bluuebunny/crossref_metadata_2025 huggingface dataset:
Overcoming Artifacts in Cyclic Voltammetry through the Use of Multiple Scan Rates and Potential Windows
Authors: Edmundson Mark , Busby F. Colin
Published: October 2011

A new technique for overcoming artifacts in the determination of electrochemical surface area (ECSA) from cyclic voltammetry (CV) data has been demonstrated. Using a CV measured at low scan rate to calculate a background, data at other scan rates can be corrected to largely eliminate artifacts due to Concentration Cell and H2 crossover effects. Additional artifacts can be minimized by limiting the upper potential limit of the CV to about 0.6V, and by using a separate scan of the capacitance region (from about 0.35 - 0.6V) to determine the electrode capacitance. Data from this "Background-Corrected" CV technique compared favorably to established techniques of CO Stripping and Flooded CVs, showing a good correlation to Pt loading, comparable adsorption/desorption peak symmetry, and reasonable resolution of features in the scans themselves. The new technique is more easily automated than the alternatives, requiring no additional gas-switching, temperature changes, or injection of liquid water. It also imposes no constraints on the RH at which measurements can be made.
Degradation Investigation of Nafion Ionomer Network In Catalyst Layers
Authors: Xu Fan , Ho Derek , Xie Jian
Published: October 2011

Degradation Nafion ionomer networks within a catalyst layer has been investigated using a simulated process, in which a series of catalyst layers with different Nafion® ionomer contents (from 28% to 10% Nafion content) were used to avoid the interference from the degradations of catalyst and membrane. The degradation of Nafion ionomer networks affected the performance and structure of the membrane electrode assembly (MEA). With the decrease of Nafion ionomer in catalyst layer, the performance of a MEA was affected within the entire range of polarization curves (i.e. kinetic, Ohmic, and mass-transport regions).
Ice Formation and Current Distribution in the Catalyst Layer of PEM Fuel Cell at Cold Start
Authors: Ichikawa Ryosuke , Tabe Yutaka , Chikahisa Takemi
Published: October 2011

In polymer electrolyte fuel cells (PEFCs), the freezing of produced water induces the extreme deterioration of the cell performance below zero. This phenomenon is serious problem in cold regions and is needed to be solved to achieve the practical use of PEFCs. In this study, we investigated the ice formation and the reaction rate in the cathode catalyst layer (CL) using a CRYO-SEM and a three-phase boundary model to clarify the freezing mechanism in the cold start at -20oC. The observation results showed that the ice distribution formed in the CL is changed by the operation time and the current density. In particular, in a case of large current density, it was shown that ice grows from the membrane side to the gas diffusion layer (GDL) side. This process can also be analyzed in detail by the model that calculates the reaction rate in the CL.
Surface Energy effects on Catalyst Degradation in Low-Temperature PEMFCs
Authors: Redmond Erin L. , Setzler Brian P. , Juhas Pavol , Billinge Simon J. , Fuller Thomas F.
Published: October 2011

An in situ method to measure particle size changes on a PEMFC cathode is demonstrated. High energy, 58 keV, x-rays and PDF analysis of the data are used to calculate the average particle diameter during accelerated degradation experiments. Stability of Pt/C and Pt-Co/C with different initial particle sizes is investigated over 3000 cycles. The most stable electro-catalyst is the alloyed electro-catalyst with the larger initial diameter.
Catalyst Durability for Fuel Cells under Start-Up and Shutdown Conditions: Evaluation of Ru and Ir Sputter-Deposited Films on Platinum in PEM Environment
Authors: Atanasoska Liliana L. , Vernstrom George , Haugen Gregory M. , Atanasoski Radoslav
Published: October 2011

Electrochemical and surface properties of Ru, Ir and Ti over-layers sputter-deposited onto 3M Pt-coated nano-structured thin film (NSTF) substrate were evaluated in PEM environment. Ti was included because it is often combined with Ru and Ir to improve stability of these highly active catalysts for oxygen evolution reaction (OER). Different OER catalyst coating thicknesses were formed by varying Ru, Ir and Ti mass in the range of 1-10 µg/cm2 per Pt-NSTF geometric area. The OER activity was assessed by quasi-steady state polarization measurements. The electrochemical data demonstrate that the OER catalytic activity of Ru and Ir in PEM compares well with their behavior in aqueous environment. The OER catalysts composition on Pt-NSTF was characterized by XPS. The XPS results indicate the organo-metallic bonds formation at the interface of Ru OER catalysts with Pt-NSTF.
Electrochemical Characterization of Platinum Alloy Catalysts - Oxide Growth and Durability
Authors: Mathew Preethi , Meyers Jeremy
Published: October 2011

The oxide growth on Pt alloy catalysts was studied by examining the surface oxidation on the Pt-Cu/C core-shell catalyst structure by combined CV and EQCM. The measurements show that the mass variation increases in a continuous linear manner as the potential is increased during the anodic oxidation, and from the in-situ molecular weight analysis, the intermediate adsorbed species is identified as hydroxide. The results are compared with the conventional unsupported Pt black and Pt/C which show that PtO is formed on the surface. From the reported results we found that the new catalyst surface is less oxidized and that surface strain imposes a barrier to surface oxidation.
Heterogeneities of Aging Through-The-Plane of a Proton-Exchange Membrane Fuel Cell Cathode
Authors: Dubau Laetitia , Durst Julien , Guétaz Laure , Maillard Frédéric , Chatenet Marian , André Johan , Rossinot Elisabeth
Published: October 2011

