bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Low-Temperature Processed and Self-Aligned InGaZnO Thin-Film Transistor with an Organic Gate Insulator for Flexible Device Applications
Authors: Furuta Mamoru , Toda Tatsuya , Tatsuoka Gengo , Magari Yusaku
Published: September 2016

High performance, top-gate and self-aligned In-Ga-Zn-O thin-film transistor (IGZO TFT) was demonstrated at a maximum process temperature of 150 °C using a coatable organic gate insulator (OGI). To achieve damage- and contamination- free interface between the IGZO channel and OGI, an organic protection layer (OPL) was proposed. We achieved good TFT properties, such as field effect mobility of 10.2 cm2/Vs, subthreshold swing of 0.19 V/dec., and hysteresis of 0.2 V, with minimizing an overlap capacitance between S/D and gate electrodes. Although the TFT showed an abnormal Vth shift under a positive gate bias stress in an ambient air, it could be suppressed by forming an additional organic passivation layer on the TFTs.
Improvement of TFT Characteristics for Low-Temperature Solution-Processed Oxide Semiconductors with Hydrogen Injection and Oxidation Process
Authors: Miyakawa Masashi , Nakata Mitsuru , Tsuji Hiroshi , Fujisaki Yoshihide , Yamamoto Toshihiro
Published: September 2016

Fabrication of highly stable solution-processed oxide semiconductor thin-film transistors (TFT) was demonstrated using a method with a hydrogen injection and oxidation (HIO) process that allows low-temperature solution processing. The characteristics of TFTs based on the indium gallium zinc oxide (IGZO) semiconductor were evaluated at a maximum processing temperature as low as 300°C. Application of the HIO process improved the TFT performance in terms of the mobility and the threshold voltage (Vth) shift under positive and negative gate bias stress.
Low-Temperature Processed Metal-Semiconductor Field-Effect Transistor with In-Ga-Zn-O/AgOx Schottky Gate
Authors: Magari Yusaku , Hashimoto Shinsuke , Hamada Kenichiro , Furuta Mamoru
Published: September 2016

In this study, metal-semiconductor field-effect transistor (MES-FET) with an In-Ga-Zn-O/AgOX Schottky gate was fabricated at 200 °C. We investigated the effects of O2 gas flow ratio during the IGZO deposition and post-IGZO annealing in air at 200 °C on electrical properties of the MES-FET. The rectification ratio (± 2 V) of over 1.0×108 and ideality factor of 1.29 were achieved for the IGZO/AgOX Schottky diode when the post-IGZO annealing was applied at 200 °C. The IGZO MES-FET was successively fabricated at a maximum processing temperature of 200 °C with good electrical properties such as an on/off current ratio of 3.6×107, field effect mobility of 13.8 cm2/Vs, and subthreshold swing of 96 mV/decade. Moreover, the IGZO MES-FET exhibited good reliability under positive bias stress. Thus, the IGZO MES-FET is a potential candidate for flexible device application.
Influence of Passivation Layers on Characteristics of High Mobility Amorphous Indium-Zinc-Tin-Oxide Thin-Film Transistors
Authors: Liu Po-Tsun , Chang Chih-Hsiang , Zheng Guang-Ting , Chang Che-Chia
Published: September 2016

We investigated the influence of passivation-layer deposition on the characteristics of a-InZnSnO thin-film transistors (TFTs). The threshold voltage (Vth) of the TFTs shifted markedly as a result of the ion bombardment induced by the passivation layers above. By adjusting the post annealing temperature, the performance of the TFTs can be modulated. The a-InZnSnO TFTs after passivation exhibited good performance with a field-effect mobility of 21.34 cm2/Vs, a threshold voltage of -5.03V, and a subthreshold slope of 0.52 V/decade.
(Invited) Highly Robust a-IGZO TFT for Foldable Displays
Authors: Lee Suhui , Billah Mohammad Masum , Mativenga Mallory , Jang Jin
Published: September 2016

We have demonstrated foldable thin-film transistor (TFT) fabricated on a free-standing plastic substrate. With extreme bending machine, the repeated extreme bending stress was applied to the TFTs up to 10,000 times. When the bending stress is applied perpendicularly to the channel current flow, the performance of conventional TFT degrades significantly after extreme bending stress. However, the bulk accumulation (BA) a-IGZO TFTs have no degradation after being applied extreme bending stress. Therefore, the TFT performance remains the same after repeated bending, indicating that BA TFTs is highly robust and thus can be applied to bendable AMOLED.
(Invited) Intrinsically-Stretchable, Transparent Thin Film Transistors
Authors: Tong Kwing , Liang Jiajie , Pei Qibing
Published: September 2016

Here, we report the development of a solution-processed thin-film field effect transistor (TFT) using silver nanowires as conductor, semiconductive single-walled carbon nanotubes as channel material, and polyurethane-co-polyethylene oxide as elastomeric dielectric. Intrinsically stretchable TFTs were fabricated in an elastomer matrix to exhibit deformability and preserve electrical conductivity at large strains. The silver nanowires were screen printed with conductivity as high as 4.67x104 S/cm. The TFTs exhibited a mobility of ~30 cm2V-1s-1, Ion/off of 103-104, switching current >100 μA, transconductance >50 μS, and relatively low operating voltages. The devices retained a mobility >10 cm2V-1s-1 at 50% strain and showed no significant loss after 500 cycles of stretching at 20% strain. Organic light-emitting diodes with brightness controllable from 0 cd/m2 (off) to 200 cd/m2 (typical display brightness) were driven by the stretchable TFTs. This approach represents an important progress toward the development of stretchable active matrix displays and other stretchable electronic devices.
(Invited) Flexible Memory Applications Using Oxide Semiconductor Thin-Film Transistors
Authors: Yoon Sung-Min , Kim So-Jung , Park Min-Ji , Yun Da-Jeong
Published: September 2016

