bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectral–temporal analysis of OAEs in normal-hearing humans: Latencies, fine structure, and multiple internal reflections
Authors: Konrad-Martin Dawn , Keefe Douglas H. , Simmons Jeffrey L.
Published: October 2013

Otoacoustic emissions (OAEs) display complexity in both time and frequency, which may be obscured in traditional response analyses. Time-frequency representations (TFR) of the eliciting stimuli and the recorded OAE provide a tool to understand this complexity. TFRs were applied to stimulus-frequency (SF) and distortion-product (DP) OAEs obtained in 25 normal-hearing adults, using three classes of stimuli: continuous tones, gated tones (tonal stimuli with well-defined onset, steady state and decay), and tone pips (band-limited impulses). Synchronous spontaneous OAEs were measured using clicks to assess their contributions to TFRs of SFOAE and DPOAEs. A common form of TFR generated from tone-pips is a collection of frequency-specific components, with each component characterized by one or more brief segments or a single long-duration segment. Frequency-pulling effects between components were observed, however, little evidence was found for interactions within transient SFOAEs in the form of intermodulation distortion. TFRs show evidence for strong emission regions or cochlear ‘‘hot spots’’ within pip responses, and multiple internal reflections within gated and pip responses. The resulting measures of OAE latencies are compared with model predictions. Thus, the TFR analysis provides a quantitative tool for measuring the spectral-temporal organization of multiple-component OAEs. [Work supported by NIH, DC003784.]
Acoustical imaging of high-frequency elastic responses of targets
Authors: Morse Scot F. , Hefner Brian T. , Marston Philip L.
Published: October 2013

Acoustical imaging was used to investigate high-frequency elastic responses to sound of two targets in water. The backscattering of broadband bipolar acoustic pulses by a truncated cylindrical shell was recorded over a wide range of tilt angles [S. F. Morse and P. L. Marston, ‘‘Backscattering of transients by tilted truncated cylindrical shells: time-frequency identification of ray contributions from measurements,’’ J. Acoust. Soc. Am. (in press)]. This data set was used to form synthetic aperture images of the target based on the data within different angular apertures. Over a range of viewing angles, the visibility of the cylinder’s closest rear corner was significantly enhanced by the meridional flexural wave contribution to the backscattering. In another experiment, the time evolution of acoustic holographic images was used to explore the response of tilted elastic circular disks to tone bursts having frequencies of 250 and 300 kHz. For different tilt angles, specific responses that enhance the backscattering were identified from the time evolution of the images [B. T. Hefner and P. L. Marston, Acoust. Res. Lett. Online 2, 55–60 (2001)]. [Work supported by ONR.]
The role of reverberation in release from masking due to spatial separation of sources in speech recognition
Authors: Kidd Gerald , Arbogast Tanya L. , Brughera Andrew , Mason Christine R. , Hartmann William M.
Published: October 2013

Arbogast et al. [ARO Mtg. (2002)] found a large release from masking obtained by spatial separation of a target talker and competing speech masker. Both stimuli were sentences from the Coordinate Response Measure corpus [Bolia et al., J. Acoust. Soc. Am. (2000)] processed by extracting the envelopes of 15 narrow frequency bands and using the envelopes to modulate carrier tones at the center of each band. By playing nonoverlapping subsets (6–8) of bands from signal and masker they minimized the energetic component while maximizing the informational component of masking. This study extends that work to determine the interaction between reverberation, masker type, and spatial release from masking. Stimuli were processed and presented as above. The target sentence was played at 0-deg azimuth while the masker sentence was played at 0 or 90-deg azimuth. Noise–masker controls were also tested. The listening environment was an IAC booth having dimensions of 12 ft×13 ft. Acoustic extremes were achieved using PlexiglasTM (highly reflective) or foam (highly absorptive). The results indicated that the amount of masking and the spatial release from masking depend both on the characteristics of the room and masker type. Discussion will center on the acoustic and perceptual factors affecting performance. [Work supported by NIH/NIDCD.]
In situ measurements of the fragipan acoustic to seismic coupling signature
Authors: Howard Wheeler , Hickey Craig J.
Published: October 2013

The phenomena of acoustic to seismic (A/S) coupling, observed and studied since the 1950s, has most recently been used to detect shallow buried objects [Sabatier and Xiang, J. Acoust. Soc. Am. 105, 1383 (1999); 106, 2143 (1999)] and monitor detonation of nuclear weapons [Orcutt, J. Acoust. Soc. Am. 105, 1038 (1999)]. At an air–surface interface airborne acoustic energy is coupled into the ground as seismic energy. The ratio of the seismic and airborne waves constitutes the A/S coupling signature, which is distinctive to the underlying structure. Seismic energy received by a geophone at the interface contains information, via reflected waves, about the underlying subsurface layer, media, and boundaries. Of particular interest in the Mississippi River Valley is the fragipan layer. The fragipan is the layer that directly affects the growth of crops, rate of soil erosion, and rate of water absorption in underlying layers. In this presentation, the A/S coupling signature data taken at an agricultural field station and forward model are discussed.
Prediction of acoustic radiation based on particle velocity measurements
Authors: Hu Qiang , Ni Zhi , Lu Huancai , Wu Sean , Zhao Yang
Published: October 2013