In this work, we investigated through-the-plane heterogeneities of an ultramicrotomed MEA aged at constant current density j = 0.24 A cm-2 in a 16 cell stack for t = 1341 h. We used structural markers to unveil the physical and chemical changes occurring at both the GDL | CL and at the CL | PEM interfaces. We evidenced that the degradation of the cathode catalytic layer is more pronounced close to the PEM than close to the GDL. Spatially-localized heterogeneities of ageing are discussed in the frame of different chemical/electrochemical environments as well as incomplete utilization of the cathodic electrocatalyst under PEMFC operation.
Patterning the Cathode Catalyst Layer - Membrane Interface of a PEMFC for Elevated Power Density
Authors: Omosebi Ayokunle , Besser Ronald S.
Published: October 2011

Nafion patterned by electron beam lithography coupled with dry etching was tested for electrochemical performance in a proton exchange membrane fuel cell. Bare (neither patterned nor etched) and blanket etched Nafion membranes were also tested for comparison. Membrane electrode assemblies (MEA) were formed by sputtering Pt onto both sides of a membrane using a shadow mask to selectively expose 1 cm2 of geometric area. The blanket etched membrane produced the best performance with a power density of ~170 mW/cm2. The maximum power density for the patterned MEA was smaller compared to the bare and blanket etched Nafion membranes. Furthermore, the etched MEA initially displayed low open circuit potential. Its diminished performance was attributed to contamination artifacts from the fabrication process. A post fabrication hydrogen peroxide wash prior to MEA assembly led to a higher open circuit potential and improved performance.
U.S. Department of Energy Polymer Electrolyte Membrane Fuel Cell Catalyst Development Activities
Authors: Martin Kathi E. , Kopasz John P. , Benjamin Thomas G. , Garland Nancy L. , Podolski Walter F. , Peterson David R. , Kleen Gregory , Papageorgopoulos Dimitrios , Ho Donna L.
Published: October 2011

The U.S. Department of Energy is supporting the research, development, and deployment of all types of fuel cells for transportation, material handling, portable power, back-up power, stationary power, and combined heat and power applications. A major focus of this support is polymer electrolyte membrane fuel cells. Key issues inhibiting their widespread penetration and commercialization of fuel cells are performance, durability, and cost and a key component is electrode technology including supports and catalysts. The approaches to improvement in electrode technology include alloys, core/shell structures, thin continuous catalyst films, non-precious metal catalysts, and alternative supports. Major progress has been realized recently. This paper provides an overview of DOE-funded advances and status.
Nanostructured Thin Film Electrocatalysts - Current Status and Future Potential
Authors: Debe Mark K. , Atanasoski Radoslav T. , Steinbach Andrew J.
Published: October 2011

3M's nanostructured thin film (NSTF) catalyst technology platform is the only practical example of an extended surface area catalyst which significantly reduces many performance, cost and durability barriers facing electrodes for H2/air PEM fuel cells for vehicles. In this paper we first discuss the recent gains in NSTF alloy ORR activities from both materials and process improvements, followed by accelerated durability tests of MEA's with these catalyst improvements. Next we discuss recent progress in tailoring NSTF anode catalysts with ultra-low precious group metal oxygen evolution reaction (OER) catalysts for high tolerance to automotive start up/shut down and cell reversal events. We follow with our progress in developing strategies and anode GDL's for optimized fuel cell water management for automotive low temperature operation. Finally we discuss a path forward to achieve the entitlement NSTF activity and comment on critical durability issues intrinsic to ultra-low loading catalysts.
The Active Surface Area of Nanoporous Metals during Oxygen Reduction
Authors: Snyder Joshua , Erlebacher Jonah
Published: October 2011

Nanoporous metals formed by electrochemical dealloying are seeing increased attention as catalysts for fuel cells because they combine the positive attributes of high geometric surface area, facile processing, and an active core/shell composition profile. Analysis of oxygen reduction in such materials is complicated by the problem of the coupled reaction/diffusion kinetics of oxygen in the small (<5 nm) pores of the material. In porous electrocatalytic media, we show that such kinetics lead to a potential-dependent active surface area that has little to do with the surface area measured by hydrogen underpotential deposition (UPD) - at high overpotential, the effective area participating in oxygen reduction is approximately equal to the geometric area, and this effective area grows when approaching lower overpotentials for oxygen reduction where there is a decreased reaction rate.
Activity and Structure of Dealloyed PtNi3 Nanoparticle Electrocatalyst for Oxygen Reduction Reaction in PEMFC
Authors: Hasché Frédéric , Oezaslan Mehtap , Strasser Peter
Published: October 2011

Here, we report a synthesis and activity study of the dealloyed, highly active PtNi3 alloy nanoparticle catalyst for the oxygen reduction reaction (ORR). The dealloyed PtNi3 exhibits 7 - 8 times higher Pt mass based activity and 6 - 7 times higher Pt surface area specific based activity for ORR than pure Pt by similar mean particle size. Further, we have tested the long-term durability of the dealloyed PtNi3 for the typical and corrosive operating fuel cell conditions. After the voltage testing with 10000 voltage cycles between 0.5 - 1.0 V vs. RHE and a scan rate of 50 mV s-1 in deaerated 0.1 M HClO4 the activated PtNi3 catalyst still shows 4 - 5 fold increase in Pt surface area specific based activity compared with that for pure Pt.
Cathode Materials for Polymer Electrolyte Fuel Cells Based on Vertically Aligned Carbon Filaments
Authors: Ruvinskiy Pavel , Rouhet Marlene , Bonnefont Antoine , Friedrich K. Andreas , Pham-Huu Cuong , Savinova Elena R.
Published: October 2011

