bluuebunny/crossref_metadata_2025 huggingface dataset:
Doping of Direct Gap Ge1

-y
Sn
y
Alloys to Attain Electroluminescence and Enhanced Photoluminescence
Authors: Senaratne Charutha Lasitha , Gallagher James Dennis , Xu Chi , Sims Patrick , Menendez Jose , Kouvetakis John
Published: October 2015

Low temperature (T < 300°C) in-situ doping protocols were developed for Ge1-y
Sn
y
alloys with compositions above the indirect-to-direct gap crossover point, which were deposited using CVD. Trisilylphosphine (P(SiH3)3) was used as the n-type dopant source while diborane (B2H6) was used for n-type doping. This enabled the fabrication of pin diode structures with compositions up to y = 0.137. These photodiodes exhibit electroluminescence at wavelengths up to 2700 nm. Furthermore, it was demonstrated that n-type doping enhances the photoluminescence obtained from these materials.
Behavior of Sodium Sulfate in Cryolite-Alumina Melts and Formation of Sulfurous Gases
Authors: Meirbekova Rauan , Haarberg Geir Martin , Thonstad Jomar , Aarhaug Thor Anders , Saevarsdottir Gudrun
Published: October 2015

The study of the behavior of sulfur compounds in the Hall-Heroult process is of particular interest not only due to the emitted harmful gases, but also its potential effect on the process of aluminum production. The source of sulfurous gases from aluminum smelters is mainly the carbon anodes, which contain sulfur in organic sulfur ring structures. Sulfur is also introduced in small amounts by the added alumina, mostly in the form of sulfates. The sodium sulfate reactions and the gaseous products emitted from electrolysis cell were studied at different conditions and analyzed by using ICP (Inductive Coupled Plasma) spectroscopy, XRF (X-Ray Florescence) and MS (Mass Spectroscopy). The sulfurous gases that were observed include: SO2, COS, CS2 and H2S.
Electrochemical Analysis for the Identification of Electrode Reaction in Ni-YSZ Anode as for Solid Oxide Fuel Cell
Authors: Im Ha-Ni , Lim Dae-Kwang , Lee Tae-Ryong , Yoo Young-Sung , Choi Mihwa , Song Sun-Ju
Published: October 2015

The impedance of Ni-YSZ cermet electrodes was investigated as a function of different partial pressure of hydrogen and water. The impedance spectra for the hydrogen/water reaction show two reactions by DRT analysis. Reaction at high-frequency region was assigned to transport of electrode – oxidation reaction within the electrode structure and the electrode / electrolyte interface. Whereas low frequency response is the adsorption of a gaseous H2O molecule from the gas phase onto the active electrode site. The data are analyzed using an equivalent circuit representing two parallel RC. The values of activation overpotential are separated under the fixed current load, which are well-fitted to the Butler-Volmer equation. Under the current load, the variation of exchange current density ( ) with pO2 indicated that the total reaction-rate is determined by charge transfer reaction at the high temperature.
Grain Boundary Engineering to Improve Ionic Conduction in Thin Films for Micro-SOFCs
Authors: Tarancón Albert , Morata Alex , Pla Dolors , Saranya Aruppukottai M. , Chiabrera Francesco , Garbayo Inigo , Cavallaro Andrea , Canales-Vázquez Jesús , Kilner John A. , Burriel Mónica
Published: October 2015

New emerging disciplines are specifically devoted to study trivial and non-trivial effects resulting from working in the nanoscale, however, the implementation of these nanostructures in real devices is still a major challenge. Thin film deposition and silicon microtechnology is probably the most promising and straightforward combination for the reliable integration of nanomaterials in real devices. In particular, the implementation of pure ionic and mixed ionic/electronic conductors (MIECs) in thin film form allows the miniaturization of multiple solid state devices such as solid oxide fuel cells (SOFCs). In this work, we will present the implementation of novel nanoionics concepts in micro-SOFCs by using micro and nanofabrication technologies. We will put special attention on the contribution of grain boundaries to the mass transport properties in interface-dominated materials such as thin films. Grain boundary engineering will be presented as a powerful tool for reducing the resistance associated to electrolytes and even control the intrinsic transport nature and performance of MIEC materials.
Vertical-Aligned Nanocomposites Oxide Thin Films with Enhanced Ionic Conductivity
Authors: Su Qing , Zhang Wenrui , Jacob Clement , Yoon Daeil , Manthiram Arumugam , Wang Haiyan
Published: October 2015

Oxide thin films with high ionic conductivity are crucial for sustainable energy production systems such as fuel cells that provide efficient and environmental-friendly energy. Key materials science efforts are associated with developing such oxides with high ionic conductivity. Of particular importance for developing thin film oxide materials is high performance and good stability in the operation temperature range. In this paper, vertically aligned nanocomposites (VAN) approach is reviewed. It creates vertical interfaces of two oxide materials and provides a new design paradigm to manipulate functionalities that cannot be obtained in individual constituents. Two major examples corresponding to ionic conducting oxide thin films in the VAN form presented are: (1) vertically aligned electrolyte/electrolyte nanocomposites with superior vertical ionic conductivity, and (2) vertically aligned electrode/electrolyte nanocomposites as an interlayer to increase the catalytic reaction probability. Finally, opportunities of tuning functionalities of such VAN systems are introduced.
Proton Conducting Micro-Solid Oxide Fuel Cells with Nanoscale Palladium Interlayers
Authors: Adam Suhare , Ramanathan Shriram
Published: October 2015

