bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion-Selective Electrode Solid Contact Base on Neutral-Carrier Ditiophosphate for Mercury Determination at Nanomolar Levels
Authors: Juarez-Gomez Jorge , Ramirez-Silva Maria Teresa , Perez-Garcia Francisco , Palomar-Pardavé Manuel , Romero-Romo Mario , Rojas-Hernández Alberto
Published: September 2014

Potentiometric studies for ion-selective electrodes solid contact based on neutral carriers that contain in their structure sulphur donor groups and an aliphatic chain is presented, this chain may confer stability to the molecule for the formation of metal complexes. The result was obtaining an ISE, for the potentiometric determination of mercury. This sensor allowed continuous mercury measurements at nanomolar levels within a wide concentration interval (1.0 x 10−9 a 1.0 x 10−1) mol L-1, with a detection limit of (9.1 ± 0.8) x 10−10 mol L-1 and a Nernstian response of (29.8 ± 0.4) mV decade-1. The ISE can be used in the 0 – 6 pH interval; it exhibited a high selectivity toward the mercury ions even in the presence of interferents, and can be used as an indicating electrode during potentiometric mercury titration with EDTA, because it is comparable, within its same class with the commercial electrodes.
Rational Design of Amperometric Gas Sensors with Ionic Liquid Electrolytes
Authors: Carter Michael T , Stetter Joseph R , Findlay Melvin W , Patel Vinay
Published: September 2014

We discuss here further issues in the application of room temperature ionic liquid electrolytes to printed amperometric gas sensors. The main issue addressed is design of the amperometric gas sensor, relative to selection of optimal ionic liquid electrolytes for the realization of new gas sensors with superior properties of robustness, stability, sensitivity and limit of detection. Examples are provided in the context of ammonia monitoring.
Mixed-Potential NOx and NH3 Sensors Fabricated by Commercial Manufacturing Methods
Authors: Kreller Cortney R. , Spernjak Dusan , Li Wenxia , Palanisamy Ponnusamy , Brosha Eric L. , Mukundan Randachary , Garzon Fernando
Published: September 2014

Meeting EPA Tier 3 emissions reduction requirements while simultaneously increasing fuel economy to meet new CAFE standards will require optimization of advanced combustion strategies and emissions control technologies. There is an immediate need for suitable exhaust gas sensor technologies to monitor internal combustion engine tailpipe emissions and to control and maintain efficient operation of the engine and exhaust after treatment systems. NH3, NOx, and HC sensors could enable onboard diagnostics and combustion control in lean-burn engines, analogous to the role of O2 sensors in stoichiometric burn engines. Commercial manufacturing methods have been used to fabricate self-heated mixed-potential sensors in a planar automotive configuration. By altering materials composition and operating conditions, we are able to obtain sensitivity/selectivity to each NH3, NOx and HCs. Additionally, these devices exhibit stable performance over months of testing as a result of the stable morphology of the electrode/electrolyte/gas three-phase interface.
Cell-Based Sensing: From 2D to 3D Cell Culture
Authors: Yang Liju , Trivedi Goral , Adcock Audrey F. , Tyson William
Published: September 2014

Cell-based biosensors use living cells or tissues as sensing element to monitor physiological and functional changes induced by external stimuli. Adoption of 3D cell cultures to cell-based biosensors is anticipated to provide more predictive results for in vivo tests, as 3D cultures resemble closer to in vivo conditions than traditional 2D monolayer culture. This study focused on the characterization of 3D cell cultures for their use as sensing elements in cell-based biosensors. We established the conditions for growing cancer cells into 3D spheroids on matrices using oral cancer cell line, CAL 27. We systematically investigated the cellular responses from the 3D culture to anticancer drugs with different action mechanisms and compared to those of traditional 2D culture. The difference in expression of drug-action related protein biomarkers in 3D and 2D cultures was also examined.
(Keynote Talk) Fabrication, Characterization, and Modeling of Field-Effect-Transistor Nanoribbon Biosensors
Authors: Vogel Eric M
Published: September 2014

A review of the fabrication, characterization and modeling of silicon-on-insulator field-effect-transistor nanoribbon chemical and biological sensors is presented. The impact of mobile ions on the sensor electrical response is shown to depend strongly on the nature of the sensor surface. Appropriate bias conditions for these sensors and a model which predicts sensor operation is described.
Use of Personal Glucose Meters for the Detection of E. Coli in Water
Authors: Chavali Ravi , Gunda Naga Siva , Naicker Selvaraj , Mitra Sushanta
Published: September 2014

We have demonstrated the applicability of personal glucose meters for regularly monitoring the bacteriological quality of potable water. The detection principle is based on the preferred consumption of glucose by E.coli, which is measured using a personal glucose meter. The drop in glucose concentrations over time was correlated to the concentration of E.coli. We could accurately detect higher levels of contamination (~2x108 CFU) within 1 hr and extremely low levels of contamination (~2 CFU) within a maximum of 8 hr. The method presented is simple, inexpensive, easy to use and has the potential to be developed into a comprehensive test kit, which can provide both qualitative and quantitative results.
(Invited) A Printed Carbon Nanotube Sensor on a Flexible Substrate
Authors: Tortorich Ryan P. , da Costa Tallis H. , Song Edward , Choi Jin-Woo
Published: September 2014

