the high temperature and low humidity condition (cell temperature = Tcell = 80°C, anode dew point = Tda = 60°C, dry air to the cathode). AKE-4 membrane also shows the good chemical durability.
Effects of Annealing Conditions on the Performance of Solution Cast Nafion Membranes
Authors: Ding Xiaoyu , Fuller Thomas F. , Harris Tequila A. L.
Published: October 2011

Effects of annealing humidity and time on performance and characteristics of solution cast Nafion® membranes were investigated experimentally. Membranes cast from commercial Nafion® dispersion were annealed at 130°C for 10, 30 or 60 min in a dry or humid oven. Membrane electrode assemblies (MEAs) were made by applying a catalyst layer on cast and commercial membranes. Cell performance, impedance spectroscopy, linear sweep voltammetry and cyclic voltammetry were measured. Results show that cast membranes annealed for 30 min in a humid oven or 10 min in a dry oven have the same performance as commercial membranes.