Thin film fuel cells with proton conducting oxide electrolytes have been fabricated and characterized. A comparison is made between fuel cells with and without Pd interlayers at the electrode-electrolyte interface. A nearly two-fold increase in power density was observed in the performance of a thin film BYZ fuel cell by the addition of a palladium interlayer. The studies contribute to engineering improvements in thin film fuel cells and in the future could be useful to understand proton conduction in complex oxides via nanoscale selective permeation layers.
Effect of Catalyst Layer and Fuel Utilization on the Durability of Direct Methane SOFC
Authors: Georges Samuel , Nóbrega Shayenne D. , Cheah Seng Kian , Steil M. C. , Bultel Yann , Rieu Mathilde , Viricelle Jean-Paul , Gelin Patrick
Published: October 2015

Solid oxide fuels cells with and without anodic catalytic layer and specific anodic current collectors were developed in order to be fueled by dry methane. Due to the cell architecture integrating a 0.1wt% Ir-CGO catalyst layer onto the anode, platinum, gold and cupper screen-printed meshes were designed and optimized to ensure efficient current collection between the anode surface and the catalyst membrane. Current density and ageing in H2 and in pure dry CH4 respectively were compared to conventional pressed grid collecting systems. Similar performances were achieved using bulk grids or gold, platinum and copper screen-printed meshes. Operation in pure dry methane is compared with and without the catalytic layer as a function of the fuel utilization. It is demonstrated that long term operation is possible provided that sufficient faradic efficiency is achieved.
Temperature Distribution Responses of a Micro-Tubular SOEC after an Electric Load Change
Authors: Mizusawa Tatsuya , Araki Takuto , Mori Masashi
Published: October 2015

A two-dimensional tubular model of a nickel + yttria-stabilized zirconia electrode supported micro-tubular solid oxide electrolysis cell (SOEC) was developed in order to investigate the temperature distribution during high-temperature steam electrolysis. High-temperature steam electrolysis using SOECs allows for highly efficient hydrogen generation, because the heat from the overpotential can be recycled in the form of a heat source for the electrolysis reaction. In this paper, the numerical model was expanded to unsteady model, and the temperature distribution responses after electric load changes of 0.2 A/cm2 to 0.0 A/cm2, 0.4 A/cm2 to 0.0 A/cm2 and 0.6 A/cm2 to 0.0 A/cm2 were calculated.
Effect of Alloy Elements on the Corrosion Resistance and Electrical Conductivity of Austenitic Stainless Steel for MCFC
Authors: Kim Kwangmin , Kim JongHee , Jo KiHoon
Published: October 2015

Bipolar plate and current collector are important stainless steel components of MCFC because they supply the pathway of the electron flow between each unit cell. However these stainless steel components are prone to corrosion in the hot corrosion environment and corrosion products forming on the surface increase the ohmic resistance. To solve these problems, alloy elements are added to modify the properties of the oxide layer on the surface. High Cr content causes the formation of thin oxide layer, therefore, improves the corrosion resistance. Mn enrichment occurs in the oxide layer and may lead to an increase in electrical conductivity.
Oxygen Reduction Durability and Activity of Tantalum Oxide-Based Electrocatalysts for Cathode of Polymer Electrolyte Fuel Cells
Authors: Matsuzawa Koichi , Ishihara Akimitsu , Uehara Naoki , Fujita Yoshio , Kohno Yuji , Matsumoto Masashi , Ohgi Yoshiro , Mitsushima Shigenori , Imai Hideto , Ota Ken-ichro
Published: October 2015

Development of non-platinum cathode is required to commercialize polymer electrolyte fuel cells. We have investigated group 4 and 5 transition metal oxides, because they have high chemical stability under acidic atmosphere. In this paper, we focused on tantalum oxide-based compounds and evaluated their durabilities and ORR activities. Durability test of the tantalum oxide-based compounds made from carbonitrides revealed that the crystalline and electronic structure of the oxide-based compounds did not change during the potential holding. In addition, we demonstrated that the new preparation method using oxy-phthalocyanine as starting material was useful for preparing nano-sized particles to increase in the ORR current.
Development of Group 4 and 5 Metal Oxide Cathode with Electron Conductive Oxide
Authors: Ota Ken-ichiro , Hamazaki Makoto , Matsuzawa Koichi , Mitsushima Shigenori , Ishihara Akimitsu
Published: October 2015

Powders of Ti and Nb metal compounds (metal complexes that contain nitrogen) were mixed and heat-treated at 1050 oC in the H2/Ar gas mixtures to obtain specimens with different oxidation state. An appropriate oxidation is essential to have a definite catalytic activity for the ORR. The onset potentials of partially oxidized Ti and Nb oxide mixture with the electron conductive oxide support had reached over 1.1 V vs RHE that is more than that of commercial Pt-C. The active point of our materials might have a better activity compared to Pt. Potential cycling test was conducted between 1.0 V and 1.5 V using triangler wave, and between 0.6 V and 1.0 V using rectangular wave, respectively. We have not detected the decay of activity in both cases even at 80oC, although the current was small.
Activity and Stability of Molybdenum-Containing Dispersed Pt Catalysts for CO Tolerance in Proton Exchange Membrane Fuel Cell Anodes
Authors: Hassan Ayaz , Iezzi Renato C. , Ticianelli Edson A.
Published: October 2015