This work presents inkjet printing of carbon nanotubes on a flexible substrate for a sensor application. An inkjet printed carbon nanotube pattern can be used as a conductive trace or an electrode for a low-cost flexible sensor or a printable electronic device. In this work, an office inkjet printer was modified to print an ink solution made of carbon nanotubes to form conductive patterns on a flexible substrate. Preparation of aqueous carbon nanotube ink was investigated and optimized to achieve good dispersion of carbon nanotubes and high conductance of the printed carbon nanotube patterns. Electrical properties of the printed carbon nanotube pattern were also characterized with a flexible substrate. For a sensor demonstration, the printed carbon nanotube electrode was tested as a working electrode of an electrochemical cell. The results show a promising feasibility for inkjet printed sensor applications.
Graphene Synthesis on Electrodeposited Substrates and Its Integration in MEMS for Sensor Applications
Authors: Tocchio Marco , Ieffa Simona , Bernasconi Roberto , Magagnin Luca , Nobili Luca , Carraro Carlo , Maboudian Roya
Published: September 2014

The synthesis of graphene on dealloyed NiCu is reported. The existence, thickness, and quality of the graphene films are discussed based on their Raman spectra. The growth of graphene on dealloyed NiCu is affected by the amount of copper in the alloy: a transition from graphitic to graphenic layers is observed with increasing copper content. Transfer procedures devised to integrate the graphene layers into functional devices are presented. The experimental results suggest the possibility of using this simple approach to develop new transducing materials integrated with silicon microdevices for sensing applications.
Integration of PVDF (Polyvinylidene Fluoride) in MEMS Production
Authors: Holz Stephanie , Kiricenko Sergej , Rissing Lutz
Published: September 2014

The combination of materials with new processing setups often leads to new opportunities in well-known technologies. Polyvinylidene fluoride (PVDF) is widely used because of its chemical resistance and thermal properties. Usually, it is shaped by spray casting to produce plumber components. PVDF is also known for its piezoelectric behavior, which can be measured in PVDF films, like it was shown by Kawai [1] and others long ago. Nevertheless, piezoelectric materials are used in the production of micro-electro-mechanical systems (MEMS), PVDF is not. Therefore, the main idea is to evaluate the possibilities and afterwards develop a way to integrate PVDF into MEMS product for example as membranes with piezoelectric behavior. It has been observed, that PVDF films which were exposed to an electrical field during drying show a higher piezoelectric behavior than those which were not or have been polarized by an electric field after drying the film.
Shape Anisotropy in Magneto-Impedance NiFe-Based Microsensors
Authors: Cortés Meritxell , Peng Tao , Woytasik Marion , Moulin Johan
Published: September 2014

The magneto-impedance response of narrow multilayered NiFe/Cu/NiFe structures realized by micromolding has been characterized as a function of both the excitation frequency and the magnetic field. It has been found that intrinsic magnetic properties do not depend on the ferromagnetic geometry, but properties related to the applied magnetic field, i.e. anisotropy field and magneto-impedance value do. The results are consistent with numerical simulations and show that the anisotropy field varies with the ferromagnetic film thickness. The highest magneto-impedance variation and anisotropy field, 170 % and 4200 A/m were found for the narrowest and thickest structure.
Wafer Bonding for MEMS Vacuum Packaging
Authors: Dragoi Viorel , Pabo Eric
Published: September 2014

Various Micro- Electro- Mechanical Systems (MEMS) devices are incorporated into mobile electronic devices. A particular category of MEMS devices require vacuum packaging by wafer bonding with the requirement to encapsulate vacuum levels of 10-3 mbar or higher with long time stability. The vacuum requirement is limiting the choice of the wafer bonding process and raises significant challenges to the existing investigation methods (metrology) used for results qualification. This paper reviews some important aspects related to process choice and provides an overview of the needs to be addresses in terms of metrology for wafer bonding.
A Facile Microfabrication Process of Self-Doping SiGe/Si Multi-Quantum Well Arrays for Thermo Electrical Characterization
Authors: Fang Zhong , Dong Tao , He Yong , Yang Zhaochu , Su Yan , Wang Kaiying
Published: September 2014

In this paper, we report a relatively facile microfabrication process of self-doping SiGe/Si multilayer quantum well (MQW) thermoelectrical arrays as well as their thermoelectrical properties. By the process, bolometer arrays (320×240) with pitch size 40 µm have been fabricated. The top view and side view SEM images show high yield (100%) of the arrays through the process. The Au interconnects are used to characterize thermal-electrical properties of individual bolometer. Their TCR (temperature coefficient of resistance) of the arrays is about -2.6%K-1 at 303K by thermal-electric characterization.
Electrochemical Characterization of Ion-Sensitive Capacitors with ALD Al2O3 as the Sensitive Dielectric
Authors: Perez Ramos Berni Manolo , Molina Reyes Joel
Published: September 2014

The design, fabrication and characterization of Ion-Sensitive Capacitive Sensors (ISCAPs) is presented. These sensors were fabricated with a single metal level CMOS process, and they incorporate special capacitive arrangements which help to improve the sensor's response (sensitivity). Specifically, the main advantage of this kind of sensor is that the measurements can be recorded by flat-band voltage shift and maximum capacitance (Cox) changes. Additionally, an integrated quasi-reference electrode has been included in the design, which provides the possibility of making measurements with both: an external or the integrated electrode. Based on previous results of the chemical and morphological characterization of materials after immersion in buffer solutions, ALD aluminum oxide (Al2O3) has been selected as the sensing material, providing both, high sensitivity and stability for measurements in the short term. It is shown that these sensors operate with both sensing mechanisms and with stability when measuring with the included quasi-reference electrode.
Post-CMOS Integration of MEMS Inertial Sensors Using Oxidized Porous Silicon Technique
Authors: Ge Daohan , Ren Naifei
Published: September 2014

