bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Ag Nanoparticles That Anchored on F-Graphene into NiO/Ni(OH)2 for Improvements in Storage Capacity and Energy Density: Nanotechnology Offers Higher Storage Ability
Authors: Ryu Su Young , Hoffmann Michael R
Published: February 2020

AgNP is synthesized on the surface of F-graphene as anchored, and characterized to form less than 20 nm in size having quantized physical properties. Application of AgNP has been investigated its effects on NiO/Ni(OH)2 supercapacitor from the comparison of specific capacitance (F g-1) and capacity (mA h g-1). It shows to be beneficial to the energy and power density of NiONi(OH)2 with reversible AgNP multi redox reactions. The specific capacitance of NiONi(OH)2 is highly enhanced by applied AgNP anchored on F-graphene (AgNP/F-graphene) from 148 F g-1 to 356 F g-1
while it results in 226 F g-1 by applied silver without F-graphene. The best result is obtained with the nafion free electrode of AgNP/F-graphene/NiONi(OH)2, as it results in 1,153 F g-1
at the experimental condition of 5 mV/s scan rate in 1M KOH.

For the specific capacity of NiO/Ni(OH)2, the identical result is observed as it improved from 266 mA h g-1
up to 545 mA h g-1
by applied AgNP anchored on F-graphene.

The performance of AgNP combined NiONi(OH)2 leads us to explore the secondary battery of Zn-Ni that combined with Zn-Ag. A preliminary galvanic-charge/discharge test using a single cell of AgNP/F-graphene/NiONi(OH)2 coupled with Zn plate demonstrates to be a potential hybrid rechargeable battery having a high power and energy density, as it resulted in about 3,433 W kg-1 for the power density and 958 W h kg-1 for the energy density, respectively, on the basis of Ni and Silver as the active material.
Tunnel Structural Heterogeneity in MnO2 Polymorphs: Origins and Effect on Ion Transport
Authors: Yuan Yifei , Yao Wentao , Byles Bryan , He Kun , Liu Cong , Song Boao , Cheng Meng , Huang Zhennan , Amine Khalil , Pomerantseva Ekaterina , Lu Jun , Shahbazian-Yassar Reza
Published: February 2020

The establishment of an accurate synthesis-structure-property relationship is the central scheme of materials science, which is particularly important for polymorphic materials possessing various structural forms with different properties. Manganese dioxide (MnO2) is a typical polymorphic material exhibiting various one-dimensional tunnel phases that are constructed by [MnO6] octahedra units, enabling its extensive applications in water desalination, (electro)catalysis and energy storage. Despite the long-range [MnO6] ordering confirmed by conventional diffraction tools, surprisingly, the electrochemical energy storage properties of a specific MnO2 tunnel phase still vary significantly in literature with unclear structural origins.

Here, we demonstrate the existence of tunnel heterogeneity featuring localized tunnel intergrowths within single MnO2 nanoparticles via atomically-resolved imaging. Furthermore, combining both ex situ and in situ transmission electron microscopy, the tunnel heterogeneity within one MnO2 nanoparticle is demonstrated to significantly affect the energy storage kinetics in sodium ion battery even down to sub-nanometer scale.

The origins of such tunnel structural heterogeneity in MnO2 are explored further, where a layer-to-tunnel (L-T) transition mechanism is identified to be responsible. The L-T transition is the essential step for the MnO2 layered precursors to gradually transform to tunnel polymorphs during the hydrothermal synthesis. The intermediate state during the L-T transition is successfully obtained and analyzed to extract the critical information regarding the atomic reconfiguration, compositional evolution and electronic structure change during this transition. It is found that the L-T transition is not homogeneous but rather topotactically happening from the layer edges into the body, which leads to the gradual splitting of 2D MnO2 layers into 1D nanowires possessing tunnel structure. The layers are transformed to 3×3 tunnels in multisteps via formation of intermediate tunnel phases exhibiting much larger openings. The transition starts by macroscopic layer distortion from adjacent Jahn-Teller active [Mn3+O6] octahedra, experiences Mn3+ disproportionation reaction and layer-interlayer Mn migration, expels doped Mg2+ out of the openings, and gradually builds the tunnels by reconstructing the Mn-O bonds.

Findings in this work could guide the controlled synthesis and selective size-engineering of MnO2 tunnels for specific applications in various fields. We also expect it to call for renewed attention to the controlled synthesis of homogeneous tunnel-specific phases with predictable properties, and to yield a more precise structure-property relationship in polymorphic materials.

