bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Bottom-up Growth of Fully Transparent Indium Tin Oxide Nanowire Layers for Enhanced Light Output for Light Emitting Devices
Authors: O'Dwyer Colm
Published: February 2020

The development of optically transparent and mechanically flexible electronic circuitry is an essential step in the effort to develop next-generation display technologies which will undoubtedly have to address so-called ‘see-through’ and conformable products. In view of the inherent limitations of silicon-based electronic circuits and the demand for portable display and communication products, the development of high performance transparent devices is the focus of much activity. With the addition of branched and cross-wired structures to assemblies of nanorods and nanowires, the potential for synthesizing materials with interesting electrical, optical, and mechanical properties is even greater. As the most important transparent conducting oxide, tin-doped indium oxide has found a wide range of applications in photovoltaics, smart windows, organic light-emitting diodes, and flat-panel displays.

The ability to realize fully transparent and conductive arrays of indium tin oxide nanowires grown as dedicated, uniform contact layers is demonstrated here to exhibit such dual functionality. The growth method mimics that of standard epitaxial growth regimes for known device architectures, allowing a one-step bottom-up method of both device and epitaxial nanowire layer fabrication. Large area nanowire arrays of various morphologies, self-catalysed and seeded during molecular beam epitaxy (MBE) are shown. We detail this new molecular beam epitaxial growth method; control of the nucleation, crystal growth direction, nanowire shape, density, conductivity and transparency is possible without necessitating neither a heterogeneous metal catalyst nor predefined placement of nanowire seeding. The electronic and photonic properties of branched nanostructured arrays are optimized for application as fully transparent contacts in the visible to near-infra red region for silicon-based light emitting devices (LEDs).

References

C. M. Eliason and M. D. Shawkey, Optics Express, 22 A642 (2014).

C. O’Dwyer, M. Szachowicz, G. Visimberga, V. Lavayen, S. B. Newcomb and C. M. S. Torres, Nat. Nanotech., 4, 239 (2009).

C. O'Dwyer and C. M. S. Torres, Front. Physics, 1, 18 (2013).

M. Osiak, W. Khunsin, E. Armstrong, T. Kennedy, C. M. S. Torres, K. M. Ryan and C. O’Dwyer, Nanotechnology, 24, 065401 (2013).

M. Osiak, E. Armstrong, T. Kennedy, C. M. S. Torres, K. M. Ryan and C. O’Dwyer, ACS Appl. Mater. Interfaces, 5, 8195 (2013).

P. D. C. King, T. D. Veal, J. Phys.
23, 334214 (2011).

J. Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu and J. A. Smart, Nature Photonics, 1, 176 (2007).

M.L. Kuo, Y.S. Kim, Mei-Li Hsieh and Shawn-Yu Lin, Nano Lett.
11, 476 (2011).
(Invited) Active Fe-Oxide on Iron Phosphorus Trichalcogenides (FePS3) Nanosheets Surface for Highly Efficient Electrocatalytic Oxygen Evolution
Authors: Song Bo
Published: February 2020

Active Fe-Oxide on Iron Phosphorus Trichalcogenides (FePS3) Nanosheets Surface for Highly Efficient Electrocatalytic Oxygen Evolution

 Ying Yin,1 Jiecai Han,1 and Bo Song2,
*

1Centre for Composite Materials and Structures, Harbin Institute of Technology, Harbin 150080, China

2Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080, China

Efficient and cost-effective oxygen evolution reaction (OER) electrocatalysts is of great importance for sustainable energy conversion technologies. Fe-based electrocatalysts have been intensively investigated because of their promising activity and earth abundance. However, the OER efficiency for most of the developed Fe-based electrocatalysts has been intrinsically limited due to their poor active site exposure yield. Herein, we report active Fe-oxide on FePS3 nanosheets as an efficient OER electrocatalyst for the first time. Benefiting from their atomic-thick structure and optimized electronic structure, the FePS3 nanosheets with Fe-oxide surface realize an improved OER activity compared with bulk FePS3. Our finding suggests that transition MPS3 (M = transition metal) nanosheets could serve as a new group of OER electrocatalysts with excellent property.

*Corresponding Author: songbo@hit.edu.cn
(Invited) Current Topics in Electronic Devices Based on Wide Band-Gap Semiconductors for Power Applications and Energy Efficiency
Authors: Carlson Eric P , Kizilyalli Isik C. , Heidel Timothy D , Cunningham Daniel W
Published: February 2020

Wide-bandgap power semiconductor devices offer enormous energy efficiency gains in a wide range of potential applications. As silicon-based semiconductors are fast approaching their performance limits for high power requirements, gallium nitride (GaN), silicon carbide (SiC), and diamond, with their superior electrical properties are likely candidates to replace silicon in the near future. Along with higher blocking voltages wide-bandgap semiconductors offer breakthrough relative circuit performance enabling low losses, high switching frequencies, and high temperature operation. The progress of the development of high voltage, high current wide-bandgap power switching devices in the APRA-E SWITCHES program is reviewed. The performance of various rectifiers and transistors, which have been demonstrated, is discussed. Material and processing challenges and reliability concerns for wide-bandgap power devices are also described. A glimpse into the future trends in device development and commercialization is offered.
(Invited) Study on the Role of Thermal Stress on Prismatic Slip of Dislocations in 4H-SiC Crystals Grown by PVT Method
Authors: Guo Jianqiu , Yang Yu , Goue Ouloide Yannick , Raghothamachar Balaji , Dudley Michael
Published: February 2020

Recent advances made towards the improvement of the quality of 4H silicon carbide (4H-SiC) have enabled many successful applications in the power device industry. Nevertheless, there is still a great interest in understanding the formation mechanism of crystal defects such as dislocations as well as their behavior during crystal growth.

