bluuebunny/crossref_metadata_2025 huggingface dataset:
Supercritical Chemical Fluid Deposition of High Quality Compound Semiconductors
Authors: Afzaal Mohammad , Aksomaityte Gabrielle , O'Brien Paul , Cheng Fei , George Michael , Hector Andrew , Howdle Steven , Hyde Jason , Levason William , Malik Mohamed , Mallik Kanad , Nguyen Chinh , Reid Gillian , Sazio Pier , Smith David , Webster Michael , Wilson James , Yang Jixin , Zhang Wenjian
Published: September 2009

The main advantage of deposition from supercritical fluids over conventional CVD is the ability to fill high aspect ratio templates. Deposition of metals, indirect semiconductors and insulators into templates with dimensions down to 3 nm has been demonstrated by others, with no apparent pore blocking. In this paper we present a demonstration that it is also possible to deposit high quality, luminescent compound semiconductor films from supercritical CO2 or CO2/hexane mixtures. Depositions of CdS and III-V materials such as InP have been achieved through careful optimisation of precursor chemistry, reactor geometry and deposition conditions, supported by detailed measurements of the semiconductor film properties.
Comparative Study on the Step Coverage Quality of Cu Film by SCFD and CVD
Authors: Shimogaki Yukihiro , Momose Takeshi , Sugiyama Masakazu
Published: September 2009

Supercritical fluid deposition (SCFD) is a hybrid approach that combines the advantages of CVD and liquid-phase deposition. It usually employs supercritical CO2 (scCO2), which can dissolve various precursors and enables deposition at relatively high precursor concentrations. SCFD can provide conformal step coverage and superior gap-filling ability due to the high diffusivity and low viscosity of scCO2. In this paper, we will discuss the step coverage of Cu-SCFD comparing with that by Cu-CVD. Numerical simulation based on kinetic analyses on SCFD and CVD showed that SCFD may be a better choice to make conformal deposition onto high aspect ratio features with small dimension in nano-meter size. CVD may be a better choice for micro-meter scale features.
Study of TiC Coatings on Nicalon Fibre Prepared by Pressure-Pulsed Reactive Chemical Vapour Deposition at Low Pressure
Authors: Jouanny Isabelle , Jacques Sylvain , Weisbecker Patrick , Rufino Benoit , Maillé Laurence , Pailler René
Published: September 2009

TiC coatings on Nicalon SiC-based fibres were obtained in two steps; the first step consisted in converting the surface of the Nicalon fibre into nanoporous carbon by a chlorine treatment at 773 K, the second step consisted in converting this nanoporous carbon film into TiC by pressure-Pulsed Reactive Chemical Vapour Deposition at low pressure with a H2/TiCl4 mixture at 1373 K. The coatings were characterized by X-ray photoelectron spectroscopy, Auger electron spectroscopy and scanning and transmission electron microscopies. Mechanical assessment was achieved by tensile tests at room temperature. The conversion rate of C into TiC was studied varying the number of H2/TiCl4 pulses from 0 to 100. The formation of a thin interlayer between the fibre and the nanoporous carbon coating was revealed as soon as only 20 pulses are used. The conversion rate increases with the number of H2/TiCl4 pulses while the fibre failure stress decreases almost linearly.
Dy3+:Al2O3 and (Dy3++Cr3+): Al2O3 Films for Temperature Sensor Applications Derived by Thermal CVD and Sol-Gel Techniques
Authors: Eckert Christopher , Pflitsch Christian , Atakan Burak
Published: September 2009

Optical surface temperature measurements can be accomplished using thermographic phosphors (TP). These TPs can be deposited using CVD or sol-gel techniques, both techniques not being used often for this purpose. In this work dysprosium doped alumina films α-Al2O3:Dy and alumina films co-doped with dysprosium and chromium α-Al2O3:M (M:=Dy3+, Cr3+) were prepared by both techniques for TP applications and the results were compared. Diketonates of Dy, Cr and Al were used for film preparation. The phosphorescence decay lifetime of the Dy3+-transitions show strong temperature dependency in a temperature range from 1100 to 1500 K while the phosphorescence lifetime of Cr3+:Al2O3 (ruby) varies sufficiently in the temperature range from 298 up to 800 K. Thus, Cr3+-doped Al2O3 films are useful as thermographic phosphor coating for lower temperatures than Dy3+-doped films, while, co-doped films are temperature sensitive in the full temperature range from 298 up to 1500 K.
Model to Investigate Interfacial Morphology Effects on Polymer Electrolyte Fuel Cell Performance
Authors: Bajpai Hemant , Khandelwal Manish , Kumbur Emin C. , Mench Matthew M.
Published: September 2009

The purpose of this work is to investigate the impact of the interfacial contact morphology between the catalyst layer (CL) and micro porous layer (MPL) on the polymer electrolyte fuel cell (PEFC) performance. A single-phase anisotropic mathematical model has been developed to evaluate the role of interfacial morphology on ohmic, thermal and gas-phase transport. The novel feature of the model is inclusion of directly measured surface morphological information of the cathode catalyst and the micro porous layers. The preliminary results indicate that thermal disruption due interface morphology has low absolute impact in comparison to ohmic disruption. Ultimately, this model will be used as a tool to understand and minimize the PEFC performance loss, and to develop guidelines for optimal CL and MPL surfaces.
Multi-scale Modeling-based Prediction of PEM Fuel Cells MEA Durability under Automotive Operating Conditions
Authors: Franco Alejandro A. , Coulon Romain , Ferreira de Morais Rodrigo , Cheah Seng Kian , Kachmar Ali , Gabriel Margaret A.
Published: September 2009