Figure 1
(Invited) Transfer Printing of 2D Materials for Ultrathin Wearable/Implantable Electronics
Authors: Choi Moon Kee
Published: February 2020

Recent application of 2D materials on flexible electronics has provided new possibility on biocompatible, ultrathin biomedical electronics. Graphene and MoS2 each are getting attention as next-generation 2D metal and semiconductor materials. However, electrical characteristics of the final integrated electronics are usually lower than expected due to the residue of polymer sacrificial layer during the transfer process. To achieve high-performance biomedical electronics, several strategies have been employed, such as the designed assembly of high-quality nanomaterials, combination of unconventional manufacturing processes with existing micro-processing technologies, new design of individual devices with deformable structures, and disease-specific system-level integration of diverse soft electronics. Here, we describe transfer printing methods for residue-free 2D materials and show ultrathin flexible biomedical devices for wearable/implantable applications. Graphene based transparent sensors and actuators can be utilized for invisible tele-medical healthcare devices, and graphene-MoS2 heterostructures can be applied to the ultrathin curved image sensors for the retina prosthetics.
The Ultrahigh Efficient Degradation of Rhodamine B By the Piezo-Catalyst Effect of Single- and Few-Layered MoSe2 Nanoflowers
Authors: Lee Jyun-Ting , Wu Jyh-Ming
Published: February 2020

In this report, we have demonstrated a high degradation activity of MoSe2 nanoflowers with abundant single-layer and few-layer structure for decomposing the Rhodamine B (RhB) dye by the piezo-catalyst effect which is a technique for converting mechanical energy into chemical energy. Similar to photocatalyst effect, the electrons and holes also can be introduced by piezo-electronic effect. Base on our experiment results, the 10 ppm RhB solution was degraded by 90 % within 30 s through the application of the ultrasonic vibration. The significantly piezoelectric potential was evidenced by the piezoresponse force microscopy (PFM), and the tunneling atomic force microscopy (TUNA). The observed k
obs rate constant is 0.3 (ppm s−1) with a highly fast degradation rate of ~ 69,889 ppm L mole−1 s−1. Moreover, the electron paramagnetic resonance (EPR) spectroscopy also demonstrated the formation of the hydroxyl radical from the MoSe2 nanoflowers during the ultrasonic vibration in dark, which is the major reactive oxygen species (ROS) for destroying the dye molecules.

Figure 1
(Invited) Multifunctional Materials for Emerging Technologies
Authors: Rosei Federico
Published: February 2020

As the age of fossil fuels is coming to an end, now more than ever there is the need for more efficient and sustainable renewable energy technologies. This presentation will give an overview on recent developments in solar technologies that aim to address the energy challenge. In particular, nanostructured materials synthesized via the bottom–up approach present an opportunity for future generation low cost manufacturing of devices [1]. We demonstrate various multifunctional materials, namely materials that exhibit more than one functionality, and structure/property relationships in such systems, including new strategies for the synthesis of multifunctional nanoscale materials to be used for applications in photovoltaics, solar hydrogen production, luminescent solar concentrators and other emerging optoelectronic technologies. [2-31].

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Bottom-up Patterning of Semiconductor Nanostructures for Large-Area Electronics
Authors: Mohabir Amar T , Weiss Trent , Tutuncuoglu Gozde , Brummer Amy , Vogel Eric M. , Filler Michael A
Published: February 2020

We demonstrate a versatile and programmable route to mask, with nanoscale precision, the surface of semiconductor nanostructures in an entirely bottom-up fashion. This capability promises to dramatically increase the manufacturing rate of high performance (i.e., > GHz, < 1 V) semiconductor devices for large-area, flexible electronics. Our approach – Selective CoAxial Lithography via Etching of Surfaces (SCALES) – involves three main steps: (1) Bottom-up synthesis of single crystalline semiconductor nanowires with an axially-encoded composition profile, (2) blanket surface-initiated polymerization of a masking material, and (3) selective removal of the masking material only from regions whose underlying surface is susceptible to an etchant. We show, among other examples, the selective patterning of dopant-modulated Si nanowires with a polymethylmethacrylate (PMMA) mask by leveraging the dependence of KOH etch rate on doping level. We will describe the role of polymerization parameters and post-polymerization etching on the patterning process with a suite of spectroscopy and microscopy techniques. Nanoscale masks produced via the SCALES process can subsequently direct the deposition of the oxides and metals needed to construct complete, fully-functional devices.
(Invited) Multi-Functional Flexible Physical and Chemical Sensor Sheets
Authors: Takei Kuniharu
Published: February 2020

Mechanically flexible and stretchable devices have been attracted much attention for a next class of electronics such as flexible photovoltaics, flexible displays, and wearable electronics. In particular, multiple sensors for potential applications such as wearable healthcare devices and Internet of Things (IoT) concepts are one of the most important components for moving forward to building the flexible sensor system platform. For healthcare application, chemical information such as pH, glucose, sodium ion, and pattaisum ion levles are very important to monitor as well as physical information such as activity, skin temperature, heartbeat, and electrocardiogram (ECG) signals. Furthermore, simultaneous multiple condition monitoring including physical and chemical information is a next class of wearable devices for convienient and safe human life. To address these challenges, in this talk, flexible physical and chemical sensor sheets using mainly inorganic nanomaterials will be introduced by proposing low-cost, macroscale, and multi-functional device integrations. Especially human-interactive flexible sensors to detect human motion, health condition, and room environment information are mainly discussed. In addition to the fundamental sensor characteristics of a strain sensor, a temperature sensor, an ultraviolet sensor, a tactile pressure sensor, and a chemical sensor, integrated device applications with several sensors on a flexible film are demonstrated as proof-of-concepts for multi-functional flexible healthcare sensor sheets.