It has been shown [Wu and Hu, J. Acoust. Soc. Am. 103, 1763–1774 (1998); 104, 3251–3258 (1998)] that the radiated acoustic pressure can be determined directly once the particle velocity distribution over an imaginary surface enclosing the object under consideration is obtained. This alternative formulation is advantageous over the classical Helmholtz integral theory, which requires the surface acoustic quantities to be completely specified before the field acoustic pressure can be calculated. The difficulty with this approach is the measurement of the fluctuating part of particle velocity in the fluid medium. This paper describes an attempt to measure particle velocities using a laser anemometer. To facilitate measurements, fine particles are sprayed in the air by a fog generator. These particles oscillate in an insonified field at the excitation frequency. Both amplitudes of particle velocities in the normal and tangential directions and phases are measured. These data are used to predict the field acoustic pressures, which are validated by measurements taken at the same locations. Since the field acoustic pressures are calculated directly, the nonuniqueness difficulties inherent in the Helmholtz integral formulation are no longer existent and the efficiency of numerical computations is significantly enhanced. [Work supported by NSF.]
MEN2B syndrome presenting as an acute respiratory emergency
Authors: Dharmshaktu Pramila , Garg Abhilasha , Manglani Danny , Dhanwal Dinesh
Published: October 2013

An 18-year-old girl presented to the emergency department with a history of noisy breathing and breathlessness progressively increasing for few days. The patient had stridor and tachypnoea. She was tall with a long thin face, wrist sign and high-arched palate suggestive of marfanoid features. X-ray of the neck revealed critical tracheal narrowing. Emergency tracheostomy was performed as a lifesaving procedure. Non-contrast CT neck revealed extratracheal compression by a mass surrounding it. Contrast-enhanced CT scan of the neck revealed heterogeneous mass arising from the right lobe of the thyroid and tracheal deviation with narrowing. Fine-needle aspiration cytology of the mass revealed medullary carcinoma of the thyroid, positive for calcitonin. Calcitonin levels were raised. Apart from the marfanoid features she had localised swellings over the lips, lower eyelid and the lateral aspects of the tongue, clinically suggestive of neuromas. A clinical diagnosis of multiple endocrine neoplasia type 2B syndrome was made. The patient underwent total thyroidectomy with central lymphnode dissection. This case highlights an unusual presentation of a rare disease.
Strength and deformation properties of Norwegian clays from laboratory tests on high-quality block samples
Authors: Karlsrud Kjell , Hernandez-Martinez Francisco Gabriel
Published: October 2013

It has for a long time been a challenge for the geotechnical profession to determine the true behaviour of clays based on soil sampling and laboratory testing. The main difficulty has been to retrieve sufficiently undisturbed samples that maintain the clay structure and correctly depict the in situ stress–strain and strength behaviour of the clay under any kind of imposed drained or undrained loading conditions. The extent and impact of the disturbance caused by sampling depends on a number of factors, such as the specific sampling equipment and sampling procedures that are used, index properties of the clay (sensitivity and plasticity index in particular), and sampling depth. Experience with laboratory tests on conventional piston samples shows that sample disturbance commonly affects the test results. In the mid 1970s, the University of Sherbrooke developed a special block sampler that was shown to give samples of very high quality. Between 1982 and 2010, the Norwegian Geotechnical Institute (NGI) has used the Sherbrooke block sampler at 22 different sites in Norway and one site in the UK. Two to five block samples were collected at each site, on which oedometer, undrained triaxial, and direct simple shear (DSS) tests were carried out in the laboratory. Essentially all samples tested showed far superior quality as compared to conventional piston samples. It was therefore considered to be valuable to summarize test results obtained on such high-quality samples, as presented herein. Deformation and strength parameters from individual tests are summarized and compared against index data for the different clays tested. This has resulted in a series of correlation diagrams. The index parameters found of most relevance to use as correlation parameters are the natural water content and clay sensitivity. The latter is expressed in two categories: medium to low sensitivity (St< 15) and high sensitivity (St> 15). The overconsolidation ratio is another key parameter. The correlation diagrams presented include the following: (i) pre-consolidation pressure, compressibility, permeability, and permeability change index as derived from oedometer tests; (ii) normalized peak and post-peak shear strength, peak effective friction angle, stiffness, and strain at failure from undrained triaxial and DSS tests. When design analyses are to be based on the results of tests on high-quality block samples, as compared to conventional piston samples of poorer quality, it is important to ensure that the end result complies with past semi-empirical experiences.
Re-evaluating niche conservatism versus divergence in the Woodland Salamander genus Plethodon: a case study of the parapatric members of the Plethodon glutinosus species complex
Authors: Wooten Jessica A. , Camp Carlos D. , Combs Jonathon R. , Dulka Eden , Reist Alexandra , Walker Donald M.
Published: October 2013

The Woodland Salamander genus Plethodon Tschudi, 1838, consists of terrestrial lungless salamanders, has been cited as an exemplar of a lineage characterized by niche conservatism. This conclusion has contributed to broader hypotheses dealing with the role of niche conservatism in speciation and the maintenance of species diversity. We re-evaluated these salamanders using newly published techniques designed to detect niche conservatism versus niche divergence using computer-based niche modeling and spatial analysis within a phylogenetic framework. We specifically studied parapatric neighbors in the species complex of Plethodon glutinosus (Green, 1818) to determine if there is evidence of a role for niche divergence at speciation or if niche conservatism characterizes the complex as has been reported for the larger genus. We found that new statistical approaches yield different results from earlier work, suggesting that niche divergence has been a much more important player in the speciation process than has heretofore been understood. Although different parts of the overall Plethodon phylogeny may be characterized by different rates of niche evolution, the rapidly burgeoning area of research centered on niche conservatism appears to be in a state of flux with regards to methods that give consistently repeatable results.
CELLULAR STRUCTURE IN CONDENSED MATTER
Authors: LEV B. I.
Published: October 2013

