bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma Deposited Metal-Oxide Nanosensors for Amine Detection
Authors: Filipič Gregor , Gruenwald Johannes , Puliyalil Harinarayanan , Zavašnik Janez , Cvelbar Uros
Published: February 2020

The metal-oxides have raised significant scientific interest in recent years, due to their sensing properties. In is notable that the gas sensing properties can be enhanced by structural and morphological manipulation of the sensor. Previously was demonstrated that increasing the sensor surface to volume ratio during synthesis with formation of sheet-like structures or nanowires can enhance the sensor sensitivity [1,2]. Among different oxides, cuprous oxide is interesting due to its wide band gap and stability [3]. Cuprous oxide nanostructures can be synthesized by different methods ranging from solution based chemical methods to thermal and plasma synthesis [4]. However one of most optimal in terms of time, simplicity and quality of synthesized nanostructures is plasma processing, especially at atmospheric pressures. For this reason, the atmospheric DC plasma source was used for deposition of CuO nano-sheets on the surface of copper electrodes [5,6]. The prepared samples were then used to detect different amines (diethylamine, trietylamine, cyclohexanamine) which are present in vapours generated in spoiled food and many industrial processes. These chemical substances are cancerogenious and represent serious health hazards to humans. The developed gas-vapour sensor exhibited an excellent resistive sensitivity for these chemicals even at temperatures below 100 °C. In performed evaluation analysis, the morphology of the CuO nanostructures was changed, but results demonstrated that sensitivity is preserved during morphological changes as long as crystallinity remains similar, and the sensor material is of nanosize-dimension at least in one direction. The obtained results were explained by theoretical investigation of sensor performance.

[1] S. Steinhauer et al., Sensors and Actuators B: Chemical, 187 (2013), 50-57

[2] C. Yang et al., Sensors and Actuators B: Chemical, 207 (2015), 177-185

[3] M. Hübner et al., Sensors and Actuators B: Chemical, 153 (2011), 347-353

[4] G. Filipič et al., Nanotechnology, 23 (2012), 194001

[5] J. Gruenwald et al., Plasma Processes and Polymers, 13 (2016), 946-954.

[6 ] J. Gruenwald et al., Plasma Processes and Polymers, 13 (2016), 766-774
(Invited) Process Development for GaN-Based Photoconductive Semiconductor Switches (PCSS)
Authors: Anderson Travis J. , Koehler Andrew D , Luna Lunet E , Gallagher James C , Hite Jennifer K. , Mastro Michael A , Jacobs Alan G , Feigelson Boris , Hobart Karl D. , Kub Fritz J
Published: February 2020

High critical field strength and saturation electron velocity of gallium nitride (GaN) makes it a promising material for future compact, high voltage, and high-speed photoconductive switches. Photoconductive semiconductor switches (PCSSs) have advantages for pulsed power applications since it is a device that turns on when illuminated with fast rise time, low jitter, and allows for high repetition rate. Semi-insulating GaN is necessary to sustain the high blocking voltages required for such devices. This is accomplished by compensation doping with doped with iron, carbon, or magnesium. However, a strong photoresponse is also necessary to enable optical triggering of the switch. We have found that carbon-doped GaN (GaN:C) simultaneously reduces the off-state leakage current and extends the blocking voltage, while still allowing for high on-state photocurrent compared to unintentionally doped GaN. However, forming a low resistance contact to highly insulating GaN:C is challenging. Our approach is to study both Si ion implantation and Si-doped confined epitaxial growth as techniques to achieve low resistance N+ contacts. Implantation and activation is a planar process that is promising for formation of contact regions while mitigating high electric field points within the device. In this work, we implant Si with a box profile to a depth of 0.4 μm into GaN:C with carbon concentrations of 5x1017 and 1x1018 cm-3 grown on SiC substrates. Then, a sputtered AlN capping layer is introduced before annealing at various temperatures to preserve the surface from decomposition during annealing. Activation anneals are performed using rapid thermal annealing as well as the previously reported multicycle rapid thermal annealing processes. The AlN capping layer is then selectively wet etched and Ti/Al/Ni/Au contacts are deposited and alloyed at 850 °C. As a comparison, Si-doped low temperature and high temperature GaN layers were grown by MOCVD using a LPCVD SiO2 mask. Top-to-top lateral PCSSs are fabricated and characterized to identify the impact of the contact processing on the ON-resistance, off-state leakage, blocking voltage, and photocurrent. Finally, as the device is a top-side illuminated lateral device, the electric fields at the surface must be properly managed to realize reliable high voltage operation. The appropriate surface passivation and encapsulation processes to realize field plate structures while simultaneously enabling top-side UV illumination will be discussed.
(Invited) III-V Piezoelectrics for Sensors, Actuators, and Resonators
Authors: Griffin Ben
Published: February 2020