Flexible charge-trap memory thin-film transistors (f-MTFTs) using oxide semiconductors were proposed and fabricated on plastic poly(ethylene naphthalate) substrate. The gate-stack of the f-MTFT was composed of all oxide layers such as In-Ga-Zn-O (IGZO) active channel, ZnO charge-trap layer, Al2O3 blocking/tunneling layers, and In-Sn-O transparent electrode, in which hybrid barrier layer structures and double-layered tunneling oxides were designed so that the f-MTFTs could exhibit stable and excellent device performance. The memory device characteristics were not degraded even under the bending situation with a given curvature radius of 3.3 mm.
Improvements in Sensing Responses to Ammonia Gas for the In-Ga-Zn-O Thin-Film Transistor Using Atomic-Layer-Deposited ZnO Nanoparticles as Gas Sensitizers
Authors: Yun Da-Jeong , Seo Gi-ho , Lee Won-ho , Yoon Sung-Min
Published: September 2016

Bottom-gate sensor thin-film transistors (TFT) using In-Ga-Zn-O (IGZO) thin films as active channel and sensing layers were fabricated and characterized, which is featured to employ ZnO nanoparticles (ZnO-NPs) as sensitizers for gas sensing. ZnO-NPs with island structures were deposited by controlling the ALD cycles and temperatures. The introduction of ZnO-NPs on the top of the IGZO channel for the sensor TFT improved the device characteristics including the stability. The response to NH3 gas was clearly confirmed for the device employing ZnO-NPs. The Vth was shifted in a negative direction under an NH3 ambient and was almost recovered to initial value. The reproducibility in sensing response was also demonstrated at repeatedly examined measurements. Controlled preparation of ZnO-NPs was effective for enhancing both stability and sensitivity of the proposed IGZO gas sensor TFTs.
Extended-Gate pH Sensors Using Self-Aligned Four-Terminal Metal Double-Gate Low-Temperature Polycrystalline-Silicon Thin-Film Transistors on Glass Substrate
Authors: Ohsawa Hiroki , Hara Akito
Published: September 2016

This study evaluates pH sensors using self-aligned four-terminal planar embedded metal double-gate low-temperature polycrystalline-silicon thin-film transistors (TFTs) on a glass substrate. The voltage variation caused by a change in pH was read as a variation in the threshold voltage of the TFTs by connecting the control gate of the TFT to a glass electrode. By changing the reference voltage applied to the refrence electrode, our experimentally obtained pH sensitivity values were found to be in agreement with the theoretical pH sensitivity values, and we confirm that these TFTs can successfully perform as pH sensors.
NMOS Logic Inverters Based on Threshold Voltage-Tunable IGZO Transistors
Authors: Liang Lingyan , Yu Jingjing , Wang Mei , Cao Hongtao
Published: September 2016

Two n-channel indium-gallium-zinc-oxide (IGZO) TFTs with varying threshold voltage (Vth) were utilized to construct the Enhancement/Depletion (E/D) NMOS inverter. Tunable Vth was achieved by capping an ultrathin SnOx film layer onto the exposed IGZO back channel surface. According to the composition evolution of the SnOx capping layers, it was believed that loosely bound oxygen in the IGZO could be consumed by the SnOx capping layer, leading to the electron density increase in the channel and the Vth negative-shift. Finally, an optimized inverter with a voltage gain up to 56.4 was realized. Also it is found that the switching voltage and the voltage gain of the inverter are sensitive to the Vth of the driver TFT and the Vth difference between the driver and load TFTs, respectively. The proposed inverter demonstrated a great potential in the high-voltage-gain, low-cost, and easy-fabrication logic circuits.
(Invited) Reliability Study of RF Power Amplifiers with GaN-on-SiC HEMTs
Authors: Lang Jenny , Lim Jang-Kwon , Hellen Johan , Nilsson Torbjörn M.J. , Schodt Bo , Poder Ralf , Belov Ilja , Bakowski Mietek , Leisner Peter
Published: September 2016

RF power amplifier demonstrators containing each one GaN-on-SiC, HEMT, CHZ015A-QEG, from UMS in SMD quad-flat noleads package (QFN) were subjected to thermal cycles (TC) and power cycles (PC) and evaluated electrically, thermally and structurally. Two types of lead-free solders (Sn63Pb36Ag2 and SnAgCu (SAC305)) and two types of TIM materials (NanoTIM and Tgon™ 805) for PCB attachment to liquid cold plate were tested for thermo-mechanical reliability. Changes in electrical performance of the devices namely reduction of the current saturation value, threshold voltage shift, increase of the leakage current and degradation of the HF performance were observed as a result of an accumulated current stress during PC. No significant changes in the investigated solder or TIM materials were observed.
Carbon-Doped GaN on SiC Materials for Low-Memory-Effect Devices
Authors: Chen Jr-Tai , Janzén Erik , Rorsman Niklas , Thorsell Mattias , Andersson Mats , Kordina Olof
Published: September 2016