In this work, results of attempts to improve the activity and stability of Mo-containing dispersed Pt catalysts for the CO tolerance in proton exchange membrane fuel cell (PEMFC) anodes are revised for the following approaches: (1) application of a heat treatment at various temperatures ranging from 400 to 700 °C on carbon supported PtMo (60:40, Pt:Mo) electrocatalyst; (2) deposition of Pt and PtMo nanoparticles on carbon-supported molybdenum carbides (Mo2C/C) and; (3) employing ternary and quaternary materials formed by PtMoFe/C, PtMoRu/C and PtMoRuFe/C. The Pt-Mo/C catalyst heat-treated at 600 °C showed higher hydrogen oxidation activity in the absence and in the presence of CO and better stability, compared to all other Mo-containing catalysts. Similar CO tolerances were observed for PtMoRuFe, PtMoFe, PtMoRu supported on carbon, and for Pt supported on Mo2C/C, which also presented better stability, as compared to as-prepared PtMo supported on carbon. However, partial dissolution of Mo, Ru, and Fe from the anodes and their migration toward cathodes during the cell operation was observed.
Development of Platinum-Niobium as a CO Tolerant Catalyst for PEFC Operating with CO Contaminated Hydrogen
Authors: Rocha Thairo A. , Colmati Flavio , Ciapina Eduardo Gonçalves , Linares José J , Gonzalez Ernesto Rafael
Published: October 2015

This paper presents the results of a bimetallic Pt3Nb/C catalyst prepared by thermal treatment in dilute reductive atmosphere (5% H2 in Ar) to obtain a CO-tolerant catalyst. The thermal treatment leads to the formation of a PtNb fcc solid solution and a Pt3Nb intermetallic phase along with some niobium oxides (NbO2 and NbO1.46). Such crystalline phases modify the electronic environment of platinum, reducing the white line of the Pt L3 absorption edge, as a result of the filling of the Pt 5d band. This, in turn, weakens the Pt-CO adsorption strength, which, in combination with the large availability of oxygenated species coming from the Nb oxides, leads to a very active CO-tolerant anode electrocatalyst, as confirmed by the CO stripping characteristics and the fuel cell performances in the absence and presence of CO in the H2 fuel stream.
Conjugate Analysis of Heat-Species-Charge Transport for Evaluating Effects of the Temperature Gradient on Cell Performance
Authors: Miyagawa Kiyofumi , Araki Takuto
Published: October 2015

Understanding the water transport phenomena in the Proton Exchange Membrane Full Cell (PEMFC) is very important to estimate the cell performance. However, temperature, electrochemical reaction and liquid water, active materials and heat transports have been interacted each other. So, the conjugate analysis considering all of them spontaneously is required. In particular, the temperature gradient has the significant influence on water transport. Then, the two-dimensional unsteady model considering distributions of temperature, spices and reaction in components of the PEMFC was developed to investigate how the temperature gradient effects on the water transport and the cell performance. The result indicated the temperature gradient invoke heat pipe phenomena. As the result, the temperature gradient promoted liquid water drainage in PEMFC. Finally, it was proved that considering the temperature gradient impacted the water transport and the cell performance, and the temperature gradient was necessary.
Stochastic Reconstruction and Transport Simulation of PEFC Catalyst Layers
Authors: Pant Lalit M. , Sabharwal Mayank , Mitra Sushanta , Secanell Marc
Published: October 2015

A stochastic method for analysis and reconstruction of PEFC porous media is presented. The method uses statistical correlation function to analyze and parametrize the porous media structure. The improved reconstruction method uses a multigrid hierarchical simulated annealing technique to significantly reduce the reconstruction time and ascertains a long range connectivity. Analysis of the catalyst layers show it to be a homogeneous porous media with strong anisotropy in in-plane and through-plane directions. The stochastic reconstruction procedure is able to reconstruct 3D structures of the catalyst layer with similar statistical correlation functions as of the reference image. Molecular and Knudsen diffusion are simulated on the reconstructions using the open source package OpenFCST. The effective transport properties of the reconstructions is similar to that of the reference structure; however, the accuracy of the reconstructions has been limited by the imaging methods.
Various Scales of Aging Heterogeneities upon PEMFC Operation – A Link between Local MEA Materials Degradation and the Cell Performance
Authors: Dubau Laetitia , Durst Julien , Castanheira Luis , Maillard Frederic , Lamibrac Adrien , Dillet Jérôme , Maranzana Gaël , Lottin Olivier , El Kaddouri Assma , De Moor Gilles , Bas Corine , Flandin Lionel , Rossinot Elisabeth , Caqué Nicolas , Chatenet Marian
Published: October 2015

PEMFC performances decay upon operation, following the degradation of their core materials. These degradations are heterogeneous within a PEMFC, whatever its operating conditions and its constitutive materials. Three distinct levels of degradation heterogeneities are observed in PEMFC cathodes. (i) The degradations are neither homogeneous along the gas channels of the bipolar plates (BP, from the inlet to the outlet), nor along the active layer thickness (from the membrane to the diffusion layer). (ii) The BP geometry also matters: repeated start/stop (fuel-starvation) events promote harsher degradation for the cathode regions facing the anode regions located under the BP land. (iii) Finally, the cells operate and age differently at the stack level. These degradations are strongly linked to the materials composing the MEA and the operating conditions, but also depend on the bipolar plates and stack design, which renders difficult any generalization of the conclusions obtained for a particular PEMFC test.
The Power of in-Situ Studies: How X-ray Absorption Spectroscopy Can Help to Develop PEMFC Catalysts with Increased Activity and Stability
Authors: Roth Christina , Kaserer Sebastian , Brieger Claudia , Caldwell Keegan M. , Melke Julia , Ramaker David E.
Published: October 2015