In this paper we discuss a comprehensive physical-based model of the PEMFC materials degradation allowing predicting the MEA durability as function of the operation conditions, initial material loadings and electrodes microstructure. The approach, build within a modular multiscale non-equilibrium thermodynamics framework, couples atomistic-based descriptions of catalyst contamination/oxidation/dissolution/ripening, dissolved catalyst migration in the ionomer, C catalyst-support corrosion and chemical PEM degradation, with the degradation-induced nano/microstructural and transport properties (of reactants and charges) evolution. By describing the feedback between the instantaneous performance and the material aging phenomena, the model provides new insights on the competition between the different degradation processes under automotive-operating conditions. The predictive capabilities of our approach are illustrated in this paper through four applicative examples: 1) PtxCoy catalysts degradation 2) competition of PEM and cathode C degradation 3) synergies between anodic CO contamination and PEM and cathode C degradation, and 4) synergies between Pt and C degradation.
New Insight into the Nature of Catalytic Activity of Pyrolysed Iron Porphyrin Based Electro-Catalysts for the Oxygen Reduction Reaction (ORR) in Acidic Media
Authors: Kramm Ulrike I. , Abs-Wurmbach Irmgard , Fiechter Sebastian , Herrmann Iris , Radnik Jörg , Bogdanoff Peter
Published: September 2009

In this contribution, catalysts, prepared by an impregnation technique have been characterized structurally and chemically via 57Fe Mößbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and by elemental analysis, respectively. On the basis of the structural characterization it was concluded that those FeN4 centres in which iron is mesomericly bonded to four nitrogen atoms, are catalyzing the ORR. Furthermore, XPS as well as Mößbauer spectroscopy revealed that with increasing pyrolysis temperature the electron density at iron atoms was increased while that of the coordinating nitrogen atoms was reduced. This behaviour was connected with a decreased electric field gradient(EFG) as estimated by quadrupole splitting. EFG is interpreted in terms of a larger iron-nitrogen-bond distance and/or a slight movement of iron out of plane. We propose that this characteristic of the centres within the graphene planes, in which the centres are incorporated, enables the higher turn-over frequency during ORR of pyrolysed porphyrins.
Iron-based Catalysts for Oxygen Reduction in PEM Fuel Cells: Expanded Study Using the Pore-filling Method
Authors: Lefèvre Michel , Proietti Eric , Jaouen Frederic , Dodelet Jean-Pol
Published: September 2009

Fe/N/C catalysts for the oxygen reduction reaction (ORR) in PEM fuel cells were synthesized via a new method. A catalyst precursor was first prepared by filling the pores of a microporous carbon black with a mixture of pore-filler (organic molecules) and iron precursor by means of planetary ballmilling. The resulting catalyst precursor was then pyrolysed either in NH3 only or, first in Ar and then in NH3. Various pore-fillers and carbon blacks were investigated. The ORR activity in fuel cell is influenced by (i) the type and mass ratio of the pore-filler and the nominal loading of iron in the catalyst precursor and (ii): the micropore surface area and nitrogen content in the catalyst. The highest kinetic activity obtained in fuel cell at 0.8 V iR-free is 429 A g-1 using 1 wt% nominal iron loading, phenanthroline as the pore-filler and Black Pearls 2000 as the microporous carbon black
Synthesis and Characterisation of Nanoparticulate WC Electrocatalysts
Authors: Essaki Kenji , Rees Eric , Burstein Gordon T. , Haslam Gareth
Published: September 2009

Tungsten carbide (WC) has been synthesized by microwave induction heating (microwave induction heating) from a precursor of tungsten, hydrogen peroxide, and carbon. Investigations were conducted into the effect of changing the precursor preparation conditions with the aim of reducing the final particle size and encouraging the complete carburization of the precursor. Using a fast evaporation technique with the precursor produced greater carburization of the resultant powder after microwaving. Adjusting the precursor carbon content affected both the temperature in the microwave reaction cell and the amount of carbon available for carburization. WC made in this way was subject to electrochemical investigation. The passivation and electrocatalytic response of the material towards the hydrogen reaction was tested and found to be significant.
Fuel Cell Systems for Aircraft Application
Authors: Friedrich K. A. , Kallo Josef , Schirmer Johannes , Schmitthals Gerrit
Published: September 2009

Future aircraft generations have to face enhanced requirements concerning productivity, environmental compatibility and higher operational availability, thus effecting environmental, technical, operational, and economical aspects of in-flight and on-ground power generation systems. Today's development in aircraft architecture undergoes a trend to a "more electric aircraft" which is characterised by a higher proportion of electrical systems substituting hydraulically or pneumatically driven components, and, thus, increasing the amount of electrical power. Fuel cell systems in this context represent a promising solution regarding the enhancement of the energy efficiency for both cruise and ground operations. The activities of DLR focus on identification of fuel cell applications in aircraft, design and modeling of possible system designs, experimental investigations regarding specific aircraft relevant operating conditions, qualification of airworthy fuel cell systems, and set up and full scale testing of fuel cell systems for applications in research aircrafts. In cooperation with Airbus several fuel cell applications within the aircraft for both ground and cruise operation have been identified. In consequence, fuel cell systems capable to support or even replace existing systems have been derived. In this context, the provision of inert gas for the jet fuel (kerosene) tank and electrical cabin power supply including water regeneration represent the most promising application fields.
Effect of Residual Water Contents in MEA on Performance Degradation Caused by Repeated Startup of Frozen Cell in PEFCs
Authors: Onoda Mitsuru , Okuzono Shigenori , Matsuura Yasuhiro , Nishimura Kazuma , Hirose Yuki , Zhou Beini , Takagi Yasuo
Published: September 2009