AlGaN/GaN on SiC HEMT structures suitable for high power, high frequency applications are demonstrated. The material manifests record breaking thermal management and electron mobility. Moreover, thanks to the fact that the buffer layer is doped with carbon, the memory effect of processed devices is very low making system design and manufacturing significantly easier and less expensive.
(Invited) RF Power Performance of Nanocrystalline Diamond Coated InAlN/AlN/GaN HEMTs
Authors: Downey Brian P. , Meyer David J. , Ancona Mario G. , Feygelson Tatyana I , Pate Bradford B , Roussos Jason A. , Tadjer Marko J. , Anderson Travis J , Hardy Matthew T , Nepal Neeraj , Eddy Charles R.
Published: September 2016

We have previously demonstrated AlGaN/GaN high-electron-mobility transistors (HEMTs) that used a coating of high thermal conductivity nanocrystalline diamond (NCD) to reduce channel temperature for a given dissipated power and simultaneously improve electrical performance compared to devices with conventional silicon nitride (SiN) passivation only. Here we examine the effect of a protective SiN interlayer of varying thickness inserted between the semiconductor surface and NCD coating on large-signal output power density as well as the reduction in channel temperature. For an InAlN/AlN/GaN HEMT with a >1 µm NCD coating and SiN interlayer ranging from 5 to 50 nm in thickness, the output power density and power-added efficiency at 4 and 10 GHz are found to be maximized for the thickest SiN interlayer. At the same time, we find the reduction in channel temperature provided by the NCD coating is not strongly dependent on thickness, which is confirmed by numerical simulation.
The Novel Way to Inspection Technique for SiC Substrate by Applying Stress Effects
Authors: Sakata Yoshitaro , Terasaki Nao , Nonaka Kazuhiro
Published: September 2016

A carrot defect under the surface of SiC substrate are detected non-destructively by applying the stress-induced light scattering method (SILSM), and the utility of SILSM will be evaluated as a novel inspection technique for SiC substrate. As the results, it was confirmed that the light scattering of the carrot defect decreased by bending stress effect. Comparing with the wave number distribution which measured by a laser Raman microcopy and the light scattering result, a wave number of decreasing light scattering area is different other areas. Thus it was forecasted a crystal lattice distortion can be monitoring with stress effect indirectly.
Characterization of Leakage Causing Visible Epitaxial Defects Nucleating from Crystal Defects in the Substrate
Authors: Das Hrishikesh , Sunkari Swapna , Naas Hans
Published: September 2016

In high volume manufacturing of SiC products, it is important to isolate and eliminate failure mechanisms at the source rather than rely on backend tests. As we enter volume production on 150mm substrates, significant cost and reliability improvements can be achieved if potential sources of defects are identified and removed. In this work we present the electrical effects of an epitaxial ‘V’ type defect, investigate and determine its source to a subset of screw dislocations in the substrate, and provide a way of screening such heavily defective substrates even before epitaxial growth.
Enhancement of the Extent of In Situ Transfer-Free Few-Layer Graphene by Solid Carbon Source for Use in Gas Sensor Applications
Authors: Noll Dennis , Schwalke Udo
Published: September 2016

Enhancement of the extent of transfer-free few-layer graphene has been achieved by the introduction of an additional solid carbon source into our silicon-CMOS compatible hydrocarbon CCVD process (1). A fivefold increase of graphene surface coverage is demonstrated by electrical testing of field-effect transistors showing typical few-layer graphene characteristics as have been reported elsewhere (2)(3). Full functionality has been achieved up to a channel length of 10µm. Furthermore, contact-mode conductive atomic force microscopy has been performed, confirming the presence of a conductive surface in the absence of other carbon allotropes like CNTs. However, microscopic electric defects can be seen on this surface. Finally, basic gas sensing properties of a graphene field-effect transistor are presented.
(Invited) Emerging Graphene Device Technologies
Authors: Östling Mikael , Smith Anderson D , Vaziri Sam , Sollami Delekta Szymon , Li Jiantong , Lemme Max Christian
Published: September 2016

Graphene has a wide range of attractive electrical and mechanical properties. This unique blend of properties make it a good candidate for emerging and future device technologies, such as sensors, high frequency electronics, and energy storage devices. In this review paper, each of the aforementioned applications will be explored along with demonstrations of their operating principles. Specifically, we explore pressure and humidity sensors, graphene base transistor for high frequency applications, and supercapacitors. In addition, this paper provides a general overview of these graphene technologies and, in the case of pressure and humidity sensors, benchmarking against other competing technologies. This paper further shows possible and prospective paths that are suitable for future graphene research to take.
Titanum Carbide MXene Flakes as Novel 2D Metallic Solution-Processed Films
Authors: Mariano Marina , Mashtalir Olha , Antonio Francisco , Ryu Won-Hee , Deng Bingchen , Xia Fengnian , Gogotsi Yuri , Taylor André D.
Published: September 2016

MXenes, a recently discovered family of two-dimensional materials, have obtained a large consideration since they exhibit properties with potential applications. Among them, their hydrophilic and metallic conductivity have opened a way to deposit them by solution process techniques. We will present Ti3C2Tx delaminated monolayers forming ultra thin films as transparent electrodes with properties exceeding comparable reduced graphene oxide films. Our films deposited by spin-coating show a low sheet resistance of 437 Ω/sq with 77 % transmittance at 550 nm light. Finally, FET transistors fabricated with our films confirmed the metallic behavior of them. These results demonstrate the presence of a novel and solution-processed two-dimensional material with both high conductivity and transparency.
Favorable Combination of Schottky Barrier and Junctionless Properties in Field-Effect Transistors for High Temperature Applications
Authors: Krauss Tillmann Adrian , Wessely Frank , Schwalke Udo
Published: September 2016