In this paper, general description of a cellular structure formation in a system of interacting particles has been proposed. Analytical results are presented for such structures in colloids, systems of particles immersed into a liquid crystal and gravitational systems. It is shown that physical nature of formation of cellular structures in all systems of interacting particles is identical. In all cases, a characteristic of the cellular structure, depending on strength of the interaction, concentration of particles and temperature, can be obtained.
Spatially-Resolved Modeling of Electric Double Layers for the Oxygen Reduction Reaction in Water-Filled Platinum Electrodes
Authors: Zenyuk Iryna V , Litster Shawn
Published: October 2013

We present a computational model for studying ion transport and reaction kinetics within water-filled pores of an ionomer-free, thin film Pt cathode inside polymer electrolyte fuel cell (PEFC). The model resolves the electric double layers (EDLs) at the water|Pt and water|membrane interfaces. We investigate the coupling of the distributed electrochemical reactions and the EDL physics, and their effect on the overall electrode performance through both the kinetics and transport. Oxygen reduction reaction (ORR) is resolved locally along the pore wall, where both acidic and alkaline mechanisms are included due to a large axial variation in pH along the pore. An important finding is the significant contribution of the alkaline mechanism to the overall current at high applied potentials and its contribution to the ionic conductivity within the water-filled pore.
Atomistic Simulation of Interface between Nafion Electrolyte and Pt Catalysts
Authors: Zhou Juanjuan , Zhou Xiangyang , Zhang Xuyang , Liu Hongtan
Published: October 2013

Molecular dynamics (MD) and ab initio molecular dynamics (AIMD) simulations were conducted in order to define the structure of Nafion/Pt interface and to probe the mechanisms of oxygen reduction and hydrogen oxidation reactions. The results indicate that the interface can be characterized by a few layers of orderly distributed molecules. The periodicity in the first layer on the surface of Pt is broken at the boundaries between hydrophilic and hydrophobic domains. In addition, the periodically distributed molecules in the first layer on top of the Pt also form a superlattice. This ordered layer favors oxygen reduction but does not favor hydrogen oxidation. The oxygen reduction path is 2Pt + O2 + H3O+ + e- → 2Pt-OH + H2O or 2Pt–OH2 + O2 + 2H3O+ + 2e- → 2Pt-OH + 4H2O. The hydrogen oxidation path is 2Pt–H2 + H2O → 2Pt-H- + H3O+.
Molecular Dynamics Study for the Friction Coefficient between a Water Droplet and a Solid Wall
Authors: Fukushima Akinori , Mima Toshiki , Kinefuchi Ikuya , Tokumasu Takashi
Published: October 2013

In this study, the channel size dependence of transport properties of a water droplet was clarified by molecular dynamics simulations. Considering several models of a micro channel, we evaluated forces between the water droplet and the solid wall. From these results, we clarified that the friction forces depend on the width of the channel and the size of the droplet. Moreover, the effect of the liquid-vapor interface was considered.
Investigation of Transport Phenomena in PEMFC Through 1-D Macro-Homogeneous Model
Authors: Setzler Brian P. , Fuller Thomas F.
Published: October 2013

A 1-D macro-homogeneous model of the PEMFC is presented with the ability to simulate electrochemical impedance spectroscopy (EIS). The model is shown to reproduce the inductive loop seen at low frequencies at moderate to high current densities. Based on the model, this feature of EIS can be assigned to modulation of membrane conductivity due to water buildup. In addition, the model is compared to experimental polarization data and EIS at low oxygen concentrations to evaluate the oxygen reduction reaction kinetics at high overpotential and oxygen transport limitations under non-condensing conditions. The results suggest that a lower reaction order and dual Tafel slope may be necessary to best describe experimental results.
Perfluorinated Sulfonic Acid Membrane and Membrane Electrode Assembly Degradation Correlating Accelerated Stress Testing and Lifetime Testing
Authors: Rodgers Marianne P. , Bonville Leonard J. , Mukundan Rangachary , Borup Rod L , Ahluwalia Rajesh , Beattie Paul , Brooker R. Paul , Mohajeri Nahid , Kunz H. Russell , Slattery Darlene K. , Fenton James M.
Published: October 2013

An important step in achieving fundamental understanding of fuel cell failure mechanisms and development of technology to mitigate these failures is accomplished by analysis of directed lifetime and failure test results. Several lifetime, accelerated stress, and drive cycle test protocols have been developed and carried out. The two major ASTs that have been developed to evaluate membrane degradation are 1) Open circuit voltage tests, which are designed to accelerate chemical degradation, and 2) Relative humidity cycling tests, which are designed to accelerate mechanical degradation. The results from these tests have been compared to field tests. The ultimate goal is to use the laboratory tests to predict data in the field. An overall predictive decay model is being developed through a combination of specific modeling and tests.
Operational Experience from a 5 kWe HT-PEFC System with Reforming of Diesel and Kerosene
Authors: Samsun Remzi Can , Pasel Joachim , Meißner Jan , Janßen Holger , Lehnert Werner , Peters Ralf
Published: October 2013