In-situ X-ray absorption spectroscopy is an exciting tool which, in contrast to many other characterization techniques, does neither require ultrahigh vacuum conditions, nor long-range order in the material under study. It thus allows us to investigate electrocatalysts directly under operation conditions. With the Δµ XANES difference approach combined with theoretical calculations, characteristic signatures give away the kind of adsorbate on the catalyst surface and its temperature- and potential-dependent coverage. Unraveling reaction and degradation mechanisms in carbon-supported Pt nanoparticle catalysts applied at the anode or cathode side of polymer electrolyte membrane fuel cells, it thus helps to tailor active and stable materials for future energy devices. In this paper, three examples ranging from the investigation of CO adsorption on an oxide-supported Pt catalyst to the detailed study of the anode and cathode catalyst in high-temperature PEM fuel cells will be presented.
Mathematical Modelling and Experimental Analysis of Thin, Low-Loading Fuel Cell Electrodes
Authors: Secanell Marc , Putz Andreas , Shukla Shantanu , Wardlaw Phillip , Bhaiya Madhur , Pant Lalit M. , Sabharwal Mayank
Published: October 2015

Cathode electrode performance quickly degrades at platinum loadings below 0.1 mg/cm2. This performance degradation has been attributed to catalyst oxide coverage, local micro-scale gas transport limitations at the catalyst sites, and two-phase flow. OpenFCST, an open-source fuel cell simulation package, is used to develop a membrane electrode assembly (MEA) model, and a catalyst layer micro-structural model, of low loading inkjet printed fuel cells. Simulations of the inkjet printed catalyst layer reconstructions estimate that the effective gas transport in the electrode is of the order of 10-4 cm2/s and it is dominated by Knudsen diffusion. The macro-scale MEA mathematical model is used to estimate cell performance, cell and catalyst layer ohmic resistances, and current, reactant and oxide coverage distributions in the electrode. MEA model cell performance and resistance are in reasonable agreement with experimental data obtained for the electrodes under a variety of oxygen partial pressures. Results show appropriate kinetic, and local transport resistance models, are necessary in order to capture the experimental trends observed at different loadings and at limiting current densities, respectively.
A Mechanistic Study of Perfluorosulfonic Acid Membrane Water Permeance Degradation in Air
Authors: Coms Frank D. , Fuller Timothy J. , Schaffer Corey P.
Published: October 2015

Perfluorosulfonic acid (PFSA) membranes subjected to aging in air form a degradation product with decreased water content and water permeance. FTIR kinetics studies performed on a range of membrane thicknesses shows that reaction exhibits zero-order kinetics, has a very weak temperature dependence and a strong dependence on air velocity. Reactions performed in nitrogen or synthetic air do not form the degradation product. The kinetic data, in combination FTIR spectra of deuterium exchanged products indicate that the degradation product results from an acid-base reaction between ultra-trace levels of atmospheric ammonia and the sulfonic acid groups of the PFSA membrane.
Improved Water Management with Thermally Sprayed Coatings on Stainless Steel Bipolar Plates of PEMFC
Authors: Gago Aldo Saul , Sanchez Daniel G , Ansar Asif Syed , Gazdzicki Pawel , Wagner Norbert , Arnold Johannes , Friedrich Kaspar Andreas
Published: October 2015

We develop a thermally sprayed Ti coating for PEMFC stainless steel (ss) bipolar plates. It is subsequently modified with Au by electro-deposition. SEM reveals that the Au/Ti coating is 30.8 µm thick and rough. The presence of TiO2 between Ti and Au is negligible, as confirmed by XRD and XPS. Potendiodynamic characteristics in O2-saturated 0.5 M H2SO4 show that the Au/Ti/ss samples have comparable corrosion currents to Au/ss but higher corrosion potentials. The interfacial contact resistance (ICR) of Au/Ti/ss is 8.6 mΩ cm2 under a compaction pressure of 140 N cm-2. The performances of PEMFCs with Au and Au/Ti are similar at cell voltages higher than 0.75 V. However, at 0.6 V the Au/Ti coating diminishes the current and pressure instabilities of the PEMFC operating under strong flooding conditions. The effect also occurs in the oscillation frequency, confirming the unique property of Au/Ti for reducing the effect of flooding.
Materials and Cell Designs for Bipolar Fuel Cells
Authors: Ahlfield John M. , Deshpande N. A. , Liu Lisha , Huang Wenjiao , Chu Deryn , Kohl Paul A
Published: October 2015

The PEM-AEM interface is a critical component in bipolar membrane fuel cell operation. In this study, interfacial materials with varying conductivities were used in order to control the location of the junction within the MEA. Use of a conductive interface consisting of a single ion conductive material resulted in devices with lower interfacial resistance as compared to a neutral interface. When comparing conductive interface materials, anion-conductive materials provided lower total membrane resistance than proton-conductive materials. This decrease is attributed to the movement of the junction from the AEM surface near the cathode to the PEM surface near the anode.
CO Adsorption on Platinum Nanoparticles - the Importance of Size Distribution Studied with in-Situ DRIFTS and DFT Calculations
Authors: Brieger Claudia , Melke Julia , Kaghazchi Payam , Roth Christina
Published: October 2015

Temperature dependent adsorption of CO has been studied on Pt/SiO2 nanoparticles with Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) under different CO concentrations and flow conditions. In all experiments almost only linearly adsorbed CO could be detected. The spectra have been fitted with three bands and were assigned with DFT calculations which specifically include the nanoparticle structure of the platinum clusters. The relative intensity of these bands strongly depends on the temperature and on the CO flow conditions. When CO is not replenished, desorption starts even at room temperature with only the two bands at lower wavenumber remaining at higher temperatures.It could be shown that for catalysts containing a size distribution of nanoparticles, not only the various adsorption sites (i.e. facets, edges and corners), but also the different cluster sizes need to be considered for the precise description of CO adsorption.
Platinum Dissolution from Carbon Supported Nanoparticles
Authors: Wang Zhongqi , Tada Eiji , Nishikata Atsushi
Published: October 2015