High-temperature capable transistors are of great interest for industrial applications, for instance, oil & gas and geothermal exploration, avionic, space, automotive and energy conversion. Especially, energy conversion electronics using wide-bandgap power transistors, i.e. SiC- or GaN-based FET, in combination with high-temperature silicon gate-driver circuits can significantly increase system efficiency and reduce costs. Our improved planar virtually dopant-free silicon-based double gate SOI FET with reactively sputtered WTiNx front-gate electrodes demonstrates ultra-low drain leakage currents at high-temperatures opening a path to record operating temperatures for silicon-based FET devices.
Wafer-Level Fabrication and Characterization of Amorphous Thin Films MoS2 Prepared by RF Magnetron Sputtering Technique
Authors: Gustavsen Kim R , Nygård Ken A , Honerød-Bentsen Preben , Du Kang , Liu Guohua , Tayyib Muhammad , Breiby Dag W , Weibye Kristian , Nilsen Ola , Aasmundeveit Knut E , Wang Kaiying
Published: September 2016

In this paper, we present a study of wafer-level process for deposition of amorphous thin film MoS2 by radio-frequency (RF) magnetron sputtering technique. Thin film deposition was performed in argon atmosphere with pressure around 10-2 to 10-4 Torr, RF power between 100-250 W and temperature from room temperature up to 250°C. X-ray diffraction indicates that the thin films are amorphous. Deposition rate and sulphur concentration showed a clear dependence on variation in RF power. Surface roughness increase as temperature was increased from room temperature up to 250°C. Photocurrent increases about 20% under white light illumination. The thin films are continuous with low roughness which might make it a potential candidate for wafer-scale production for advanced electronics or sensor applications.
Fabrication of a-C Semiconductor Nanoparticles for Quantum Dots Surface Emitting Laser Using High-Density Plasma in Localized Area
Authors: Kobayashi Ryutaro , Nagata Yoshiya , Okafuji Keigo , Ohtomo Shinpei , Naragino Hiroshi , Honda Kensuke
Published: September 2016

Novel synthesis method to fabricate Si-added a-C nano-particles could be established using the radio-frequency plasma-enhanced vapor deposition system (RF-PeCVD)(13.56 MHz, SAMCO Co., Ltd Model BPD-1) with porous aluminum plate loaded between the cathode and the anode. The mechanism of nano particles formation was clarified by verifying the relation between the shape of particles and the condition of RF PeCVD such as r.f. power, chamber pressure and plate thickness. Si-added a-C nano-particles with minimum diameter of 14.8 nm could be fabricated with r.f. power of 50 W, chamber pressure of 60 Pa and plate thickness of 0.7 mm. These nano particles showed photon-to-current conversion functionality under 360 nm irradiation, and can be applied for photo electronic device in nano-meter size. sp2
impurities that causes the degradation of semiconductor properties could be reduced by the decrease of r.f. power and the increase of flow rate of H2 gas during CVD synthesis. Semiconductor properties such as carrier mobilities of Si-added a-C nano-particle were able to be improved up to those of practically-used semiconductor in photo electronic devices.
Development of Silicon and Carbon Based p-Type Amorphous Semiconductor Films with Optical Gap Variable for High-Efficiency Multi-Junction Solar Cells
Authors: Naragino Hiroshi , Nagata Yoshiya , Okafuji Keigo , Ohtomo Shinpei , Shimizu Yuta , Honda Kensuke
Published: September 2016

P-type boron-doped amorphous silicon and carbon alloy (B-doped a-SixC1-x) thin films with wide optical gap selective from 1.80 to 2.50 eV were successfully deposited by radio frequency (r.f.) plasma-enhanced chemical vapor deposition (CVD) method using a mixed solution of tetramethylsilane (TMS) and trimethylborate (TMOB) as a liquid source. Optical gaps of the B-doped a-SixC1-x films could be controlled by changing Si/(C + Si) ratio of the film. From photo-electrochemical measurement under UV illumination, it was clarified that the B-doped a-SixC1-x film with an optical gap of 2.50 eV has the p-type semiconducting property and photoelectric conversion function with a quantum yield of 1.63 %. The rectifying action of a p-n heterojunction comprising p-type B-doped a-SixC1-x film and n-type Si (100) substrate was observed. The open circuit voltage (VOC) and short circuit current density (JSC) of the heterojunction were estimated to be 200 mV and 45 mA/cm2, respectively. The results indicate that p-type B-doped a-SixC1-x films with controllable optical gaps is a promising p-layer material for multi-junction solar cells.
Identification of Polarization Losses in High-Temperature PEM Fuel Cells by Distribution of Relaxation Times Analysis
Authors: Schindler Stefan , Weiß Alexandra , Galbiati Samuele , Mack Florian , Danzer Michael A. , Zeis Roswitha
Published: September 2016

In this study, Distribution of Relaxation Times (DRT) analysis is applied for identification of polarization losses in High Temperature Polymer Electrolyte Membrane Fuel Cells (HT-PEMFCs). Electrochemical impedance spectra recorded for different air stoichiometries and current densities are analyzed. While basic impedance analysis broadly recognizes the presence of three features, DRT reveals at least six distinct processes occurring on different time scales. By varying the stoichiometry and current bias, three of those processes are attributed to mass transport and cathodic kinetics. Furthermore, the DRT analysis suggests that the cathode kinetics may involve two different processes, as opposed to a single-feature process that is often assumed. These results have improved our understanding of the loss mechanisms in HT-PEMFCs and provide valuable guidance for fuel cell optimization.
A New Membrane Electrode Assembly Structure with Novel Flow Fields for Polymer Electrolyte Fuel Cells
Authors: Park Jaehyung , Pasaogullari Ugur , Bonville Leonard J.
Published: September 2016