An integrated fuel cell system consisting of a fuel processor for diesel and kerosene and high-temperature polymer electrolyte fuel cell (HT-PEFC) stacks was developed and tested. This paper reports on the operational experience from system tests with different middle distillates. The key components, the autothermal reformer and the HT-PEFC stack, showed robust performance during system tests. An electrical peak power of 5.56 kW was reached in the system. Performance losses were observed for the water-gas shift reactor as well as for the catalytic burner. Due to the limited partial load capability of the reformer, the system was operated with constant reformer load. As a consequence, the hydrogen utilization of the stack was rather low at partial load operation of the system. The target hydrogen utilization of 83% was realized at the target maximum system power of 5 kW.
Integrated Methanol Steam Reformer/Electrochemical Hydrogen Compressor
Authors: Chen Ru , Fan Rong , Duong Hau H. , Chisholm Calum R. I. , Kaye Ian W.
Published: October 2013

An electrochemical hydrogen compressor (EHC) based on a solid acid electrolyte is built. The EHC operates at temperatures from 230 to 250 °C. The EHC can be used to separate hydrogen from simulated reformate containing more than 2 % CO. The EHC can be directly combined with a methanol steam reformer (MSR). The electrochemical hydrogen compressor with an internal reformer is tested with methanol. The MSR/EHC has the capability of generating hydrogen from methanol, separating hydrogen from impurities, and compressing hydrogen to high pressures.
Efficient Use of Resources in Energy Converting Applications
Authors: Jacobs Nadine , Büsselmann Julian , Theuring Steffen , Zobel Marco , Dyck Alexander
Published: October 2013

The present work deals with testing procedures based on Fuel Cell Testing and Quality Assurance (FCTESQA) for Proton Exchange Membrane Fuel Cells (PEM FCs) stacks. Within these procedures parameters like pressure, temperature, humidification and stoichiometry have been varied. All this leads to optimized operating parameters to improve the efficiency of the stack. The optimization should lead to a more efficient Micro-combined heat and power (Micro-CHP) system with an integrated PEM FC stack. It is one of the most efficient principals for utilization of energy content of fuels, whether fossil or renewable. There are a lot of advantages for Micro-CHP systems like high overall efficiency, possible grid independency and flexibility in supply on demand. In any case, some research aspects must be taken into account, such as the complex gas purification, gas humidification, and the low temperature gradient for the heat exchangers in a heating system.
Investigation of the Purging Effect on the Performance of Dead-End Anode PEM Fuel Cell Vehicle: A Driving Cycle Test
Authors: Gomez Alberto Gomez , Sasmito Agus P. , Shamim Tariq
Published: October 2013

The dynamic behavior of the PEM fuel cell performance is one of the main factors for successful operation of fuel cell vehicle. Maintaining the fast time response whilst keeping the stable and high stack performance is of importance, especially during acceleration and deceleration. In this paper, we evaluate the transient response of a PEM fuel cell stack with a dead-end anode during the European legislated driving cycle together with the effect of purging factors. The dead-end anode PEM fuel cell stack comprises of 24 cells with 300 cm2 active catalyst area and operates at low hydrogen and air pressure. The humidified air is supplied to the cathode side; whereas the dry hydrogen is fed to the anode. The liquid coolant is circulated to the stack and radiator to maintain the thermal envelope throughout the stack. The effects of purging frequencies, purging durations, coolant flow rate together with the effect of cathode stoichiometry are examined with regard to the stack performance during the transient driving cycle.
Nafion-1,2,3-Triazole Composite Membrane for Fuel Cell
Authors: KIM Je-Deok , Jun Mun-Suk , Rhee Hee-Woo
Published: October 2013

The mechanical stability of Nafion - 1,2,3-triazole composite membrane and conductivity and cell performance in the single cell were investigated by dynamic elastic modulus and fuel cell measurement system, respectively. The thermal stability of the composite membrane was increased than that of Nafion 112. The viscosity was also improved after activation treatment of the membrane. The maximum conductity of 0.07 S/cm and maximum power density of 582 mW/cm2 were obtained at the single cell test. A long term stability of around 140 h was obtained at the high cell temperature of 100 oC and low RH = 30 %.
Neutron Imaging of Water Transport in Polymer-Electrolyte Membranes and Membrane-Electrode Assemblies
Authors: Hussey Daniel S , Spernjak Dusan , Wu Gang , Jacobson David L , Liu Dazhi , Khaykovich Boris , Gubarev Mikhail V , Fairweather Joseph D. , Mukundan Rangachary , Lujan Roger , Zelenay Piotr , Borup Rod L
Published: October 2013

Neutron imaging was been widely used to study the water distribution in proton exchange membrane fuel cell flow fields and gas diffusion layer. However, due to the limitation of spatial resolution, there has been little focus on the water transport process in the membrane and catalyst layer. Here we report on measurements made on thick membranes under saturation gradients which show no “jump condition” and on thick cathode catalyst layers to understand the water transport issues in a non-precious metal catalyst. Finally, we speculate on the possibility of obtaining neutron images with ~1 µm spatial resolution.
Investigation of Water Transport in Perforated Gas Diffusion Layer by Neutron Radiography
Authors: Lu Zijie , Waldecker James , Xie Xingbin , Lai Ming-Chia , Hussey Daniel S , Jacobson David L
Published: October 2013