While basal plane slip is most frequently observed in 4H-SiC crystals grown by PVT method, prismatic slip of dislocations has also been reported before. [1] The glide of threading edge dislocations (TEDs) on the prismatic planes ({1-100}), for example, leaves long segments of prismatic dislocations in their wake, some of which, if adopting enough screw component, become screw type dislocations. On one hand, these screw dislocations can cross-slip onto the basal planes, generating more BPDs in the substrate crystals. On the other hand, the existence of screw BPDs segments with Burgers vector 1/3[11-20] in the substrate will be harmful for the quality of epilayers since such dislocations, if intersecting with substrate surface, will replicate into the epilayer without conversion to TEDs.

In this study, we have observed three types of straight prismatic dislocation segments in a commercial wafer. These are three different types of dislocations with either screw or mixed characters and are formed by the prismatic slip of different types of TEDs with Burgers vectors and line directions along one of the three 1/3<11-20> directions. The three types of prismatic dislocations are each distributed non-uniformly in the wafer. We believe this non-uniformity is a result of the resolved shear stress distribution caused by the radial temperature gradient in the growing crystal boule, since TEDs only start gliding on the prismatic planes in regions where the critical resolved shear stress is reached. From thermal model simulation, we obtained the distributions of the resolved shear stress for all three types of prismatic dislocations by assuming an appropriate profile for the radial temperature variation. Based on these results, a simulated map can be generated to predict the spatial distributions of prismatic dislocations in the wafer. The map is then compared with X-ray topographic images and correlation is found between the two. It is shown that the prismatic dislocations are mainly distributed on the periphery of the boule and the exact distribution of each type depends highly on the difference in radial temperature profile.

[1] Huanhuan Wang, Shayan Byrappa ,Fangzhen Wu, Balaji Raghothamachar, Michael Dudley, Edward Sanchez, Darren Hansen, Roman Drachev, Stephan G. Mueller, Mark J. Loboda, Materials Science Forum Vols. 717-720 (2012) pp327

Figure 1
Electric Field-Driven Particle Separation in a Bifurcating Microchannel
Authors: Li Di , Lu Xinyu , Song Yongxin , Wang Junsheng , Li Dongqing , Xuan Xiangchun
Published: February 2020

Separating particles from a heterogeneous mixture is important and necessary in many engineering and biomedical applications. Current electrokinetic particle separation techniques primarily rely on dielectrophoresis, where the electric field gradients are generated by either active microelectrodes or inert micro-insulators. We demonstrate in this talk that particles can be continuously separated by size when passing through a bifurcating microchannel under the application of a DC electric field. This sheathless label-free separation relies on the wall-induced electrical lift force that acts to focus particles to the center of the main-branch and deflect them to size-dependent flow paths in the two side-branches. We also develop a numerical model to predict and understand this separation.
Monocrystalline Ni12P5 Hollow Spheres with Ultrahigh Specific Surface Area As Advanced Electrocatalysts for the Hydrogen Evolution Reaction
Authors: Chang Jinfa , Li Songtao , Li Guoqiang , Liang Liang , Ge Junjie , Liu Changpeng , Xing Wei
Published: February 2020

Hydrogen is an ideal energy carrier with an energy density of 140 MJ kg-1 and water as its final product, which is considered as an ideal candidate for the replacement of fossil fuels.1 To date, most H2 is produced today through nickel-catalyzed conversion of CH4 to H2 and CO followed by a water gas shift reaction to yield H2 and CO2. However, this approach is based on unsustainable fossil energy and discharges greenhouse gas. Water is an ideal source for H2 production as it is carbon-free, plentiful and almost costless. Water electrolysis, with only H2 and O2 as the final product, is a highly promising route in environmental benign H2 generation.2, 3 Although the ultimate goal is to couple hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) to an integrated efficient device for whole water electrolysis, one of the most crucial issues that must be solved is the development of highly efficient and durable catalysts for water oxidation and reduction.3

In this study, monocrystalline Ni12P5 hollow spheres with ultrahigh specific surface area (222.5 m-2 g-1) were prepared by a water-in-oil microemulsion method (Figure 1). The over potential required for 10, 20 50 and 100 mA cm-2 current densities are 144, 173, 225 and 277 mV in strong acidic solution with a Tafel slope of only 45 mV dec-1, ranking among the most active nonprecious HER catalysts. Moreover, the monocrystalline Ni12P5 hollow spheres catalyst exhibited a highly active and stable performance during a 3,000 cycling tests through cyclic voltammetry and a 12 hour duration chronopotentiometry test. The results indicate the highly promising application potential of the monocrystalline Ni12P5 hollow spheres catalysts in hydrogen generation to replace Pt. These promising features make Ni12P5 hollow spheres ideal candidates for the next generation HER catalysts. These catalysts with novel monocrystalline structure can be extended to electrochemical applications in various fields, such as supercapacitors, fuel cells, batteries and electrochemical sensors, and so on.

Figure 1. The illustration of synthesis procedure for the Ni12P5 hollow spheres and the water electrolysis behavior of the catalysts.

Acknowledgments
 

This work is supported by the Strategic priority research program of CAS (Grant No. XDA09030104), the Jilin Province Science and Technology Development Program (Grant No. 20130206068GX, 20140203012SF, 20160622037JC) and the Recruitment Program of Foreign Experts (Grant No. WQ20122200077).