In this work, a low-cost and CMOS-compatible fabrication method to produce CMOS-MEMS porous silicon inetial sensors by using a thick oxidized prous silicon (OPS) layer is demonstrated. The OPS layer was fabricated before the standand CMOS process used for defining the contour of MEMS structures as well as dielectric isolation. This OPS techique has a substantial cost advantage over DRIE techniqe and can porduce very thick layers without severe stress problems. Two kinds of MEMS inertial structures have been produced and the residual stresses of the OPS substrate were measured.
Enhancement of La0.6Sr0.4Co0.2Fe0.8O3
-δ Activity by Ion Implantation for Low-Temperature SOFC Cathodes
Authors: Huang Yi-Lin , Pellegrinelli Christopher , Lee Kang Taek , Perel Alexander , Wachsman Eric D.
Published: September 2014

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) has been demonstrated to be one of the best performing mixed ionic-electronic conductors (MIEC) for SOFC cathode materials. Surface exchange on LSCF, however, limits the oxygen transport and the performance. In this study, we investigated a composite cathode with surface modification of LSCF for enhanced oxygen dissociation on the surface, while utilizing LSCFs ability to transport oxygen through the bulk. Manganese ions were ion implanted into LSCF bar samples. Various implantation energies and ion concentrations were used to create samples with different Mn-ion depth profiles. The oxygen transport properties were characterized by electrical conductivity relaxation (ECR), using DC four-point probe measurements during the oxygen re-equilibration processes. The oxygen transport properties, chemical diffusion coefficient (Dchem) and chemical surface reaction coefficient (k
chem) were obtained by fitting ECR data using the diffusion equations. The changes of k
chem for different Mn doping levels and energies were determined. The Mn ion implanted LSCF samples showed an enhanced k
chem, improving the overall oxygen reduction reaction (ORR) for LSCF cathodes.
High Performance Infiltrated Backbones for Cathode-Supported SOFC's
Authors: Gil Vanesa , Hansen Kent Kammer
Published: September 2014

A four-step infiltration method has been developed to infiltrate La0.75Sr0.25MnO3+δ (LSM25) nanoparticles into porous structures (YSZ or LSM-YSZ backbones). The pore size distribution in the backbones is obtained either by using PMMA and/or graphites as pore formers or by leaching treatment of samples with Ni remained in the YSZ structure at high temperatures. All impregnated backbones, presented Rs comparable to a standard screen printed cathode, which proves that LSM nanoparticles forms a pathway for electron conduction.
Performance Comparison between Ni–SDC and Ni–YSZ Cermet Electrodes for Carbon Dioxide Electrolysis on Solid Oxide Electrolysis Cell
Authors: Singh Vandana , Muroyama Hiroki , Matsui Toshiaki , Eguchi Koichi
Published: September 2014

In this article, two Ni-based cermet electrodes have been fabricated and their electrochemical performances have been evaluated for CO2 electrolysis on solid oxide electrolysis cell (SOEC). It was found that Ni–SDC cermet electrode showed lower cathodic overpotential than Ni–YSZ electrode. The improved cell performance indicated that Ni–SDC cermet was a better and more effective electrode material for CO2 reduction. The results revealed that the conductivity of Ni–SDC cermet cathode for CO2 reduction strongly depended on the operating parameters, and the effect of these operating parameters on the electrochemical activity of Ni–SDC cermet cathode was closely interlinked. The most critical operating parameter for CO2 reduction was appeared to be the gaseous atmosphere, which can be controlled by changing the oxygen partial pressure at Ni–SDC electrode.
3D Multiphysics Modelling and Design Optimisation of a Complete SOFC System Operating in Jülich
Authors: Peksen Murat , Al-Masri A , Peters Ro. , Blum L , Stolten D
Published: September 2014

Forschungszentrum Jülich has been giving particular attention to the high-end 3D multiphysics modelling of complete SOFC systems, including all auxiliary components such as the fuel cell stack, afterburner, heat exchanger, pre-reformer and baffle plates. Our previous model has been developed so that the current emphasis of research has been given to the 3D design optimisation of the fuel cell system in terms of thermomechanical behaviour. The long-term steady state operation has been the focus. Coupled CFD/FEM is used to predict the thermofluid flow and heat radiation, electrochemical and chemically reacting species transport, as well as the thermomechanics, including the long-term creep behaviour and elastoplasticity.
Influence of Reactions of Carbon Black and Fuel Diffusion Process on Power Generation Characteristics of Rechargeable Solid Carbon Fuel Cells(RSCFCs)
Authors: Chen Ying , Tanaka Hiroki , Sugiyama Shiori , Hatori Sayuri , Izumi Takaaki , Ihara Manabu
Published: September 2014

Rechargeable Solid Carbon Fuel Cells (RSCFCs) that use directly supplied carbon black (CB) as fuel were developed. The influence of the CO supply rate depended on the CO generation rate and the CO diffusion rate on the power generation was investigated. High power density was achieved by using a larger specific surface area CB fuel due to the increase in CO generation rate. Two types of cell setting were evaluated, horizontal and vertical setting. With horizontal cell setting, densely supplied CB enhanced the power density because the increase in the CO generation rate was greater than the decrease in CO diffusion rate due to the increase of CB surface area per unit column volume. However, CB supply density should decrease during the power generation due to the CB consumption by Boudouard corrosion reaction. In contrast, with the vertical cell setting, CB supply density must be almost constant because CB maintains contact with the anode surface by its own weight. Moreover, the performance of RSCFC was improved by using anode with high porosity. With 27 % porous anode, the maximum power density (PMax
) was 24.1 mW/cm2 at 50 mA/cm2, and with 33 % porous anode, the PMax
was 34.6 mW/cm2 at 70 mA/cm2. The total TPB (Triple Phase Boundary) length in anode might be decreased with increasing porosity of anode, but the power density of RSCFC with CB fuel was increased.
Nanostructured Low-Temperature Solid Oxide Fuel Cell with High Power Density
Authors: An Jihwan , Kim Young-Beom , Park Joonsuk , Gur Turgut M. , Prinz Fritz B.
Published: September 2014