With the commercial success of film bulk acoustic resonators as RF filters for handsets, the manufacturing base of III-V piezoelectric thin films, namely aluminum nitride, is well established. The technology has recently expanded beyond RF filters to include microphones, ultrasonic transducers, near zero power wakeup devices, transducers for extreme environments, etc. This talk will discuss the expansion of the film’s applications and the advances in the material set needed to enable the next generation of devices.
(Invited) Low-Temperature Activation Method for InGaZnOx Thin-Film Transistors
Authors: Furuta Mamoru , Mehadi Aman S G , Magari Yusaku , Daichi Koretomo
Published: February 2020

Metal oxide thin-film transistors (TFTs) have attracted considerable attention for use in next-generation high-definition and large-area flat-panel displays (FPDs) owing to their excellent electrical properties such as high mobility (>10 cm2/Vs), large-area uniformity, and compatibility with low-temperature process. An InGaZnOx (IGZO) is widely employed as a channel material of oxide TFT. Although an IGZO film can be deposited by sputtering without an intentional substrate heating, an IGZO TFT requires a post-annealing around 300°C due to the recovery defective states induced during the sputtering process. A post-annealing required for improving TFT characteristics and reliability is often named as “activation annealing”. The activation annealing around 300°C limits the fabrication of oxide TFTs on flexible substrates. Several activation methods for oxide semiconductor, such as simultaneous UV and thermal annealing, electrical assisted thermal annealing, and high-pressure annealing, have been proposed to reduce annealing temperature at ~150°C. Another approach is an improving film quality of the sputtered IGZO.

In this presentation, a new method to achieve high quality sputtered IGZO film will be presented. Proposed deposition method reduced density of states near conduction band, and could reduce an activation annealing temperature to 150°C. Detail mechanism to achieve low-temperature activation of IGZO TFT will be discussed.
Back-Channel Etched Double Layer In-W-O/In-W-Zn-O Thin-Film Transistors
Authors: Li Zhen-Hao , Kuo Po-Yi , Chen Wen-Tzu , Liu Po-Tsun
Published: February 2020

The thin-film transistors (TFTs) with back-channel etched (BCE) type enable channel length to be narrow and reduce parasitic capacitances owing to its shorter overlaps between the gate and source/drain (S/D) electrodes. In this study, a high-performance BCE-type oxide thin-film transistor was proposed for investigation. A novel stacked double layer In-W-O (IWO) / In-W-Zn-O (IWZO) channel structure was fabricated and developed. Respectively, IWZO exhibits a high resistance to back-channel etching damage and IWO channel achieve a high mobility. The double layer IWO/IWZO TFTs are promising candidates for driving active matrix organic light-emitting diode (AMOLED) and high resolution display applications in the future. The double layer IWO/IWZO TFTs with S/D pattern by H2O2 + KOH can exhibit the high-performance electrical characteristic. The field-effect mobility (µFE) ~ 21.1cm2/V-s, subthreshold swing (S.S.) ~ 0.15 V/dec., threshold voltage (VTH) ~ -0.092 V, and on/off ratio ~ 4.88×108 can be achieved.
Oxide TFT Comparator Suitable for Bio Sensor Platform
Authors: Kang In Hye , Han Ye Lin , Hwang Sang Ho , Baek Yeong Jo , Bae Byung Seong
Published: February 2020

As the interest in personal health care is increasing, research on Bio-Information Technology (BIT) continues to be as vigorous as ever. Particularly, efforts are being made to develop products using bio-sensors capable of free movement and prompt detection. Therefore, a health care device with SOG (System-on-glass) technology is required due to the advantages of miniaturization, low cost, and simple process. These bio-sensor platforms must be consisting of the fully integrated circuit in order to be in contact with or embedded in the human body.