References

1. X. Zou and Y. Zhang, Chem. Soc. Rev., 2015, 44, 5148-5180.

2. M. G. Walter, E. L. Warren, J. R. McKone, S. W. Boettcher, E. A. S. Qixi Mi and N. S. Lewis, Chem. Rev., 2010, 110, 6446–6473.

3. S. D. Ebbesen, S. H. Jensen, A. Hauch and M. B. Mogensen, Chem. Rev., 2014, 114, 10697-10734.

Figure 1
Anion Exchange Membrane Electrolyzers Showing 1 A/cm2 at Less Than 2 V
Authors: Masel Richard I , Liu Zengcai , Sajjad Syed
Published: February 2020

This paper will describe the performance of alkaline water electrolyzers using newly developed Sustainion™-X5 membranes.

Sustainion™ membranes have a styrene base, and mixtures of other components to produce a high conductivity in alkaline systems. The membranes are stable when soaked in 1 M KOH at room temperature for months. A CO2electrolyzer has run for over 4000 hours with no loss in performance. Initial tests also show stability in 1 M KOH at 60°C, See Figure 1, although no long term tests have yet been completed.

The work here considers the performance of the membranes in model alkaline membrane electrolyzers. We manufactured a small MEA using platinum coated carbon paper as a cathode and a IrO2 coated carbon paper as an anode and a Sustainion™-X5 membrane. The MEA was mounted into Fuel Cell Technologies 5 cm² cell hardware with carbon flowfields. The cell was heated to 60 °C and 1 M KOH was fed into the anode and cathode.

Figure 2 shows how the cell voltage varied with time at a fixed current of 0.8 A/cm² and 1 A/cm². The data were taken on a single cell, at a fixed current of 1 A/cm² during the day and 0.8 A/cm² at night. Initially the cell produced 0.8 A/cm² at 1.74 V and 1 A/cm² at 1.81 V, but the voltage rose to nearly 2V after 150 hours of operation. Disassembly of the cell showed that the carbon paper on the anode was corroding leading to a loss of anode catalyst.

We have also started work on nickel catalysts. The initial results were modest, but additional results will be presented at the meeting.

Acknowledgement

Parts of this work were supported by ARPA-E under contract DE-AR0000684 and by 3M. The opinions here are those of the authors and may not reflect the opinions of ARPA-E or 3M.

Figure 1
Manganese Oxide/Poly(3,4-ethylenedioxythiophene) Hybrid Electrocatalysts for the Oxygen Reduction Reaction in Alkaline Fuel Cells
Authors: Lambert Timothy N. , Vigil Julian A.
Published: February 2020

Manganese oxide/poly(3,4-ethylenedioxythiophene) (MnOx/PEDOT) nanostructured hybrid thin films are readily prepared using a simple anodic electrodeposition process from aqueous solution. Using this approach, MnOx/PEDOT films with thicknesses and mass loadings up to 100 nm and 40 μg cm-2 were prepared, then tested for oxygen reduction reaction (ORR) activity in alkaline electrolyte using rotating disk electrode and rotating ring disk electrode methods. MnOx/PEDOT provided improvements over MnOx-only and PEDOT-only control films, with > 0.2 V decrease in onset and half-wave overpotentials and > 1.5 times increase in current density. The MnOx/PEDOT film exhibited only a slightly lower reaction order (n = 3.86-3.92) than the 20% Pt/C benchmark electrocatalyst (n = 3.98) across all potentials. MnOx/PEDOT also displayed a more positive half-wave potential and superior electrocatalytic selectivity for the ORR upon methanol exposure than 20% Pt/C. The high activity and synergism of MnOx/PEDOT towards the ORR is attributed to effective intermixing/dispersion of the two materials, intimate substrate contact and the improved charge transfer processes attained by co-electrodepositing MnOx with PEDOT. PEDOT has previously been demonstrated in fuel cells to limit methanol crossover. PEDOT has also been used as a catalyst support in fuel cells. These facts, combined with the substantially lower cost of Mn versus Pt (Mn is ~ 17,000 times cheaper), augurs for further development and testing of MnOx/PEDOT hybrid materials as ORR electrocatalysts with application in alkaline fuel cells.

This work was supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
Iridium-Platinum Core-Shell Nanoparticles As Catalysts for the Oxygen Reduction Reaction
Authors: Strickler Alaina Leigh , Jackson Ariel , Jaramillo Thomas F
Published: February 2020

Fuel cells are a promising source of renewable, clean energy. Widespread commercialization of fuel cell technology, however, has been hampered by technological and economic hurdles due to inadequate device efficiencies and expensive Pt electrocatalysts. To address these challenges, considerable research has focused on enhancing the kinetics of the oxygen reduction reaction (ORR) at the cathode which is the dominant source of voltage loss in state-of-the-art fuel cells.1 Recent work has sought to increase intrinsic catalyst activity and reduce Pt loading via core-shell nanoparticles where a Pt shell surrounds the core of a different metal or alloy. These nanostructures provide the ability to increase Pt mass activity through a larger Pt surface area to volume ratio as well as enhance the Pt intrinsic activity by altering its electronic structure though stain and ligand effects. These electronic changes dictate the binding energies of reaction intermediates to the catalyst surface and thus reactivity for the ORR. To identify a core material capable of improving ORR activity, we utilized a systematic approach for catalyst design developed in a previous study. This study found that activity can be improved by selecting a core material that is theoretically predicted to over-weaken the oxygen binding energy when covered with a Pt monolayer.2 The oxygen binding energy can then be strengthened towards its optimum by increasing the Pt shell thickness and through nanoscale effects where undercoordinated sites demonstrate stronger binding to adsorbates. Through this method, iridium was identified as a promising core material. Therefore, this work focuses on the synthesis, characterization, activity, and stability of Ir-Pt core-shell nanoparticles. Ir-Pt nanoparticles with three different compositions were synthesized using a highly scalable, inexpensive polyol method. TEM, STEM-EDS, and XPS were used to characterize particle size and composition. ORR activities of the Ir-Pt catalysts were compared to synthesized Ir-only and Pt-only nanoparticles as well as to the state-of-the-art commercial standard Pt catalyst, TKK. Electrochemical analysis demonstrates the high activity of the Ir-Pt catalyst with a specific activity of approximately 2 times that of TKK. This catalyst also demonstrates high stability after 10,000 stability cycles showing improvements in both mass and specific activity upon cycling with the latter increasing to 2.6 times that of TKK.