The effect of residual water content in the MEA on performance degradation caused by repeated cold starts of a frozen cell at -30deg. C was investigated. The results indicated that when the residual water content in the MEA was low, a condition occurred in which both the diffusion and electrochemical activation capability of the ionomer in the catalyst layer of the cathode declined and degradation of cell performance increased compared with the high residual water content. Significant functional decay of the anode activation and polymer electrolyte membrane were not measured. Presumably, dry operation of the cell during startup from a frozen state caused the decline in ionomer performance, resulting in degraded cell performance.
Heat and Mass Transfer in Polymer Electrolyte Fuel Cells in Ultra-Low Humidity Operation
Authors: Fu Richard S. , Zhang Xiaoyu , Pasaogullari Ugur
Published: September 2009

A computational and experimental study on the operation and performance of polymer electrolyte fuel cells (PEFC) under low humidity conditions is performed. It is postulated that high ohmic overpotentials due to low hydration in the membrane and catalyst layers cause a significant increase in temperature, which in turn further increases the ohmic resistance. The model results show that as the cell voltage decreases, the temperature increases and causes a decrease in water activity of the ionomer phase despite the larger amount of water produced at higher current densities. This finding is supported by the measured increased in the ohmic resistance of experimental cells.
Computational Analysis of Dry Purge in Polymer Electrolyte Fuel Cells
Authors: Roy Arnab , Pasaogullari Ugur , Renfro Michael W. , Cetegen Baki
Published: September 2009

A three-dimensional, single phase, isothermal model is developed to predict the high frequency resistance (HFR) variation with time during dry air purge of a polymer electrolyte fuel cell (PEFC) with straight channels. For the first time, an investigation of HFR characteristics of a PEFC following the purge is carried out. Predicted membrane water content during and after the purge is used to calculate the HFR from known membrane ionic conductivity relations. Only cathode purge is considered as typical in the industry to minimize waste of hydrogen. Results show that the governing factor of water distribution in the membrane during purge is through plane and in-plane concentration gradient and HFR relaxation is mainly governed by concentration differential between inlet and outlet.
Broadband Dielectric Spectroscopic Studies of Annealed Nafion® Membranes
Authors: Mauritz Kenneth A. , Hassan Mohammad K.
Published: September 2009

The dynamics of macromolecular motions as coupled to proton migration in annealed Nafion® membranes was explored using broadband dielectric spectroscopy. These fundamental molecular processes are of interest at temperatures above 100o C; in particular, spectral changes were investigated in real-time at 140º C. Loss permittivity vs. frequency spectra of both β and α relaxations showed increased relaxation times with annealing and that water de-sorption was mainly responsible for these behaviors. Spectra were analyzed using the Havriliak-Negami equation and relaxation/conductivity parameters were obtained from equation fitting to experimental data to understand the nature and coupling of conduction and relaxations as annealing progressed in the instrument. A parameter N, reflecting the connectedness of charge hopping pathways, indicated tortuous random pathways. As N decreased with increased annealing time, the conductivity network appears to accumulate more charge traps.
Enhanced PEMFC Performance and Durability at 120{degree sign}C and Low Relative Humidity Using Heteropolyacids
Authors: Brooker Robert P. , Baker Phillip , Kunz Harold R. , Bonville Leonard , Parnas Richard
Published: September 2009

At the University of Connecticut, the addition of silicotungstic acid, a heteropolyacid, to Nafion® electrolyte has been found to significantly increase the cathode reaction rate. This material has been shown to increase the platinum activity at high temperatures and low relative humidity, conditions which provide for more efficient heat rejections, improved impurities tolerance and more useful waste heat. The availability of this modified fuel cell could have a significant impact on the commercialization of PEMFCs for vehicular, stationary, and portable applications. A patent has been obtained on this invention, and another patent application has been submitted.
In Situ Detection of Reactive Oxygen Species in PEM Fuel Cells
Authors: Trogadas Panagiotis , Ramani Vijay
Published: September 2009

Preliminary results are presented in this study concerning i) the ex-situ identification of reactive oxygen species (ROS) within a model Fe+2/H2O2 solution using fluorescence spectroscopy; and ii) the effect of cerium oxide particle size on its radical scavenging properties and hence on the fluoride emission rate (FER) of composite Nafion® / CeO2 membranes. On the degradation diagnostics front, it is demonstrated that fluorescence fiber-optic measurements can sense the ex-situ formation of hydroperoxyl (HOO*) radicals in a Fe+2/H2O2 solution through a decrease in the fluorescence intensity in the presence of the radicals. Work to extend these studies for hydroxyl radicals and to achieve in-situ estimation is ongoing. On the degradation mitigation front, it is seen that lowering the CeO2 particle size leads further reduces the FER from composite membranes by 30-50%.
Influence of the Electrolyte on the Particle Size Effect of the Oxygen Reduction Reaction on Pt Nanoparticles
Authors: Ashton Sean J. , Novo Andres , Mayrhofer Karl J. , Arenz Matthias
Published: September 2009