Polymer electrolyte fuel cells (PEMFC) suffer dramatic loss of an operating voltage due to a significant cathode overpotential calling for economically unviable noble metal catalyst loadings in the cathode active layers. Therefore significant effort is put into the investigation of the cathode oxygen reduction reaction (ORR) and the development of novel electrocatalytic materials. In this presentation we discuss catalytic materials based on platinum nanoparticles supported on vertically aligned carbon nanofilaments. They are intended to improve mass transport, Pt utilization and corrosion stability of the cathode. They are also of interest as a model system for shedding light on the kinetics and mechanisms of fuel cell reactions.
Carbon Supports for Non-Precious Metal Proton Exchange Membrane Fuel Cells
Authors: Leonard Nathaniel D. , Nallathambi Vijayadurga , Calabrese Barton Scott
Published: October 2011

The impact of micro- and mesoporosity of the carbon substrate on nitrogen content and activity of metal-nitrogen-carbon (MNC) catalysts is addressed via electrochemical, structural, and compositional techniques. A closed vessel containing the metal, nitrogen, and carbon precursors controls mass losses due to convection of high temperature byproducts. The resulting catalysts were characterized morphologically using nitrogen physisorption, coupled with DFT analysis to calculate pore size distributions. Bulk nitrogen content was observed using CHN combustion analysis, and the catalysts were characterized electrochemically by rotating ring-disk measurements. The influence of mesoporosity on nitrogen adsorption indicates the importance of precursor transport to potential active sites during pyrolysis.
ORR and Fuel Cell Performance of Pt Supported on N-Functionalized Mesoporous Carbon
Authors: Shrestha Sujan , Ashegi Sasha , Timbro Jeffrey , Lang Christopher M. , Mustain William E.
Published: October 2011

Nitrogen functionalized ordered mesoporous carbon (NOMC) was synthesized and decorated with Pt nanoparticles using a modified polyol process. After characterizing porosity and surface chemistry, their activity towards oxygen reduction reaction was studied using a thin-film rotating disk electrode and as a cathode in a proton exchange membrane fuel cell. In both tests, lower specific activity but higher mass-specific activities were found for Pt/NOMC compared to Pt/Vulcan carbon.
Electrochemical Characterization of Adsorbed and Immobilized Cu Triazole Complexes: Some Mechanistic Aspects
Authors: Goenaga Gabriel A. , Belapure Ashesh , Zhang Congling , Papandrew Alexander , Foister Shane , Zawodzinski Thomas
Published: October 2011

We have synthesized and electrochemically characterized a variety of adsorbed Cu complexes of substituted triazoles for use as catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. To validate our methods versus previously reported Cu catalysts, we focused our preliminary work on the synthesis and electrochemical characterization of the ORR catalytic activity of adsorbed Cu diamino triazole (Cu-DATZ) complexes. The effects on the performance of parameters such as Cu salts, ligand to metal ratio, adsorption temperature and carbon pretreatment were studied. To develop a deeper understanding of these materials we examined ORR mechanistic aspects such as the number of electrons transferred and the reaction order with respect to oxygen.
Preparation of Carbon-Based Catalysts from Nitrogen-Containing Aromatic Polymers
Authors: Chokai Masayuki , Nabae Yuta , Kuroki Shigeki , Hayakawa Teruaki , Kakimoto Masa-aki , Miyata Seizo
Published: October 2011

Carbon-based, non-precious-metal catalysts for the oxygen reduction reaction were prepared from polyimides, polyamides, and azoles, by pyrolysis at 900ºC under flowing N2. The catalytic activity for electrochemical oxygen reduction was evaluated by the onset potential, measured at a current density of -2 μA cm-2. Pyrolyzed polymers with high N content showed higher onset potentials. In particular, one catalyst derived from azole (Az5) had an onset potential of 0.82 V, despite being prepared without the use of any metals. Additionally, a catalyst prepared by multistep pyrolysis of polyamide mixed with FeCl2 had high N content and high oxygen reduction activity, with an onset potential of 0.95 V. A membrane electrode assembly prepared using this catalyst had an open circuit voltage of 0.99 V, and a maximum output of 0.48 W cm-2.
Factors for Improvements of Catalytic Activity for Zirconium Oxide-Based Oxygen-Reduction Electrocatalysts
Authors: Ohgi Yoshiro , Ishihara Akimitsu , Matsuzawa Koichi , Mitsushima Shigenori , Ota Ken-ichiro , Matsumoto Masashi , Imai Hideto
Published: October 2011

Zirconium oxide based catalysts were evaluated as a non-precious cathode for polymer electrolyte fuel cells. Samples were prepared from zirconium carbonitrides under controlled oxygen partial pressure from 10-2 to 10-22 atm at 1000oC. Significant decrease in lattice parameter and Zr and O occupancy at around specific mass fraction revealed from high resolution XRD with Rietveld analysis, indicating formation of oxygen vacancies in monoclinic ZrO2. It is extrapolated from XRD, XPS, TOF-SIMS analyses that the oxide might be formed with the defects such as oxygen vacancy at both surface and bulk. Additionally, formation of the oxide with high concentration of the defects might be caused by behavior of the carbon on the surface. The oxygen vacancies could be active sites for the ORR, and increasing such oxygen-vacancy sites is one of the factors to improve the catalytic activity for the ORR in Zr-CNOs.
C-SiO2 Supported Catalysts for Durability and Performance Improvement in PEM Fuel Cells
Authors: Uzunoglu Aytekin , Dundar Furkan , Ata Ali
Published: October 2011