1. Stephens, I.E.L., et al., Energy & Environ. Sci.
5
, 6744-6762, (2012).

2. A. Jackson et al., ChemElectroChem 1, 67-71 (2014).
Simplified Microwave Assisted Solvothermal One Pot Synthesis of Highly Active Nickel-Iron Layered Double Hydroxide as Oxygen Evolution Reaction Catalyst
Authors: Dresp Sören , Strasser Peter
Published: February 2020

The increasing demand for solar fuels and hydrogen as most promising energy carrier requires new materials for electro-catalytic splitting of water or the back-transformation of hydrogen into electricity. Especially, the oxygen electrode caused by sluggish kinetics is hampering progress for cheap hydrogen made by electrolysis. Moreover the low abundance and the high costs of current highly active noble metal catalysts require new developments for novel cheap and abundant materials. Therefore we have developed a new two-component catalyst system consisting of Nickel-Iron layered double hydroxide (NiFe-LDH) and Fe-N doped carbon material (Fe-N-C) as non noble bifunctional catalyst for the oxygen electrode in alkaline unitized reversible fuel cells/electrolyzers (URFC). The combination of NiFe-LDH known as most active non-noble catalyst for the oxygen evolution reaction (OER) in alkaline media and Fe-N-C known as highly active catalyst for the oxygen reduction reaction (ORR) resulted in a combined overpotential with their respective advantages. Highly crystalline NiFe-LDH was prepared by a simple and time-saving microwave assisted solvothermal synthesis route. The crystallinity was confirmed by X-ray diffraction (XRD) spectroscopy and Transmission electron microscopy (TEM) verified morphological characteristics. Rotating Ring disk (RRDE) measurement revealed high selectivity for the multi-component catalyst. We further investigated the behaviour in a membrane based reversible electrolyzer using an anion exchange membrane (AEM, Tokuyama A201). Compared to noble catalyst systems such as Iridium and Platinum the membrane electrode assembly (MEA) measurements proved the ability to compete and supported the initial high activities.
Engineered Carbon Supports for Low Precious-Metal-Content Catalysts
Authors: Stephenson Thomas , Lubers Alia , McCool Geoff , Romero Henry , McKinney Samuel , Halevi Barr
Published: February 2020

In the development of PEMFC fuel cells much attention and development is devoted to the "active" portion of the catalysts system, the precious metal nano-particles. While this approach has led to great improvement in specific activity, existing catalysts are still not meeting the combination of performance and cost necessary for the commercialization of PEMFC.

A key limitation to catalysts today arises from reliance on carbon black(CB) supports that serve to disperse and stabilize the precious metal catalyst nanoparticles, but which corrode under certain operating conditions. Carbon support modifications that rely on "top-down" graphitization of CB's have so far improved resistance to carbon corrosion, but at the cost of reduced stabilization of precious metal dissolution.

Pajarito Powder developed a "bottom-up" approach where Engineered Carbon Support are made from organic precursors that yield a highly tailorable carbon support with great corrosion resistance. This method which is based on technologies licensed from the University of New Mexico, Northeastern University, and Los Alamos National Laboratory allows manufacture of highly graphic carbonaceous powders with excellent control of pore sizes and particle roughness.

Pt/C catalysts made using these Engineered Carbon Supports maintain performance under carbon corrosion test protocols and thus demonstrate their utility in achieving the performance/price balance needed for commercializing PEMFCs. The catalyst characteristics and performance, as well as economics of this approach will be presented and discussed.

Figure 1
Numerical Simulation of PEFC Stack System for Design of Configuration and Control of Anode Systems
Authors: Takayama Tsutomu , Yoshimura Hideto , Motegi Haruki , Tsukamoto Takayuki , Takayama Ryo , Yoneda Masakazu
Published: February 2020

Overview

 Performances of cell stacks are simulated, focusing on driving state of anode system. This simulation technique takes overall transport phenomena in PEFC fuel cell systems, such as transport of gas species and liquid water in both anode and cathode channels and across MEA, thermal balance, electrochemical reactions and current distributions. Injector and exhaust systems are modeled by boundary conditions, mimicking actual driving conditions. Relation between cell performances and driving state of anode system, for example, consumption of hydrogen, build-up of liquid water and cross-over nitrogen and purging by control of injector and/or ejector can be discussed based on simulated results. Over-all performance of anode system is one of crucial issue for durability and cost-reduction of fuel cell systems. These results show good applicability of this kind of simulations on design of PEFC stack system.