We evaluated Pt dissolution from carbon supported nanoparticles (Pt/C) by inductively-coupled plasma-mass spectrometry (ICP-MS) and a channel flow double electrode (CFDE). On Pt/C, the observed both anodic and cathodic dissolution of Pt2+ under potential cycling; the later dominated at an E
U of 1.4 V. Besides, the cathodic dissolution of Pt2+ decreases with increasing mean particle size (d
p) of the Pt NPs. Both dissolutions were enhanced by elevating the temperature from 25 to 65 oC. The CFDE showed its applicability to dissolution tests using supported nanoparticles.
Modeling Platinum Oxide Growth of PEMFC Cathode Catalysts
Authors: Arisetty Srikanth , Liu Yuxiu , Gu Wenbin , Mathias Mark
Published: October 2015

Oxide growth on Pt catalysts in an N2/H2O atmosphere was investigated as a function of potential, and temperature. A coulometric method was employed to measure oxide coverages on Pt/Vulcan and PtCo/HSC catalysts. Data suggests that oxide coverage grows monotonically from zero at 0.6VRHE to a monolayer of oxide coverage at 0.95 VRHE. Potentiostatic-hold measurements indicate that oxide growth follows two steps, first Pt to PtO followed by PtO to PtO2 occurring more slowly. Characterization of the thermodynamics and kinetics of the above two reactions indicate faster growth in PtCo compared to Pt catalysts. The kinetics of place exchange oxide is thus shown to be enhanced by the alloying element cobalt. The effects of temperature and particle curvature were significant but secondary relative to the impact of potential. The results provide the understanding needed to correlate Pt oxide growth to ORR kinetics and catalyst degradation.
Recent Progress in Nanostructured Thin Film (NSTF) ORR Electrocatalyst Development for PEM Fuel Cells
Authors: Steinbach Andrew J. , van der Vliet Dennis , Hester Amy E , Erlebacher Jonah , Duru Cemal , Davy Isaac , Kuznia Monika , Cullen David A.
Published: October 2015

In this paper, we provide an overview of several recent development activities towards improving the activity of nanoporous PtxNi1-x thin film electrocatalysts on the 3M Nanostructured Thin Film (NSTF) support. Significant improvements in electrocatalyst specific area and mass activity have been achieved through optimization of electrocatalyst fabrication parameters (deposition, annealing, and dealloying), which influence electrocatalyst composition and structure. Membrane electrode assemblies (MEAs) which incorporate improved NSTF PtxNi1-x cathode catalysts have demonstrated performances which approach or exceed several U.S. Department of Energy 2020 performance and PGM-content targets.
Local Structure and Proton Transport in HT-PEFCs Measured with Neutron Scattering
Authors: Holderer Olaf , Ivanova Oxana , Khaneft Marina , Hopfenmüller Bernhard , Lüke Wiebke , Majerus Anne , Appavou Marie-Sousai , Szekely Noemi , Krutyeva Margarita , Kentzinger Emmanuel , Zorn Reiner , Lehnert Werner
Published: October 2015

The structural properties and proton transport processes of High Temperature Polymer Electrolyte Fuel Cells (HT-PEFCs) are studied on a broad range of length- and timescales with different neutron scattering techniques. We show structural properties of the proton conducting membrane and of the catalyst layer. Proton transport is measured with quasielastic neutron scattering techniques. The sensitivity of neutrons to individual isotopes, especially in the case of hydrogen and deuterium, makes neutron scattering a perfect tool for such studies. Complementary techniques such as transmission electron microscopy, PFG-NMR and X-ray scattering round up the picture of the different fuel cell components.
Thermo-Stable Non-PFSA Cation-Conductive Fluoropolymers for Medium-Temperature PEMFCs
Authors: Xu Shaoyi , Jiang Rong , Gao Yong
Published: October 2015

A non-PFSA fluoropolymer was synthesized from NafionTM via a free radical coupling reaction with 2,3,5,6-tetrafluoroaniline followed by a protonation step using diluted sulfuric acid. The resulted polymer membrane is highly cation-conductive with the enhanced thermal stability. This polymer could be used in medium-operation-temperature PEMFCs (e.g., 100-200 oC) that can adopt CO-rich hydrogen feedstocks.
Molecular Engineering of Ion-Conducting Polymers for Fuel Cell Membrane Applications
Authors: Lee Woo-Hyung , Mohanty Angela D , Bae Chulsung
Published: October 2015

Aromatic polymers functionalized with various sulfonate groups and ammonium cations were synthesized for use in proton exchange membranes (PEMs) and anion exchange membranes (AEMs), respectively. The effect of these different ionic side groups of polymers on membrane transport properties will be discussed. On second part, high-molecular-weight quaternary ammonium (QA)-tethered aromatic polymers that are void of alkaline labile C–O bonds were prepared to achieve improved stability of AEM fuel cells. This new class of hydrocarbon polymers showed high hydroxide ion conductivity and excellent alkaline stability at 80 °C. Overall, this work provides a new synthetic strategy for preparation of AEMs with good fuel cell performance and excellent stability.
Hydroxide Transport in Next Generation Anion Exchange Membranes
Authors: Sarode Himanshu N , Pandey Tara P , Yang Yuan , Knauss Daniel M , Coughlin E. Bryan , Liberatore Matthew W , Herring Andrew M
Published: October 2015