To display the sensing signal, we need analog-to-digital converter (ADC) circuit and 7-segment decoder which can be integrated using n-type amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) on a substrate. These bio-sensor platforms consist of an integrated circuit that converts the analog signal to a digital signal and the 7-segment decoder to show the signal level.

TFTs are required to realize the SOG which integrates all devices on substrates like a glass and plastic etc. Oxide semiconductor TFTs such as a-IGZO TFTs show better performance than amorphous silicon TFTs. Owing to their transparency and higher mobility compared to the amorphous silicon TFTs, a-IGZO TFTs have been studied widely.

Figure shows 9 comparators for digitizing, 9-to-4bit priority encoder and 7-sement decoder for display. An OP amp-based comparator includes two inputs, one is an analog input (Vin) and the other is a reference voltage (Vref) generated by a serially connected resistor array. The input signals are compared with the reference voltages by the comparators, which output “0” or “1” according to the analog input level. Then the binary outputs of the comparator are converted to the binary format (A3, A2, A1, and A0) by a digital encoder. The 4bit outputs (A3, A2, A1, and A0) of the ADC are the inputs of the 7-segment decoder. Among the four outputs of ADC, ‘A0’ is the least significant bit and ‘A3’ is the most significant bit. The outputs of 7-segment decoder are labelled as a, b, c, d, e, f, and g which correspond to each segment of 7-segment display.

The 4bit binary codes from ADC are converted to input signals (a to g) of a 7-segment display. Those circuits with a-IGZO TFTs can be used in applications such as the fully integrated bio-sensor platform and wearable device which are transparent and flexible.

The most complex one in that platform is OP Amp which is comparator to generate binary code and needs high gain to accomplish good performance. The comparator is a circuit that plays an important role in the ADC, and the operation of the ADC is difficult to expect without the correct operation of the operational amplifier. Thus, we proposed OP Amp type comparator with oxide TFT for bio sensor platform.

Figure 1
Interfacial Reaction between Metal and Oxide
Authors: Lee Sang Min , Hwang Sang Ho , Baek Yeong Jo , Han Ye Lin , Kang In Hye , Bae Byung Seong
Published: February 2020

Transparent oxide semiconductor thin film transistor (TFT) is being used in display such as OLED (organic light emitting diode) display and LCD (liquid crystal display). The active oxide layer in oxide TFT is transparent, comprising band gap higher than 3.0 eV.

In TFT fabrication metal layer contacts to the active oxide layer and the reaction between active oxide layer and metal degrade TFT characteristics due to thin metal oxide formation. In this paper the reaction between the amorphous indium- gallium -oxide (a-IGZO) and metal was studied. Metal oxide formation was reported with interfacial micro-structures between a-IGZO and the metal electrode. TiOx is formed at the interfacial region between Ti and IGZO layers by oxygen out-diffusion from IGZO.

The reaction depends on process parameters such as temperature, annealing time and the environment of annealing. For several metals such as Al, Ti, and Mo, the interfacial reaction by thermal anneal was compared for various annealing conditions. The a-IGZO was deposited on ITO electrode layer and the 0.8 mm diameter metal electrodes are formed on a-IGZO layer. After annealing at various conditions, formation of metal oxide was verified by electrical characteristics. The leakage current and breakdown voltages were measured. Figure 1 shows typical I-V characteristics between metal and ITO electrode.

Figure 1
(Invited) Human Interactive Flexible Multi-Functional Sensor Sheets
Authors: Takei Kuniharu
Published: February 2020

Human interactive and friendly sensor sheets have a great attention for internet of things (IoT) concept including healthcare and medical applications to collect multiple information from the variety of surfaces. To cover the device conformally and comfortably in the case of human body, mechanical flexibility with different types of sensors is required to monitor health conditions. Realizing the application needs to develop the device concepts and structures for macro-scale, multi-functionality with low cost process. In this talk, flexible multi-functional sensor sheets using mainly printing methods of inorganic nanomaterials will be introduced especially for healthcare and IoT applications as the future human interactive electronics. In addition to the proof-of-concept applications, stability and reliability of the printed flexible sensors will be discussed for moving forward to building more practical sensors in the market.
Improvement of Quantum Dot Light-Emitting Diodes (QD-LED) with Photonic Crystals
Authors: Ho Shih-Jung , Huang Shang-Jie , Chen Hsueh-Shih
Published: February 2020