In the present work it is shown that the observed particle size effect for the oxygen reduction reaction on Platinum is independent of the nature of the anions in solution, i.e. although detecting different absolute reaction rates the same order in activity as a function of the particle size is observed in sulfuric acid as in perchloric acid solution. This finding is discussed based on the well known effect of specific anion adsorption on the order of activity for low index Pt single crystals.
A New Plurimetal Carbon Nitride Electrocatalyst for PEMFCs Based on Pd, Au, and Fe
Authors: Negro Enrico , Di Noto Vito
Published: September 2009

This report describes the preparation of a new plurimetal carbon nitride electrocatalyst based on Pd, Au and Fe and how its chemical composition, morphology and electrochemical performance are affected by a series of post-synthesis treatments involving leaching with mineral acids and annealing steps. Cyclic voltammetry with the thin-film rotating ring-disk electrode (CV-TF-RRDE method) is used to study the fundamental ORR electrochemistry and selectivity of the resulting materials. The latter are also studied under operative conditions at the cathode of single fuel cells. The pristine electrocatalyst shows a very promising performance in the ORR. Furthermore, the different post-synthesis treatments allow to identify the role of the various metal species in the active site. Finally, the measurements carried out in a single cell lead to the identification of the main morphological features responsible for obtaining an efficient ORR electrocatalyst.
High Resolution MRI Investigation of Transversal Water Content Distributions in PEM under Fuel Cell Operation
Authors: Shim Jae Young , Tsushima Shohji , Hirai Shuichiro
Published: September 2009

Investigation of water management in polymer electrolyte membrane fuel cells (PEMFCs) is a fundamental and important issue for their implementation. Consequently, it is necessary to investigate water content distribution in PEMs under typical fuel cell operating conditions. Our research group has therefore investigated transversal water content distribution in PEMs under fuel cell operating conditions using a magnetic resonance imaging (MRI) system. However, the spatial resolution limitations impeded our prior studies to elucidate the distribution of water contents in a thin membrane. We investigated water content distribution in a thin membrane using a high spatial resolution magnetic resonance imaging (MRI) system to overcome spatial resolution limitations in a thin membrane in this study. Transversal water content distribution in PEM (e.g. Nafion 115) was investigated at room temperature and ambient pressure using a high spatial resolution (e.g. < 10 micrometer) MR imaging system.
NMR Study on PEFC Electrodes
Authors: Sun Che-Nan , Zawodzinski Thomas A.
Published: September 2009

Water transport within a polymer electrolyte fuel cell (PEFC) electrode has been probed. A method to reveal tortuosity within the PEFC electrode is demonstrated. NMR relaxation and diffusion measurements are applied to yield information about molecular local interaction and long range diffusion, respectively, within the electrode sample. The diffusion coefficient (D) and relaxation time (T1) are measured from electrode samples which have been prepared using a complete decal process followed by equilibration under various RH conditions. Tortuosity within the electrode can be quantified by comparing the diffusion coefficient and relaxation result.
Impact of Flow Field Characteristics on Water Management of a Proton Exchange Membrane Fuel Cell Using Magnetic Resonance Imaging
Authors: Dunbar Zachary W. , Masel Richard
Published: September 2009

Fuel cells are envisioned as a next generation power source to supply clean power for a variety of applications. Currently, water management remains a challenge for proton exchange membrane fuel cells, particular at low temperatures or during power transients. Water formed during oxygen reduction impacts the fuel cell in many ways. In this study, the cathode flow fields are examined using Magnetic Resonance Imaging (MRI). High resolution images are gathered, illustrating the effects of fuel cell flow field geometry and surface energy on water distribution. It is also found that irregularities in the surface of the flow channel can contribution to water stagnation inside the fuel cell, even at significant gas flow rates which would be expected to expel any water build up.
Durability of Electrocatalysts in Polymer Electrolyte Fuel Cells
Authors: Inaba Minoru
Published: September 2009

Durability of electrocatalysts in polymer electrolyte fuel cells has been a major critical issue for commercialization of electric vehicles and stationary cogeneration systems. Though various methods mitigation have been proposed and the durability of fuel cell stacks has been greatly improved, further improvement of durability is needed for use in automotive applications. Here degradation phenomena of electrocatalysts for the cathode and the anode in PEFCs are reviewed and the mechanisms for degradation are discussed.
Excellent Durability of Carbon-Supported Pt Cathode Catalysts Covered with Silica Layers
Authors: Matsumori Hiroshi , Takenaka Sakae , Matsune Hideki , Kishida Masahiro
Published: September 2009

Multi-walled carbon nanotube-supported platinum electrocatalysts (Pt/CNT) for cathode in polymer electrolyte fuel cells were covered with silica layers (SiO2/Pt/CNT) in order to improve the durability. SiO2/Pt/CNT had a high catalytic activity in spite of uniform coverage of Pt metal with silica which was an insulator. The catalytic activity of SiO2/Pt/CNT did not change appreciably during the durability test (repeated potential cycling between 0.05 and 1.20V vs. RHE), whereas Pt/CNT was seriously deactivated. Silica layer which enveloped Pt metal particles in SiO2/Pt/CNT prevented the agglomeration of Pt metal particles as well as the growth of Pt metal particles in size through dissolution and redeposition of Pt metal.
Investigation of the Corrosion Stability of Stainless Steels under Simulated Low and High Temperature Proton Exchange Membrane Fuel Cell Operating Conditions
Authors: Richards Justin , Schmidt Kerstin , Cremers Carsten , Tübke Jens , Lückmann Andre
Published: September 2009