The influence of gas diffusion layer (GDL) modifications by laser perforation technique on fuel cell water management is investigated in this study. The liquid water distribution in membrane-electrode-assembly (MEA) and water breakthrough in GDL are visualized using high resolution neutron radiography. The perforated GDL reduces water transport resistance, enhances water breakthrough in GDL, and promotes uniform water distribution in MEA. The observed effects account for the improved fuel cell performance caused by the perforated GDL.
A Comparison of Laboratory Based and Synchrotron Based Nano X-ray CT for PEFC Micro Porous Layer
Authors: Khajeh Hosseini Dalasm Navvab , Kotaka Toshikazu , Tabuchi Yuichiro , Pasaogullari Ugur
Published: October 2013

The nano-structure of micro porous layers (MPLs) used in polymer electrolyte fuel cells (PEFCs) has introduced new challenges to existing tomography techniques. X-ray Microscopy (XRM) has fundamental abilities such as: 1) non-destructive 3D tomography, 2) high energy, enabling deeper penetration and internal imaging, and 3) strong absorption and phase contrast dependence to elemental composition. The nanostructure of an MPL was analyzed by two nano-scale XRM techniques: 1) Xradia Ultra XRM-L200 laboratory based X-ray microscope, and 2) synchrotron based transmission X-ray microscope (TXM) at beamline 32-ID C of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). The synchrotron X-ray CT resulted in better resolution and edge sharpness at the solid/pore boundary. Additional comparison between these techniques is performed by obtaining the key MPL nanostructural parameters and transport property such as bulk porosity, pore size distribution, tortuosity, and effective oxygen diffusivity.
Impact of CeOx Additives on Cathode Catalyst Layer Poisoning
Authors: Banham Dustin , Ye Siyu , Cheng Tommy , Knights Shanna , Stewart S. Michael , Garzon Fernando H
Published: October 2013

The impact of CeOx crystallite size on CeOx dissolution was investigated. Three CeOx additives were prepared having crystallite sizes of 6, 13, or 25 nm. An ex-situ method was developed to evaluate the chemical stability of these three CeOx samples, as well as one commercially available CeOx. It was determined that surface area, rather than crystallite size, is the best predictor of chemical stability. In-situ membrane electrode assembly (MEA) testing of the four CeOx additives demonstrated that prior to accelerated stress testing (AST), negligible dissolution of the CeOx additives occurs. Following AST cycling, it was found that end of life (EOL) performance was identical regardless of differences in total CeOx dissolution observed from the ex-situ testing. Finally, it was shown that increasing the anode RH during AST cycling leads to significantly higher EOL performance losses which was attributed to increased CeOx dissolution.
Progress towards Robust Anion Exchange Membranes for Fuel Cell Applications
Authors: Sarode Himanshu , Vandiver Melissa , Caire Benjamin , Liu Ye , Horan James L , Yang Yating , Li Yifan , Herbst Daniel , Lindberg Gerrick E. , Tse Ying-Lung Steve , Seifert Sönke , Coughlin E. Bryan , Knauss Daniel M , Yan Yushan , Voth Gregory , Witten Thomas , Liberatorre Mathew , Herring Andrew M
Published: October 2013

Extensive transport and modeling studies have been performed on a series of polymers based on vinylbenzyltrimethylamonium cations. Flouride is used as a non-reactive surrogate for hydroxide to increase the computational efficiency of transport calculations that can be performed. Interesting effects of water and residual chloride in the film have been explained. In ordered di-block polymers we have strong theoretical evidence for narrow water domains that facilitate rapid transport of anions. With this model we will be able to predict diblock polymer structures that require less water for efficient anion transport. In addition to these studies we are discovering new base stable polymer backbones and cations. A large part of this effort is dedicated to discovering new methods for the production of robust thin anion exchange membranes.
Molecular Design Aspect of Anion Exchange Polymer Electrolytes
Authors: Kim Yu Seung , Fujimoto Cy , Hibbs Michael , Choe Yoong-Kee , Kim Dae-Sik , Chung Hoon , Yim Sung-Dae
Published: October 2013

Anion exchange polymer electrolytes play an important role both in separator (membrane) and in electrode binder (ionomer). Depending on their role, polymer electrolytes must possess certain properties which are essential to improve the alkaline membrane fuel cell performance & durability. In this study, we will present molecular design aspects of anion exchange polymer electrolytes for the use of membranes and ionomeric binders. In-depth studies on chemical degradation of polyaromatic anion exchange membranes and importance of perfluoirnated structure in the catalyst layer will be discussed in addition to the effects of cation type on chemical degradation and interaction with electro-catalysis.
Synthesis and Conductivity of Multiwalled Carbon Nanotubes Modified Poly(Vinyl Alcohol)/Poly(Diallyldimethylammonium Chloride) as Alkaline Anion-Exchange Membranes
Authors: Zhang Jing , Gao Ying , Zhou Tianchi , Qiao Jinli
Published: October 2013

