bluuebunny/crossref_metadata_2025 huggingface dataset:
Advanced Skutterudite-Based Unicouples for a Proposed Enhanced Multi-Mission Radioisotope Thermoelectric Generator: An Update
Authors: Chi Ike Suchih , Smith Kevin , Huang Chen-Kuo , Firdosy Samad , Yu Kevin , Phan Brian , Sujittosakul Sutinee , Li Billy Chun-Yip , Paik Jong-Ah , Gogna Pawan , Chanakian Sevan , Ni Jennifer , Aranda Michell , Pinkowski Stanley , Hendricks Terry , Fleurial Jean-Pierre , Caillat Thierry
Published: February 2020

Radioisotope Thermoelectric Generators (RTG’s) have been used on several NASA missions when they enable or significantly enhance the ability of a mission to meet its objectives. The current state-of-the-art RTG power source, Curiosity rover’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), has operated for more than one Martian year (687 earth days) on the red planet. In order to increase the power and conversion efficiency of future MMRTG systems and extend the lifetime of future rover missions, an effort was started in 2013 to mature advanced thermoelectric technology for use in a proposed Enhanced Multi-Mission Radioisotope Thermoelectric Generator (eMMRTG). The conceptual design approach of the eMMRTG is to replace the heritage MMRTG couples in the thermoelectric module assembly with more advanced skutterudite (SKD)-based couples without any significant design changes to the generator. The new SKD thermoelectric materials not only can provide higher thermoelectric performance, but also can operate at higher maximum operating temperature than MMRTG thermoelectric materials. As a result, the proposed eMMRTG would preserve all the MMRTG’s multi-mission capability while offering an expected enhancement in power, relative to MMRTG, of about 25 % at beginning-of-life and potentially lower power degradation rates leading to a ≥ 50% increase in power at end-of-design life (17 years) with an 80W power output goal at 17 years. Here, we will report on the progress for demonstrating manufacturability and validating performance of these advanced SKD unicouples jointly developed and tested by Jet Propulsion Laboratory (JPL) and Teledyne Energy Systems, Inc. (TESI).
High Efficient Thermoelectric Materials with Embedded Nanostructures By Electrochemical Synthesis
Authors: Kim Jiwon , Myung Nosang Vincent , Lim Jae-Hong
Published: February 2020

The thermoelectric (TE) energy-conversion efficiency of TE materials has been steadily improved over recent decades. This efficiency is expressed in terms of a dimensionless number zT = S2σT/k, which is simply referred to as the figure-of-merit, where S is the Seebeck coefficient, σ is the electrical conductivity, k is the thermal conductivity, and T is the absolute temperature. Limited success at increasing zT has been achieved by focusing on k reduction, which is thought to increase phonon scattering by incorporating complex lattice structures, such as superlattices, heterostructures, and nanocomposites, into the material. For some materials, k can be reduced to a minimum by placing the substance in an amorphous state; however, this behavior is typically associated with a substantial decrease in the charge carrier mobility and, therefore, in σ. This strong interdependence among the key parameters of zT has delayed the release of new high-zT TE devices for use in industry. Therefore, this study adopts a different approach, which focuses on controlling the mechanisms and processes that tend to de-couple the key parameters and maximize the zT numerator. Particular attention is paid to mechanisms that optimize the power factor (P.F.), which is equal to σS2. In this work, we tailored nanocomposite embedded structure in Bi-Te and Sb-Te based films, resulting in allowed the realization of intriguing TE performance based on interfacial energy-barrier scattering. The TE performance of nanocrystalline films is optimized by tailoring the Vb employed in the energy-filtering mechanisms in two positions: 1) at the grain boundaries of the single-phase nanocrystalline films and 2) at the interfaces of the hetero-nanocomposites. More details will be presented
(Invited) Zintl Phase Thermoelectrics: Engineering Transport through Crystal Chemistry
Authors: Zevalkink Alexandra
Published: February 2020

Intermetallic Zintl phases form complex composite structures characterized by covalently-bonded polyanions stabilized by the surrounding cations. The Zintl polyanions occur in an astounding variety of forms, including isolated 0-dimensional clusters, 1-D chains, and 2-D slabs, making this an ideal class of compounds to study structure-property relationships in complex semiconductors. AM
2
X
2 compounds in the CaAl2Si2 structure type are one of the most successful classes of Zintl thermoelectrics - particularly in light of recent reports of zT ~ 1.5 in n-type MgMg2Sb2. This talk will explore the role played by the defect chemistry of AM
2
X
2 compounds. We have shown both experimentally and using first principles calculations that the low formation energy for cation vacancies in this structure type enables tuning of the electronic properties via either alloying or by directly varying the cation content. In addition, by using high pressure, we have investigated the transport properties of AM
2
X
2 compounds synthesized using high pressure. While AM
2
X
2 compounds in the CaAl2Si2 structure are typically narrow gap semiconductors, those in the related tetragonal BaZn2P2 structure type are exclusively metals or semimetals and are known to exhibit superconductivity. In the first example of a phase transition between these two technologically important structures types, we show that SrAl2Si2 (trigonal CaAl2Si2-type structure at ambient pressure) can be obtained as a metastable phase in the tetragonal BaZn2P2 structure type by employing high-pressure, high-temperature synthesis. Our study shows that the changes in the electronic density of states lead to the emergence of phonon-driven superconductivity in the tetragonal polymorph. By accessing structural motifs that are not thermodynamically stable at ambient conditions, we are thus able to directly investigate the relationship between structure and electronic properties in AM
2
X
2 Zintls.
Design and Application of Strained Interface Heterostructures in Resistive Switching Devices
Authors: Bowman William J , Schweiger Sebastian , Pfenninger Reto , Izadi Ehsan , Darbal Amith , Crozier Peter A , Rupp Jennifer L. M.
Published: February 2020