Stainless steels for low and high temperature proton exchange membrane fuel cell present several advantages over graphitic materials. The fabrication of bipolar plates from these kinds of alloys could reduce weight of the stack and provide high mechanical stability. Test results show that bipolar plates fabricated from standard V2A or V4A steel can withstand the corrosive conditions in a low-temperature (50 {degree sign}C) proton exchange membrane fuel cell. For water cooled applications with an operating temperature around 80 {degree sign}C and thus resulting heavily corrosive conditions, two high-alloyed steel specimens have proven to be suitable. Further analyses show variations in corrosion resistance after pre-treating steel samples with e.g. physicochemical surface treatments, electro-polishing, thermal annealing and corrosion protective coating solution. The high temperature PEMFC test condition with 85% phosphoric acid and 160 {degree sign}C operation temperature leads to visible corrosion traces on all specimens except one.
Study on the Cathode Fabricated by Spinning Process and Its Performance in PEFC
Authors: Kotera Seigo , Watabe Hiroyuki , Fujii Katsuya , Terada Ichro , Matsubara Chie , Uyama Hiroshi
Published: September 2009

This report describes a new method for the fabrication of the "spun" electrode consisting of ionomer and catalyst supported on carbon. The obtained spun electrodes have a porosity and in-plane gas permeability more than ten times as large as an electrode made by conventional coating process. Spun electrodes are introduced to the membrane electrode assembly (MEA) for PEFC by direct fabrication on a membrane. The performance of MEAs was evaluated and it showed lower mass transfer loss than that using a coated cathode.
Negative Resistance Values in Locally Resolved Impedance Spectra of Polymer Electrolyte Fuel Cells
Authors: Schneider Ingo A. , Bayer Michael H. , Wokaun Alexander , Scherer Guenther G.
Published: September 2009

This work demonstrates that the appearance of negative resistance values in locally resolved impedance spectra of PEFCs is, in general, a direct consequence of down the channel inhomogeneities due to changing concentration of oxidant, fuel or water along the flow channels. It is shown that the local polarization resistance becomes negative, as the local change in i)concentration polarization and/or ii)ohmic loss exceeds the total perturbation voltage amplitude at low frequencies. This forces the local cell current to decrease despite a higher total cell polarization. For the first time, this effect is shown here as a consequence of fuel and water depletion along the flow channels of a linear PEFC. Based on our earlier experimental results for the effect of oxygen depletion in H2/air PEFCs, we present a pseudo 2D transient model to further illustrate the impact of mass transport limitations along the cathode flow channels on locally resolved impedance response.
Progress Toward Accurate Through-Plane Membrane Resistance and Conductivity Measurement
Authors: Cooper Kevin
Published: September 2009

An instrument and procedure for evaluation of the through-plane ionic resistance and conductivity of PEMs is presented. The approach facilitates rapid evaluation of bare membranes over a wide range of temperatures and relatively humidity conditions. Use of bare membrane is a key feature because a primary application is characterization of the ionic conductivity of developmental materials for which testing a fuel cell is not practicable. Accurate evaluation of through-plane resistance and conductivity requires adjusting the measured high frequency resistance for non-membrane ohmic contributions. Non-membrane ohmic contributions, referred to in this work as the cell resistance, was determined by extrapolating, to zero thickness, a linear regression of the measured high frequency resistance vs. membrane thickness. The cell resistance was a function of temperature and relative humidity. Using the through-plane resistance corrected for the cell resistance, the area specific resistance and conductivity of dispersion-cast Nafion® NRE-212 was observed to be the same in the through-plane and in-plane directions.
Activity and Stability of Pt Monolayer Core Shell Catalysts
Authors: Ball Sarah C. , Burton Sarah L. , Christian Elvis , Davies Andrew , Fisher Janet , O'Malley Rachel , Passot Sylvain , Tessier Béatrice C. , Theobald Brian , Thompsett David
Published: September 2009

Pt and Pt alloy catalysts for the PEMFC cathode fall short of the high activities per gram of Pt required to enable large scale automotive PEMFC commercialization. Thrifting of the active Pt component in the ORR catalyst via the formation of core shell catalysts is an exciting approach to resolve this issue. Pt monolayers have been deposited onto Pd3Co, Pd3Fe and Ir cores using scaleable proprietary methods. Characterisation of these materials, via cyclic voltammetry, LEIS and XPS, showed successful Pt coating of the surface and enhanced catalyst stability in liquid electrolyte cycling tests compared to the bare cores. Electrolyte analysis indicated leaching of base metals and Pd/Ir, so further optimisation is required to generate a uniform pinhole free Pt shell. RDE testing showed 3.7 x Pt activity for PtML/Pd3Co and preliminary MEA tests show great promise, with mass activity up to 2 x that of Pt only.
Structure and Activity of Novel Pt Core-Shell Catalysts for the Oxygen Reduction Reaction
Authors: Ball Sarah C. , Burton Sarah L. , Fisher Janet , O'Malley Rachel , Tessier Béatrice C. , Theobald Brian , Thompsett David , Zhou Wei-Ping , Su Dong , Zhu Yimei , Adzic Radoslav
Published: September 2009