A new membrane electrode assembly (MEA) assembled with a carbon foam flow field is investigated in comparison to a conventional channel/land flow field. The carbon form flow field is designed to reduce contact resistance and provide more uniform compression. In the new MEA, the carbon paper substrate is eliminated and the entire gas diffusion layer (GDL) consists of only the micro-porous layer (MPL). These MEAs have an improved interfacial contact between the MPL and the catalyst layer, which is optimized for gas transport and water removal. The carbon deposited foam flow field provides effective pathways for water evacuation from the cell so that flooding can be reduced at high current densities, which results in a stable voltage during the polarization measurement, and high current density operation.
PEMFC Reactant Mass Transfer Coefficient Measurement and Separation – Method Extension to the Mixed Kinetic and Mass Transfer Control Regime
Authors: St-Pierre Jean , Reshetenko Tatyana V.
Published: September 2016

A kinetic and mass transfer model for a proton exchange membrane fuel cell (PEMFC) current distribution was derived and validated with data obtained with a dilute oxygen stream and three diluents (5 % O2 + 95 % He, N2 or C3F8). The overall mass transfer coefficient k increased by a factor of ~2 to ~4 with a decrease in cell potential from 0.75-0.8 to 0.2 V. Mass transfer coefficients pertaining to gas phase molecular diffusion km
, and, gas phase Knudsen and solid phase ionomer diffusion ke

+K
respectively increased by 20 % and a factor of ~2. Below 0.6 V, the km
and ke

+K
increase is relatively smaller and is ascribed to the larger heat generation, local temperature and diffusion coefficients. The increase in km
and ke

+K
between 0.75 and 0.6 V is relatively larger and is attributed to the development of steep oxygen and diluent concentration gradients affecting oxygen movement.
Temperature and Humidification Effect on Mass Transfer of PEMFC Via EIS and Soft X-Ray Measurement
Authors: Jao Ting-Chu , Sasabe Takashi , Uemura Suguru , Yoshida Toshihiko , Hirai Shuichiro
Published: September 2016

Proper water management is essential for proton exchange membrane fuel cells (PEMFCs) to approach high current densityand high power density operation. Therefore the analysis of water and mass transport ability within PEMFC are one of the important issues that needs to be solved. Electrochemical impedance spectrum (EIS) and soft X-ray visualization technique are useful methods for diagnosing mass transportation resistance and water behavior, respectively. In this study, a correlation between EIS and visualization images were used to investigate the mass transfer phenomenon. The operated oxygen concentration, cathode gas humidity and cell temperature had been discussed in this study. The visualization image implies the mass transport arc which was mainly caused by water flooding within or nearby the catalyst layer.
Experimental Study of Thermal Conductivity and Compression Measurements of the GDL-MPL Interfacial Composite Region
Authors: Bock Robert , Shum Andrew , Khoza Thulile , Seland Frode , Hussain Nabeel , Zenyuk Iryna V , Burheim Odne Stokke
Published: September 2016

MPL and GDL in a PEM fuel cell assembly are often treated as separate layers in the literature. However, there exists a considerable interfacial region where the two different materials merge. The MPL consists of fine carbon particles, a binder and a solvent that is applied on top of the fibrous GDL. In the process of coating, the MPL intrudes into the GDL and forms an MPL-GDL-composite region. This region has properties that differ from either of the materials that it consists of. Through-plane thermal conductivity and thickness variation under different compaction pressures were measured for such a composite region of commercial gas diffusion layer (GDL), Freudenberg H1410, and custom-made MPL. Thermal conductivity at 9.2 bar compaction pressure for GDL only is 0.111 ± 0.009 W K-1 m-1, for MPL only 0.08 ± 0.02 W K-1 m-1, and for the composite region is 0.124 ± 0.005 W K-1 m-1. X-Ray Computed Tomography images of the materials ascertain the level of penetration for the MPL into the GDL.
Determining the Impact of Dynamic Load Conditions on Interfacial Liquid Water Accumulation in Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers Using Synchrotron X-Ray Radiography
Authors: Banerjee Rupak , Ge Nan , Lee Jongmin , George Michael Gerald , Liu Hang , Muirhead Daniel , Shrestha Pranay , Chevalier Stéphane , Hinebaugh James , Bazylak Aimy
Published: September 2016

Automotive power demand is dynamic, so the transient multiphase transport behavior must be understood and considered in the design of next generation polymer electrolyte membrane (PEM) fuel cell materials. In-operando synchrotron X-ray radiography was used to measure the changes in liquid water saturation of the gas diffusion layer (GDL) during changes in operational current density. Through in-operando visualizations at high temporal and spatial resolutions, we observed that the liquid water saturation of the GDL increases with increasing current density, but a threshold saturation in the GDL is eventually reached, despite further increases in current density. A time lag between the change in current density and the onset of increasing GDL saturation was also observed.
Investigation of Solvent Effects on the Dispersion of Carbon Agglomerates and Nafion Ionomer Particles in Catalyst Inks Using Ultra Small Angle X-Ray Scattering Method
Authors: Yang Fan , Xin Le , Uzunoglu Aytekin , Stanciu Lia , Ilavsky Jan , Son Steven , Xie Jian
Published: September 2016