Resistive switching memories operating on ionic carriers are considered as next generation storage-class memories to replace electronic transistor memory technologies. Strain engineering is a relevant optimization route to introduce defects for resistive switching materials based on mixed ionic-electronic conducting oxides. Interfacial strain control of electrical conductivity [1] was reported for sideways-contacted Gd0.1Ce0.9O2-δ|Er2O3 (GCO|ERO) microdot heterostructures with alternating monolayers of insulating ERO and mixed-conducting GCO, whose lattice mismatch yielded compressive strain in the GCO layers.

We use ionic heterostructures as strain-modulated memristive devices based on the model system GCO|ERO to tune the property of “memristance.” Modulation of interfacial strain and interface count is used to engineer the Roff/Ron ratio and the system’s persistence [2]. By employing Raman microscopy and TEM on heterostructures with a range of monolayer thickness down to 3-5 nm, we observed an evolution in the near-order crystal symmetry from a mostly relaxed isotropic structure—present in devices with ~100 nm monolayers, to predominantly anisotropic strain fields in devices with monolayers of several nm. Resistive switching in these model systems is discussed.

Via sideways contacting, unique model experiments isolate the impact of electroforming on a symmetric device, revealing that reversing the electroforming polarity mirrors the memristive response about zero volts without affecting memristance. In addition to GCO|ERO we explore alternative insulating straining oxides which impart varying degrees of tensile strain on GCO. Strain mapping via TEM precession-enhanced electron nanodiffraction resolves lattice distortion in these systems with nanometer spatial resolution, and strain data are correlated with interface composition and electronic structure measured by electron energy-loss spectroscopy, providing atomic-level insights regarding strained heterostructure design [3].

Acknowledgements

We acknowledge ScopeM at ETH Zürich and the John M. Cowley Center for High Resolution EM at ASU, and thank the staff for their support.

References

[1] S. Schweiger, M. Kubicek, F. Messerschmitt, F. Murer, J.L.M. Rupp. ACS Nano 8 (2014) 5032

[2] S. Schweiger, R. Pfenninger, W.J. Bowman, U. Aschuauer, J.L.M. Rupp. Adv. Mat. (In press)

[3] W.J. Bowman, S. Schweiger, E. Izadi, A.D. Darbal, J.L.M. Rupp, P.A. Crozier. (In preparation)
(Keynote) Current and Future Directions in Power Electronic Devices and Circuits Based on Wide Band-Gap Semiconductors
Authors: Kizilyalli Isik C. , Cunningham Daniel W , Manser Joseph S. , Carlson Eric P
Published: February 2020

Electricity generation currently accounts for 40% of primary energy consumption in the U.S., and over the next 25 years is projected to increase more than 50% worldwide.  Electricity continues to be the fastest growing form of end-use energy. Power electronics are responsible for controlling and converting electrical power to provide optimal conditions for transmission, distribution, and load-side consumption. Estimates suggest that the fraction of electricity processed through power electronics could be as high as 80% in the US by 2030 (including generation and consumption), approximately a twofold increase over the current proportion. Development of advanced power electronics with exceptional efficiency, reliability, functionality, and form factor will provide the U.S. with a competitive advantage in deployment of advanced energy technologies. Additionally, widespread integration of innovative converters offers substantial energy saving opportunities both directly, by inherently more efficient designs, and indirectly, by facilitating higher levels of adoption for fundamentally higher performing materials. High impact opportunities exist across a variety of applications, including power supplies, motor drives, automotive (including DC fast charging infrastructure), data centers, and aerospace, as well as grid and distributed energy resources (wind, solar PV, MV/HVDC, FACTS). Fast switching power semiconductor devices are the key to increasing the efficiency and reducing the size of power electronic systems. For the last three decades, silicon power devices (MOSFETS, IGBTs, and diodes) have dominated the power device market. During this time there have been tremendous improvements in silicon power device performance. However, these devices are now approaching the physical limits of silicon. Alternative wide-band gap semiconductor materials, such as silicon carbide (SiC) and gallium nitride (GaN) are enabling a new generation of power devices that will far exceed the performance of silicon-based devices. Wide band-gap semiconductors enable continued improvement of the efficiency and reduced system size of power electronics. In this presentation, future directions in emerging wide bandgap semiconductor devices will be discussed. Furthermore, we will discuss the development and deployment of a new class of efficient, lightweight, and reliable power converters through transformational advances in circuit topologies, advanced control and drive electronics, and innovative packaging.
(Invited) The Current Status and Future Prospects of SiC Devices
Authors: Sung Woongje
Published: February 2020

Although silicon power devices have served well as the key technology for power electronics for several decades, silicon-based technology is reaching its physical limits, in terms of power handling and switching frequency capabilities. Thanks to its superior material properties, SiC is the most promising post-silicon alternative for high voltage, high frequency, and high temperature power conversion applications. Since the advent of the first SiC Schottky Barrier Diode (SBD) in the 1990’s, numerous research groups have devoted their efforts to commercialize SiC devices such as MOSFETs, JFETs, and Thyristors. In this talk, issues regarding current SiC devices and processing technology will be identified and future research directions will be discussed.
Fabrication of Deep 4H-SiC Microstructures Via Inductively Coupled SF6/O2 Plasma
Authors: Luna Lunet E , Tadjer Marko J. , Myers-Ward Rachael L. , Anderson Travis J , Hobart Karl D , Kub Francis J
Published: February 2020