Numerical Modeling and Results

 Simulation is performed by our own simulation software for PEFCs, which is capable of simulating full-stack fuel cell system for fuel cell vehicles (up to 400 cells) under transient operating conditions. An important feature of this software is that macroscopic models are applied for microscopic phenomena in the MEA such as electrochemical reactions and proton/water transport. Heat transfer and fluid of liquid-gas two phase fluid with phase changing are also taken into account. These models are coupled with multi-dimensional heat and mass transport equations, including effective parameters for gas diffusivity and permeability in the GDL and equivalent hydraulic diameter in the flow channel. This software can also simulate cathodic degradation by carbon corrosion reactions.

 Performances of up to 400 cells stacks are simulated. A numerical model of anode system is constructed by adding transient boundary conditions for an injector and an exhaust system with an ejector. These transient boundary conditions represent open / close timings of injector and ejector under actual driving conditions. Distributions and consumptions of hydrogen, build-up of cross-leak nitrogen and condensate liquid water can be shown under constant (up to 30A) loading.

 Simulated results show difference of cell potential between of stacked cells, and relation between performance distributions and balances of transport phenomena in stack systems. Effects of configuration of stack systems are also shown. Based on these results, design of stack systems and control schemes of anode system can be discussed. Those discussion can provide useful information for improving durability of stacked cells by avoiding depletion of hydrogen, and / or examination of control schemes which can efficiently utilize hydrogen fuel.
(Invited) Fuel Cell Stack Technology of Toyota
Authors: Suzuki Toshiyuki
Published: February 2020

Toyota Motor Corporation launched the Prius, the world’s first mass-production hybrid vehicle (HV), in 1997. The global popularization of the Prius and other HVs has helped to counteract the negative effects of vehicles on the environment. As emerging markets continue to develop economically and the world’s population grows, vehicles are likely to have an even greater impact on the environment. Therefore, if vehicles are to remain of benefit and interest to society in the next one-hundred years, it will be even more important to find answers to issues related to energy and the ideal form of mobility in the future. Through the development of hybrid, plug-in hybrid, and battery electric vehicles, Toyota is already acting proactively to encourage the use of electricity. In addition, Toyota has also taken the step of developing fuel cell vehicles (FCVs) to help promote the use of hydrogen for contribution to environment.

A fuel cell (FC) generates power by electrochemical reactions through an electrocatalyst using hydrogen and oxygen in the air. Since these reactions generate only water as a by-product, FCs are regarded as an extremely clean and efficient means of generating power, with the potential to help resolve energy and environmental issues in the future. Greatly enhancing the performance and reducing the size and cost of the FC stack is an important part of measures aimed to facilitate the widespread adoption of FCVs.

A FC stack consists of a wide range of materials, including various types of mechanical elements and electronic parts. In particular, cells inside the FC use many materials that are not found in conventional vehicle parts. In contrast to the research phase, which prioritized efforts to enhance the functional performance of the FC stack, the new mass-production MIRAI FCV was developed as a normal industrial product with an emphasis on both performance and the applicability of manufacturing methods. This article describes several examples of manufacturing methods adopted to ensure high quality and productivity while reducing cost.
Differential Electrochemical Mass Spectroscopy Study of CO2 Concerned Anode Reaction in Polymer Electrolyte Fuel Cell
Authors: Tamura Shigehisa , Jia Siyuan , Sato Kazutaka , Shironita Sayoko , Umeda Minoru
Published: February 2020

For a power generation of a polymer electrolyte fuel cell (PEFC), reformed hydrogen gas is fueled to the anode. The reformed hydrogen gas contains a small amount of carbon monoxide and 10-30% carbon dioxide [1]. The carbon dioxide is reported to be reduced at Pt electrode [2, 3]. In this study, CO2 reduction is performed at various potential of Pt/C-based membrane electrode assembly(MEA). The product of CO2reduction was analyzed by a mass spectrometer.

Electrocatalyst of Pt/C (Pt: 45.7 wt%) was sprayed on a gas diffusion layer. The electrolyte membrane was sandwiched by two pieces of the gas diffusion layers which were coated electrocatalyst layers (metal amount: 1.0 mg cm-2), and then, it was hot-pressed to obtain on MEA. Geometric electrode area of the MEA was 3×3 cm2. The prepared MEA was installed in a single cell having a dynamic hydrogen electrode (DHE) as a reference electrode. The temperature of the single cell was controlled at 80°C. Humidified carbon dioxide gas (purity: 99.995%) and humidified hydrogen gas (purity: 99.999%) were supplied to the working electrode and counter electrode, respectively, at a flow rate of 50 cm3 min-1. Cyclic voltammograms were measured at a potential scan rate of 10 mV s-1and the potential scan range was between 0.00-1.38 V vs. DHE. The exhaust gas was introduced directly into the mass spectrometer (JEOL, JMS-Q1050GC Ultra Quad GC/MS ).

Figure 1 shows a result of differential electrochemical mass spectroscopy measured at 0-1.38 V vs. DHE. In Fig. 1 (a), cyclic voltammograms at the Pt/C-based MEA were obtained under CO2 and Ar atmospheres. Under the CO2 atmosphere, a typical anodic current at around 0.5 V vs. DHE is observed. This is due to the re-oxidation of the CO2 reductant which was generated at < 0.1 V vs. DHE by the CO2 reduction. Mass spectra of m/z = 2, 16, 45 versus electrode potential under CO2 atmosphere shown in bottom of Figure 1 (b)-(d). The m/z = 2, 16, 45 were originaled from hydrogen, methane and formic acid. Generation of m/z = 16 is seen at < 0.2 V vs. DHE, and m/z = 2, m/z = 45 are seen at < 0.1 V vs. DHE. It was found that there is a potential dependency for CO2reduction at Pt/C-based MEA. Consequently, adsorbed CO2reductant on the Pt remains in the potential range of 0-1.38 V vs. DHE which influences the hydrogen oxidation reaction.