Although a lot of investigations and developments are still required for practical application as products, these studies may help to open a door for the next step of flexible electronics.
(Invited) Hybrid Nanomanufacturing of Heterostructured Wearable Devices for Self-Powered User Interface
Authors: Wu Wenzhuo
Published: February 2020

The seamless and adaptive interactions between functional devices and their environment (e.g., the human body) are critical for advancing emerging technologies, e.g., wearable devices, consumer electronics, and human-machine interface. The state-of-the-art technologies, however, require a complex integration of heterogeneous components to interface the environmental, mechanical stimulus, which is ubiquitous and abundant in the above applications. These limitations have severely hampered the advancement and broader utilization of related technologies. Moreover, all existing technologies require a power source, which complicates the system design and limits operation schemes.

In this talk, I will discuss our recent progress in developing self-powered human-integrated nanodevices through the hybrid nanomanufacturing of heterostructured nanodevices. This new class of wearable devices are conformable to human skins and can sustainably perform self-powered, non-invasive functions, e.g., physiological monitoring and gesture recognition, by harvesting the operation power from the human body. Such an operation scheme is fundamentally hinged on the polarization induced current term in Maxwell’s displacement current. This research is expected to have a positive impact and immediate relevance to many societally pervasive areas, e.g., biomedical monitoring, consumer electronics, and intelligent robotics.
(Invited) Tunable and Efficient Hot Carrier Generation from Plasmonic Au-Pd Nanoalloy Photocatalyst
Authors: Stofela Sara K.F. , Kizilkaya Orhan , Taheri Mohammad , Leite Tiago R , Shelton William A , Baxter Jason B , Sprunger Phillip T , McPeak Kevin Michael
Published: February 2020

Noble metals are the most studied plasmonic materials due to their chemical stability, small ohmic losses and high DC conductivity. However, the majority of electronic states in the valence band of these metals require at least 2 eV to excite. Therefore, even Au, which is often used for near-infrared hot carrier applications, has a band structure that is not ideal for this low energy wavelength regime. One possible route to improving the efficiency of hot carrier generation in noble metals at near-infrared wavelengths, is to shift their electronic density of states (EDOS) closer to the Fermi level via alloying with a transition metal.

Here, we present the tuning of optical and electronic properties of co-evaporated Au-Pd alloy thin films at different compositions by taking ultraviolet photoelectron spectroscopy (UPS) measurements to represent the EDOS, ellipsometry measurements to show the modulated dielectric function and the calculated plasmonic quality factors, and infrared-pump/THz-probe spectroscopy measurements for studying the dynamics of the hot carrier generation in the near-infrared regime. For comparison, calculated EDOS and hot carrier distributions for these alloys are also shown. Furthermore, we characterized the alloy thin film structural properties by grazing incidence x-ray diffraction (GIXRD).

Our GIRXD results show that all Au-Pd alloy thin films are true alloys (single phase). UPS data supports our initial hypothesis that adding Pd to Au considerably increases the EDOS in the near-infrared region. The calculated hot carrier distribution show that adding Pd to Au increases the number of carriers generated, and that the Au-Pd alloys thin films generate hotter holes than electrons. Finally, time-dependent changes in ∆E/E from 1550 nm-pump/ THz-probe spectroscopy illustrate that for Pd and Au-Pd alloys there is a change in the conductivity attributed to contributions arising from both thermal and nonthermal electron distribution, while for Au there is no evidence of transitions under 1550 nm pump-excitation. We hypothesize this is due to a lower generation rate of hot carriers in Au than for Pd and Au-Pd alloys in the near-infrared regime.
(Invited) Toward Highly Efficient Solar Water Splitting: A Concurrent Electrical, Optical, and Catalytic Design
Authors: He Jr-Hau
Published: February 2020

Energy crisis is a broad and complex global topic. Natural resources such as gas and oil are in limited in supply. Development towards renewable resources is one of the most important technologies in the world. Currently, photocatalytic and photoelectrochemical (PEC) water splitting devices under the irradiation of sunlight have received much attention for the production of renewable hydrogen from water. Solar energy conversion and storage through photoelectrolysis of water using semiconductors as both light absorber and energy converter to store solar energy in simple chemical bond, H2, become highly desirable approaches to solving the energy shortage challenge.