A new type of cross-linked polymer blend membranes consisting of poly(vinyl alcohol) (PVA), poly(diallyldimethylammonium chloride) (PDDA) and multiwalled carbon nanotubes (MWCNTs) have been prepared and evaluated as anion conducting polymer electrolytes. In particular, the anion conductivity (OH-) and water uptake of PVA/PDDA membranes modified with different structures’ MWCNTs were investigated, ie., MWCNTs-COOH, MWCNTs-OH and pristine MWCNT. It is found that the conductivity and water uptake of PVA/PDDA membrane both decreased with addition of 1 wt.% MWCNTs. However, the presence of MWCNTs played an important role in cutting down water uptake. The OH- conductivities were all gradually increased with increasing temperature, where the maximum OH- conductivity of 0.0166 S cm-1 was obtained for PVA/PDDA/MWCNTs at room temperature, and increased with temperature up to 80oC.
Analysis of Ice Distribution in Cathode Catalyst Layer and Shutdown Mechanism at PEFC Cold Start
Authors: Yamada Kazuki , Suzuki Kengo , Tabe Yutaka , Chikahisa Takemi
Published: October 2013

In polymer electrolyte fuel cells, the freezing of produced water deteriorates the cell performance below zero. In this study, we investigated the freezing phenomena in the cathode catalyst layer (CL) by the experiments, and identified the effects of current density, cathode gas pressure, and oxygen concentration. It was shown that the ice distribution and the estimated amount of ice produced in the CL till the shutdown depends on the current density, while they are independent of the cathode gas pressure and the oxygen concentration. To clarify the main cause dominating these tendencies, we introduced the effect of ice formation on an increase in the through-plane electrical resistance of the CL into the three phase boundary and the CL models, and examined the mechanism in the CL. The calculation results correspond to the experimental current density dependency, and the ice distribution is independent of the gas pressure and the oxygen concentration.
Morphological Analysis of Polymer Electrolyte Fuel Cell Electrode Using High Resolution X-ray Computed Tomography and Subsequent Performance Analysis
Authors: Mandal Pratiti , Litster Shawn
Published: October 2013

Here we present a study on the morphology of the porous polymer electrolyte fuel cell (PEFC) electrodes as well as the individual catalyst agglomerates that assemble into the electrode structure, and how those characteristics influence fuel cell performance. The agglomerates and the porous electrode structure were three-dimensionally imaged using non-invasive and non-destructive nano-scale resolution X-ray computed tomography (nano-CT). The GDE fabricated from the same catalyst layer slurry (ink) as the imaged samples were electrochemically evaluated in a PEFC. By using the same ink batch in the two imaging steps, and in the fuel cell testing and then systematically varying ink processing, we have delineated the complex relationships between catalyst ink, electrode structure, and PEFC performance. At the higher current densities, we found that the electrode comprising smaller agglomerates performed better than the one comprising relatively larger agglomerates.
Microscopic Analysis of Interlayer Structure and Oxygen Transport Behaviors in Porous Electrode in PEMFC
Authors: Suzuki Takahiro , Tsushima Shohji , Hirai Shuichiro
Published: October 2013

Multilayered porous electrodes which are composed of catalyst layer (CL), micro-porous layer (MPL) and gas diffusion layer (GDL) are used in proton exchange membrane fuel cells (PEMFCs). In this study, structural analysis of the electrode was performed by scanning electron microscopy (SEM) visualization. It was revealed that micro-scale cracks were formed at an interface in multilayered porous electrodes. Based on these observations, oxygen transport in the interlayer was analyzed by lattice Boltzmann method (LBM) with liquid water behaviors taken into account. The LBM analysis showed that large interfacial crack enhances formation of in-plane liquid water film in the interface, resulting in less oxygen gas transport.
Defect Detection in Fuel Cell Gas Diffusion Electrodes Using Infrared Thermography
Authors: Bittinat Daniel Christopher , Bender Guido , Porter Jason Morgan , Ulsh Michael
Published: October 2013

Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are energy conversion devices that offer high power densities and high efficiencies for mobile and other applications. Successful introduction into the marketplace requires addressing cost barriers such as production volumes and platinum contents. The electrode is currently a cost intensive component within PEMFCs because platinum is employed as the catalyst. For cost reduction, it is vital to maximize efficiency and minimize waste during the manufacturing of electrodes, including gas diffusion electrodes (GDEs), by developing quality control (QC) diagnostics for fuel cell materials that can be applied to the moving material during large scale production. In this work, we report on developing a QC diagnostic for GDEs, involving creating an exothermic reaction on the electrode surface and using infrared (IR) thermography to measure the resulting temperature profile. Experiments with a moving substrate were conducted to demonstrate the applicability of the diagnostic for real-time web-line inspection.
PEMFC Cathode Contamination with Acetylene - Potential Dependency
Authors: Zhai Yunfeng , St-Pierre Jean , Ge Junjie
Published: October 2013

Proton exchange membrane fuel cells exposed to 300 ppm C2H2 were studied in situ with chronopotentiometry, chronoamperometry, cyclic voltammetry and gas chromatography. Fuel cells significantly lost and fully regained performance at all tested cell potentials. The performance changes were due to the presence of C2H2 or reaction products on the Pt catalyst surface. Two cyclic voltammetry peak potentials were identified and respectively ascribed to reduced acetylene species or CO (0.57 to 0.76 V vs HRE), and adsorbed C2H2 (1.04-1.1 vs HRE). Gas analysis partially confirmed the existence of these species because only C2H2, CO2 and CO were identified and revealed an increase in C2H2 conversion from ~1 to 100 % in the 0.55 to 0.85 V cell voltage range.
Cell Performance Distribution in a PEMFC Stack during Contamination
Authors: St-Pierre Jean , Virji Maheboob B.V.
Published: October 2013