[1] K. Kortsdottir, C. D. Fernandez, R. W. Lindstrom, ECS Electrochem. Lett.,
2, F41-F43 (2013).

[2] N. Hoshi, S Kawatani, M. Kudo, Y. Hori, J. Electroanal. Chem., 467, 67–73 (1999).

[3] S. Shironita, K. Karasuda, K. Sato, M. Umeda, J. Power
Sources, 240, 404-410 (2013).

Figure 1
Synthesis and Properties of Partially Fluorinated Anion Exchange Membranes Containing Ammonium-Functionalized Fluorenyl Groups
Authors: Ozawa Mizuki , Miyake Junpei , Miyatake Kenji
Published: February 2020

Anion exchange membrane fuel cells (AEMFCs) are one of the promising energy conversion devices because of their high efficiency and possible use of non-precious metal catalysts. However, the existing anion exchange membranes, main component of AEMFCs, do not show sufficient ion conductivity and stability. In this study, we report a novel series of AEMs composed of perfluoroalyl chains and ammonium-functionalized fluorenyl groups (Fig. 1). The perfluoroalkyl groups are expected to provide chemical stability as well as flexible membrane forming capability, while the ammonium-functionalized fluorenyl groups contain high ionic density for high ion conductivity. We have investigated in details synthetic procedure, structure, and properties of the title AEMs.

The hydrophobic monomer containing perfluroaklyl groups was synthesized by Cu-catalyzed Ullmann coupling reaction, and fluorenyl-containing monomers were synthesized by Sandmeyer reaction. Precursor polymers were synthesized by Ni-mediated Ullman coupling reaction. Then, chloromethyl groups were introduced onto the precursor polymers by Friedel-Crafts reaction. The chloromethyl groups were quarternized with trimethyl amine by Menshutkin reaction.

It is known that the chloromethylation reaction often accompanies with unfavorable side reactions such as cross-linking. By carefully optimizing the Friedel-Crafts reaction conditions, we have successfully controlled the degree of chloromethylation. In fact, the number and the position of chloromethyl groups substituted on fluorenyl groups were controllable.

The chloromethylated precursors were soluble in organic solvent and the solutions were cast to thin films. The ion exchange capacities obtained by titration were lower than calculate from DC. The difference of IEC value was increased with increase of DC. It is suggest that when ionic group density becomes higher, there is an ammonium group which is not functioning as ionic groups by their steric hindrance. The quaternized polymer membranes exhibited high hydroxide ion conductivity and the maximum conductivity was 29 mS/cm in water at 80 °C for the membrane with IEC = 1.6 meq/g. It was found that meta-linked polymers in the hydrophilic component showed slightly higher ion conductivity than that of para-linked polymers. Other properties such as morphologies and stabilities will also be reported.

Acknowledgement

This work was partly supported by Japanese Science and Technology Agency (JST), CREST.

 

 

References

1) Manai Shimada, Shigefumi Shimada, Junpei Miyake, Makoto Uchida, Kenji Miyatake, J. Polym. Sci., A: Polym. Chem.,
2015, 7,935-944.

2) Hideaki Ono, Junpei Miyake, Shigehumi Shimada, Makoto Uchida and Kenji Miyatake, J. Mater. Chem. A, 2015, 3, 21779–21788.

Figure 1
Pore Structure Effect of Cathode Catalyst Layer on Performance and Durability of PEMFC
Authors: Kim Sang-Kyung , Lee Hye-Yeong , Peck Dong-Hyun , Kim Chang-Soo
Published: February 2020

Porosity and pore size of cathode catalyst layer was controlled by changing catalyst layer coating methods. Two-layered catalyst layer of dense and porous layers was also compared in order to get optimum porosity of catalyst layer in the view point of both performance and durability. Performance and durability of MEA’s with different porosity were compared and impedance and ECSA of them were analyzed. Porosity and pore size were measured and observed by mercury intrusion method and SEM images. Porous catalyst layer was generally favorable. However porosity of catalyst layer could be further advanced with two-layered structure of different pore structures.
Thermal Behaviour of Nafion Thin Films
Authors: Zhang Chi , Ozhukil Kollath Vinayraj , Karan Kunal
Published: February 2020

Sub-micron Nafion films are relevant to several electrochemical devices including polymer electrolyte fuel cells, sensors and actuators. Such thin films are invariably fabricated from dispersion of the ionomer in suitable solvent, e.g. by drop-casting, spin-coating or self-assembly. Often a thermal treatment or annealing step is applied to improve the mechanical properties of the film and relax the polymers. Thus, understanding the response of the ionomer thin film subjected to thermal changes is important. Furthermore, thermal characteristics of the ionomer such as glass transition temperature and thermal expansion coefficient can provide fundamental insight into structure and the nature of the interaction with the substrate.

We have initiated an in-situ thermal ellipsometry and thermal FTIR study to probe the response of 20-650 nm thick Nafion thin films supported on SiO2 substrate. Ellipsometry experiments yield the thickness change as a function of temperature. This set of data yields thermal expansion coefficient of the Nafion films. The change in slope of the thickness change with temperature provides information on the nature of phase transition – glassy to rubbery or disorder-to-order. The thermal FTIR is being used as a complimentary technique to probe whether the phase change phenomenon manifests as a dramatic change in response in one of the characteristic peaks.