We focus on the effort to develop an efficient Si-based PEC water splitting device. We introduce the surface textured Si heterojunction PEC cell consisting of ultrathin amorphous Si/crystalline Si as efficient and robust photoelectrodes. The solar to hydrogen conversion efficiency has been improved to 13.26%, which is the highest ever reported for Si-based photocathodes. Later on, we design the cascading energy band structure in Si via doping for facilitating carrier separation and novel electrode structures for 360° light harvesting for hydrogen generation with ultrahigh current densities of 61.2 mAcm-2. The cells have been further demonstrated with excellent hydrogen production rate. In addition, our method can significantly improve the stability of Si-based solar cells in water to sustain up to 300 hr. These multifunctional designs provide the potential for the future development in the renewable energy market.
(Invited) Comparison of High Voltage, Vertical Geometry Ga2O3 Rectifiers with GaN and SiC
Authors: Yang Jiancheng , Fares Chaker , Carey Patrick H , Xian Minghan , Ren Fan , Tadjer Marko J. , Chen Yen-Ting , Liao Yu-Te , Chang Chin-Wei , Lin Jenshan , Sharma Ribhu , Law Mark E , Raad Peter E. , Komarov Pavel L. , Smith David J , Kuramata Akito , Pearton Stephen J.
Published: February 2020

There are continuing rapid developments in vertical geometry Ga2O3 for high voltage switching applications. Ga2O3 is emerging as a viable candidate for certain classes of power electronics with capabilities beyond existing technologies due to its large bandgap, controllable doping and the availability of large diameter, relatively inexpensive substrates. These applications include power conditioning systems, including pulsed power for avionics and electric ships, solid-state drivers for heavy electric motors and advanced power management and control electronics.There are already cases where the performance exceeds the theoretical values for SiC. Existing Si, SiC (vertical devices), and heteroepitaxial GaN (lateral devices) enjoy tremendous advantages in terms of process maturity, an advantage that is especially true for Si, where the ability to precisely process the material has resulted in devices such as super-junctions that surpass the unipolar “limit”. Despite these challenges, a compelling case can be made for investigation of UWBG materials. Continued development of low defect substrates, optimized epi growth and surface treatments and improved device design and processing methods for Ga2O3 are still required to push the experimental results closer to their theoretical values. Even 3 µm epi layers with doping concentration of 1016 cm-3 should have a theoretical breakdown voltage of ~1800V. The actual experimental value of VB is currently well below the theoretical predictions. Thermal management is a key issue in Ga2O3 power devices and initial studies have appeared on both the experimental and theoretical fronts. We will summarize progress in edge termination design, temperature measurement using thermoreflectance-based thermography to measure the thermal rise and decay of the active diodes, reverse recovery switching times and develop of large current arrays.
(Invited) Electrical Properties of (100) β-Ga2O3 Schottky Diodes with Four Different Metals
Authors: Jiang Kunyao , Lyle Luke A. M. , Favela Elizabeth , Moody Diamond , Lin Tianxiang , Das Kalyan K. , Popp Andreas , Galazka Zbigniew , Wagner Guenter , Porter Lisa M.
Published: February 2020

Due to its large bandgap (~4.6-4.8 eV), wide range of n-type doping, and single-crystal wafer availability, β-Ga2O3 holds promise for high-efficiency power devices. R&D of β-Ga2O3 has been conducted in Japan for more than a decade; however, funded research programs on this semiconductor material began in the U.S. only five years ago, highlighting its early stage of development. Device development of a semiconductor technology requires the ability to produce suitable ohmic and rectifying (Schottky) contacts. Whereas ohmic and Schottky contacts have been demonstrated on n-type β-Ga2O3, certain characteristics of contacts to β-Ga2O3 differ from contacts to other wide bandgap semiconductors. For example, we found that morphology was problem with many ohmic contact metals, and it was concluded that metal work function is not a dominant predictive factor for forming an ohmic contact to β-Ga2O3 [1]. Furthermore, thermal instability of the standard ohmic contact metallization (Ti/Au) is a concern for operation of devices at elevated temperatures. Schottky contacts to β-Ga2O3 have shown dependence on the orientation, growth method, and choice of metal. For example, on (-201) β-Ga2O3 Schottky barrier heights calculated from I-V measurements were typically between 0.9 and 1.3 eV and displayed little dependence on the metal work function [2]. Our preliminary measurements of selected metals on (100) β-Ga2O3 substrates yielded lower ideality factors and a correlation between barrier height and metal workfunction. The results for Schottky contacts on the (100) surface show some similarities to those previously reported on the (010) surface. In this presentation specific examples of ohmic and Schottky contact metallizations to β-Ga2O3 will provide a platform for more detailed discussion. [1] Y. Yao, R.F. Davis, and L.M. Porter, J. Electron. Mater. 46(4), 2053-2060 (2016). [2] Y. Yao, R. Gangireddy, J. Kim, K. Das, R.F. Davis, and L.M. Porter, J. Vac. Sci. Technol. B 35(3), 03D113.1-7 (2017).
(Invited) Modeling Mechanical Behaviors and Lifetime of a Polymer Electrolyte Membrane in Fuel Cell Dynamic Operations
Authors: Hasan Morshed , Goshtasbi Alireza , Chen Jixin , Santare Michael H , Ersal Tulga
Published: February 2020

Mechanical failure of a polymer electrolyte membrane (PEM) such as pin-hole and delamination has been identified as a major degradation source in a PEM fuel cell. The hydration/dehydration cycles of a membrane during the fuel cell operation, and the resulted mechanical stress, are in general responsible for the mechanical failures. For example, the cyclic mechanical stressor has shown a significant role in propagating a crack through the thickness of a membrane [1], although there is also the synergistic acceleration from the chemical stressor [2]. It is of interest to thoroughly investigate the mechanical behaviors of a membrane under in-situ cyclic conditions, so that alleviating strategies focusing on the fuel cell operating conditions could be developed.