A PEMFC stack was contaminated with 50 ppm propene in air. The average performance decreased by 243 mV until a steady state was reached. After the propene injection was interrupted, the average performance increased until a new steady state was attained that exceeded the initial value by ~6 mV. Propene contamination amplified the uneven cell performance distribution along the stack length. End cells showed a larger performance change than the other cells with respect to the pre-contamination phase of respectively 24 and 15 mV. The effect was ascribed to interactions between propene and the uneven temperature distribution. Propene contamination affects both oxygen reduction kinetics and mass transfer as revealed by impedance spectroscopy measurements.
Conductive AFM Study to Differentiate between the Surface Ionic Conductivity of Nafion and Electrospun Membranes
Authors: Dowd Regis Paul , Nguyen Trung Van , Moore David S , Pintauro Peter N , Park Jun Woo
Published: October 2013

Multi-mode atomic force microscopy (AFM) was used to differentiate between Nafion® and electrospun composite nanofiber membranes. The results of this experiment will guide the design of new class of proton exchange membranes (PEM). Characterizing the electrospun composite nanofiber membranes will allow us to identify properties that are ideal for the next generation PEM. Engineering the proton conducting membrane for a PEM fuel cell that allows protons and inhibits other species to cross is vital to its long-term operation. When species other than protons are allowed to cross a PEM, issues arise in the form of electrode flooding, adverse chemical reactions, and reduced fuel cell efficiency.
Investigation of a PEM Water Electrolyzer Based on a Sulfonated Polysulfone Membrane
Authors: Siracusano Stefania , Baglio Vincenzo , Lufrano Francesco , Staiti Pietro , Aricò Antonino S.
Published: October 2013

A sulfonated polysulfone (SPSf) membrane was prepared and used as polymer electrolyte in water electrolysis cell. The behaviour of SPSf in PEMWE was investigated by polarization, electrochemical impedance spectroscopy and chrono-amperometry. The performance was compared to a commercial Nafion 115 membrane. A low series resistance of 0.13 W∙cm2 was measured for the SPSf membrane at 80 °C under water electrolysis. At the same potential value, 1.8 V, the current density values in the polarization curves were 1.29 A·cm-2 and 1.08 A·cm-2 for the cells with Nafion and SPSf membrane, respectively. During a chrono-amperometric measurement, the current density remained constant throughout the test, indicating a suitable stability of the SPSf based cell. The good performance, low cost and excellent lifetime stability of SPSf make this polymer a promising solid electrolyte for the application in PEM electrolyzers.
Novel PdIr/C Catalysts for the Hydrogen Oxidation Reaction in Alkaline Media
Authors: Jervis Rhodri , Mansor Noramalina , Gibbs Christopher , Murray Claire A. , Tang Chiu C. , Brett Dan J. L.
Published: October 2013

A novel PdIr/C supported alloy nanoparticle catalyst has been developed for use in the hydrogen oxidation reaction (HOR) at the anode of an Alkaline Anion Exchange Membrane (AAEM) fuel cell. The catalyst has been characterised using Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDX) and Synchrotron X-ray Powder Diffraction (SXPD). Electrochemical testing suggests it has a comparable activity for HOR as Pt/C and is a good candidate for use on the anode of an AAEM fuel cell.
A Comprehensive Corrosion Study on Metallic Materials for HT-PEFC Application
Authors: Weissbecker Vitali , Reimer Uwe , Wippermann Klaus , Lehnert Werner
Published: October 2013

This work investigates various commercially available austenitic stainless steels and Ni-based alloys as possible metallic bipolar plates for high-temperature polymer electrolyte fuel cells (HT-PEFCs). The dynamic formation and depletion of passivation layers that depend strongly on applied potential were analyzed in 85 wt. % phosphoric acid at RT and 130 °C by means of steady-state polarization. Alloy 2.4869 (Cronix 80) reveals the lowest corrosion rates of 3 – 26 uA∙cm-2 at 130 °C in the passive region under anodic polarization from 0 V to 1.0 V. Negative potentials lead to reduction of the passive layer and to susceptibility to corrosion in the ongoing polarization. Interestingly, the promising alloy 2.4856 with additions of molybdenum and niobium shows a lower corrosion resistance. The release of metal ions was measured using inductively coupled plasma – optical emission spectrometry (ICP-OES). This study clearly demonstrates that the use of bare stainless steels and Ni-based alloys as bipolar plates is not realizable due to meager corrosion resistance.
Characterization of PBI Membranes for High Temperature PEM Fuel Cells
Authors: Yeager Gary W , Krishnan Lakshmi , Early Thomas , Zhang Chunxin , Hjuler Hans A. , Terkelsen Carina , Yang J , Li Q , Steenberg Thomas
Published: October 2013

High Temperature Polymer Electrolyte Membrane (HT-PEM) Fuel Cells provide an attractive alternative to Low Temperature PEM fuel cells with respect to fuel flexibility, simplified cooling system, balance of plant and higher value waste heat without reactant humidification. Optimization of the PEM is critical to achievement of these performance benefits and PEMs derived from phosphoric acid-doped polybenzimidazoles (PBIs) are the most successful for high temperature operation. However, PBI-based membranes face a number of challenges, including oxidative stability and durability in a fuel cell. In this work we present single-cell fuel cell performance using m-PBI membranes with hydrogen.
The Role of Heat Treatment in Enhanced Activity of Manganese Oxides for the Oxygen Reduction and Evolution Reactions
Authors: Gorlin Yelena , Nordlund Dennis , Jaramillo Thomas Francisco
Published: October 2013