The results obtained so far indicate that the thermal expansion coefficient of Nafion films 60 nm and lower thickness is changes with thickness but those of the films above 60 nm thickness converges to that of the bulk material. No distinct transition in slope of thickness change is observed. That is, no glass transition like behavior is observed. No thickness-dependent response in FTIR peak is observed. A sharp change in the 638-626 cm-1 doublet region is observed at temperature corresponding to the so-called a transition for Nafion.

To the best of our knowledge, there have been no prior studies on in-situ thermal ellipsometry or in-situ thermal FTIR of Nafion thin films.
An FIB-SEM Study on Correlations between PEFC Electrocatalyst Microstructure and Cell Performance
Authors: Okumura Makito , Noda Zhiyun , Matsuda Junko , Nishihara Masamichi , Hayashi Akari , Sasaki Kazunari
Published: February 2020

The electrocatalyst layer of the polymer electrolyte fuel cells (PEFCs) has a complicated porous microstructure. Since the structure allows gas, proton, and electron transport, and water management, cell performance depends strongly on their 3-dimensional microstructure. Understanding on the correlations between the electrocatalyst microstructure and the cell performance is therefore essential in improving the PEFC electrochemical performance. The purpose of this study is thus to clarify these correlations using focused-ion-beam coupled scanning electron microscopy (FIB-SEM).

We used the standard electrocatalyst (TEC10E50E) and varied the Nafion-to-electrocatalyst ratio (hereafter the Nafion ratio) for the electrocatalyst layer because the Nafion ratio affects the electrocatalyst microstructure and the cell performance[1],[2]. After model cell preparations, current-voltage (IV) performance was measured and thus each electrode overvoltage contribution was separated. We then considered FIB-SEM working condition and method of image processing to observe electrocatalyst microstructure by the FIB-SEM technique. In particular, because it was difficult to distinguish between solid and pore in SEM images due to the complicated porous microstructure, we solved this problem by separating solid and pore objectively by auto-image thresholding technique[3]. Then, we examined the correlations between the 3D microstructure and the cell performance.

According to the results of IV characteristics of several cells with different Nafion contents, in case Nafion ratio was 28 wt.%, IV performance was the highest. In case Nafion ratio was less than 28 wt.%, whilst IV performance was lower than that of 28 wt.%, the cells can still generate high current densities. On the other hand, in case Nafion ratio was higher than 28 wt.%, the cells can exhibit a lower cell voltage due to a much higher concentration overvoltage. In order to examine the correlations between the 3D microstructure and the cell performance, we observed electrocatalyst microstructure by the FIB-SEM. Figure 1 describes the observation process. According to the results of 3D analysis of samples with different Nafion contents, we could confirm that gas transport pathway in the electrocatalyst layer was filled with Nafion ionomer with increasing Nafion ratio. Details on the FIB-SEM observation conditions and the microstructure-performance correlations are presented at the symposium.

(1) S. Jeon, J. Lee, G.M. Rios, H.-J. Kim, S.-Y. Lee, E Cho, Intl. J. Hydrogen Energy 35 (2010) 9678-86.

(2) T. Suzuki, S. Tsushima, S. Hirai, Intl. J. Hydrogen Energy 36 (2011) 12361-12369.

(3) J. Bernsen, 8th ICPR (1986) 1251-1255.

Figure 1
Computational Modelling of Cationic Contamination in PEFCs: a Multiphase Mixture Approach
Authors: Banas Charles Joseph , Pasaogullari Ugur
Published: February 2020

Cationic contamination in polymer electrolyte membrane fuel cells (PEFCs) can lead to accelerated degradation and loss of performance. There are several mechanisms to introduce these cationic impurities; including transport with the inlet fuel/air streams, or from degradation of the fuel cell and balance of plant components. Many common cations tend to have a higher affinity to the sulfonic acid side chains of the polymer electrolyte membrane (PEM) than protons, resulting in preferential uptake of these contaminants into the PEM. Once occupying these sites, the impurity cations contribute to the loss of performance by lowering the water content of the membrane and reducing the ionic conductivity.[1] To compliment experimental results, numerical studies have been performed[2,3] to understand the coupled impact of cation occupancy in the membrane with the water transport in the cell and the overall cell performance. Early generations of these models had assumed a constant cation occupancy in the cathode that was used as a boundary condition to solve the cation transport via a Stefan-Maxwell diffusion process. By coupling the contaminant occupancy to the water content of the membrane and electro-kinetics of the catalyst layers, cell performance has been shown to decrease down to as little as one third its non-contaminated levels.[3] This study builds off of previous models to develop a steady state, one dimensional, cation contamination model of a PEFC to examine the impact of cation transport to the membrane electrode assembly (MEA) via a water bridge across the gas diffusion layer (GDL) as shown in Figure 1. The multiphase mixture (M2) model, proposed by Wang and Cheng[4], is used to derive species transport equations for the reactant gases and water that permits two phase water transport in the GDL and catalyst layers. This resulting water distribution acts as to promote cation transport from the gas flow channels across the GDL, where the dissolved cations can evolve out of the liquid phase water and into the MEA, occupying the sulfonic acid sites of the membrane. A baseline non-contaminated case is presented to study the cell performance and species distribution normal operating conditions. Then, the model is employed to show how the saturation of the cathode effects cation distribution across the GDL and how the presence of dissolved cations in the catalyst layer impacts the contaminant occupancy and overall cell performance.