High aspect ratio deep reactive ion etching (DRIE) of single-crystalline silicon carbide (SiC) holds promise for fabricating next-generation harsh-environment (e.g. high temperature, high power, reactive environments) micro- and nanoelectromechanical systems (MEMS/NEMS). However, unlike Si, SiC microfabrication via DRIE remains in its infancy. In particular, high aspect ratio SiC DRIE poses a significant challenge in SiC MEMS development. To tackle this issue, SiC DRIE process parameters (e.g. cycle time, power, backside substrate cooling) were investigated to achieve high aspect ratio SiC microstructures with close to vertical sidewalls. Overall, the SiC processing work described here helps to bridge the knowledge gap between Si and SiC microfabrication and support the adaption of single-crystalline SiC-based micro- and nanodevices.
(Invited) Vertical GaN Devices Enabled By Selective Area P-Type Doping
Authors: Koehler Andrew D. , Anderson Travis J , Nath Anindya , Jacobs Alan G , Tadjer Marko J. , Feigelson Boris , Goorsky Mark S. , Hobart Karl D , Kub Francis J
Published: February 2020

A key element for enabling high performance vertical GaN power electronic devices is the capability to realize selective area p-type doping. The ability to arbitrarily define p-type regions through ion implantation eliminates the need for epitaxial regrowth on etched surfaces, which is currently a well-known technological roadblock. However, activation of implanted Mg is also a challenge, since activation of the Mg acceptors requires annealing at temperatures above the thermodynamic stability limits of GaN in atmosphere. Implementing the symmetric multi cycle rapid thermal annealing (SMTRA) technique has been shown to activate up to ~10% of the implanted Mg dopant atoms. This technique includes a temporary thermally stable capping layer, annealing in a nitrogen overpressure, and performing a well-optimized annealing temperature profile including multiple spike anneals. Vertical GaN junction barrier Schottky (JBS) diodes and Schottky barrier diodes (SBDs) with implanted junction termination extension (JTE) are demonstrated using the SMRTA process, as are process module development toward trench MOSFET devices.
(Invited) Engineering Metal Oxide Semiconductors for Flexible Electronics
Authors: Martins Rodrigo
Published: February 2020

Metal oxides are contributing for generating a free real state electronics that is able to add new electronic functionalities onto surfaces, which currently are not used in this manner and where silicon cannot contribute [1,2]. The already high performance developed n- and p-type TFTs have been processed by physical vapor deposition (PVD) techniques like rf magnetron sputtering at room temperature which is already compatible with the use of low cost and flexible substrates (polymers, cellulose paper, among others). Besides that a tremendous development is coming through solution-based technologies very exciting for ink-jet printing. In this presentation we will review some of the most promising new technologies for n- and p-type thin film transistors based on oxide semiconductors and its currently and future applications.

Moreover, we will refer also to the exploitation of cellulose-based hydrogel as dielectric in TFT on paper as well as to the engineering procedures governing the selection or development of printable nanostructured metal oxide nanoparticles for chromic, photovoltaic, photocatalytic, sensing, electrolyte-gated TFTs, and power storage applications.

Figure 1
Amorphous Nanorod Boron As Anode Material for Lithium Ion Batteries at Room Temperature
Authors: Lau Miu Lun , Deng Changjian , Barkholtz Heather Marie , Xu Tao , Liu Yuzi , Wang Hao , Connell Justin Grant , Parrish Riley , Smith Kassiopeia , Xiong Hui (Claire)
Published: February 2020

We report an amorphous boron nanorod anode material for lithium ion batteries prepared through smelting non-toxic boron oxide in liquid lithium. Boron in theory can provide capacity as high as 3099 mAh g-1 by alloying with Li to form B4Li5.1 However, experimental studies of boron anode were rarely reported for room temperature lithium-ion batteries. Among the reported studies the electrochemical activity and cycling performance of bulk crystalline boron anode material are poor at room temperature. In this work, we developed amorphous nanostructured one-dimensional (1D) boron material aiming at improving lithium ion diffusion in boron at room temperature. The amorphous boron nanorod anode exhibited, at room temperature, a reversible capacity of 170 mAh g-1 at a current rate of 10 mA g-1 between 0.01 and 2 V. The anode also demonstrated good rate capability and cycling stability. Lithium storage mechanism was investigated by both sweep voltammetry measurements and galvanostatic intermittent titration technique (GITT). The sweep voltammetric analysis suggested that the contributions from lithium ions diffusion into boron as well as the capacitive process are 57% and 43%, respectively. Results from GITT indicated that the discharge capacity at higher potentials (> ~ 0.2 V vs, Li/Li+) could be ascribed to a capacitive process and at lower potentials (< ~0.2 V vs, Li/Li+) to diffusion control. Solid state nuclear magnetic resonance (NMR) measurement further confirmed that the capacity is from electrochemical reactions between lithium ions and the amorphous boron nanorod.