Lowering the operating temperature of solid oxide fuel cells is an on-going effort to minimize thermal and microstructural degradation of cell components. Here, we report fabrication routes to realize a high power density solid oxide fuel cell operating in the low temperature regime (<500 °C). Using nanosphere lithography methods, we prepared a three-dimensional silicon template, which is then used to construct a nanostructured free-standing solid oxide fuel cell by combining various chemical/physical vapor deposition methods. The resulting cell achieved a high power density of over 1 W/cm2 at 450 °C.
Electrochemical Characterization of La0.9Sr0.1Ga0.8Mg0.2O3-δ Thin Film Electrolyte Deposited by Radio Frequency Magnetron Sputtering
Authors: Endo Yoichi , Terai Takayuki , Suzuki Akihiro
Published: September 2014

To reveal the mechanism of the conductivity change of La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) thin film from the bulk, the LSGM thin films with different thickness deposited on sapphire substrate by radio frequency magnetron sputtering was studied. The grains in thick (1.8 μm~) film had a nearly sphere shape and approximately 0.3 μm in size. The grains in thin (~0.6 μm) film had a nearly spatulate and approximately 0.1 μm in size. The lattice constant of the 0.6 μm thickness film was decreased from that of the bulk by the influence of the substrate. The conductivity values in 3.0 and 0.6 μm thickness film at 700 oC were 2.3×10-3 and 1.1×10-3 Scm-1, respectively. Their activation energy were 1.07 and 1.26 eV, respectively. The thicker the film is, the conductivity increases and the activation energy decreases. This should be caused by the smaller bulk resistivity than the grain boundary resistivity.
Electronic Structure Measurements of Heteroepitaxial Solid Oxide Fuel Cell Cathode Thin Films
Authors: Yu Yang , Ludwig Karl F , Pal Uday Bhanu , Gopalan Srikanth , Basu Soumendra Nath
Published: September 2014

Synchrotron based total reflection x-ray fluorescence (TXRF) and hard x-ray photoelectron spectroscopy (HAXPES) technique have been utilized to measure the compositional changes and evolution of surface chemistry of strontium doped lanthanum cobalt iron oxide (LSCF) annealed at 800 °C, as a function of strontium dopant concentration and gas composition. TXRF is a useful way to depth-profile the surface composition of material at elevated temperatures in real time. The capability of HAXPES to overcome surface contamination issues helps better understand the segregation phenomena. This study demonstrates that the formation of Sr carbonate results in enhanced kinetics of Sr surface segregation in LSCF thin films with presence of CO2 when annealing at 800 °C and lowering the Sr dopant concentration results in a decrease Sr surface segregation.
Effect of Operating Conditions on the Electrochemical Performance of Ni-YSZ Cermet Anode for Solid Oxide Fuel Cells Using Octane Fuel
Authors: Yamamoto Daisuke , Tomomichi Keita , Yamagami Shun , Yamada Yuki , Kinoshita Masahiro , Yoshinaga Masashi , Sasaki Kazuya
Published: September 2014

Ni-yttria stabilized zirconia (YSZ) cermet is evaluated as anode material for the solid oxide fuel cells operated by the direct internal steam reforming of iso-octane. Effect of the cell temperature and the steam/carbon ratio in the fuel was examined from the point of view of the cracking reaction performance, identification of the elementary process which governs power generation and durability. When both steam/carbon ratio and cell temperature are high enough, iso-octane is cracked to generate H2 and CO. The cracking reaction of iso-octane on the surface of the Ni-YSZ anode governs the reaction rate of the anode electrode. Outlet gas composition from the cell was analyzed by gas chromatography, and the single cell property was measured by the electrochemical method.
Ceria Based Composite Membranes for Oxygen Separation
Authors: Gurauskis Jonas , Ovtar Simona , Kaiser Andreas , Søgaard Martin , Hendriksen Peter Vang
Published: September 2014

Composite membranes composed of gadolinium doped cerium oxide (Ce0.9Gd0.1O2-delta, denoted CGO) as the main oxygen ion carrier and lanthanum strontium ferrite ((La0.6Sr0.4)0.98Fe0.02O3-delta, denoted as LSF) as electronic conductor were fabricated and tested. A composite film (15 μm) was deposited on a bi-layer tube consisting of a porous magnesium oxide support coated with a thin CGO layer. On top of the dense membrane layer another porous CGO layer was deposited. The CGO layers act as backbones for infiltration with a suitable catalyst that can facilitate the surface exchange processes on the membrane. Composite membranes (where no catalysts were infiltrated in the CGO layers) were tested and demonstrated oxygen fluxes close to 1 ml×min-1×cm-2 at 900 °C when flowing air on one side and a gas with an oxygen partial pressure of log pO2=-2 on the other side of the membrane. Work is ongoing to characterize also membrane performance in the presence of different infiltrated catalysts.
(Plenary) Remaining Technical Challenges in R&D for Automotive PEM Fuel Cell System
Authors: Hirano Shinichi , Waldecker James
Published: September 2014