We have interfaced a two-dimensional transient fuel cell transport/performance model in Comsol [3] with a viscoelastic-plastic membrane mechanical model in the fuel cell geometry [4]. Using the combined model we have studied the impacts of dynamically cycling hydration, current and voltage on a membrane [5]. Furthermore, we have developed a model-based method to predict the crack propagation rate. It is expected that the crack propagation rate could be used as a metric to differentiate various dynamic driving cycles from the mechanical durability aspect, thereby creating a pathway to a transfer function for mechanical durability. The modeling results will be validated with RH cycling data. The role of the chemical stressor will also be discussed in using this mechanical durability transfer function.

References:

[1] G, Ding, M. Santare, A. Karlsson, and A. Kusoglu, “Numerical evaluation of crack growth in polymer electrolyte fuel cell membranes based on plastically dissipated energy”, Journal of Power Sources 316, 114-123 (2016).

[2] A. Kusoglu and A. Weber, “Electrochemical/Mechanical Coupling in Ion-Conducting Soft Matter”, Journal of Physical Chemistry Letters 6, 4547−4552 (2015).

[3] A. Goshtasbi, P. Garcia-Salaberri, J. Chen, K. Talukdar, D. Sanchez, and T. Ersal, "Through-the-Membrane Transient Phenomena in PEM Fuel Cells: A Modeling Study." Journal of The Electrochemical Society, Under Review.

[4] N. Khattra, A. Karlsson, M. Santare, P. Walsh, and F. Busby “Effect of time-dependent material properties on the mechanical behavior of PFSA membranes subjected to humidity cycling”, Journal of Power Sources 214, 365-376 (2012).

[5] M. Hasan, A. Goshtasbi, J. Chen, M. Santare, and T. Ersal, "Model-Based Analysis of PFSA Membrane Mechanical Response to Relative Humidity and Load Cycling in PEM Fuel Cells." Journal of The Electrochemical Society, 165(6), F3359-F3372 (2018).
Development of Hydrophobic Coating for Gas Diffusion Media in PEM-Based Electrochemical Hydrogen Pump
Authors: Lee Myoungseok , Huang Xinyu
Published: February 2020

Anode flooding is one of the critical issues in proton exchange membrane (PEM)-based electrochemical hydrogen pump. One way to to mitigate it is to make the gas diffusion media highly hydrophobic. The coating mateirals much be compatible with other critical materials in the PEM electrolyzer.. It was discovered that a mixture of Nafion™ and oxidized carbon nanotubes (O-CNT) coated onto the porous gas diffusion medium can render it hydrophobic with an effective contact angle of 130°. Electrochemical pump testing has shown that, with the help of the coating, the flood-recovery performance of the hydrogen pump was greatly improved. A hydrogen pump cell with an uncoated GDL was not able to recover from a flooded state, while a hydrogen pump cell with a coated GDL was able to recover its performance within 100 secs.
Improved Methods for Simultaneous Neutron and X-Ray Tomography of Operating Fuel Cells
Authors: LaManna Jacob M , Hussey Daniel S , Baltic Elias , Jacobson David L
Published: February 2020

Neutrons and X-rays provide complementary, non-destructive information on the operating conditions inside fuel cells. As previously reported, NIST has developed a fuel cell to facilitate simultaneous, multimodal tomography on the Neutron and X-ray Tomography (NeXT) system at the NIST Center for Neutron Research. The original cell design served as a developmental testbed but suffered several drawbacks such as CT artifacts caused by cell design and scan parameter choices and long, 18 hour tomography scans where the cell would need to operate at steady-state. Multiple improvements to the NeXT system and the tomography reconstruction workflow has resulted in a reduction of scan times down to as low as 4 hours with a reduction in CT artifacts. The improvements to reconstruction quality and the development of registration and segmentation tools that work on the multimodal datasets allows for the tracking of the gas diffusion layer – catalyst layer interfaces. This will improve the conversion of measured water thickness to saturation as local compression effects and MEA waviness can be accounted for. A new cell design to further reduce reconstruction artifacts and a new method for hybrid high resolution radiography and tomography will be discussed.
Investigation of Gas Transport Properties of PEMFC Catalyst Layers by Using a Microfluidic Device
Authors: Suzuki Takahiro , Nakata Yasuhiro , Tsushima Shohji
Published: February 2020

Gas transport properties of catalyst layers (CLs) used in proton exchange membrane fuel cells (PEMFCs) are one of the important factors which affects cell performance. The gas transport properties are strongly affected by the porous structure of the CLs. In this study, a measurement system of gas diffusion flux through the CLs by using a microfluidic device was developed. Parallel channels were made on a Si chip by microfabrication techniques. Air and nitrogen were supplied to the two parallel channels in the device, respectively. Oxygen was transferred to a nitrogen flow channel through the CL under a rib between the two channels. Oxygen partial pressure in the nitrogen flow channel was measured at the outlet of the channel by using an optical oxygen sensor. The porous structure of the measured CLs was characterized. Effective gas diffusivity and tortuosity factor of the CLs can be calculated based on the measured gas transfer and porous structure properties.