References:

1. M. Worle and R. Nesper, Angew Chem Int Edit, 2000, 39, 2349-2353.

Figure 1
(Invited) Solution-Processed Charge Transfer Doping of Transition-Metal Dichalcogenides (TMDs) with Redox-Active Molecules
Authors: Zhang Siyuan , Hacker Christina A. , Pookpanratana Sujitra
Published: February 2020

The promise of flexible, stretchable, and transparent circuitry has driven intense research in carbon-based and two-dimensional (2D) material-based electronics, such as organic semiconductors, graphene and transition-metal dichalcogenides (TMDs). For integrated circuits applications consisting of CMOS, p-n diodes and other logic components, both n-type and p-type semiconductors are equally important. Controlled doping of two-dimensional semiconductors promises a powerful tool to tailor their electrical and optical properties toward next generation electronic and optoelectronic devices. In this study, solution-processed charge transfer doping of four transition metal dichalcogenides MX2, where M is either Mo or W and X either S or Se, is achieved using molecular reductants and oxidants. Sub-hundred-micron size (ca. 50 to 100 μm) of MX2 were exfoliated via gold-mediated transfer technique.1 The doping type and strength can be conveniently controlled by the redox potential of the metal-organic molecules, the concentration of dopant solutions and treatment time.2 The doping effects are observed through the evolution of electrical characteristics of MX2 field effect transistor devices. I-V characteristics of MX2 field effect transistor (FET) devices treated with both p- and n-dopants are measured, from which the charge carrier densities induced by the doping were estimated. Detailed physical characterizations including photoemission (UPS and XPS), Raman and photoluminescence (PL) spectroscopy are used to study the doping effect and to understand the underlying mechanism. The origin of the doping is attributed to the shift of Fermi level and work function through the charge transfer process between molecular dopants and 2D semiconductors. Overall, we have demonstrated a solution-based charge transfer doping using molecular oxidants and reductants to p- or n-dope several 2D semiconductors. This technique provides a simple yet effective route to tailor the band structure of the 2D materials, and control the resulting electrical and optical properties.

References

(1) Desai, S. B.; Madhvapathy, S. R.; Amani, M.; Kiriya, D.; Hettick, M.; Tosun, M.; Zhou, Y.; Dubey, M.; Ager, J. W.; Chrzan, D. Adv. Mater. 2016, 28, 4053.

(2) Tarasov, A.; Zhang, S.; Tsai, M. Y.; Campbell, P. M.; Graham, S.; Barlow, S.; Marder, S. R.; Vogel, E. M. Adv. Mater. 2015, 27, 1175.
Optimizing the Interface of a Bipolar Membrane Fuel Cell: An Experimental Study
Authors: Park Andrew Michael , Neyerlin K.C. , Bender Guido , Long Hai , Pivovar Bryan S
Published: February 2020

Bipolar membrane fuel cells (BMFCs) have been discussed in the past few years as a potential game-changer for the fuel cell community (1). In the most favorable alignment for fuel cell operation, BMFCs comprise an acidic anode (HOR) and an alkaline cathode (ORR), where protons and hydroxide ions are formed, respectively. The ions migrate through a proton or anion exchange membrane to the bipolar junction, where they combine to form water. Optimizing this interfacial reaction is critical to a high performance cell, but outside of recent modeling work (2, 3), few studies have paid specific attention to it.

In this study, a series of BMFC membrane electrode assemblies (MEAs) were fabricated where the proton exchange side comprised a Nafion 211 membrane and ionomer, and the alkaline membrane/ionomer were varied. All MEAs contained platinum on carbon electrode catalysts and were investigated via polarization curves and impedance. Initial MEAs made with several different AEM polymers exhibited an exorbitant cell resistance, attributed to the bipolar interface. To reduce cell resistance, bipolar membrane fabrication conditions were altered to study parameters that impact observed performance. Altering fabrication conditions resulted in nearly a 3x reduction in overall resistance, translating to large gains in BMFC performance. These fabrications methods will be summarized with results presented, which should help inform rational design and future work for BMFCs.

References

1. M. Ünlü, J. Zhou and P. A. Kohl, The Journal of Physical Chemistry C, 113, 11416 (2009).

2. K. N. Grew, J. P. McClure, D. Chu, P. A. Kohl and J. M. Ahlfield, J. Electrochem. Soc., 163, F1572 (2016).

3. Q. Li, J. Gong, S. Peng, S. Lu, P.-C. Sui, N. Djilali and Y. Xiang, J. Power Sources, 307, 358 (2016).

Figure 1. Example polarization curves for BMFC MEAs in H2/O2 at 60°C with and without membrane pretreatment.

Figure 1
Material-Process-Performance Relationships of Roll-to-Roll Coated Fuel Cell Electrodes
Authors: Mauger Scott A , Neyerlin K.C. , Yang-Neyerlin Ami C. , Ulsh Michael
Published: February 2020

Roll-to-roll (R2R) coating is the most economical and highest throughput method for producing fuel cell electrodes. R2R coating encompasses many different methodologies to create uniform films on a moving web substrate (Figure 1a). One of the methodologies, gravure coating, uses rollers patterned with grooves or wells that fill with liquid, which is then transferred from the gravure roller to the substrate when the come into contact, creating a film (Figure 1b). Here, we present our work that utilized gravure coating to create highly uniform proton exchange membrane fuel cell electrodes on diffusion media. In addition to X-ray fluorescence, we utilized an in-line reactive impinging flow technique, developed by NREL, to characterize electrode uniformity.1

Additionally, we explored the materials-process-performance relationships associated with R2R coating of PEMFC electrodes. Lab-scale fabrication of electrodes sequentially builds up the thickness of the electrode through spraying multiple layers of a dilute dispersion to create a homogenous electrode. In contrast, with gravure coating a concentrated dispersion is coated, forming a thick, wet film that dries to form the electrode. Using several electrochemical diagnostic techniques2,3and electron microscopy, we explored the foundational relationships between ink formulation, coating physics, drying conditions, and substrate to understand how parameters such as ionomer-to-carbon ratio, solvent blend, and diffusion media porosity influenced electrode morphology, concentration gradients of materials, and critical MEA performance parameters such as surface area, activity, and oxygen transport (Figure 1c).