Cost and durability are still challenging for commercialization enabling automotive fuel cell technology. Mass transport, oxygen reduction reaction (ORR) activity and fuel cell stack materials such as bipolar plates are high cost impact areas. Significant research and development (R&D) efforts have been pursued in each area individually. To fill the gap to the target, further R&D is necessary to develop a concept which is attributed to those factors concurrently. For example, catalyst research aims not only to improve ORR mass activity but also to enhance mass transport performance in the high current density region. Therefore further R&D focus for catalyst area will be shifted from the catalyst material itself to the catalyst layer structure to enhance the ORR activity and overcome mass transport in the membrane electrode assembly. The technical outlook and research approaches for the remaining technical challenges for automotive PEMFCs will be discussed.
(Plenary) Advanced Visualization Tools to Investigate PEM Fuel Cell Materials
Authors: Yip Ronnie , Lee Jongmin , Hinebaugh James , Fishman Zachary , Ellis Jonathan S. , Botelho Steven Joseph , Kotaka Toshikazu , Tabuchi Yuichiro , Bazylak Aimy
Published: September 2014

Significant advancements have been made towards the commercialization of polymer electrolyte membrane (PEM) fuel cells in recent years. However, prohibitive costs and limited durability still remain as barriers toward deep market penetration, and these challenges largely stem from an incomplete understanding of how the nanoscale and microscale features of the porous materials in the PEM fuel cell affect multiphase and thermal transport within the bulk and at the interfacial regions of these porous layers. Non-traditional tools are needed more than ever to address these challenges. In the Thermofluids for Energy and Advanced Materials (TEAM) Laboratory at the University of Toronto, we employ a variety of advanced visualization tools to characterize the nanoscale and microscale features of the porous layers of the PEM fuel cell within ex-situ and in-situ environments. Accurate material characterizations are used as inputs for developing our predictive models, and visualizations serve as validations for our numerical modelling work. Our goal is to develop predictive numerical models that will serve as design tools that we can use to prescribe three-dimensional material properties for tailored thermal and liquid water transport for the next generation of PEM fuel cell technologies.
(Invited) Electrochemical Properties for UHV-Prepared Pt/M Well-Defined Single Crystal Surfaces
Authors: Todoroki Naoto , Iijima Yuki , Takahashi Yu , Kondo Takayuki , Asakimori Yu , Bando Yohe , Wadayama Toshimasa
Published: September 2014

We investigated the electrochemical properties of various-monolayer (ML)-thick Pt-shell model surfaces. The m-ML-Pt shell/Au(111) (m = 1–3) was prepared through epitaxial growth of Pt on a clean Au(111) surface at 300 K, and the n-ML-Pt shell/Ni–Pt(111) (n = 1–4) was generated through thermal segregation of substrate Pt atoms during 1-ML-thick Ni deposition onto a clean Pt(111) surface at 823 K followed by additional epitaxial growth of Pt at 473 K in ultra-high-vacuum molecular beam epitaxy (UHV-MBE) systems. Surface structures of the Pt-shell surfaces were verified using a scanning tunneling microscope in UHV. Oxygen reduction reaction (ORR) activities and structural stabilities of the shell surfaces were evaluated in oxygen-saturated 0.1 M HClO4. The results obtained reveal that not only surface strains but also nanoscale surface morphologies of the most dense plane of Pt(111) are correlated with ORR enhancements and that the 3-ML-thick Pt shell stabilizes the topmost surfaces of Pt/M bimetallic systems.
MEA Pt/C Cathode Catalyst Degradation during Repeated Anode Gas Exchange Cycles: In-Situ XAFS, STEM-EDS and Electrochemical Analysis
Authors: Samjeské Gabor , Higashi Kotaro , Takao Shinobu , Nagamatsu Kenichi , Nagasawa Kensaku , Sekizawa Oki , Kaneko Takuma , Uruga Tomoya , Iwasawa Yasuhiro
Published: September 2014

The effects of repeated start-up/shut-down cycles on degradation of Pt/C cathode catalysts in polymer electrolyte fuel cells (PEFC) were investigated by repeated anode gas exchange (AGEX) cycles. The degradation of MEA Pt/C catalysts during the AGEX cycles was examined at three different areas of the MEAs by in-situ XAFS and STEM-EDS. The steady decreases of the electrochemical surface area and ORR performance by the AGEX processes were observed. In contrast to the aspects averaged over the whole MEA areas, in-situ XAFS can provide the position-dependent structural and electronic information on Pt nanoparticles at different positions in the MEA during the AGEX cycles. The white line peak intensity in in-situ XANES spectra at Pt LIII-edge decreased in the order for the MEA regions, top > bottom ≥ middle. STEM images showed that Pt particles dropped off from the carbon supporting particles in the cathode catalyst layer and large cracks and voids formed in the top area of the MEA. These aspects of the in-situ XANES spectra and STEM images are correlated with each other and the MEA degradation.
Enhanced CO Tolerance of PEFC Anode Catalyst by Optimized Degree of Activation of Resorcinol-Formaldehyde Carbon Support
Authors: Narischat Napan , Takeguchi Tatsuya , Mori Takeshi , Ogino Isao , Mukai Shin R. , Ueda Wataru
Published: September 2014

In this study, a series of resorcinol-formaldehyde carbons (RFCs) were prepared by varying the degree of activation such as 0, 42, and 58, in order to control their surface areas and porosity. Then, these RFCs were used as supports to prepare Pt2Ru3 anode catalysts. These catalysts were characterized by many techniques including BET, DH calculation, XRD, STEM and CO tolerant by polymer electrolyte fuel cell (PEFC) single cell analysis. It was found that higher degree of activation of RFCs (i.e. rc1400ac42 and rc1400ac58) have larger micropore and mesopore volume. In case of CO tolerant by PEFC single cell unit, Pt2Ru3/rc1400ac58 showed the same performance as the commercial Pt2Ru3/C in pure H2 (0.76 V at 0.2 A/cm2), but Pt2Ru3/rc1400ac58 showed superior performance at 2000 ppm CO contamination. Nafion dispersion of Pt2Ru3/rc1400ac58 was also found to be better than that of the Pt2Ru3/C, since pore structure was optimized by degree of activation.
Nanostructured Platinum and Carbon Supported Pt-Ni Catalyst for Polymer Electrolyte Fuel Cell
Authors: Hong Phuong Vu Thi , Man Tran Van , Phung Le My Loan
Published: September 2014