Recent performance and cost studies predict that the high PGM loadings in the electrodes of today's direct hydrogen fuel cells will prove a limiting factor in their commercial viability for automotive applications. Significant breakthroughs in electrocatalyst technology yielding materials with high activity, low cost and good durability are required. This paper reports on a collaborative effort which has focussed on the exciting core-shell oxygen reduction catalysts pioneered by Brookhaven National Laboratory. These materials promise high catalyst activity and PGM thrifting although to date, are typically fabricated by in-situ electrochemical techniques. Following the development of scalable syntheses, extensive catalyst characterisation methods have been employed to analyse and verify the success of a scaled PtML/Pd3Co/C catalyst. Although synthetic challenges remain, the scaled core-shell materials yield RDE activities of 0.72 A/mgPt, constituting an impressive 3.7x improvement in Pt activity relative to Pt/C and exceeding the 0.44 A/mgPt automotive target.
Analysis of Electronic State of Pt Small Particles on Carbon Substrate by sXPS
Authors: Toyoda Eishiro , Hatanaka Tatsuya , Takahashi Naoko , Jinnouchi Ryosuke , Morimoto Yu
Published: September 2009

The effect of the size of a platinum particle on its electronic structure was measured by soft X-ray photoemission spectroscopy and calculated by a first principle calculation. The measured particle size dependence of d-band center, which is considered as a good indicator of the electronic state related with the catalytic activity for oxygen reduction reaction, showed the shift of the d-band center to lower in energy, i.e. further away from the Fermi level, for smaller particle less than about 2nm. This trend did not agreed with the theoretical calculation result.
Proton Dynamics in a Polymer Electrolyte Membrane, Sulfonated Polyether Sulfone (SPES): A Computational Study
Authors: Choe Yoong-Kee , Tsuchida Eiji , Ikeshoji Tamio , Ohira Akihiro , Kidena Koh
Published: September 2009

The nature of proton dynamics in highly hydrated sulfonated polyethersulfone (SPES) (λ = 67.5) has been studied theoretically by means of quantum chemical calculations and first-principles molecular dynamics (MD) simulations. Comparison of results on SPES with those on Nafion shows that, in highly hydrated case, the nature of proton dynamics in both membranes is very similar, exhibiting remarkable contribution of the Grötthuss type proton transport.
Nanoscale Membrane Based on Filled Nanoporous Anodic Alumina with Proton-conducting Polymer for Fuel Cell Applications: Primary Morphological Evaluation
Authors: Mohajeri Mahdi , Omidvar Hamid , Hasani-Sadrabadi Mohammad M. , Dashtimoghadam Erfan , Tabaian Seyyd Hadi , Alfi Masoud
Published: September 2009

In this study, at the first an alumina substrates with oriented nanochannels were prepared via controlled anodizing process. Then structurally modified chitosan macromolecules with binary cross-link agents at optimum composition (12 and 2 wt. % of sulfosuccinic acid and glutaraldehyde) was introduced in the nanopores of inorganic substrate. Scanning electron microscope approved the uniform presence of a chitosan based nanorods inside the nanochannels of alumina substrate.
Design and Development of High-Performance Hybrid Inorganic-Organic Fuel Cell Membranes
Authors: Laberty-Robert Christel , Sel Ozlem , Valle Karine , Perreira Franck , Sanchez Clement
Published: September 2009

We develop a sol-gel based strategy for the synthesis of hybrid organic-inorganic membranes for PEMFC. This approach consists in growing a functionalized (-SO3H) mesoporous SiO2 network in a hydrophobic fluorinated polymer (PVDF-co-HFP). We used different processes to fabricate these membranes including solvent casting and spray-coating. These different methods allow a control of the microstructure of the inorganic network in the polymer at different scales which in turn does influence proton transport throughout the inorganic mesostructured network. The interfacial area between the hydrophobic and hydrophilic domains can be tuned and conductivity values comparable to Nafion at 60{degree sign}C under 100% humidity were achieved.
On the Mechanism of Proton Transport in Model Perfluorosulfonic Acid Systems: Ab Initio Molecular Dynamics Simulations
Authors: Habenicht Bradley , Paddison Stephen J.
Published: September 2009

Model perfluorosulfonic acid systems were constructed by functionalizing the inner walls of carbon nanotubes with fluorosulfonic acid groups. These systems were studied using ab initio molecular dynamics to investigate the nature of the interactions between water and the sulfonic acid groups and the dynamics of the water and hydrated protons as a function of water content. Specifically, the influence of the separation distance of the sulfonic acid groups on the dissociation of the proton, the formation of Zundel or Eigen ions, and proton transport and diffusion. The systems were created by decorating (14,0), (16,0) and (17,0) zig-zag carbon nanotubes with two or three -CF2SO3H groups. Water molecules were then added to hydrate the systems to values of 1-3 H2O/SO3H, resulting in a total of nine distinct simulation cells. The geometry of the cells was optimized and then heated to 300K via repeated velocity rescaling. Once equilibrated, trajectories were obtained in a microcanonical ensemble for up to 20 ps.
Water Sorption and Transport Properties of Polymer Electrolyte Membranes: New Insights from Theory
Authors: Roudgar Ata , Monroe Charles , Eikerling Michael H.
Published: September 2009

Pertinent polymer electrolyte membranes (PEM) channel protons through random networks of water-filled pores. Their operation hinges on sufficient amounts of water for proton conduction. This requirement affects structure and properties on > 6 scales. Theoretical research on PEM employs a hierarchy of physical models to address these multiscale challenges. The first part of this contribution focuses on recent progress in ab initio calculations of structural correlations and proton dynamics at dense interfacial arrays of protogenic surface groups. These results have vital implications for the design of PEM that could attain high proton conductivity at minimal hydration. The second part explores the realms of equilibrium and dynamic water sorption and swelling of PEM. The outlined approaches in modeling provide capabilities to predict the membrane response to changing external conditions and to extract parameters of bulk water transport in PEM and vaporization exchange at the membrane surfaces from measured water fluxes through the membrane.
Molecular Level Investigation of PBI Based High Temperature Fuel Cells
Authors: Cheng Chin-Hsien , Sui P.C. , Djilali Ned , Su Ay
Published: September 2009