Figure 1 (a) NREL’s roll-to-roll coating station, (b) illustration of the gravure coating processes, and (c) polarization curves and electrochemical impedance spectra comparing spray-coated and roll-to-roll coated electrodes.

Acknowledgements: This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08GO28308 with the National Renewable Energy Laboratory. Funding provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Fuel Cell Technology Office, program manager Nancy Garland. S.A.M. would also like to thank Guido Bender and Brian Green for assistance with reactive impinging flow measurments.

1. Zenyuk, I. V., Englund, N., Bender, G., Weber, A. Z. & Ulsh, M. Reactive impinging-flow technique for polymer-electrolyte-fuel-cell electrode-defect detection. J. Power Sources
332,372–382 (2016).

2. Thompson, E. L. & Baker, D. Proton Conduction on Ionomer-Free Pt Surfaces. ECS Trans.
41,709–720 (2011).

3. Neyerlin, K. C. et al. New Insights from Electrochemical Diagnostics Pertaining to the High Current Density Performance of Pt-Based Catalysts. 230th ECS Meeting Abstracts (2016).

Figure 1
Conflicting Roles of Nitrogen Doping in Carbon Nanotubes As Anode and Cathode Catalyst Support for Direct Methanol Fuel Cells
Authors: Gan Lin , Du Hongda , Lv Ruitao , Li Jia
Published: February 2020

Nitrogen doping in carbon nanotubes (CNTs) is of great interest because it endows the inherently inert surface of CNTs with a variety of chemical functionalities. For instance, nitrogen-doped carbon nanotubes (NxCNTs) have been shown a promising electrode catalyst support for polymer electrolyte membrane fuel cells because the doped nitrogen atoms can promote a high dispersion of the metal catalyst nanoparticles on the NxCNT surface, which is essential for achieving a high utilization and thus high catalytic performance. However, beyond the role in nanoparticle dispersion, how nitrogen doping affects the catalytic performance in the anode and in the cathode of a realistic membrane-electrode-assembly (MEA), still remains elusive.

In this report, we performed a comparative study of NxCNTs at three different N doping levels as the anode and cathode catalyst support in both rotating disk electrode (RDE) and realistic direct methanol fuel cell (DMFC) test. Our results show that nitrogen doping can play significantly conflicting roles in the anode and cathode performance: (i) A very low doping level (1at.%) is sufficient to induce a homogenous distribution of both anode (PtRu) and cathode (Pt) catalyst nanoparticles. (ii) In RDE test, while nitrogen doping can substantially increase the specific activity of the anodic methanol oxidation, it brings no specific activity enhancement in the cathodic oxygen reduction reaction (ORR), suggesting that nitrogen doping can hardly affect the ORR electrocatalysis on the Pt surface. (iii) In MEA test, a low nitrogen doping level at 1 at.% in NxCNTs as anode catalyst support resulted in a higher power density compared to non-doped CNT support at both 30 and 60°; increasing nitrogen-doping content decreased the power density, likely due to a decreased electron conduction. In contrast, at the cathode, NxCNTs support mainly showed a lower power density, particularly at 60°, which is rationalized by the increased hydrophicility and thus unflavored removal of the water. Taken together, our results provide important guidelines for application of NxCNT support at the appropriate electrode of DMFCs.
Strategies for Effective Utilization of Hydrogen in Cylindrical PEM Fuel Cells
Authors: Suseendiran S R , Pearn-Rowe Samuel , Rengaswamy Raghunathan
Published: February 2020

PEM Fuel Cells (PEMFC) are attractive because of advantages such as low-temperature operation, no emission of harmful gases and high efficiency. However, the bipolar plates used in the state of the art planar architecture is costly and increases the dead weight of the cell. In addition, the flow channels in the planar fuel cell lead to difficulty in removing the water produced in the cathode during operation of the cell. Cylindrical PEM fuel cells, on the other hand, do not require bipolar plates and also there is no need for precisely machined flow channels. Thus, cylindrical PEM fuel cells are cheap, efficient in water management, and possess higher volumetric and gravimetric power density compared to planar PEM fuel cells. Because of the absence of flow channels in the cylindrical PEMFC, utilization of hydrogen should be enhanced by other means. Effective hydrogen utilization can be realized by controlling operating conditions and also through incorporation of baffles inside the tube. The operating conditions which affect hydrogen utilization are hydrogen flow rate and the cell pressure. Higher flow rates lead to higher velocities, which in turn prevent hydrogen from reaching the anode diffusion layer. Very low flow rates may increase the voltage loss due to concentration polarization. In the case of pressurized cells, high pressure can increase the possibility of a hydrogen leak. The initial results suggest that both the hydrogen flow rate and the cell pressure should be optimized for extracting the best performance from the cylindrical cell. CFD simulations performed on the tubes suggest that the amount of hydrogen reaching the anode differs for different baffle shapes. Therefore, the shape and position of baffles are crucial for improving cylindrical fuel cell performance. The aim of the present work is to analyze the interaction between these operating conditions and design parameters and to propose strategies for better utilization of hydrogen in cylindrical PEM fuel cells.