The Pt-Ni bimetallic nanoparticles supported on nano carbon (PtxNiy/C) have been synthesized by the polyol reduction under ultrasonic irradiation. The morphology, structure and specific area of synthesized materials were characterized by X-Ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption (BET). The electrocatalytic activity for alcohol oxidation of the synthesized PtxNiy/C materials and the commercial 10wt.% Pt loaded on activated carbon catalyst (Aldrich Sigma, Pt/C_com) was investigated by cyclic voltammetry (CV) and chronoamperometry (CA). The catalytic activity for oxygen reduction reaction (ORR) of PtxNiy/C was investigated by CV and linear sweep voltammetry (LSV). The major size of synthesized metallic particles was around 2 nm. The Pt2Ni1/C exhibited excellent catalytic properties for alcohol oxidation compared to other catalysts on the same support. The CNTs were found to be more effective than carbon Vulcan for use as a support for alcohol oxidation catalysts. The linear sweep voltammograms showed that PtxNiy/C, which has the least coverage of oxygenated species, was the best catalyst for ORR with its onset potential of 0.624 V. From the slope of Koutecky-Levich plot for ORR using PtxNiy/VC materials as catalysts it was found that the overall electron transfer number ranged from 3 to 4, leading to the suggestion of H2O2 formation as an intermediate of the ORR.
Electrochemical Performance of MEAs with Pt/SnO2 Mixed with Conductive Fillers
Authors: Nagamatsu Yohei , Kanda Kohei , Noda Zhiyun , Hayashi Akari , Sasaki Kazunari
Published: September 2014

SnO2 can act an alternative PEFC electrocatalyst support to the conventional carbon black, for preventing catalyst support corrosion. In this study, current-voltage characteristics of MEAs with SnO2 support are improved by controlling the content of electron-conductive fillers and proton-conductive Nafion ionomer.
Modeling Hierarchical Non-Precious Metal Catalyst Cathodes for PEFCs Using Multi-Scale X-ray CT Imaging
Authors: Komini Babu Siddharth , Chung Hoon T , Wu Gang , Zelenay Piotr , Litster Shawn
Published: September 2014

This paper reports the development of a model for simulating polymer electrolyte fuel cells (PEFCs) with non-precious metal catalyst (NPMC) cathodes. NPMCs present an opportunity to dramatically reduce the cost of PEFC electrodes by removing the costly Pt catalyst. To address the significant transport losses in thick NPMC cathodes (ca. >60 µm), we developed a hierarchical electrode model that resolves the unique structure of the NPMCs we studied. A unique feature of the approach is the integration of the model with morphology data extracted from nano-scale resolution X-ray computed tomography (nano-CT) imaging of the electrodes. A notable finding is the impact of the liquid water accumulation in the electrode and the significant performance improvement possible if electrode flooding is mitigated.
Analysis of Material and Charge Transfer in the Fiber Catalyst Layer for Polymer Electrode Fuel Cells
Authors: Ishitobi Hirokazu , Yoshida Takuya , Nakagawa Nobuyoshi
Published: September 2014

Nanofiber electrocatalysts for polymer electrode fuel cells has been proposed in recent years. In this study, we analyzed material transfer rate and electrode reaction rate in the nanofiber catalyst layer using rotating disk electrode. Carbon alloy nanofiber was examined for a cathode catalyst. We focused on effects of the fiber length and catalyst loading on the catalyst layer activity. The transport situation was discontinuously changed at a higher loading amount of relatively long catalysts. The material transfer rate was increased at higher catalyst loading with longer nanofibers. This phenomena is explained by the difference of layer structure between the fiber catalyst and the particle-like catalyst. Relatively long (6.9 mm, for example) catalyst with catalyst loading at around 1 mg cm−2 is appropriate condition of catalyst layer because of its high material transfer rate inside the catalyst layer.
(Invited) Development of PFSA Ionomers for the Membrane and the Electrodes
Authors: Kinoshita Shinji , Tanuma Toshihiro , Yamada Kohta , Hommura Satoru , Watakabe Atsushi , Saito Susumu , Shimohira Tetsuji
Published: September 2014

Perfluorosulfonic acid (PFSA) ionomer is one of the key materials used in polymer electrolyte fuel cell (PEFC). Most of the membranes used in high performance and high durability PEFC are made from PFSA ionomers. The ionomer for the membrane is required to perform well at high temperatures up to 120 °C at low relative humidity (RH). The ionomer for the electrode, besides transporting the protons to the membrane, its function in cathode of delivering the oxygen to the Pt surface is highlighted in the recent progress of high activity catalyst enabling low Pt loading. Asahi Glass Co., Ltd. (AGC) is also proposing the PFSA ionomer to be used for creating hydrophilic microporous layer (MPL) in between the gas diffusion media (GDM) and the catalyst layer to achieve better performance in low RH conditions. The monomer structures and their copolymer properties as well as their cell performance examined are presented in this paper.
Mechanism of Perfluorosulfonic Acid Membrane Chemical Degradation under Low RH Conditions
Authors: Coms Frank D. , Xu Hui , McCallum Tom , Mittelsteadt Cortney
Published: September 2014