Ink formulation is important to improve the performance of membrane electrode assembly (MEA) in polymer electrode fuel cells (PEMFCs). In this study, ultra-small angel x-ray scattering method was applied to study the dispersion of carbon black in different solvent to get a better understanding of the influence of the solvent on the dispersion of carbon black. The dimension of carbon black aggregates before and after adding Nafion ionomer was compared in different solvent. Dielectric constant and viscosity were found to be the key factors that affect the dispersion of carbon black in solvents. Carbon black particles in a solvent with higher dielectric constant will tend to form larger aggregates after adding Nafion ionomer. The higher viscosity of a solvent will prevent the aggregation of carbon black particles after the addition of Nafion ionomer.
(Invited) Fuel Cell Stack Technology of Toyota
Authors: Suzuki Toshiyuki
Published: September 2016

Fuel Cell Vehicle (FCV) can be one of the solutions to energy issues and climate change. In December 2014, Toyota started selling the FCV called “MIRAI” in Japan. The FC system is composed of Toyota-self-developed parts, like Fuel Cell (FC) stack which doesn’t require any external humidifier. The FC stack can realize 15 year durability, which is 3 times longer compared to the conventional stack, by improving cell flow field structure and membrane electrode assembly. In production engineering, we adopted new manufacturing methods, such as intermittent coating of catalyst layer, one-by-one production and cell performance inspection using indirect cooling system.
Development Study of an Air Independent Fuel Cell System for an Autonomous Underwater Vehicle (AUV)
Authors: Hitscherich Manuel , Cremers Carsten , Stolten Detlef , Pinkwart Karsten , Tübke Jens
Published: September 2016

The paper is focused on the design concept of a fuel cell system for an autonomous underwater vehicle (AUV) developed within a common project of the German Navy research institute WTD 71, Fraunhofer ICT and the norwegian defense research institute “Forsvarets forskningsinstitutt (FFI)”. The presented work is therefore based on the boundary conditions for the system defined in this project. However, a more general approach is pursued by not only presenting the developed fuel cell system, but by defining a design strategy and applying it to the framework of the development in the project. For this, constraints and objectives which define the development will be defined as boundary conditions. Most of these boundary conditions also apply to the general development of air independent underwater systems and can therefore be used to outline similar systems. Based on the literature and the constraints, system and subsystem solutions for fuel cell systems are discussed to find the most suiting system for the AUV. The different system solutions are discussed on the basis of different objectives for the system design, namely space, runtime, stability and efficiency.
Gas Diffusion Media for Open-Cathode Fuel Cells in Atmospheric Flight
Authors: Atkinson Robert W. , Hazard Matthew W. , Rodgers Joseph A. , Stroman Richard O'Neil , Gould Benjamin D.
Published: September 2016

Operating a proton exchange membrane fuel cell (PEMFC) in a planar, open cathode configuration can enable significant reductions in overall device weight and system complexity compared to a conventional fuel cell stack. This decrease in device weight makes an array of open-cathode, planar fuel cells a compelling candidate power source for unmanned aerial vehicles (UAVs) that can utilize the flow of ambient air over the vehicle-mounted cells to improve oxygen transport, waste heat rejection, and ultimately, water transport in the open-cathode. The effectiveness of each of these processes is largely influenced by the thickness and porosity of the cathode gas diffusion layer (GDL). We relate these cathode GDL properties to open-cathode fuel cell polarization behavior in a broad range of atmospheric conditions in active air flow and in passive, air-breathing mode to study the effect of gas diffusion layer thickness and porosity on cell performance through polarization and AC impedance measurements. Reducing cathode GDL porosity leads to a decrease in cell temperature and ohmic resistance, which improves water retention. Reducing cathode GDL thickness facilitates O2 and H2O transport, increasing oxygen availability to the electrocatalyst at the expense of improved water retention. After observing open-cathode fuel cell performance in a broad range of environmental conditions including ambient temperature, relative humidity, altitude, and in active and stagnant air flows, we find that application of a thicker cathode GDL (315 μm) with lower porosity (75%) yields the highest open-cathode fuel cell voltages and power generation; the open-cathode fuel cell achieves a maximum power-to-weight ratio of 1.44 kW kg-1.
GISAXS Analysis for Ionomer Thin Films
Authors: Dudenas Peter , Kusoglu Ahmet , Hexemer Alex , Weber Adam Z
Published: September 2016

An overview of GISAXS analysis for ionomer thin films is presented. Experimental procedures to prepare and measure thin films using GISAXS is described. Typical features of ionomer scattering images are discussed before detailing three different types of analysis which can be used in conjunction with one another to elucidate additional information from scattering patterns. Example data are provided to illustrate these techniques.
Numerical Analysis of Nanostructure Around Ferrous Ion in Hydrated Nafion Membrane
Authors: Kawai Kiyoto , Mabuchi Takuya , Tokumasu Takashi
Published: September 2016

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 with considering Grotthuss mechanism. The local maximum point of diffusion coefficient of proton changes according to the amount of ferrous ions. The distribution of ferrous ions depends on the balance between the energy of structural change of side chain of Nafion and the coordination energy of ferrous ion around sulfonate groups. The coordination energy of ferrous ion is dominant in the case of λ = 3. On the other hand, the energy of structural change of side chain is dominant in the case of λ = 9 or higher. These two energies are balanced in the case of λ = 6. Positive correlation between the number of water clusters and the diffusion coefficients in the case of λ = 12.
First-Principles Study on Alloy Nanoparticles for Polymer Electrolyte Fuel Cell Catalyst
Authors: Nanba Yusuke , Rivera Rocabado David Samuel , Ishimoto Takayoshi , Koyama Michihisa
Published: September 2016