Several types of CLs were fabricated and characterized. The thickness and overall porosity of the CLs were evaluated from scanning electron microscopy and weight measurement. Pore size distribution and effective porosity were evaluated by using nitrogen physisorption measurement. Then effective diffusivity of CLs can be calculated by measuring oxygen partial pressure at the inlet and outlet of the flow channel. The CL, which has 1.0 of ionomer to carbon ratio, was evaluated. Oxygen partial pressure at the outlet of the nitrogen flow channel decreases with flow rate as shown in Figure 1. Effective gas diffusivities obtained from each flow rate showed almost constant value. Tortuosity factor was calculated from the effective diffusivity and measured structural properties and indicated around 3. This evaluation method was applied to the CLs containing a different type of carbon materials, which show different porous structure. Adding multi-walled carbon nanotube in the CL(1) instead of carbon black resulted in an increase of effective gas diffusivity, while geometrical porosity was decreased.

Acknowledgments

A part of this work was financially supported by JSPS KAKENHI Grant Number 16K18028. This study was supported by Osaka University Nanofabrication Platform [F-18-OS-0006] in Nanotechnology Platform Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

References

T. Suzuki, R. Hashizume and M. Hayase, J. Power Sources, 286, 109 (2015).

Figure 1
Structuring GDL’s for Improved Water Management
Authors: Csoklich Christoph , Schmidt Thomas J. , Büchi Felix N.
Published: February 2020

In polymer electrolyte fuel cells, at high current densities, water management in gas diffusion layers (GDL) is a potentially limiting process. Liquid water present in the void space of the GDL increases the tortuosity of the gas transport path from channel to catalyst layer and thus the mass transport overvoltage increases. The concept of improving water management in GDL by mechanical structuring is already 10 years old1, though it’s potential has not been systematically assessed, and therefore not been exploited yet. This work aims at exploring the fundamental understanding of regularly perforated GDL’s (see Figure 1a/b) by a systematic performance analysis under different cell operating conditions. Figure 1c shows an exemplarily cell performance analysis for different operating conditions for Toray 060 TGPH GDL with the perforations given in Figure 1 a/b. Experiments shown are for GDL without MPL, more conditions and underlying systematics will be discussed in the presentation.

1. Gerteisen, D., Heilmann, T. and Ziegler, C. Enhancing liquid water transport by laser perforation of a GDL in a PEM fuel cell. J. Power Sources,
177, 348–354 (2008).

Figure 1
Water Transport in the Gas Diffusion Layer of PEM Fuel Cells: An Energy Approach
Authors: Herescu Alexandru
Published: February 2020

The design of a fibrous gas diffusion layer (GDL) that manages water effectively over the full range of fuel cell operating conditions has to account for the morphology of the gas-liquid interfaces under complex geometrical and wetting configurations, encountered within the fiber matrix. An energy minimization approach is taken to capture the interface evolution of water breaking through the pores. Water in contact with fibers can take the shape of an axisymmetric or non-axisymmetric droplet depending on the fiber diameter, the droplet volume and the contact angle. The energy barrier between the two morphologies as well as the percolation pressure of water through the pores, are determining factors in the process of liquid fingers formation. We consider a droplet breakthrough model which sets the contact line delimiting the protruding gas-liquid interface along both wetting and non-wetting fibers, yielding mixed wetting conditions. The breakthrough pressure of water through a mixed wetting pore is determined to be 40% larger than through a wetting pore, a ratio which is consistent with experimental results. ESEM images indicate that the model captures accurately the interface evolution while accounting for the specific geometrical features and wetting properties of the GDL. It is advantageous to corroborate a realistic pore model such as the one proposed in this study, with existing models including the pore network model to characterize and design optimal transport features of the porous medium.
Electrochemical Impedance Diagnosis of Abnormal Operational Conditions for Reliability of Polymer Electrolyte Fuel Cells in Marine Power Application -Sea Salt Contamination-
Authors: Nakajima Hironori , Kitahara Tatsumi , Dan Kenta
Published: February 2020