A highly versatile and robust hydrogen peroxide vapor test has been employed to probe the chemical degradation of Nafion® NRE212CS membranes under a wide variety of RH environments. Under very low RH conditions, chain scission processes become operative leading to an increase in the carboxylic acid content and a subsequent decrease in high humidity chemical stability of the membranes. Durability tests of Na+-exchanged Nafion® membranes were undertaken to distinguish possible chain scission mechanisms. The impact of Ce3+ mitigation was also investigated.
Development of Hybrid Membranes Nafion-ZrO2 for PEM Fuel Cells
Authors: Gutiérrez Cynthia Karina , Montemayor Sagrario M. , Rivas Gandara Sandra , Pineda Jose Luis , Ledesma García Janet , Chavez Abraham Ulises , Arriaga Luis Gerardo
Published: September 2014

A hybrid membrane was synthesized by the sol-gel process using Nafion as a polymeric matrix, modified with 1% wt. of ZrO2 (N-ZrO2), the obtained membrane has a thickness of 160 μm. The proton conductivity was evaluated by four-electrode method, with relative humidity and temperature established at 50-100 % and 30-100 ˚C respectively. The hybrid membrane was compared to Nafion 115 (127 µm). The N-ZrO2 showed a proton conductivity of 0.05 S/cm (30 °C, 100 % RH), while the proton conductivity of Nafion 115 is 0.07 S/cm (30 °C, 100 % RH). First results showed a promising performance of the N-ZrO2 membrane for PEM Fuel Cells application at high temperature and low relative humidity. PEMFC performance was determined at temperatures of 30 and 100 ˚C and relative humidity of 50 and 100%, and in electrochemical hydrogen compression at 30 ˚C with a saturated gas flow of 120 ml/min.
Imidazolium Trifluoromethanesulfonate sPEEK Composites for Anhydrous High Temperature Proton Exchange Membrane Fuel Cells
Authors: De Almeida Nicole , Goward Gillian
Published: September 2014

Imidazolium Trifluoromethanesulfonate (IFMS) was inserted into a sPEEK host, and a systematic evaluation of the pristine sPEEK, and reference composites was performed. With electrochemical impedance spectroscopy (EIS) data from the series of polymer, solid-acid, and composites, it was shown that both the anion and cation are involved in proton conduction as well as the sulfonate group on the polymer. EIS also depicted the maximum salt content for highest proton conductivity, collected in anhydrous conditions at 120°C, of 1.1*10-3 S/cm with the least amount of salt, which was 37%. These dynamics were observed in 1H solid state NMR.
PTFE Distributions in Diffusion Media of PEFCs and Related Effects on Water Transport
Authors: Wargo Eric A. , Schulz Volker P , Kumbur Emin Caglan
Published: September 2014

The objective of this work is to examine the impact of polytetrafluoroethylene (PTFE) distribution on water transport in the diffusion media of polymer electrolyte fuel cells (PEFCs). The structure of a commercial gas diffusion layer (GDL) sample was captured previously using X-ray computed tomography. In this study, several PTFE distribution cases are generated on the internal surface of the measured GDL structure. The full/pore morphology model is applied to capture the impact of the PTFE distributions on water transport in the GDL.
Impact of Contact Pressure Cycling on Non-Woven GDLs of HT-PEM Fuel Cells
Authors: Rastedt Maren , Pinar Francisco Javier , Wagner Peter
Published: September 2014

The Gas Diffusion Layer (GDL) plays an important role in the performance of a fuel cell, but it also strongly controls the durability of the membrane-electrode-assembly (MEA). Mechanical damages like fiber intrusion at high contact pressure can lead to hydrogen crossover and electrical short circuit formation. In this paper a non-woven GDL is analyzed by electrochemical methods in a fuel cell test station under contact pressure cycling between 0.2 and 1.5 MPa. These results are compared ex-situ with the microscopic structural changes in the material investigated by micro computed tomography in combination with a specially designed compression tool. The optical measurements allow the identification of GDL defects. A clear correlation between the loss of internal resistance and hydrogen crossover current and the emerging of small cracks and fiber intrusions could be established.
Gas Diffusion Layer Fabrication with Coating of Carbon Fiber Dispersion
Authors: Tanuma Toshihiro
Published: September 2014

In PEFCs (Polymer Electrolyte Fuel Cells), the gas diffusion layer (GDL) is one of the largest cost factors among the components. In order to reduce manufacturing cost, GDLs fabricated using a coating of carbon fiber dispersion have been developed. The coating dispersion is composed of carbon fibers with a diameter of 11 mm, ionomer, and solvents. After coating the slurry, the carbon fiber layer was dried and hot-pressed before using it as a cathode GDL. The performance of a membrane electrode assembly (MEA) employing the dispersion-cast GDL was equal to that using a conventional GDL.
Effect of Wettability of Micro-Porous Layer on Microscopic Water Transport Phenomena in PEFC
Authors: Aoyama Yusuke , Suzuki Kengo , Tabe Yutaka , Chikahisa Takemi , Tanuma Toshihiro
Published: September 2014

The wettability of the micro-porous layer (MPL) is attracted as a key to improve the performance of a polymer electrolyte fuel cell (PEFC). This paper directly observed the cross-sectional distribution of liquid water inside the cathode MPL to elucidate the effect of wettability of the MPL on microscopic water transport phenomena in the PEFC. The performances of cells with hydrophobic and hydrophilic MPLs were measured, and the internal water distributions of the MPLs were observed by using the freezing method and cryo-scanning electron microscope (cryo-SEM). The results show that the water exists inside the hydrophilic MPL as liquid even during the high temperature operation while no liquid water exists inside the hydrophobic MPL under the same condition. It is estimated that the hydrophilic MPL drains liquid water from the catalyst layer (CL) and promote liquid water transport through the MPL.
Numerical Analysis Considering the Effects of Liquid Water on PEMFC Unsteady Performance
Authors: Fukuda Takanori , Araki Takuto
Published: September 2014