References

 1. T. Okada, in Handbook of Fuel Cells, Cells– Fundamentals, Technology and Applications., W. Vielstich, H. A. Gasteiger, A. Lamm and H. Yokokawa. Editors, John Wiley & Sons, Ltd (2010).

 2. M. F. Serincan, U. Pasaogullari and T. Molter, Int. J. Jydrogen Energy, 35, 11 (2010).

 3. M. A. Uddin and U. Pasaogullari, J. Electrochem. Soc., 161, 10 (2014).

 4. C. Y. Wang and P. Cheng, Int. J. Heat Mass Transfer, 39, 17 (1996).

Figure 1
Novel Anode Catalysis for Ammonia Solid Oxide Fuel Cell
Authors: Hashinokuchi Michihiro , Zhang Mengjia , Yokochi Ryuji , Doi Takayuki , Inaba Minoru
Published: February 2020

Ammonia (NH3) is attractive as a hydrogen carrier and a suitable fuel for solid oxide fuel cells (SOFCs) because it has high hydrogen density and can be easily liquefied at an ambient temperature., However, the activity of conventional Ni cermet anodes of SOFCs for NH3 oxidation is much lower than that when H2 is used as a fuel [1]. It is necessarily to improve the anode activity for NH3 oxidation for realizing NH3-fueled SOFCs.

There are many studies on the Ni-based anodes for NH3-SOFCs. However, the number of report on the bimetallic anode for NH3-SOFCs is limited. Previously, we have investigated the activity of Ni-M (M = Fe, Mo ,Ta, W and Nb) cermet anodes for NH3-SOFCs at temperature of 700 - 900 °C [2-5]. In these studies, we found that the anode polarization was greatly improved by transition metal additives, which favored the formation of metal (and/or alloy) nitrides in the anode under operation condition. Furthermore, the activation energy of NH3 oxidation at the anode was strongly dependent on the metal additive, suggesting that a metal-nitrogen biding energy of catalysis was related to the catalytic activity for NH3 oxidation. Among these anodes, Ni-Fe and Ni-Mo cermet anodes were highly active for the electrochemical oxidation of NH3 at 700 °C and expected for the active anode of NH3-SOFCs at intermediate temperature.

In this study, we further investigated the effects of Fe and Mo additives to Ni cermet anode on the cell performance at temperature of 500 - 600 °C. Fig.1 shows the current density versus voltage (I–V) curves for the electrolyte supported cells: Ni40-Fe60/SDC, Ni97-Mo3/SDC and Ni/SDC|LSGM|SSC at 600 °C. The thickness of LSGM electrolyte was 300 µm. The cell performance was significantly improved by the addiction of Fe and Mo as shown in Fig.1. The formation of alloy nitrides in both Ni-Fe and Ni-Mo anodes was observed under operation condition. The role of alloy nitrides in the NH3oxidation will be discussed.

Acknowledge

This work was supported by “Kyoto Regional Scientific Innovation Hub” from MEXT in Japan and by JSPS-KAKENHI Grant Number C16K05958.

Reference

[1] Q. Ma et al., J. Power Sources 161 (2006) 95.

[2] W. Akimoto et al., Solid State Ionics 256 (2013) 1.

[3] M. Hashinokuchi et al.,Solid state Ionics 285(2016) 222.

[4] M. Hashinokuchi et al., ECS Transactions 68 (2015) 2739.

[5] R. Yokochi et al., ECS Transactions 68 (2015) 2745.

Figure 1
Reduction of Thermal Stress during Soec Unsteady Operation
Authors: Watanabe Kentaro , Maeda Atsushi , Mizusawa Tatsuya , Araki Takuto , Mori Masashi
Published: February 2020

In recent years, natural energy sources such as solar and wind power have been introduced into the electric grid. However, the wind and solar power suffer instability with respect to changes in the weather. As the proportion of these energies increases, a technique to store a surplus electric power is required. The hydrogen generation systems using solid oxide electrolysis cells (SOECs) are expected as large-capacity power storage facilities with the ability to stabilize the electrical power supply.

For the use of the SOEC, it is important to grasp the unsteady characteristics, especially temperature distribution which is the one of the biggest destruction factor of the cell. In this study, the unsteady, two dimensional, tubular numerical model of a cathode supported micro-tubular SOEC was developed to clarify the temperature distributions and its responses .The temperature of anode surface were measured directly by K-type thermocouples during the simultaneous electrochemical performance measurements. The operating condition of SOEC was controlled to reduce the unsteady temperature distribution in SOEC.

Rough description of the numerical model is shown in Fig.1. The model calculates heat-mass-charge transports and electrochemical reactions, simultaneously. The construction materials of SOEC cathode electrode was mixed materials of nickel (Ni) and yttria-stabilized zirconia (YSZ). The electrolyte was YSZ, and the anode electrode was mixture of lantern strontium manganite (LSM) and YSZ. The thicknesses of cathode electrode, electrolyte and anode electrode were 200 mm, 20 mm and 20 mm, respectively. The cell length was about 50 mm, with an outer diameter of about 2 mm. The flow rate of hydrogen and steam was set to be same. The operating temperature was 1123K. Experiments of SOEC were conducted in same conditions.

The calculated temperature distributions at steady states are shown in Fig.2. The temperature decreased at 1.1 V, 1.2 V and increased at 1.3 V, 1.4 V. The maximum temperature gradient was observed around z=0.042 at 1.4 V. This position was consistent with the point where a clack was observed during a measurement.

The maximum temperature gradients change during potential sweep with various intermediate voltage are shown in Fig.3. This shows that the maximum temperature gradient could be reduced by controlling the sweeping conditions.

Figure 1