Polymer electrolyte fuel cells (PEFCs) for marine vessels have been expected to reduce the pollutant emissions on the sea. Since marine PEFCs operate under harsh conditions, such as ship vibrations and sea salt exposure, the diagnosis of abnormal operational conditions is of a great importance to improve the reliability and durability of PEFCs in marine power application. Electrochemical impedance spectroscopy (EIS) is a technique suitable for real-time diagnosis of PEFCs in operation. In the present study, EIS was used to assess the factors to determine the performance of PEFCs, namely operating temperatures, cathode fed air conditions of relative humidity, flow rates and sea salt (NaCl) contamination. EIS spectra were obtained through Fast Fourier Transform (FFT) EIS techniques, while a transmission line model (TML) with the ohmic resistance of the ionomer was used as an equivalent circuit for the analysis. Under conditions of dehydration (dry-up), we observed an increase in the ionomer/electrolyte membrane ohmic resistances and the charge transfer resistance. When liquid water was excessive (flooding), mass transfer resistance drastically increased in the cathode. All resistance also increased after NaCl solution was injected into the cathode inlet. In particular, charge and mass transfer resistances were the main factors that led to an increase in the polarization loss. Injecting distilled water after detecting NaCl contamination at an earlier stage is effective to mitigate irreversible degradation.
Effect of Ionomer Solvents for Pore Size Control of Imidazolium-Base Ionomers in Aemfc
Authors: Park Hyun Jin , Lee So Young , Kim Hyoung-Juhn , Lee Young Moo
Published: February 2020

Anion exchange membrane fuel cells (AEMFCs) have a low activation overvoltage due to the fast oxygen reduction reaction (ORR) response to alkaline conditions compared to the acidic condition of proton exchange membrane fuel cells (PEMFCs). The reasons for low activation overvoltage in AEMFCs are diversely studied. Recently, the binder ionomer in the catalyst layer of polymer electrolyte membrane fuel cells has attracted increasing attention because of its critical role in power performance and the durability of the catalyst layer. Ionomer covers the catalyst surfaces, providing anion transport between the catalyst surfaces and the membrane, as well as mechanical connection. Several requirements as a binder are to have high ion conductivity, gas permeability, and electron conductivity. For durability of membrane electrode assembly (MEA), the binder must have high oxidative stability, and mechanical integrity, less excessive swelling is detrimental. Unususally as AEMs and binder materials, functional groups such as quaternary ammonium (QAs), phosphonium, guanidinium, tertiary sulfonium, pyridinium, and imidazolium ionic liquid (IILs) are used as cation groups. Among them, the QAs has higher chemical and thermal stability than phosphonium, guanidinium and tertiary sulfonium ions. However, the QAs groups tend to be degraded by OH- counterion in high pH environments. In this study, we prepared a binder using IILs instead of the commonly used QAs. Imidazolium-based binders are uncomplicated to design the polymer and easy to synthesize. Furthermore, effect of different alcohols in ionomer binder solution on the shale and pore size of catalyst layer is presented here. The aim of this study is to find out the effect of alcohols in binder ionomers for alkaline fuel cell performance.

Figure 1
Entrance Effects on the Flow Distribution in Manifold of Commercial-Size Proton Exchange Membrane Fuel Cell Stacks
Authors: Huang Fuxiang , Qiu Diankai , Peng Linfa , Lai Xinmin
Published: February 2020

The air flow distribution in manifold is critical to the performance of commercial-size proton exchange membrane fuel cell (PEMFC) stack. Most of the existing works focus on the optimization of cell part of PEMFC stack ignoring the entrance effects, which cannot reflect the real situation of the working PEMFC stack. In this study, CFD model is employed to study the entrance effects on the flow distribution in manifold of PEMFC stack. A novel experiment setup is developed, which based on a 200-cell PEMFC stack with thin stamped bipolar plates and an active area of 256 cm2. The air flow distribution in manifold with different inlet pipe diameters are measured by experiments to validate the CFD model. Different of inlet pipe diameters and end plate inlet configurations are considered in the CFD model. The flowfield and flow rate distribution in manifold are obtained to evaluate the entrance effects on the flow distribution in manifold. The numerical results show that both of the inlet pipe diameter and end plate inlet configuration have great effects on the flow distribution in the manifold of commercial-size PEMFC stack, and a judicial matching of their configuration can provide the ideal uniform flow distribution. In addition, we determined the inlet pipe diameter and end plate inlet configuration of a 35 kW-class PEMFC stack that comprises 200 cells. The experimental results and numerical analysis are beneficial to optimization of commercial-size PEMFC stack design.

Figure 1
PEMFC Catalyst Testing: From RDE to GDE Setup
Authors: Arenz Matthias , Inaba Masanori , Du Jia , Zana Alessandro , Jensen Anders Westergaard , Sievers Gustav Wilhelm , Escudero-Escribano María
Published: February 2020

The thin film-rotating disk electrode (TF-RDE) method is the standard method for screening the performance of electrocatalysts for polymer electrolyte membrane fuel cells (PEMFCs). It is fast and requires only small amount of catalysts, however, the measured activity not only depends on the intrinsic catalyst properties, but also ink and catalyst film properties, respectively [1, 2]. In addition, the RDE method has an inherent limitation of low reactant mass transport, which limits the accessible reaction rates and potential ranges. This limitation makes it difficult to predict the performances of the catalysts in membrane electrode assembly (MEA) where much higher mass transport is required and higher overpotentials are applied.

Recently, we introduced a new half-cell configuration aiming to bridge the gap between the RDE method and MEA, a gas diffusion electrode (GDE) setup [3, 4] that combines the strength of TF-RDE method and at the same time alleviates its weakness (i.e. low reactant mass transport).