Anion Exchange membranes (AEMs) are being developed for a variety of applications. Among these are fuel cells and electrolyzers that require the AEM to conduct hydroxide anions. Measurement of the ionic conductivity of hydroxide is challenging because the hydroxide is a strong nucleophile and attacks polar groups in the AEM and also rapidly reacts with atmospheric CO2 to form the less conductive carbonate and bicarbonate counter anions. We have developed a rigorous method to fully exchange AEMs into the hydroxide form while excluding CO2 and remove all residual inorganic salt from the film prior to measurement. These measurements of the hydroxide ion conductivity coupled with self diffusion measurements of water and the similarly sized fluoride anion in these films are beginning to shed insight into how hydroxide anion transport can be maximized in state of the art AEMs.
Tethering Cations to Aromatic Polymers via Flexible Spacers to Enhance the Performance of Alkaline Fuel Cell Membranes
Authors: Jannasch Patric
Published: October 2015

Conventional anion-exchange membranes based on aromatic polymers with cationic groups placed in benzylic positions on the polymer backbone normally suffer from poor alkaline stability and limited OH− conductivity. However, recently it has been shown that both the conductivity and alkaline stability of anion-exchange membranes can be significantly enhanced by instead placing the cationic groups on flexible and hydrolytically stable alkyl spacers. The present contribution briefly reviews the latest results and developments concerning this synthetic approach to improved alkaline membranes for fuel cells.
Proton and Metal Cage-Based Anion-Conductive Fluoropolymers for AMFCs
Authors: Xu Shaoyi , Jiang Rong , Gao Yong
Published: October 2015

A new class of fluoropolymers (polymers 9 and 14) have been synthesized and tested as novel anion-conductive materials. Proton and lithium cages, which are alternative to conventional quaternary ammonium hydroxide are utilized as anion-exchange groups in these polymers. Such cage-based fluoropolymers can potentially be developed into chemically stable and anion-conductive membranes that can find applications in alkaline membrane fuel cells (AMFCs), metal-air batteries and many other electronic devices.
New Polymer Structures for Anion Exchange Membranes
Authors: Zhu Liang , Pan Jing , Hickner Michael
Published: October 2015

There has been a strong and growing interest in the use of anion exchange membranes for electrochemical technologies. A key part of the research in this burgeoning sub-field is the search for polymeric anion exchange membranes that are stable, highly conductive, and scalable to quantities that are useful for cell engineering. Our group has been one of the pioneers in the design and scale-up of a number of different anion exchange membrane platforms based on commercially-relevant polymeric substrates. We have devised scalable post-polymerization modification chemistry to covert inexpensive polymers to performance-competitive anion exchange membranes and have used this platform to increase conductivity, improve mechanical properties and decrease water uptake. This range of new anion exchange membrane structures is currently being evaluated in cell testing for various devices and being evaluated for further scale-up activities.
Tomographic Analysis of Polymer Electrolyte Fuel Cell Catalyst Layers: Methods, Validity and Challenges
Authors: Thiele Simon , Vierrath Severin , Klingele Matthias , Zengerle Roland
Published: October 2015

Tomographic analysis of catalyst layers is one of the key methods to evaluate morphological properties in polymer electrolyte fuel cell PEFC catalyst layers. The most important applications for tomographic reconstruction are process control during manufacturing and investigations of ageing phenomena. We discuss all methods for tomographic imaging that are applicable for PEFC catalyst layers with an emphasis on focused ion beam / scanning electron microscopy tomography (FIB-SEMt). For now, no single tomographic method suffices to image all morphological properties of interest. Multi-tomographic approaches are therefore necessary. Phase fractions and phase-distributions are the most important properties to calculate within a tomographic reconstruction. We review further parameters that may be extracted from tomographic reconstructions and discuss open issues in first modeling approaches. Finally we discuss the validity of analyses within tomographic representations.
Accurate Ex-situ Measurements of PEM Fuel Cells Catalyst Layer Dry Diffusivity
Authors: Salari Sina , McCague Claire , Tam Mickey , Saha Madhu S , Stumper Jüergen , Bahrami Majid
Published: October 2015

Polymer electrolyte membrane fuel cells (PEMFC) efficiently convert the reaction energy of hydrogen and oxygen to electricity, water and heat. The oxygen reduction reaction occurs in composite nanostructured catalyst layers (CL) formed from Pt nanoparticles supported on a network of carbon particle agglomerates. Oxygen reaches the reaction site through diffusion. Understanding the diffusion properties of CL is vital to proper design and operation of CL and PEMFC. Measuring the diffusivity of thin porous layers is challenging, as is selecting a suitable substrate and appropriate CL coating procedures. In this work, CL is coated on 70 μm thick hydrophobic porous polymer substrates with a Mayer bar coater. Several samples are prepared and their thickness are measured accurately. The diffusivity of the CL and the substrate are measured using a dry diffusivity test bed and the resulting CL-diffusivity values are determined for different Pt loadings.
FIB+SEM Tomography and Numerical Simulation of Corroded PEM Fuel Cell Cathodes
Authors: Star Andrew G. , Fuller Thomas F
Published: October 2015

Carbon support corrosion in proton exchange membrane fuel cell cathodes causes severe polarization losses due to mass transport resistance and underutilization of the platinum catalyst. Tomography by focused ion beam and scanning electron microscope serial sectioning has recently been demonstrated on PEM fuel cell cathodes and the technique is used here to image and generate 3D reconstructions of small volumes (~3mm3). Morphological changes following extensive carbon corrosion were observed and quantified. Direct simulations performed on a 3D reconstruction generated from electron microscopy data allow for calculation of effective transport properties, notably effective diffusion coefficients, porosity, and tortuosity.
3D Imaging of Fuel Cell Electrode Structure Degraded under Cell Voltage Reversal Conditions Using Nanoscale X-Ray Computed Tomography
Authors: Mandal Pratiti , Hong Bo Ki , Oh Jong-Gil , Litster Shawn
Published: October 2015