The reduction of Pt used as electrocatalyst is one of the central issues toward the large-scale penetration of the technology into the society. For this purpose, it is important to understand the essential nature of Pt-based electrocatalyst. First-principles method based on density functional theory is applied to investigate the stability and the structural features of Pt-based electrocatalyst. Nanoparticle models with 711 atoms, which correspond to ca. 3 nm in diameter, are calculated by the massive parallel computer system in this study. Pt608Co103 models with Pt-skin and solid solution configurations are compared. The stability of Pt608Co103 at the operation temperature is discussed on the basis of excess energy and configuration entropy. The interatomic distances in the nanoparticle is analyzed for Pt608Co103 and Pt711 nanoparticle models as well as Pt bulk model.
Development of Novel Hierarchically Microporous-Mesoporous Carbon and Carbon Nanospheres Based Materials and PEMFC Single Cells
Authors: Lust Enn , Sepp Silver , Nerut Jaak , Vaarmets Kersti , Kanarbik Rait , Tallo Indrek , Jäger Rutha , Härk Eneli , Ereth Kasatkin Piia , Taleb Masoud
Published: September 2016

Microporous-mesoporous carbon materials synthesized from molybdenum and tungsten carbides by high-temperature chlorination method were used as supports for catalysts activated with platinum nanoclusters. The characteristics obtained have been compared with those for carbon material synthesized from D-glucose by hydrothermal carbonization followed by additional chemical activation with CO2. The scanning electron microscopy, X-ray diffraction, Raman spectroscopy, high resolution transmission electron microscopy and low temperature N2 and Ar as well as CO2 adsorption methods were used to characterize the structure of the materials prepared. The materials exhibited high specific surface area and remarkable differences in their microporous-mesoporous structure. Platinum has been deposited onto the porous carbon materials in the form of nanoparticles or agglomerates of nanoparticles. All catalysts (studied by cyclic voltammetry and rotating disc electrode methods) showed high activity towards oxygen reduction and hydrogen adsorption from 0.1 M KOH and 0.5 M H2SO4 solutions.
Oxygen Reduction Reaction at Carbon-Based Particles Prepared by Microwave-Assisted Catalytic Decomposition Measured in Acetonitrile
Authors: Kodera Fumihiro , Yoshida Narumi , Ishikawa Hiroya , Saito Ryo , Nakagawa Shogo , Miyakoshi Akihiko , Umeda Minoru
Published: September 2016

New carbon-based particles prepared using methane by microwave-assisted catalytic decomposition has been developed. The carbon-based particles contained a nanographene-covered nickel, carbon nanotube, and others. In non-aqueous solvent, an oxygen reduction reaction (ORR) at the carbon-based particles treated with acidic solution in advance was evaluated by a porous microelectrode based on electrochemical methods. The ORR was compared to commercially available carbon fiber, polycrystalline platinum, and polycrystalline gold microelectrode.
Graphitic Carbon Nitride-Graphene Hybrid Nanostructure as a Catalyst Support for Polymer Electrolyte Membrane Fuel Cells
Authors: Mansor Noramalina , Jia Jingjing , Miller Tom , Suter Theo , Belen Jorge Ana , Gibbs Christopher , Shearing Paul R. , McMillan Paul F. , Mattevi Cecilia , Shaffer Milo , Brett Daniel J.L
Published: September 2016

Graphitic carbon nitrides form a class of semiconducting graphene-like polymeric materials with visible light absorption and photocatalytic properties. In addition to high nitrogen content and tunable structure, it was shown that graphitic carbon nitride based on polytrazine imide (PTI) sheets exhibit excellent anti-corrosion ability in ex-situ fuel cell environments. However, in bulk form, their low surface area and poor conductivity limits their applications in fuel cells. In this work, PTI was exfoliated to form an ink made from single to few-layer nanosheets. The ink was then processed to produce 3D networks of carbon nitride nanosheets/reduced graphene oxide (PTI-rGO) hybrid aerogel with large interconnecting pores for fast mass transport of reactants and high surface area. The material was decorated with platinum nanoparticles, and then investigated for its electrochemical properties and applications as a catalyst support for polymer electrolyte membrane (PEM) fuel cells. Initial results show that the cathode catalytic activity of Pt/rGO-PTI hybrid is significantly improved in comparison to Pt/PTI or Pt/rGO. In addition, the in-situ fuel cell performance of Pt/PTI as anode catalyst is comparable to commercial Pt/C especially at low densities, making it attractive as an alternative, durable anode catalyst support material to conventional carbon black.
Accelerated Durability Tests for Pt-Nanoclusters Modified Carbide Derived Carbons Catalysts in Acidic Solution
Authors: Vaarmets Kersti , Sepp Silver , Nerut Jaak , Lust Enn
Published: September 2016

The accelerated durability test (ADT) of carbide derived carbon (CDC) electrodes activated with Pt-nanoparticles were performed for 30,000 cycles in 0.5 M H2SO4 aqueous solution. Hierarchical microporous-mesoporous carbon supports C(Mo2C) were prepared from molybdenum carbide using high temperature chlorination method at different fixed synthesis temperatures from 600 °C to 1000 °C. The Pt-nanoparticles were deposited onto the C(Mo2C) using the NaHB4 method. The X-ray diffraction, low temperature nitrogen combined with CO2 sorption, thermogravimetric analysis and high-resolution scanning electron microscopy methods were used to characterize the catalysts materials. For detailed understanding of the Pt-nanoparticles degradation mechanism the particle size distribution analysis was performed. It was found that the main decrease in electrochemical surface area took place after 1,000 polarization cycles. During the ADT the half wave potential values depend weakly on the number of cycles and electrochemical impedance results show that only 20% decrease in the electrode capacitance has been observed.
Effect of Model Fuel Impurities for Reformed Jet Fuels on the Hydrogen Oxidation at Platinum Based Catalyst under HT-PEMFC Conditions
Authors: Cremers Carsten , Rau Maria Sol , Niedergesäß André , Pinkwart Karsten , Tübke Jens
Published: September 2016