In the presentation, the two approaches, TF-RDE and GDE measurements are compared and their weaknesses and strengths in measureing activity and stability of PEMFC catalysts discussed. Benchmark data and best practise guidlines are given.

[1] M. Inaba et al., Journal of Visualized Experiments, 2018, e57105

[2] M. Inaba et al., Journal of Power Sources, 2017, 353, 19-27

[3] G.K.H. Wiberg et al., Review of Scientific Instruments, 2015, 86 (2), 024102

[4] M. Inaba et al., Energy & Environmental Science, 2018, 11, 988-994
Kinetic Isotope Effect of the Oxygen Reduction Reaction on Carbon-Supported Platinum Electrocatalysts
Authors: Rezaei Talarposhti Morteza , Asset Tristan , Dai Sheng , Artyushkova Kateryna , Zenyuk Iryna V. , Atanassov Plamen
Published: February 2020

Proton exchange membrane fuel cells (PEMFC) can partially satisfy the energy need with the least anthropogenic impact on nature. However, they suffer from great costs, partly induced by their expensive catalytic material, platinum, necessary to catalyze the oxygen reduction reaction (ORR) occurring at the cathode. Hence, it becomes essential to either synthesize electrocatalysts without platinum1, or to maximize the performance of the fuel cell per unit mass of platinum2 by increasing the exposure of its active sites for the ORR.3 We studied the oxygen reduction reaction (ORR) mechanism on Pt nanoparticles (NPs) supported on several Vulcan-type carbon blacks with various physicochemical characteristics. Those materials were thoroughly investigated by various microscopic, spectroscopic and electrochemical methods, such as kinetic isotope effect (KIE) studies. KIE studies were used to assess an eventual change of the rate determining step (RDS). The rate constants of the RDS were calculated in 0.5M H2SO4 and 0.5M D2SO4 at the onset potential. The KIE values are reported in Figure 1, as a function of Scarbon/SPt,H
. Scarbon/SPt,H
corresponds to the ratio between the carbon specific surface and the platinum electrochemically active surface and acts as an indicator of the Pt NPs density onto the carbon surface. A low Scarbon/SPt,H
shows KIE = 1, which corresponds to what is commonly observed on Pt electrocatalysts for the ORR and implies that the rate determining step is proton independent.4 An identical value was observed on the commercial Pt/C (40 wt. % on Vulcan XC72R carbon, i.e. with the high density of Pt NPs), i.e. KIE = 1.11 ± 0.08. At high Scarbon/SPt,H
a KIE = ca. 1.5 is observed, hence, providing evidence for a shift from a proton independent to a proton dependent mechanism with the increase of the Scarbon/SPt,H
: the involvement of the proton in the ORR RDS is dependent on the density of Pt NPs on the electrocatalyst surface.

(1)Chen, Y.; Asset, T.; Lee, R.; Artyushkova, K.; Atanassov, P. J. Phys. Chem. C 2019, acs.jpcc.9b01480.

(2)Robson, M. H.; Serov, A.; Artyushkova, K.; Atanassov, P. Electrochim.
Acta 2013, 90, 656–665.

(3)Matanović, I.; Garzon, F. H.; Henson, N. J. J. Phys.
Chem. C 2011, 115 (21), 10640–10650.

(4)Tse, E. C. M.; Varnell, J. A.; Hoang, T. T. H.; Gewirth, A. A. J. Phys. Chem. Lett. 2016, 7 (18), 3542–3547.

Figure 1
Platinum Nanoparticles on Plasma-Pretreated Carbon Nanotubes Prepared By Atomic Layer Deposition As Polymer Electrolyte Membrane Fuel Cell Catalysts
Authors: Koo Junmo , Kim Dong Hwan , Kang Eun Heui , Shim Joon Hyung
Published: February 2020

Polymer electrolyte fuel cells (PEMFC) are attracting attention as the next generation power supply for electric vehicles, unmanned aerial vehicles and submarines. However, the high price of fuel cell catalysts i.e. platinum (Pt) or platinum alloys is considered a major hurdle to the development of economical fuel cell electric vehicles. Another problem with Pt catalysts is the low stability of long term operation due to separation and aggregation of the catalyst from the carbon support resulting from repeated on-off switching. Recently, atomic layer deposition (ALD) has been proposed as a technique for synthesizing metal nanoparticles. ALD is considered to be the most advanced deposition technology that can control material size and composition in the atomic scale. In addition, ALD has demonstrated large scale conformal deposition of uniform films and particles over high aspect ratio trenches and complex three dimensional contours. In this study, Pt nanoparticles were successfully deposited on carbon nanotubes (CNTs) by ALD. The key to the success of high quality ALD Pt production has been found to be a plasma pretreatment that introduces functional groups that make the CNT surface ready to initiate the ALD nucleation. ALD Pt-CNT catalysts were evaluated as cathode catalysts for PEMFC membrane-electrode-assemblies (MEAs). As a result, even though the Pt load is significantly reduced, the performance is significantly improved compared to commercial PEMFC MEAs in terms of power and stability.