In this study, modified C-SiO2 support materials with various SiO2 loadings were prepared. Also, Pt/C-SiO2 and Pt-Co/C-SiO2 catalysts were synthesized with 45 wt% Pt and 20 wt% Co loadings. The amount of SiO2 content was determined by Thermo Gravimetric Analysis (TGA) at elevated temperatures. Cathode side of the custom made MEAs with synthesized catalysts were cycled between 0.6V and 1.2V for 24 hours at 20 mV/s scan rate under Hydrogen and Nitrogen purge. Nyquist plots were obtained with Impedance Spectroscopy analysis. The results indicated that the durability of the catalyst layer increased with increasing SiO2 content. It was also found that the presence of Cobalt in the catalyst layer had a positive effect on the fuel cell durability.
An Optimization Study of PtSn/C Nanocatalysts Prepared by Microwave-assisted Heating and Their Application in Direct Ethanol Fuel Cell: A Comparative Study of PtSn/C Nanocatalysts
Authors: Almeida Thiago , Palma Livia , Leonello Paulo , Koukoh Koukou Boniface , De Andrade Adalgisa R.
Published: October 2011

Direct Alcohol Fuel Cells (DAFCs) have become a more and more attractive energy source for portable devices. Nevertheless, one of the major drawbacks for its implementation is high catalysts cost. For operation at low temperatures (50-90 ºC), these cells require electrode materials with high catalytic activity, which calls for the use of precious metals like Pt associated with Sn, Ru, and other metals on the electrode. The aim of this work was to perform a systematic study of the parameters that can influence the composition, morphology, and catalytic activity of PtSn/C nanoparticles and compare two different methods of nanocatalyst preparation, namely microwave-assisted heating and thermal decomposition of polymeric precursors.
Comparative Study of Different Carbon Nanotube-Supported Platinum Bimetallic and Trimetallic Catalysts for Methanol and Ethanol Oxidation
Authors: Dong Lifeng , Dong Hongzhou , Yu Liyan , Zhang Qian , Bai Jincheng , Sui Jing , Ma Bo
Published: October 2011

We report here effects of single-walled carbon nanotube-supported Pt-based bimetallic catalysts (Pt-Cr, Pt-Mn, Pt-Fe, Pt-Co, Pt-Ni, and Pt-Sn) and trimetallic catalyst (Pt-Cr-Co) on methanol and ethanol oxidation. In comparison to a Pt catalyst, the introduction of other elements can improve catalytic oxidation characteristics in terms of oxidation potential, oxidation current density, and the tolerance to poisoning by absorbed species. Meanwhile, the Pt-Cr-Co trimetallic catalyst has better catalytic properties than Pt-Cr and Pt-Co catalysts. For instance, in comparison to a Pt catalyst for methanol oxidation, the addition of Fe, Ni, and Sn improves the tolerance to poisoning, increases the oxidation current density, and decreases the oxidation potential, respectively.
Analysis of Nafion Fuel Cell Membrane Chemical Durability Using Broadband Dielectric Spectroscopy
Authors: Hassan Mohammad K. , Nalawade Amol , Abukmail Ahmed , Patil Yatin , Mauritz Kenneth A.
Published: October 2011

Changes in macromolecular dynamics associated with the Tg -related β relaxation of Nafion®, with chemical degradation, were investigated using broadband dielectric spectroscopy. Loss permittivity vs. frequency spectra showed peak splitting reflecting microstructural heterogeneity. Spectra were analyzed using the conductivity-modified Havriliak-Negami equation and the Kramers-Krönig integral transform, both of which showed broadening and peak splitting for degraded samples. Peak broadening and bi and tri-modal character of the spectra of degraded samples was also manifest in distributions of relaxation times which reflected a broadening of molecular weight distribution and related microstructural heterogeneity induced by chemical degradation.
Characterizing Through-Plane and In-Plane Ionic Conductivity of Polymer Electrolyte Membranes
Authors: Cooper Kevin
Published: October 2011

Ionic transport resistance is a key performance property of polymer electrolyte membranes (PEMs) and can be determined for transport within the plane of material (in-plane, longitudinal or transverse directions) and through the thickness of the membrane (through-plane). The conductivity of extruded Nafion® 112, dispersion-cast Nafion® NR-212 and two Gore-Select® membranes that contain a non-conductive support were characterized as a function of orientation, temperature and relative humidity. The conductivity of extruded Nafion 112 was highest in the extrusion direction and lowest in the through-plane orientation. In contrast, the conductivity of dispersion-cast NR-212 was isotropic. The effective conductivity of Gore-Select material was higher in-plane vs. through-plane, consistent with the analytical treatment of a membrane composed of layers of unequal intrinsic ion transport resistivity. The results highlight the need to make measurements in the relevant orientation.
Understanding the Ionomer Structure and the Proton Conduction Mechanism in PEFC Catalyst Layer: Adsorbed Nafion on Model Substrate
Authors: Paul Devproshad , Fraser Andrew , Pearce Joshua , Karan Kunal
Published: October 2011

To understand the structure/property of the ionomer in the CL, adsorbed Nafion thin films were prepared on model substrate, SiO2 terminated silicon wafer, by spontaneous adsorption of Nafion from its 0.1 to 5 wt% solution. Fitting of Variable Angle Spectroscopic Ellipsometry (VASE) data yielded thickness of adsorbed films ranging from 4 nm at low concentrations (0.1 wt% film) to 306 nm at high concentrations (5wt% film). Contact angle measurements indicated that the low (0.1 wt%) and high (3 wt%) films to posses hydrophobic surface but the intermediate concentration (0.5 wt% and 1.0 wt%) film surface to be hydrophilic. Conductivity measurements of adsorbed films over a range of RH showed that all films prepared from 1 wt% and lower concentrations solutions to possess similar conductivities at high RH. However, the 5wt% film showed much higher conductivity indicating a different proton conduction mechanism for low and high concentration films.
Investigation of Water-Molecule Network in Hydrated Polymer Electrolyte Membranes by Raman Spectroscopy: Effect of Polymer Structure and Cation Impregnation
Authors: Tsushima Shohji , Iwamoto Yuki , Horai Atsushi , Tabuchi Yuichiro , Hirai Shuichiro
Published: October 2011