Keywords: Cylindrical PEM fuel cells, Hydrogen flow rate, Cell pressure, Baffle shape and Baffle spacing
A Core-Shell Fibrillar Electrocatalyst for the PEMFC Cathode By Microwave Accelerated Galvanic Displacement of Nickel with Platinum
Authors: Ercolano Giorgio , Farina Filippo , Cavaliere Sara , Rozière Jacques , Jones Deborah J.
Published: February 2020

Currently Pt/Ni alloy [1] and de-alloyed [2] Pt/Ni nanoparticles, and the 3M nanostructured thin film catalyst of de-alloyed Pt/Ni films on whiskers [3] are some of the few to have met the DoE 2020 mass activity target of 0.44 A/mg Pt at 0.9 VIR free. The origin of the extraordinary activity shown by the Ni/Pt system is attributed to a delicate balance between a thin Pt shell and the sub-surface Ni content [1]. One approach to the preparation of highly active Ni/Pt electrocatalysts is by galvanic displacement of Ni from nanofibres with platinum [4]. We have recently found that is possible to reduce significantly the reaction time for Pt-Ni galvanic displacement by using a microwave-assisted procedure on Ni nanofibres, which leads to high mass activity catalysts (>0.5 A/mg Pt) in only 2 minutes. The shell thickness and density are controlled by extent of Ni/Pt displacement (Pt loading), itself controlled by the concentration of Pt ions in solution. By tuning the Pt content, Pt/Ni core/shell electrocatalysts were prepared that do not require electrochemical etching of surface Ni or de-alloying before utilisation. In addition the nickel core can be leached leaving chemically stable Pt4Ni thin tubular structure.

References:

[1] V. R. Stamenkovic, B. Fowler, B. S. Mun, G. Wang, P. N. Ross, C. A. Lucas and N. M. Marković, Science 315 493–497 (2007).

[2] P. Strasser and S. Kühl, Nano Energy 26 1–12 (2016).

[3] M. K. Debe, R. T. Atanasoski and A. J. Steinbach, ECS Trans. 41 937–954 (2011).

[4] S. M. Alia, Y. S. Yan and B. S. Pivovar, Catal. Sci. Technol. 4 3589–3600 (2014).

Acknowledgement: This project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 700127 INSPIRE. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme.
Influence of Methanol Crossover on Cathode Catalyst in Direct Methanol Fuel Cell
Authors: Komárková Zuzana , Fiala Roman , Matolin Vladimir
Published: February 2020

The crossover effect is in the case of direct methanol fuel cell (DMFC) much more significant in comparison with PEMFC. Proof that the methanol crossover is a big issue in this field is a fact that there exist lots of publications describing the innovative procedures how to diminish this phenomenon [1-4].

In this work we present the investigation of influence of methanol crossover on the cathode catalyst. The durability of cathode catalyst exposed by methanol is studied. Moreover, the regenerative behavior after exposition has been found.

The comparison of commercial catalyst with our own sputtered Pt, Pt-Co and Pt-Ru thin film as a catalyst is presented. Additionally, the technic enabling measurement of the crossover in DMFC using micro-reactor and mass-spectrometry is introduced.

[1] ARICÒ, Antonino S., et al., Membranes, 2015, 5.4: 793-809.

[2] SUDAROLI, B. Mullai; KOLAR, Ajit Kumar.. Energy, 2016, 98: 204-214.

[3] MEENAKSHI, S., et al. Electrochimica Acta, 2013, 89: 35-44.

[4] WAN, Nianfang, et al.. Journal of power sources, 2007, 163.2: 725-730.
Ni-Based Hydrogen Oxidation Reaction Electrocatalysts for Alkaline Anion-Exchange Membrane Fuel Cells: Systematic Study on the Doping Effect
Authors: Davydova Elena S. , Dekel Dario R.
Published: February 2020

Recent developments in hydroxide conducting anion exchange membranes have contributed to the growing interest in alkaline anion exchange membrane fuel cells (AEMFC) which has the potential to be the next fuel cell generation as in principle this technology allows to replace platinum-based catalysts for affordable metal catalysts. Until now, there are a few research studies describing initial development of hydrogen fueled AEMFC [1], and practically no work done on completely platinum group metal (PGM)-free catalysts for AEMFC. Though some progress was made in the development of low cost electrocatalysts for oxygen reduction reaction (ORR) in base media [2], much less attention was paid to the electrocatalysis for hydrogen oxidation reaction (HOR) in alkaline solutions. Attempts to move away from the use of PGMs results in prohibitively large voltage losses on the anode in the base media (Fig. 1).

This work provides an extensive literature review on both theoretical and experimental advances in HOR electrocatalysts for AEMFCs. In addition, this work provides new insights into new Ni-based electrocatalysts for the HOR in alkaline medium that are being developed in our group at the Technion, including RDE, XRD, XPS, TPD/TPR/TPO, SEM results and some aspects of DFT calculations.

[1] H.A. Miller et al. Angew. Chem. Int. Ed. 55 (2016) 6004.

[2] M.R. Tarasevich et. al. Russ. J. Electrochem. 52 (2016) 193.

[3] E.S. Davydova et. al. (2017), in preparation.

[4] Zhuang Z. et al. Nat. Commun. 7 (2016) 10141.

[5] Zheng J. et. al. Sci. Adv. 2 (2016) e1501602.