A three-dimensional, non-isothermal, and unsteady numerical model considering liquid water transport inside a gas diffusion layer (GDL) has been developed to investigate its effect on cell performance. Liquid water in GDL had extremely wide size distributions, as visualized by synchrotron X-ray. It was assumed that liquid water in GDL form droplets with different diameters, which would affect the thermal conductivity and diffusion coefficient. On the other hand, liquid water in the flow channel should not be discounted as it has larger liquid water mass compared with that in GDL. In this paper, the impact of liquid water in the flow channel and droplets in GDL on the steady and unsteady responses of proton exchange membrane fuel cells (PEMFC) power generating characteristics was discussed. It was found that liquid water in the entire system has a significant influence on voltage responses.
Modeling Thermal Transport in Heterogeneous Porous Media of PEM Fuel Cells Using Pore Network Model
Authors: Konduru Vinaykumar , Medici Ezequiel , Allen Jeffrey S
Published: September 2014

Thermal and mass transport in the porous transport layers (PTL) of polymer electrolyte membrane (PEM) fuel cells is studied using a pore network model. The solid phase of the PTL is modeled as a network of solid cylinders and the pore phase is modeled as a network of hollow tubes. The two networks are coupled together at the nodes. The network of pores and solid-cylinders are generated independently using Weibull probability distribution function. In the current work, a new formulation of the thermal transport has been developed which incorporates the effect of compression under the lands of bipolar plate on thermal transport. The parameters of PTL used to model compression are obtained from experimentally obtained thermal conductivity values reported in literature. In this paper, a description of the model along with the technique of determining the parameters for compression and the effect of solid phase distribution on the thermal transport in the porous media of fuel cells is presented.
Computational Modelling of Cation Contamination in PEFCs
Authors: Uddin Md. Aman , Pasaogullari Ugur , Molter Trent
Published: September 2014

A steady-state, one dimensional computational model is developed to predict the effect of foreign cation contamination in polymer electrolyte fuel cells (PEFCs). The model solves the coupled transport phenomena of cations, oxygen, and water. Foreign cation (i.e. Na+) contamination in the air stream found to significantly decrease the performance of PEFC by decreasing protonic current density from 0.72A/cm2 to 0.25 A/cm2 at a constant cell voltage of 0.7 V. Foreign cation decreases the oxygen diffusivity causing a decrease in dissolved oxygen concentration in CCL. It also decreases the equilibrium potential due to reduction in proton concentration in the ionomer phase in cathode.
Vibrational Spectroscopy and 2D Correlation Analysis as a Probe of Structure in Ionomer Membrane Materials
Authors: Korzeniewski Carol , Byun Chang Kyu
Published: September 2014

Infrared spectroscopy is being applied to gain new insights into structural properties of fuel cell membrane materials and to aid in determinations of membrane water content. In the area of structure elucidation, two-dimensional (2D) correlation methods are being adapted in the analysis of spectral data sets collected during water uptake into fluorinated ionomer materials. Synchronous 2D correlation plots assist in the resolution of spectral regions complicated by overlapping bands and indicate distinctions in transformations centered within hydrophilic relative to more hydrophobic ionomer domains. Asynchronous 2D correlation plots reveal relationships in the dynamics of side chain and backbone motions that accompany changes in membrane hydration state.
Study of the Constrained Expansion of Nafion within the Hardware of a PEMFC
Authors: Folgado María Antonia , Ferreira-Aparicio Paloma , Chaparro Antonio M.
Published: September 2014

A study is presented of the expansion of Nafion under compression inside a fuel cell. Under compression between the flow field plates, Nafion elongates and protrudes inside the channels due to a plastic deformation. The thickness of protruded membrane is larger than the uncompressed one, and does not change appreciably by water absorption. On the other hand, the height of the protrusion increases by water absorption, slightly more when the membrane is compressed in its dry form than if it is compressed in fully humidified, expanded, form. Bumps in the protruded membrane are observed that probably reflect changes in the Nafion microstructure. Single cell characterization shows that the assembly with pre-expanded membranes gives rise to about 7% improvement in the maximum power density, attained at 1.6A·cm-2 under standard testing conditions. Such improvement is fully attributed to a decrease in the internal resistance. The pre-expanded Nafion, therefore, should be used when high current density demands are foreseen, whereas for low current density, dry membrane assembly may perform like the pre-expanded.
Impact of Load Cycling at High Current Densities on the Degradation Behavior of Membrane-Electrode-Assemblies
Authors: Rastedt Maren , Schonvogel Dana , Wagner Peter
Published: September 2014

Nowadays high temperature polymer electrolyte fuel cells suffer from performance and long-term stability issues. Detailed understanding of the degradation effects is thus a key aspect for the improvement of this type of fuel cells. Degradation can be categorized into thermal, (electro-) chemical and mechanical effects. This paper focuses on the latter process, investigating two different types of membrane electrode assemblies by accelerated stress tests at high current densities in which, compared to common procedures, the device is driven at higher current densities between 0.6 – 1.0 A/cm². In addition to voltammetry and polarization curves, the assemblies are analyzed by electron microscopy methods and especially micro-computed tomography which allows a non-destructive investigation of the hidden interfaces within the MEA structure, giving a direct view on mechanical defects. Load cycling at high current densities revealed significant contributions to the degradation of the catalyst layer. But no influence on the membrane could be found.