Jet fuels like the commercial Jet-A and Jet-A1 fuels or the military JP-8 fuels have a high importance for many applications. Currently their replacement by biomass derived drop-in fuels is under investigation. As those exhibit much lower contents of impurities, the question was if fuel cells could benefit from this replacement. For this purpose the effect of H2S and CO on the hydrogen oxidation at platinum based catalyst under HT-PEMFC conditions was reviewed and the effect of further relevant impurities in particular ethene, toluene and thiophene investigated on catalyst and partially on single cell level. It could be shown that Pt catalyst under HT-PEMFC conditions showed a significant tolerance towards all those impurities. Furthermore, using our recently developed HT-DEMS set-up that thiophene which was added with toluene to a fuel stream can be oxidized at the Pt catalyst under HT-PEMFC conditions.
Phosphoric Acid Tolerant Oxygen Reduction Reaction Catalysts for High-Temperature Polymer Electrolyte Fuel Cells
Authors: Schenk Alexander , Gamper Stefan , Grimmer Christoph , Bodner Merit , Weinberger Stephan , Hacker Viktor
Published: September 2016

Operating polymer electrolyte fuel cells (PEFCs) at temperatures of above 100 °C can be beneficial over low-temperature operation. However, different operating temperatures require also different kinds of electrolytes. For operating PEFCs at temperature in-between 150 and 200 °C, typically phosphoric acid doped polybenzimidazole is the electrolyte of choice. Unfortunately, state-of-the-art platinum catalysts are deactivated by adsorption of phosphate species on their active catalyst sites, thus the overall performance of the fuel cell system drops. In order to overcome this hurdle, it is necessary to identify suitable catalyst systems with high tolerance towards phosphate poisoning.
(Invited) The Implications of Cation Clustering in Anion Exchange Membranes on Conductivity and Mechanical Properties
Authors: Herring Andrew M , Coughlin E. Bryan , Liberatorre Mathew W. , Pandey Tara P , Sarode Himanshu N , Liu Ye , Di Noto Vito , Vezzù Keti
Published: September 2016

Anion exchange membranes (AEMs) contain cations that act as dipoles. The dipoles interact with each other and give rise to clustering in the AEM and this clustering can affect the ionic conductivity and mechanical properties of the polymer. Polymers designed to have dispersed cations can, when wet, have their cations cluster as the material undergoes an order-disorder transition at some temperature at which the system has enough energy to reorganize. Clustering is often unavoidable in AEMs and imposes a limit on the increase in conductivity that can be achieved by increasing IEC. Above a certain IEC AEMs do not show increased ionic conductivity only increased swelling on exposure to higher RH. Understanding these phenomena is essential to designing high performance AEMs. Here we propose an AEM based on a scalable random copolymer with rapidly deployed photo-crosslinking to lock the morphology in place to avoid cation clustering.
Power Generation Characteristics of the Direct Formic Acid Fuel Cell Using Silica Containing Carbon Nanofiber as the Anode Supports
Authors: Tsujiguchi Takuya , Mohamed Aslam Norraihanah , Onishi Ryo , Matsuoka Fumihiko , Yamazaki Nozomi , Osaka Yugo , Kodama Akio
Published: September 2016

In order to prepare high Pd containing Pd/SECNF (SiO2 containing carbon nanofiber) catalyst, which showed high formic acid oxidation reaction activity, the effect of the time and frequency on the ultrasonication before the chemical reduction process was investigated. It was found that 45 kHz and 45 min was the optimum condition. Based on this condition, Pd/SECNF containing 80 wt% of Pd was successfully prepared. Using this catalyst for the DFAFC anode, power generation characteristics was investigated. It was found that the performance was similar to the conventional DFAFC using Pd/C for anode catalyst although the catalytic activity of Pd/SECNF was higher than that of Pd/C. This is due to the high anode mass transport resistance in the anode catalyst layer in the case of Pd/SECNF.
Fluorination Behavior of Uranium-Zirconium Mixture by Hydrogen Fluoride
Authors: Ono Takahiro , Sato Nobuaki , Nezu Atsushi , Uchiyama Takafumi , Matsuura Haruaki
Published: September 2016

Due to the accident of Fukushima Daiichi nuclear power plant, fuel debris has been produced inside the nuclear reactor vessels. To reprocess fuel debris, a pyroprocess of selective fluorination and a molten salt electrolysis have been proposed. The aim of this study is to investigate the fluorination behavior of uranium - zirconium oxide mixture. The samples have been prepared as follows. First, UO2 was made by the reduction using Ar - H2 mixture gas for U3O8 at 1000oC. Second, UO2 and ZrO2 were mixed by the molar ratios of some. Finally, these samples were treated in the environment of either oxidation or reduction. To evaluate fluorination behavior of these mixtures, a thermogravimetric differential thermal analyzer and a powder X-ray diffractometer. Depending on pre-treated environment of the mixtures, the difference of fluorination behavior is identified. How much degree of fluorination is the best to introduce into molten salt is going to under consideration.