[6] http://www.infomine.com/

Acknowledgements. This work was partially funded by the Grand Technion Energy Program (GTEP), by the European Union's Horizon 2020 research and innovation programme under grant agreement No 721065, by the Ministry of Science, Technology & Space of Israel through the M.era-NET Transnational Call 2015, NEXTGAME project grant 3-12948, by the Ministry of National Infrastructure, Energy and Water Resources of Israel, and by the 2nd Israel National Research Center for Electrochemical Propulsion (INREP2-ISF).

Figure 1
Highly Stable Mn-Based Nanocarbon Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions in Reversible Fuel Cells
Authors: Wu Gang
Published: February 2020

Carbon has many advantages over transitional metal oxide for being an oxygen reduction reaction (ORR) electrocatalyst due to high activity, low cost, excellent electrical conductivity, and high surface area. Nevertheless, its intrinsic instability in oxygen evolution reaction (OER) potential regime (>1.23 V vs. RHE) has largely inhibited the potential for bifunctional ORR and OER applications in reversible electrochemical energy devices. Here, we reported a new class of highly stable carbon nanocomposite bifunctional catalysts consisting of substantial carbon tubes growing from a very thick and dense graphitic substrate, which is derived from an inexpensive dicyandiamide as carbon/nitrogen precursor simultaneously catalyzed by Fe, Co, Ni, and Mn during carbonization. The dense substrate leverages the characteristics of high degree of graphitization carbon derived from Mn; active nitrogen-doped carbon tubes are stemmed from FeCoNi during carbonization process. The bifunctional stability and activity of the carbon nanocomposite catalysts were found greatly dependent on content of Mn. The existences of various metal/metal oxides and effective nitrogen doping was responsible for its high bifunctional activities for the ORR and the OER. The unprecedented stability of the bifunctional catalyst was verified by using various accelerated stress tests up to 60,000 potential cycles (0-1.9 V vs. RHE) at 25oC and 100-hour life test at constant current density of 10 mA cm-2 at 60oC. Instead of degradation, ORR and OER activity was considerably increased during the long-term potential cycling tests, indicating more active sites gradually exposed. The OER current was verified to be a sole outcome of oxygen evolution, rather than carbon or metal oxidations. The remarkable electrochemical stability of this catalyst was primarily attributed to its unique hybrid carbon structures featured with a very high graphitization degree, thick graphitic layers, and abundances of carbon tubes grown from a dense substrate. More importantly, the irreversible formation of β-MnO2 phase and FeCoNi based metals oxides provide crucial protection roles in enhancing carbon corrosion resistance.
(Invited) Which Lib Cathode Will Dominate for the EV and ESS --- from the Industry Point of View?
Authors: Xu Zhiyong
Published: February 2020

For the lithium ion batteries, there has always been an argument that which cathode will dominate. In this talk, we will outline pros and cons for each cathode material from the industry point of view.
Which LiVOPO4 Phase Works Best for Two Li Cycling?
Authors: Hidalgo Marc Francis Villarojo , Lin Yuh-Chieh , Omenya Fredrick , Chernova Natasha , Ong Shyue Ping , Whittingham M. Stanley
Published: February 2020

Vanadyl phosphates show promise as cathode materials in Li-ion batteries due to the ability to hold multiple Li-ions per redox center. Specifically, the V5+/V4+ and V4+/V3+ couples allow for the material to hold up to two Li-ions per vanadium. The great structural diversity of this family, producing seven VOPO4 and three LiVOPO4 polymorphs, raises a question on which of them would work the best as a Li-ion battery cathode. The electrochemical performance of some of the polymorphs was reported in the literature, but the comparison is complicated by differences is materials morphologies, electrode preparation methods, current densities, and voltage windows used. Here we use LiVOPO4-2H2O as the precursor to synthesize all three LiVOPO4 phases: α1 (layered, tetragonal), β (orthorhombic), and ε (triclinic), and compare their electrochemical performances under the same conditions. The transformation between phases and their relative stabilities are studied using x-ray diffraction and differential scanning calorimetry. The role of oxygen partial pressure in phase stability is discussed based on the experimental data and first-principle calculations results. The electrochemical performance of each phase is evaluated using galvanostatic discharge-charge between 1.5 to 4.5 V at various current rates. The lithium diffusion coefficients are calculated using cyclic voltammetry and galvanostatic intermittent titration technique. These tests reveal that all the three phases can work as multi-electron cathodes; the Li transport details specific to each phase are discussed in conjunction with the structures.

This research is supported as part of the NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0012583.
LiNi0.8Mn0.1Co0.
1O2 Cathode Materials with High Physicochemical Stability By Addition of Binding Oxides
Authors: Kang Beomhee , Koo Yehyun , Hong Soonhyun , Kim Chunjoong
Published: February 2020

Lithium-ion batteries are expanding beyond the power sources of conventional small-sized appliances, and as power sources for electric vehicles and hybrid electric vehicles. However, in order to expand them to the power source of medium and large-sized devices, it needs more improved energy density and stability than existing lithium ion batteries. As a cathode with high energy density, nickel-rich layered oxide in lithium nickel cobalt manganese trivalent oxide (LiNi1-2xMnxCoxO2, NMC) has attracted great attention. In particular, nickel-rich NMC material showed excellent initial discharge capacity compared with Ni low NMC, but the secondary particle intergranular fracture of aggregation occurs during the charging/discharging process, resulting in mechanical deterioration of the material. As a result, capacity decreased due to the increase of charge and mass transfer resistance of battery.