In this study we use ex-situ Mn L-edge X-ray absorption spectroscopy and electrochemical characterization to understand the relationship between surface properties of five differently prepared manganese oxides (MnOx) electrocatalysts and their activity for the oxygen reduction and evolution reactions (ORR, OER). We prepare the five catalysts by electrodepositing MnOx on polished glassy carbon electrodes and heat treating them under different conditions: no heat treatment (“no ht”), 250°C, 350°C, 450°C, and 500°C. We find that “no ht” catalyst, despite having the lowest (pseudo)capacitive current, is capable of the largest changes in Mn oxidation state, as the applied potential switches from an ORR to an OER relevant value. Heat treatment at 450°C or 500°C, leading to a significant increase in (pseudo)capacitance, is on the other hand associated with only minor changes in the surface oxidation state. Investigation of (pseudo)capacitive behavior of the same MnOx thin films electrodeposited on a high surface area rather than polished carbon support reveals that the observed differences in pseudocapactive current can be explained by changes in the surface area of the electrocatalysts. Characterization of the electrocatalytic activity of the thin films demonstrates that the catalysts exposed to the two highest temperatures are associated with enhanced bifunctional activity for the ORR and the OER. The enhancement in the ORR activity is attributed to the formation of a Mn2O3 phase, while the enhancement in the OER activity is primarily explained by the increase in the electrochemical surface area of the catalyst.
Development of Ultra-Low Loading Pt Alloy Cathode Catalyst for PEM Fuel Cells
Authors: Popov Branko N , Xie Tianyuan , Kim Taekeun , Jung Won-Suk , Rotchford Joseph C , Kriston Akos , Kim Hansung , Ganesan Prabhu
Published: October 2013

Low loading Pt and Pt-alloy hybrid cathode catalysts are developed for PEM fuel cell application. A novel low temperature pyrolysis procedure was developed for the synthesis of graphitic carbon composite supports and a polyol synthesis was employed for uniform Pt deposition on the carbon composite supports. Rotating ring disk electrode and fuel cell studies indicated the synergistic effect of hybrid cathode catalyst (HCC) which combines the catalytically active carbon composite support and Pt catalyst. The support durability test results indicated that both the HCC250-2nd generation catalyst and Pt/USC-AGC catalysts satisfy the 2017 DOE target of 30 mV loss after 400 h potential holding at 1.2 V under high current density operation in H2/air. The Pt/CCC140-3rd and Pt/USC-AGC catalysts show much lower mass activity loss (<40% loss) after 400 h potential holding experiment.
CV or not CV: Development of Electrode Diagnostics for High-Temperature Polymer Electrolyte Fuel Cells
Authors: Engl Tom , Waltar Kay , Gubler Lorenz , Schmidt Thomas J.
Published: October 2013

In order to achieve reliable data regarding high temperature polymer electrolyte fuel cell degradation (HT-PEFC) a novel diagnostic technique for electrochemically active surface area (ECSA) determination was developed. In situ cyclovoltammetric monolayer CO oxidation charge measurements were combined with real-time CO2 exhaust gas analysis. Different evaluating methods were developed to overcome the problem of side reactions during CO stripping. Furthermore, a calibration curve for absolute ECSA determination via CO stripping was established. These methods were additionally successfully extended and implemented to locally resolved ECSA measurements. In summary, this paper introduces novel fundamental HT-PEFC diagnostics for improved understanding of degradation phenomena.
In Situ, Ionic Conductivity Measurement of Ionomer/Binder-Free Pt Catalyst under Fuel Cell Operating Condition
Authors: An Seong Jin , Litster Shawn
Published: October 2013

This paper presents an experimental investigation of the ionic conductivity within ionomer-free, extended surface platinum (Pt) electrodes. Nanostructured thin film (NSTF) electrodes with low platinum loading and no ionomer binder offer comparable power densities to conventional Pt/C electrodes under properly humidified conditions and are a promising electrode for cost reduction and improved durability. Despite these advantages, the charge transport on these electrodes is not clearly understood. Here we present a new in situ technique that we have applied to directly measuring the ionic conductivities within operating polymer electrolyte fuel cell (PEFC) electrodes made of Pt black catalyst without an ionomer or binder. The effects of various fuel cell conditions such as electrode polarization, oxygen concentration, and humidity are investigated.
Effect of GDL Material on Thermal Gradients along the Reactant Flow Channels in PEMFCs
Authors: See Evan , Kandlikar Satish G
Published: October 2013

Water and thermal management techniques remain as keyroadblocks to widespread commercial implementation of PEMFCs.Typically, within PEMFCs a temperature gradient is seen betweenthe inlet and the outlet of the flow channels. The thermal propertiesand morphological structure of the gas diffusion layer (GDL) arebelieved to play an important role in the temperature variation. Inthis work, an experimental PEMFC with thin foil thermocoupleswere used to measure the temperature just above the membranenear the inlet and outlet locations. Four commercially availableGDLs (Toray TGP-H-060, MRC-105, SGL 25BC, andFreudenberg H2315) were tested in order to investigate their rolein liquid water transport. The GDL morphology was analyzedusing confocal laser scanning microscopy. Thermal gradients weremeasured for all four GDLs at various conditions. It is seen thatthe GDL material properties, in particular the in-plane thermalconductivity, plays an important role in the overall cellperformance due to changes temperature profile and waterdistribution in the flow channels.