A challenge faced by polymer electrolyte fuel cells for transportation applications is hydrogen starvation at the anode that can arise from a variety of sources such as water flooding, ice formation, foreign impurities, etc., which typically causes cell voltage reversals through water electrolysis and carbon corrosion at high anode potentials. Here we present electrochemical diagnostics and nano-scale X-ray computed tomography (nano-CT) of fuel cell electrodes with Pt/C catalysts degraded under cell voltage reversal conditions. It is found that the cell performance decreases and Ohmic resistance increases significantly after reversal tests. Anode cyclic voltammetry indicates new peaks due to severe carbon corrosion. Nano-CT imaging of the internal structure reveals that the thickness of the anode is reduced by approximately 40 % after the reversal tests, but the interface between the membrane and electrode appears mostly intact over the interfacial area even after the cell voltage reversals.
In Situ Humidity Measurements at the CL Surface By MEMS-Based Sensors
Authors: Tsujikawa Jun , Minami Ryotaro , Araki Takuto
Published: October 2015

Water management is essential for optimizing the performance of proton exchange membrane fuel cells, then for measuring the local humidity inside membrane electrode assembly (MEA), the thin film humidity sensors (TFHS) are fabricated by the micro-electro-mechanical systems (MEMS) based techniques. The sensor was placed between the catalyst layer (CL) and the microporous layer (MPL) at the cathode. The sensor thickness is only about 9 μm, and the slight effects on total cell performance were observed with the insertion of it. In-situ measurement with a humidity sensor showed the capacitance and RH increased with the increase of the current density linearly up to 0.3 A/cm2. The capacitance change became moderate the region more than 0.3 A/cm2, because the relative humidity reached 100% at the 0.3 A/cm2 and water started to accumulate.
Simultaneous Measurements of Liquid Water Distributions and Catalyst Layer Surface Temperature inside Operating PEMFC
Authors: Watanabe Kentaro , Tsujikawa Jun , Araki Takuto
Published: October 2015

In order to investigate the effects of temperature gradient on water distribution and performance of PEMFC, in situ visualization of liquid water in the cell with temperature gradient in the through-plane direction was performed by using X-ray computed tomography (CT). In addition, the local temperature at the interface between cathode CL and MPL were measured with a thin film thermocouple fabricated using micro electro mechanical systems (MEMS) based techniques. The temperature gradient in the GDL was applied by the heaters embedded in the separators to provide the temperature difference of 5oC at anode and cathode side. The liquid water was not visualized in the case of cathode side temperature is higher than that of the anode separator. On the other hand the liquid water was observed in the cathode GDL if the anode side temperature was higher, and the cell voltage was lower. Then it is concluded that the temperature gradient in the GDL has a significant influence on the liquid water distribution in the cell.
Ultra-Low Pt Loading Catalyst Layers for PEMFC Using Reactive Spray Deposition Technology
Authors: Yu Haoran , Baricci Andrea , Roller Justin , Wang Yang , Casalegno Andrea , Mustain William E , Maric Radenka
Published: October 2015

Reactive spray deposition technology (RSDT) is a cost-effective method for producing high performance proton exchange membrane fuel cell (PEMFC) membrane electrode assemblies (MEAs). In this study, we used the RSDT process to deposit catalyst-coated membrane (CCM) with Pt supported on Ketjen Black (KB), multi-wall carbon nanotube (MWCNT), and reduced-graphene oxide (rGO) with ultra-low Pt loading in order to elucidate the influence of the support and Pt dispersion on the catalyst perfromance. The electrochemically active surface area (ECSA), activity for oxygen reduction reaction (ORR) and PEMFC performance are investigated and compared.
An Open Cathode Fuel Cell for Atmospheric Flight
Authors: Gould Benjamin D. , Hazard Matthew W. , Rodgers Joseph A. , Stroman Richard O'Neil
Published: October 2015

Our previous work has shown that fuel cells are ideal power sources for long endurance unmanned air vehicles (UAVs) (1). An open-cathode fuel cell system has the cathode exposed to the open air to harness the motion of a UAV through the atmosphere to provide O2 to the cathode. By removing the balance of plant (BOP) associated with pumping and preconditioning the incoming air, an open cathode fuel cell may be an ideal power source for atmospheric flight because of its simplicity and reduced weight. A custom open cathode fuel cell based on flexible circuits is fabricated and characterized in a custom wind tunnel/environmental chamber setup to ascertain whether open cathode fuel cells can operate in atmospheric flight conditions. A numerical model is also developed to quantify the associated loss mechanisms in the cell. Wind tunnel experiments show that open cathode operation is possible without catastrophic failure over a wide range of ambient temperatures (5-55 °C), ambient relative humidities (22-90% RH), air speeds (2.6-15.4 m s-1) and altitudes (< 10-914 m); with the largest losses associated with mass transport and catalyst activation.
Statistical Analysis of Salt Deposition inside PEFC GDL from X-Ray Tomography
Authors: Banas Charles Joseph , Pasaogullari Ugur
Published: October 2015