High temperature operation of polymer electrolyte membrane fuel cells (PEMFC) has many advantages such as reduce the complexity of water management, increase the tolerance of CO poisoning and enhanced electrode kinetics, etc. Traditional PEMFC (Nafion® based) is not suitable for high temperature operation because it requires water to sustain the proton conductivity. The content of water is very low at high temperature operation. Membrane material which is able to show good proton conductivity at low water content condition is required to perform the high temperature operation. Polybenzimidazoles (PBI) based membrane doping with acid is one of the materials that shows good performance at high temperature operation. This paper presents a molecular level simulation by molecular dynamics technique. The information obtained from the study is very helpful in understanding the fundamental knowledge of acid-doped PBI membrane.
Activity of Pt-Sn Catalyst Prepared by Reactive Spray Deposition Technology for Ethanol Electro-oxidation
Authors: Fatih Khalid , Neagu Roberto , Alazate Vanesa , Neburchilov Vladimir , Maric Radenka , Haijiang Wang
Published: September 2009

Direct liquid fuel cells (DLFCs) are promising power sources for small devices operating under ambient conditions, such as electronic portable devices. A one-step, open atmosphere reactive spray deposition technique (RSDT) was used for the first time as a flame-based technique to produce Pt-Sn catalyst for ethanol oxidation reaction. TEM images show catalyst particle size in the range of 2 to 6 nm. XRD patterns confirm crystalline Pt and a possible amorphous to weakly crystallized SnO2 phase. Pt-Sn / 90-10 % showed a superior catalytic performance compared to Pt or Pt-Sn mixtures with higher Sn content.
Identification of Dominant Transport Mechanisms in PEMFC Cathode Catalyst Layers Operated under Low RH
Authors: Xie Zhong , Zhao Xinsheng , Gazzarri Javier , Wang Qianpu , Navessin Titichai , Holdcroft Steven
Published: September 2009

Mass transport phenomena under reduced RH were studied in H2/O2, air and heliox. IR corrected limiting current density and EIS were employed to identify the predominant transport mechanism at various RHs and current densities. It was found that the limiting current density decreased with increasing RH in H2/O2 fuel cell; EIS reveals that the low frequency arcs expand with increasing current density, but contract with increasing RH. The hydration-related low frequency arcs were hidden by gas phase diffusion arcs when operated under air or heliox. It was speculated that low frequency arcs are related to the dissolution and diffusion of reactant in the ionomer thin film. Under low RH operation, oxygen transport in the ionomer thin film within catalyst layer may become an important factor in cell voltage loss.
Codes and Standards for Stationary Fuel Cell Installations and Testing of Single PEMFC as Applicable in the USA
Authors: Ubong Etim
Published: September 2009

With the proliferation of the various distributed power plants including fuel cell for mobility and stationary applications, there is a need to address the issues of codes and standards by all the players. At the moment, various states in the U.S. and the Federal Government agencies are expanding their infrastructural networks to accommodate the vast growing demand for alternative energy and soon, various nations will expand their fuel cell installations too. Knowledge of the fuel cell installation's codes and standards will reduce incidents and accidents and makeovers and streamline the quality of installation. The relevance of codes and standards is that the infrastructure will satisfy the applicable regional or national codes. The second part of this report addresses the applicable test protocol for testing single proton exchange membrane- PEM fuel cell as developed by the U.S. Fuel Cell Council (USFCC). This enables test results from various laboratories and institutions to be compared on the same basis. This work addresses mechanical and electrical installation codes requirements and low temperature PEM operating below 80 oC.
Stability Study of Nitrogen-Modified Carbon Composite Catalysts for Oxygen Reduction Reaction in Polymer Electrolyte Membrane Fuel Cells
Authors: Liu Gang , Li Xuguang , Popov Branko
Published: September 2009

The objectives of this paper are to evaluate the nature of the active sites, the stability and degradation mechanism of nitrogen-modified carbon composite (NMCC) catalysts for oxygen reduction reaction in polymer electrolyte membrane (PEM) fuel cells. Two NMCC catalysts were synthesized using our previously reported method (ECS Transactions 11 (1) (2007) 241) at pyrolysis temperatures of 800 and 1100 oC, respectively. The catalyst pyrolized at 800 oC containing pyridinic nitrogen showed higher initial activity but much lower stability due to the protonation reaction in the acidic environment. The catalyst pyrolized at 1100 oC mainly containing graphitic (quaternary) nitrogen exhibited good long-term stability. The proposed nitrogen-modified active sites (pyridinic and graphitic nitrogen) for the non-precious metal catalysts can explain both the observed activity and stability of the catalysts.
SO2 Adsorption on Carbon-Supported Pt Electrocatalysts
Authors: Punyawudho Konlayutt , Monnier John , Van Zee John W.
Published: September 2009