We examined Raman spectra in both perfluorinated sulfonic acid (PFSA) and hydrocarbon (HC) membranes under different RH conditions to investigate water-molecule network. Raman spectra showed variation with relative humidity among these membranes and was affected by polymer structure. The PFSA membrane showed broad peak in Raman spectra while the HC membrane showed narrow peak even in low RH condition. These observations suggest that water-molecule network is intensively established in the PFSA membrane. We also confirmed that the K-form and the Na-form membrane showed less formation of water-molecule network than the H-form, while Na-form membrane showed less water-molecule network than the K-form. These results indicated that dissociation and ionic radius of cations affected formation of water-molecule network in these membranes.
Investigation of HT-PEFCs by Means of Synchrotron X-ray Radiography and Electrochemical Impedance Spectroscopy
Authors: Maier Wiebke , Arlt Tobias , Wippermann Klaus , Wannek Christoph , Manke Ingo , Lehnert Werner , Stolten Detlef
Published: October 2011

Differently conditioned high temperature polymer electrolyte fuel cells (HT-PEFCs) were investigated by electrochemical impedance spectroscopy to study the influence of the break-in procedure on the overall fuel cell performance during the heating-up procedure as well as during different operating conditions. It is shown that a classical 70 h break-in procedure leads to the best fuel cell performance compared to fuel cells which are used after a rapid break-in or rather without any break-in procedure. A combination of synchrotron X ray radiographic measurements with in-situ performed time-dependent impedance spectroscopy was used to investigate the de-/hydration processes within the electrolyte of the membrane electrode assembly (MEA) components of a dynamically operated HT-PEFC. This helps to understand the fuel cell performance under different operating conditions.
Measurement of Hydrogen-Gas Solubility and Diffusivity in Polymer Electrolyte Membrane by NMR Method
Authors: Nagahisa Ryosuke , Kuriya Daiki , Ogawa Kuniyasu , Takata Yasuyuki , Ito Kohei
Published: October 2011

Polymer electrolyte membrane (PEM) used for fuel cells and water electrolyzers is permeable to hydrogen gas, and the permeation causes to decreases performance as electrochemical system. So, it is necessary to figure out the mechanism of hydrogen gas permeation and to develop PEM that has lower gas permeability. In this study, we developed a new measurement system for hydrogen-gas solubility and diffusivity in PEM based on NMR technique, which enables us to estimate the solubility and diffusivity without assuming theoretical dissolution model. We apply the system to the dissolved hydrogen-gas in dry Nafion®117. The solubility obtained is proportional to ambient pressure and 2.9×10-5 mol/cm3@0.7MPa. The diffusivity is 3×10-10 m2/s. These values are discussed with comparing the values measured in conventional method.
The Effect on PEMFC Contamination of Functional Groups of Some Organic Contaminants
Authors: Cho Hyun-Seok , Ohashi Masato , Van Zee J. W.
Published: October 2011

Ex-situ data for the effect of caprolactam on PEMFC contamination is compared with previously reported data on aniline. Both species have been detected in lechant solutions from materials that may be used in system components and this paper discusses the data relative to fundamental contamination mechanisms such as ion exchange, adsorption, and parallel electrochemical reactions. The protonated caprolactam showed much higher affinity to the membrane at high temperature so that available proton sites are decreased. This result can be explained by the ring opening reaction of lactam which is endothermic reaction. In contrast to aniline, caprolactam does not affect significantly the hydrogen adsorption/desorption reaction of a Pt/C catalyst electrode. However, it affects the peaks associated with the Pt oxidation and PtOx reduction and tends to decrease these reactions.
Super Proton Conductive Nafion Nanofibers: Discovery, Fabrication, Properties, and Fuel Cell Performance
Authors: Dong Bin , Chen Hong , Snyder Joshua , Elabd Yossef A.
Published: October 2011

In this study, we report on the discovery, fabrication, properties and fuel cell performance of Nafion nanofibers. Fibers of Nafion on the order of 50 nm in diameter were discovered in fuel cell electrodes and were found to have an impact on fuel cell performance. Therefore, we explored the fabrication of nanofiber-based electrodes. High purity (99.9 wt%) Nafion nanofibers were produced via electrospinning and the proton conductivity of a single Nafion nanofiber was an order of magnitude higher than Nafion bulk films. The fabrication and testing of membrane electrode assemblies with nanofiber-based electrodes is currently under exploration.
Nanofiber-Based Composite Membranes for Fuel Cells
Authors: Ballengee Jason B. , Pintauro Peter
Published: October 2011

A composite membrane, composed of 70 vol% 660 equivalent weight perfluorosulfonic acid (from 3M Company) and 30 vol% polyphenylsulfone, was fabricated and characterized. A newly developed dual fiber electrospinning method was utilized for membrane fabrication, where the two polymers were simultaneously electrospun into a dual-fiber mat. Follow-on processing converted the mat into a fully dense and functional fuel cell ion-exchange membrane with polyphenylsulfone nanofibers embedded in an ionomer matrix. The proton conductivity of the composite membrane was high, e.g., 0.070 S/cm at 80oC, 50% relative humidity. The dimensional stability of the membrane upon water uptake was excellent, with an in-plane (areal) swelling of only 5% in room temperature water.
Mesoporous Nafion Membranes for Fuel Cell Applications
Authors: Jiang San Ping , Lu Jinlin
Published: October 2011