Cationic contamination causes reduction in PEM fuel cell performance and durability, two of the key factors limiting commercialization of the technology. Recent findings have shown that gas diffusion layers help prevent certain airborne particulate salts from reaching the membrane and catalyst layers. This paper uses micro x-ray computed tomography to examine the salt precipitation patterns in the GDL, and to understand how these affect the cell in terms of mass transport losses. The output of this analysis is a quantification of the changes in porosity after salt precipitation. Analysis shows that the crystallinity of the salt deposit is very dependent on the local amount of liquid water saturating the GDL and flow field. The salt build up can reduce local porosity of the GDL by 27%.
Gas Crossover in Polymer Electrolyte Membranes
Authors: Jung Aeri , Kim Min Soo
Published: October 2015

Numerous studies have been carried out to achieve good performance and high durability; however, durability of the system is still required to be improved. As the durability of the system emerges as one of the critical problems, understanding the degradation mechanism in the system is the key step for a better system design. Gas crossover has an influence on the degradation of the membrane electrode assembly, thus, it is essential to quantify the gas crossover. In this study, the effect of various parameters on gas crossover with different gases and the detecting technique to measure accurate gas crossover rate are investigated experimentally. Furthermore, crossover phenomena under various current densities are analysed.
Proton Conductivity of Graphene-Based Polymer Electrolyte Membrane
Authors: Khan Aamer , Asmatulu Ramazan , Hwang Gisuk
Published: October 2015

A polymer electrolyte membrane fuel cell (PEMFC) is the one of promising alternative energy systems, however, the one of bottlenecks of the PEMFC performance is a poor key transport property, e.g., proton conductivity in catalyst layers. Recently, it has been reported that the addition of a rapidly emerging material, i.e., graphene, to the catalyst layer significantly improves the performance, but the understandings of the role of the graphene on the performance improvements are limited so far. The graphene-based PEM, i.e., Nafion®, is coated on the bulk Nafion® membrane, and the proton conductivity is measured using an impedance spectroscopy with respect to the graphene content from 0 to 3 wt% at the ambient temperature and liquid-water equilibrated state. It shows the proton conductivity enhancement with the increasing graphene content. The proton conductivity is compared using those of the carbon black (CB)- and carbon nanotube (CNT)-based PEM, showing that graphene-based PEM provides greater enhancement. The results suggest that the unique structures of the graphene could improve the proton conducting pathways within PEM. The obtained results provide an insight into an optimal material for improving the proton transport of PEM.
Molecular Simulation of Proton Conductivity in Nafion Membrane Contaminated with Ferrous Ion
Authors: Kawai Kiyoto , Mabuchi Takuya , Tokumasu Takashi
Published: October 2015

We have performed a numerical analysis of the effect of ferrous ion contamination on proton transport property and nanostructure of solvent molecules in hydrated Nafion using molecular dynamics simulation. In the case of hydration level 3, our results suggest that ferrous ion contamination has an influence of either enhancing or inhibiting of proton transport depending on the amount of contaminated ferrous ions. The ferrous ion has two coordinate sulfonate groups. Structural changes of Nafion membrane were observed with increasing contaminated ferrous ions. In the case of hydration level 9, the correlation between the trend of diffusion coefficient of hydronium ions and the results of structural analysis was not observed. In the case of large amount contaminated condition, the number of coordinated ferrous ions around sulfonate groups was saturated and the majority of contaminated ferrous ions does not exist in first solvation shell
Water Uptake in Novel, Water-Stable, Heteropoly Acid Films
Authors: Motz Andrew R , Horan James L , Kuo Mei-Chen , Herring Andrew M
Published: October 2015

High temperature, low humidity fuel cell operation is one method of increasing the potential of commercialization of fuel cell vehicles. In order for performance to be suitable under these conditions, new polymer electrolyte membrane material needs to be synthesized and characterized. One particularly important property is water content. Water is an important aspect of polymer electrolytes, often having strong influence on ion transport and fuel cell performance. A novel material has been made, containing a heteropoly acid covalently bound to a fluoroelastomer. This material was analyzed with DVS to gain insight on water sorption. The data suggested that the water content is similar to Nafion® with respect to humidity, thus some other parameter is likely to cause improved performance under high temperature and low humidity operation.
Oxygen Reduction Reaction Activities for Various-Monolayer-Thick Pt Shells on Pt
x
Ni100-x
(111)
Authors: Asano Masato , Kawamura Ryutaro , Todoroki Naoto , Wadayama Toshimasa
Published: October 2015

We studied the oxygen reduction reaction (ORR) activities for two monolayer (ML)-thick Pt on Pt
x
Ni100-x
(111) (Pt2ML/Pt
x
Ni100-x
(111)) model core–shell catalysts fabricated by molecular beam epitaxy (MBE). Low-energy electron diffraction patterns for all Pt2ML/Pt
x
Ni100-x
(111) showed six-fold surface symmetry with long-range ordering, indicating a (111) atomic arrangement of the topmost Pt shell layers. Furthermore, scanning tunneling microscopy images of the Pt2ML/Pt50Ni50(111) and Pt2ML/Pt25Ni75(111) surfaces exhibited Moiré-like height modulations, which are likely induced by large lattice mismatches between the topmost Pt(111) shell layers and the Pt–Ni(111) substrates. The ORR activity of Pt2ML/Pt
x
Ni100-x
(111) increased with the Ni composition; the enhancement factors are 8-, 18-, and 25-fold vs. Pt(111) for Pt2ML/Pt75Ni25(111), Pt2ML/Pt50Ni50(111), and Pt2ML/Pt25Ni75(111), respectively. The results suggested that the Pt surface strains induced by lattice mismatches between the Pt shells and Pt–Ni substrates increased with the Ni composition, leading to a marked enhancement in ORR activity, particularly for Pt2ML/Pt25Ni75(111).