 In this study, the metal hydroxide is synthesized by co-precipitation with the addition of oxide materials, which acts as a binding agent in the primary particles. The addition of binding oxides improves the physical and chemical bonding of LiNi0.8Mn0.1Co0.1O2 (NMC811) Particles particles through the control at the precursor stage and it aims at securing the stability of the structure by preventing the crack formation, which is attributed to the mechanical stress of the primary particle phases during repeated cyclings. SEM and XRD analysis were performed to confirm the morphology, size and crystallinity of the powder and spherical particles with a layered structure (space group R-3m) were identified. In order to quantitatively analyze the local position and metal composition ratio of the binding oxide material and lithium in the particles, we studied the NMC811 and the binding oxide through EDS and ICP analysis. The electrochemical analysis was aimed to maintain the capacity over 90% at the lifetime characteristics (0.2 C, 100 times charge/discharge) and the energy density of the cathode material with the binding oxide. In addition, electrochemical characteristics and physical stability were evaluated by observing changes in real time surface characteristics by charging/discharging process using surface analysis such as in-line XPS.
Single Electrode Entropy Change for LiCoO2 Electrodes
Authors: Richter Frank , Gunnarshaug Astrid , Burheim Odne Stokke , Vie Preben J. S. , Kjelstrup Signe
Published: February 2020

Heat effects and temperature are known to be of great importance to a Li-ion battery’s performance and lifetime expectancy. In this context the reversible heat effects, i.e. effects that are associated with charge transfer and electrode reaction entropy, play an important role [1, 2]. These effects are however scarcely investigated, especially with respect to the single electrode reaction entropy. These values can be obtained when measuring a symmetric cell under a temperature gradient, i.e. two similar electrodes at zero current and at different temperatures [3-4]. We report values of the thermoelectric potential of the symmetric cell consisting of two identical LiCoO2electrodes separated by an electrolyte:

Al(s,T) | Li(1-x) CoO2
(s,T) | EC, DEC, LiPF6(diss) | Lix CO2(s,T + ΔT) | Al(s,T+ ΔT)

The electrodes are commercial LiCoO2 electrodes on an aluminium current collector, each kept at temperatures; T and T + ΔT. The electrolyte is 1 M lithium hexafluorophosphate (LiPF6) in a EC DEC mixture (1:1, volume wise) soaked in a separator. The cell is assembled as a pouch cell, and the electrodes are thermostatted to the specified temperatures.

We show that there are two significant contributions of opposite sign to the thermoelectric signal relative to the temperature difference; commonly known as the Seebeck coefficient. The contribution from the Peltier heat is obtained from the steady state value after 3-5 days. The second contribution, which manifests itself within hours, is a Soret effect. From these results, we report the transported entropy of Li+ and estimate the heats of transfer for the electrolyte components.

The attached figure shows a cross section of the cell used in these measurements, where one side is heated by hot water and the other cooled by cold water. The pouch cell is sandwiched between these two sides and layers of copper containing thermocouples, so that the actual temperature difference on the surfaces of the pouch cell is known and uniform.

References;

Takano, K., et al., Entropy change in lithium ion cells on charge and discharge. Journal of Applied Electrochemistry, 2002. 32(3): p. 251-258.

Viswanathan, V.V., et al., Effect of entropy change of lithium intercalation in cathodes and anodes on Li-ion battery thermal management. Journal of Power Sources, 2010. 195(11): p. 3720-3729.

S. K. Ratkje, M. Ottøy, R. Halseid, M. Strømgård, Thermoelectric power relevant for the solid-polymer-electrolyte fuel cell, Journal of membrane science 107 (1995) 219–228.

S. Kjelstrup, P. J. S. Vie, L. Akyalcin, P. Zefaniya, J. Pharoah, O. S. Burheim, The seebeck coefficient and the peltier effect in a polymer electrolyte membrane cell with two hydrogen electrodes, Electrochimica Acta 99 (2013) 166-175.

Figure 1
Silicon Nanoparticles/Carbon Composites as Anodes for High-performance Lithium-ion Batteries
Authors: Xiao Lisong , Sehlleier Yee Hwa , Dobrowolny Sascha , Schulz Christof , Wiggers Hartmut
Published: February 2020

Silicon has emerged as the most promising anode candidate for next-generation lithium-ion batteries (LIBs) owing to its high theoretical specific capacity of 3579 mAh/g combined with a relatively low working potential and its natural abundance. However, the practical application of pristine Si in anodes is seriously hindered by its low intrinsic electrical conductivity and the large volume variation during charging and discharging. The resulting mechanical stress causes rapid pulverization of the silicon, and isolation and disconnection of the active materials from the current collector. These failure events mostly cause a rapid degeneration of the Si electrodes.

In this study, Si nanoparticles (Si-NPs) were synthesized in a hot-wall reactor using monosilane as precursor. This process enables producing high purity Si NPs with a large production rate of up to 1 kg/h. Particle size, morphology, and crystallinity of the Si-NPs can be tuned towards optimized properties for battery applications by adjusting the synthesis parameters. In order to overcome the above mentioned failure scenarios of Si-NP-based anodes, Si/carbon nanocomposites such as Si-CNT, Si/graphene, Si-CNT/porous carbon, and Si-CNT/graphene composites have been developed to improve mechanical as well as electrical properties. As a highly promising product, the Si-CNT/ graphene nano-heterostructure demonstrates a high reversible initial capacity of 1665 mAh/g and very stable cycling performance over 500 cycles with a capacity decay of only 0.02% per cycle. Besides, the composite exhibits also a high-rate capability of 755 mAh/g (45.3% retention) at 10 C. These superior results imply that Si/carbon nano-heterostructures can be used for the development of high-performance lithium-ion batteries for durable and high-rate uses.