Ordered mesoporous structures were successfully introduced into Nafion membranes via a soft micelle templating method, using a nonionic block copolymer surfactant, PEO127-PPO48-PEO127 (Pluronic F108). The mesoporous Nafion or meso-Nafion membranes were characterized by the AFM, SAXS, TGA and conductivity measurements. The results show that the meso-Nafion has a very high water retention capability. The proton conductivities of meso-Nafion are also much higher than that of Nafion 115 membranes particularly at reduced relative humidity (RH) and elevated temperatures. At 80oC and 40%RH, the conductivity of meso-Nafion is 0.07 Scm-1, more than 3 times better than Nafion 115. At 60%RH and 80oC, the cell with meso-Nafion reached a stable power output of 0.63 Wcm-2, more than 2 times higher than the cell with pristine Nafion 115 under identical experimental conditions. The cells with meso-Nafion membrane also demonstrate much better stability at elevated temperature of 120oC and reduced humidities.
PolyPOM Hybrid Membranes from Practical Chemistries with very High Proton Conductivities
Authors: Horan James L. , Kuo Mei-Chen , Ren Hui , Jessop Jeri D. , Frey Matthew H. , Herring Andrew M.
Published: October 2011

The heteropoly acids (HPA) are a protogenic moiety that could potentially enable proton exchange membranes that operate in fuel cells under hotter and drier conditions. We now report the incorporation of HPAs into polymers based on either trifluorovinyl ether (TFVE) monomers or functionalized Dyneon{trade mark, serif} materials. The proton conductivity of the TFVE polymers depends strongly on co-monomer chemistry, where long methylene chains appear to be better but does not increase linearly with respect to HPA loading. Some of these polymers show phase changes between crystalline states under drier conditions and an amorphous state when the polymer is wetter. All of the polymers have very low swelling at high RHs. The Dyneon{trade mark, serif} materials have very high proton conductivties for relatively low loadings of HPA, but their cnductivity is strongly dependent on film processing. The strength of these films mimics their parent polymer. All of these materials are amenable to mass manufacture.
High Temperature Proton Exchange Membranes Based on Various Heteropoly Acids(HPW, HSiW, HPMo or HSiMo) Functionalized Silica Nanocomposites with Tunable Mesoporous Structure and Superior Proton Conductivity for Fuel Cells
Authors: Zeng Jie , Jiang San Ping , Li Lin
Published: October 2011

Our recent results on the synthesis and characteristics of high temperature proton exchange membranes based on various heterpoly acids (e.a. phosphotungstic acid, silicotungstic acid, phosphomolybdic acid and silicomolybdic acid) functionalized mesoporous silica nanocomposite were investigated in details for applications in PEMFC and direct methanol fuel cells (DMFCs). The HPA-meso-silica nanocompsoites were characterized by small angle FTIR, TGA, TEM, conductivity and fuel cell performance. Spectroscopy results indicate the interactions between the Keggin anions of HPW (H3PW12O40•nH2O) and meso-silica and the possible formation of (≡SiOH2+)(H2P4W12O40-) species1. The results show that the proton conductivity of the HPA-meso-silica nanocomposites depends strongly on the content of HPW and exhibits three distinct regions as a function of HPW contents. The threshold for a good proton conductivity of the nanocomposite is ~10 wt%. The best proton conductivity is 0.14 Scm-1 at 100 °C under 90 %RH with activation energy of ~13.5 kJ mol-1, obtained on 80%HPW-meso-silica nanocomposites.
Monomers, Polymers and Cross-Linked Membranes for Membrane Fuel Cells and Electrolysis
Authors: Kerres Jochen A. , Chromik Andreas , Krajinovic Katica , Katzfuss Anika , Seyb Corina , Aniol Karin , Atanasov Vladimir , Kaz Till , Haering Thomas , Kruger Andries , Schoeman Hannes , Bessarabov Dmitri , Krieg Henning
Published: October 2011

This contribution comprises an overview about work in the development of ionomers/ionomer (blend) membranes for fuel cells. The topics include the development of novel sulfonated monomers and homo- and copolymers; the preparation of ionically cross-linked membranes prepared by mixing these polymers with different polybenzimidazoles (PBI); the application of these membranes to PEFC and DMFC; development of novel base-excess PBI/sulfonated polymer/H3PO4 blend membranes, and test of these membranes in fuel cells at intermediate fuel cell operation temperatures (170-200°C). These membranes have been tested in a DMFC. The i/U polarization curves of the membranes showed a better performance than Nafion®. Acid-base blend membranes were also applied to the HyS electrolysis process, showing good stability and electrolysis performance. Phosphonated polymers and ternary blend membranes for the application in intermediate T fuel cells have been developed as well. These membranes showed good, their chemical stability being even better than that of pure PBI membranes.
Functionalized Silica Composite Membranes for Direct Methanol Fuel Cells
Authors: Yun Sukhwan , Parrondo Javier , Lo Chih-Ping , Ramani Vijay
Published: October 2011