Adsorption of SO2 on Pt/C catalysts was investigated by temperature programmed desorption (TPD). SO2 concentrations were varied from 5 ppm to 1% (vol) and adsorption isotherms were determined at 25, 50, and 80{degree sign}C. Desorption temperatures of SO2 increased as adsorption temperatures of adsorption were increased, and SO2 concentrations were lowered. TPD experiments following exposure to room temperature O2 (after the first TPD event) gave an additional SO2 peak at temperatures higher than the initial SO2 peak, thus identifying two different types of SO2 adsorption. Two adsorption energies were indentified as weak and strong adsorption. 18O2 isotope was introduced during oxygen titration to verify adsorption mechanism and dissociative species. Langmuir isotherms were plotted and led to isosteric adsorption of SO2 for weak and strong adsorption.
Performance Durability of Polyaniline-derived Non-precious Cathode Catalysts
Authors: Wu Gang , Artyushkova Kateryna , Ferrandon Magali , Kropf Arthur Jeremy , Myers Deborah , Zelenay Piotr
Published: September 2009

This research has focused on performance durability of the newly-developed polyaniline (PANI)-derived non-precious metal cathode catalysts. These catalysts show high oxygen-reduction activity in electrochemical and fuel cell testing, reflected by the onset and half-wave (E1/2) potentials of oxygen reduction in RDE testing of 0.90 V and 0.77 V, respectively. Best-performing catalysts also exhibit insignificant H2O2 yield of less than 1%. Catalyst performance in fuel cell testing strongly depends on the choice of nitrogen precursors, transition metals used, and carbon supports. As expected, catalyst stability is affected by the operating voltage of the fuel cell, with more stable performance observed at low operating voltage and open cell voltage, than at intermediate voltages. Physical and electrochemical characterization of the catalysts, also in the presence of hydrogen peroxide, has been carried out to provide insight into the origin of possible degradation mechanisms.
The Characterization of Co-Ru-Pt Ternary Catalyst Prepared by Electrochemical Process
Authors: Kwon Oh Joong , Ahn Sang Hyun , Cho Insoo , Kim Jae Jeong
Published: September 2009

The Co-Ru-Pt and Co-Pt-Ru catalysts (named according to preparation sequence) were prepared on a carbon paper through the electrochemical processes such as an electrodeposition and a galvanic displacement reaction. The catalysts having various compositions were prepared by controlling the electrochemical process, and the electrochemical property of each catalyst was investigated through diverse electrochemical analysis methods. From the correlation between the composition, obtained by inductively coupled plasma - atomic electron spectroscopy (ICP-AES), and the CO stripping analysis, the optimum composition of Co-Ru-Pt and Co-Pt-Ru were proposed with the reports about composition-dependant catalyst activity of Co-Ru-Pt and Co-Pt-Ru catalysts.
Development of Bifunctional Electrodes for Closed-loop Fuel Cell Applications
Authors: Altmann Sebastian , Kaz Till , Friedrich K. A.
Published: September 2009

Unitized regenerative fuel cells (URFC) in combination with photovoltaic modules are attractive systems for space missions because of their extended operation times and low weight. Electrical energy, being stored throughout the planetary day, can be converted into electricity by the fuel cell during the night. An important topic for URFC development is the function of the so-called bifunctional oxygen electrodes which generally require a combination of favourable properties for fuel cell and electrolysis mode. In this work different oxygen electrode configuration for the operation in a unitized reversible fuel cell are compared. Different possibilities for bifunctional electrodes based on the primary catalysts are compared, namely a mixture of catalysts, layered structures with the two different catalyst layers, and segmented areas with single catalysts. It was shown that the mixture of both catalysts (Pt and IrO2) performs best for the present stage of electrode development.
Exploring Fuel Cell Cathode Materials: A High Throughput Calculation Approach
Authors: Gavartin Jacob , Sarwar Misbah , Papageorgopoulos Dimitrios , Gunn David , Garcia Sonia , Perlov Alexander , Krzystala Arek , Ormsby Dan L. , Thompsett David , Goldbeck-Wood Gerhard , Andersen Amity , French Sam
Published: September 2009

The high throughput calculation methodology and plane wave density functional theory is applied to simultaneously assess surface stability of Pt3Co, Pd3Co and Pt3Ag alloys and their catalytic activity with respect to oxygen reduction reaction (ORR). It is argued that mechanical surface strain introduced by alloying is an important factor controlling a materials catalytic activity along with chemical modification of the near-surface layers.
Preparation of Platinum Catalyst on Silver Membranes for PEMFC with Green Electroless Deposition
Authors: Taubert Jenny , Loy Douglas A.
Published: September 2009

As an alternative to platinum on carbon electrocatalysts for polymer electrolyte fuel cells, we have deposited platinum on silver membranes using electroless reduction of platinum salts with isopropanol. To speed discovery and optimization of the electroless chemistry, we developed two visual screening experiments to identify which formulations deposited active platinum catalysts. Once an environmentally friendly or green formulation was identified, we optimized the chemistry looking at catalyst activity and morphology as a function of temperature and reactant concentrations.
First-principles-based Reaction Kinetics Model for Oxygen Reduction Reaction on Pt3Ni(111)
Authors: Viswanathan Venkatasubramanian , Rai Varun , Pitsch Heinz
Published: September 2009

We apply a first-principles-based reaction kinetics model recently developed for Oxygen Reduction Reaction (ORR) on Pt3Ni(111). This model builds upon the detailed determination of the structure of the adsorbate layer on the catalyst surface using a combination of Density Functional Theory (DFT) and Dynamic Monte Carlo (DMC) simulations. We show that the active pathway for ORR on Pt3Ni(111) seems to proceed through a pathway that has a higher intrinsic rate than on Pt(111). The results from the first-principles based kinetics model presented here provides an explanation for the enhanced catalytic activity for ORR on Pt3Ni(111).