Novel silica aerogels functionalized with sulfonic acid were synthesized and employed in the preparation of composite membranes for DMFC applications. The additives had an ionic conductivity on the order of 100 mS/cm at 60oC and 100% relative humidity. An enhancement in ionic conductivity was observed when using the functionalized aerogels as inorganic fillers within an SPEEK matrix to prepare composite membranes. The addition of 10 wt% of the sulfonated silica aerogel to SPEEK doubled the conductivity of the membrane. The methanol permeability of the composite membranes was higher that pristine SPEEK membranes although the values measured for composite membranes with 10 wt% additive were still acceptable for use in DMFC applications.
Rigid Rod Poly(Phenylene Sulfonic Acid) PEMs and MEAs with Grafted and Crosslinked Biphenyl Groups: Mechanical and Electrical Properties
Authors: Si Kun , Litt Morton H.
Published: October 2011

Biphenyl was grafted on rigid-rod aromatic polysulfonic acids (IEC~8 mEq/gm.) to generate crosslinkable polyelectrolytes. Crosslinking conditions were studied and film properties before and after crosslinking were studied. All films broke at 6 to 9% elongation. The elastic moduli were between 0.8 and 2.2 GPa at relative humidities between 22 to 30%; it rises as RH drops and can drop drastically at high humidity if not crosslinked. As is usual for this class of materials, conductivity was high, even at low humidity and with the loss of 24% of starting sulfonic acids by grafting and crosslinking. The sample reported here had a conductivity of 100 mS/cm at 120oC and 30% RH. Fuel cell testing of an MEA by the FSEC showed properties that paralleled those of NRE211® films (power was ~95% that of the standard over the cell working range) in spite of high hydrogen permeation due to nano-tears in the MEA.
The Electro-Oxidation of Ethanol in Alkaline Medium at Different Catalyst Metals
Authors: Bayer Domnik , Cremers Carsten , Baltruschat Helmut , Tübke Jens
Published: October 2011

In this contribution, the electro-oxidation of ethanol in alkaline medium is studied with differential electrochemical mass spectrometry (DEMS). Starting from platinum as model catalyst, the influence of the catalyst on the ethanol oxidation reaction is investigated with other metals, i.e. palladium, gold and nickel. It was found that the reaction products and their current efficiencies depend strongly on the catalyst used. At platinum the reaction to acetate is the major current producing path while the current efficiency for carbon dioxide is low. At higher ethanol concentrations ethyl acetate is formed. During the ethanol oxidation at palladium the current efficiency for acetate is even higher and only traces of carbon dioxide are formed. However, an ethyl acetate formation was not observed. Gold shows a significant activity for the ethanol oxidation with ethyl acetate being the only detected product. The activity of nickel towards the ethanol oxidation in alkaline medium is negligible.
Graphene-Riched Co9S8-N-C Non-Precious Metal Catalyst for Oxygen Reduction in Alkaline Media
Authors: Wu Gang , Chung Hoon T. , Nelson Mark , Artyushkova Kateryna , More Karen L. , Johnston Christina M. , Zelenay Piotr
Published: October 2011

In this work, a non-precious metal catalyst consisting of Co9S8 nanoparticles surrounded with nitrogen-doped graphene-like carbon (Co9S8-N-C) was developed for oxygen reduction in alkaline media. Improved activity has been measured with the Co9S8-N-C catalyst relative to Pt/C and a non-precious metal catalyst based on Fe instead of Co (Fe-N-C). An extensive physical characterization, including XRD, SEM, TEM, and XPS and electrochemical kinetic analysis was conducted to provide insight into the catalyst morphology and structure.
Anion Conductive Membrane Prepared by Plasma Polymerization for Direct Methanol Alkaline Fuel Cell
Authors: Sudoh Masao , Niimi Sachi , Kurozumi Tomohiro , Okajima Yoshiki
Published: October 2011

Direct methanol alkaline fuel cells have been tested to suppress methanol crossover and to improve the anodic activity in alkaline media. Plasma-polymerization with 4-vinylpyridine and hexafluoropropene followed by quaternization using 1-bromopropane was conducted to prepare an anion conductive ionomer in the catalyst layer and anion conductive membrane using a porous film. Plasma-polymerized membranes on various porous films were characterized by water uptake, ion conductivity and methanol permeability. The performance of the direct methanol alkaline fuel cell using the prepared anion conductive membrane was observed. The highest open circuit voltage (OCV) was 0.93 V for the 10-min-polymerized membrane. The water flux from the cathode to the anode along with the OH anion decreased with the decreasing moles of water vapor in the cathode feed, and water was observed to be transported backward from the anode to the cathode due to the low water content in the cathode feed.
Effect of Chemical Treatment on Interfacial Contact Resistance of Ferritic Stainless Steel as Bipolar Plate for PEMFC
Authors: Kim Kwang Min , Kim Jong Hee , Kim Kyoo Young
Published: October 2011

Ferritic stainless steel is a good candidate material for bipolar plate, however stainless steel is limited to use as a bipolar plate due to its high ICR. In order to reduce ICR value, chemical treatment is performed by immersion in the acidic and alkali solutions. Immersion in the HCl solution makes the specimen surface rougher because of metal dissolution. The rough surface decreases the ICR value since the real contact area between the specimen surface and carbon paper increases. Immersion in the NaOH solution do not result any change in the surface topology. However, the ICR value decreases because the passive film immersed in NaOH solution enriches in Cr oxy-hydroxide with the bound water acting as a donor-type impurity.
Low Stoichiometry Operation of a Polymer Electrolyte Membrane Fuel Cell Employing the Interdigitated Flow Field Design
Authors: Berning Torsten , Odgaard Madeleine , Knudsen Kær So̸ren
Published: October 2011

Fuel cell operation on dry reactant gases under low stoichiometry conditions employing the interdigitated flow field is investigated using a multi-fluid model. It is assumed that the MEA contains a water uptake layer which facilitates water absorption to the membrane and hence prevents the anode gas phase from drying out. It is shown that the membrane humidity increases with decreasing stoichiometric flow ratios to values of λ ≈ 7. Operating the cathode side at a stoichiometric flow ratio of 1.2 appears feasible under steady state conditions, while our simulations suggest that the anode stoichiometry may even be as low as 1.05. The effect of operation pressure and temperature on the membrane water content is studied. Finally, experiments are suggested to determine the kinetic absorption coefficient and the specific surface area of the electrolyte inside the catalyst layers.
Understanding the Stress Response of Seals in Fuel Cell Subject to Temperature Cycling
Authors: Cui Tong , Chao Yuh , Van Zee J. W.
Published: October 2011

This paper studies a polymer used for sealing or gasket materials in PEM fuel cells and its viscoelasticity, which leads to decreases in the sealing force. Experimental data for the stress relaxation behavior of the polymer, a liquid silicone rubber, are presented for a changing temperature profile. The data show that the sealing force changes considerably due to both thermal expansion and stress relaxation. A two-step model is presented to predict the change of sealing force under temperature cycling
Effect of CO2 on the Alkaline Membrane Fuel Cell
Authors: Grew Kyle N. , Ren Xiaoming , Chu Deryn
Published: October 2011

Alkaline solutions can undergo the conversion of hydroxide (OH-) to carbonate (CO3=) and bicarbonate (HCO3-) in the presence of carbon dioxide (CO2). This presents a challenge to the Alkaline Membrane Fuel Cell (AMFC), where CO2 may be introduced via an atmospheric air oxidant and as a reaction product of alcohol fuels. CO2 has several implications on the AMFC, including the exchange of OH- counterions in the anion exchange (AE) membrane and ionomer for the larger, less mobile (bi)carbonates. The (bi)carbonates may be purged during operation; however, their presence can decrease the ionic conductivity and effect the thermodynamics and electrochemical kinetics. These processes make component and cell characterization difficult and subjective to the environmental and operational history of the materials and cells. The interactions of CO2 with the AE membrane are needed and examined in this work.
Permeability of a PEMFC Gas Diffusion Layer Based on Morphology
Authors: Nishiyama Enju , Murahashi Toshiaki
Published: October 2011

The transport of gases and water through the gas diffusion layer of a PEMFC was investigated with a focus on the morphological characteristics of the carbon paper GDL. The capillary pressure and permeability of the GDL, which play important roles in water transport, were derived as functions of liquid saturation using a pore size distribution (PSD) model. A GDL gas permeability model is proposed on the basis of empirical pressure drop functions for the laminar flow across banks of tubes. The calculated relationship between gas permeability and porosity was in good agreement with the experimental data. The observed permeability of GDLs of different thickness suggests that the permeability, or mean pore diameter at the surface, is larger than that of the core. Calculated results indicated that diffusion loss of reactant gases is mainly determined by the PSD of the surface layer of the GDL.
Modeling the Variation of Relative Humidity along the Cathode Feed Channel of a PEM Fuel Cell
Authors: Baghalha Morteza
Published: October 2011

A water balance model for a local location across a PEFC was previously developed. Below a critical current density, water removal out of the cathode catalyst layer (CCL) to cathode side proceeds by vapor diffusion. Above the critical current density, excessive water generation leads to the build-up of an excess liquid pressure in the CCL, which acts as a driving force for hydraulic fluxes to polymer electrolyte membrane (PEM) and gas diffusion media (GDM) of cathode. These fluxes are a function of local cell operating conditions such as the local relative humidity in cathode feed channel (CFC). Assuming no water condensation/evaporation in the CFC, water vapor balance along CFC under steady state condition was considered in the present study. A simplified 1D analytical solution for prediction of RH variation along the CFC was developed in this work. An adjustable design factor was also introduced in the governing equations to compensate for deviations from such simplifying assumptions as the isothermal condition. For typical PEFC operating conditions, the model showed significant variations of the relative humidity and water fluxes along the CFC.
Layered Titanates Intercalating Organic Guest Spacers for Organic/Inorganic Proton Conductors
Authors: De Bonis Catia , D'Epifanio Alessandra , Mecheri Barbara , Traversa Enrico , Miyayama Masaru , Licoccia Silvia
Published: October 2011

Two layered organic/inorganic tetratitanate derivatives containing sulfanilic acid (SA) were synthesized from potassium tetratitanate (K2Ti4O9) or its acid form (H2Ti4O9). Scanning electron microscopy (SEM) observations were performed to investigate the microstructural features of the samples. The thermal stability of the compounds was tested by thermogravimetric analysis (TGA). The effect of the presence of organic guest molecules in the layered tetratitanates was investigated in terms of proton exchange capacity (PEC) and conductivity (σ), to evaluate the use of these compounds as fillers for nanocomposite proton exchange membranes for fuel cell applications.
Development of the New Model for the Proton Hopping by Molecular Dynamics Simulation
Authors: Sakai Hironori , Yoshida Taiki , Tokumasu Takashi
Published: October 2011

The aim of this study is refinement of proton(s) hopping rate by applying new model for Molecular Dynamics (MD) calculation with Empirical Valence Bond (EVB) method. The overview about this new model is an acceptor selection method based on energy prediction instead of the one based on distance. The effect of water molecules outside the Eigen cation was mainly considered in this new model. Then, microenvironment interaction to the formation of the cluster and proton hopping were reasonably expressed as an actual condition. This procedure was applied for proton hopping. The total number of cluster formation and cancel were also analyzed.