Quantum dots (QDs) are known as key materials in next-generation displays. They have high quantum efficiency and narrow full width at half maximum (FWHM), which enables fabrication of highly efficient display with wider color gamut than other displays. To increase light extraction and material utilization of QDs in a display, photonic crystals with desired photonic stopband are introduced into light-emitting diodes (LEDs). While the photonic crystal stopband matches excitation peak (i.e. 450 nm from blue LED), green and red emitting QDs in LEDs can be largely improved via excitation photons resonance. Therefore, it is promising to prepared a high intensity QD-LED with low QD usage, reducing cost and tiny amount of cadmium, to produce a more environment-friendly and competitive QD-LED products. However, conventional preparation processes of photonic crystals are time-consuming and difficult to scale-up. For example, photonic crystal thin films are generally prepared by vertically deposition self-assembly or laser interference lithography methods are not suitable to mass production QD-LEDs. In this research, a facile method to prepare photonic QD-LED have been investigated. The inverse photonic crystal with stopband at 450 nm in PDMS was fabricated by centrifuge self-assembly, forced impregnation with titanium butoxide and calcination at 550 oC for 6h. A photonic QD glue was prepared by mixing inverse photonic crystal, quantum dot and PDMS. After vacuum degassing, a photonic QD-LED was fabricated by dispensing the glue and cured at 120 oC for 30 min. The photonic QD-LED has shown a 22% increase in the luminescence intensity than that of general QD-LEDs with conventional scatter particles.
(Invited) Textile-Based Energy Storage Devices
Authors: Zheng Zijian
Published: February 2020

Wearable textile-based energy storage devices are the energy storage that make use of and/or shaped into textile fibers, yarns, and fabrics, which are promising for wearable electronic applications. To date, the major challenge in the development of wearable energy storage devices is how to improve the electrochemical properties of the device while acquiring high flexibility and durability under different wearing conditions. Recently, our laboratory has developed several energy storage yarns and fabrics through utilizing various low-dimensional and nanoscale materials, which show record−high electrochemical performances as well as excellent flexibility of their kinds. These textile−based devices can be readily integrated into different textile forms by means of weaving, embroidery, and heat pressing for wearable applications.
(Invited) Semiconductor Nanoheterostructures for Photoconversion Applications
Authors: Hsu Yung-Jung
Published: February 2020

With the inherently high degree of complexity, nanoheterostructures composed of two or more materials joined in unique architectures may exhibit superior synergetic properties that are difficult or impossible to acquire from their individual constituents. For semiconductor nanoheterostructures, the relative band alignment of the constituents promotes effective charge separation to bring them desirable properties for photoconversion applications. Several representative works from our lab including Au-CdS [1,2], Au-ZnS core-shell nanocrystals [3,4], Au-decorated TiO2 nanorods [5], Au-decorated ZnO nanocrystals [6], and Au@Cu7S4-decorated TiO2 nanowires [7] will be introduced to demonstrate the promising potentials of semiconductor nanoheterostructures.

References

[1] Chen, W.-T.; Yang, T.-T.; Hsu, Y.-J. Chem. Mater. 2008, 20, 7204-7206.

[2] Yang, T.-T.; Chen, W.-T.; Hsu, Y.-J.; Wei, K.-H.; Lin, T.-Y.; Lin, T.-W. J. Phys. Chem. C 2010, 114, 11414-11420.

[3] Chen, W.-T.; Hsu, Y.-J. Langmuir 2010, 26, 5918-5925.

[4] Chen, W.-T.; Lin, Y.-K.; Yang, T.-T.; Pu, Y.-C.; Hsu, Y.-J. Chem. Commun. 2013, 49, 8486-8488.

[5] Pu, Y.-C.; Wang, G.; Chang, K.-D.; Ling, Y.; Lin, Y.-K.; Fitzmorris, B. C.; Liu, C.-M.; Lu, X.; Tong, Y.; Zhang, J. Z.; Hsu, Y.-J.; Li, Y. Nano Lett. 2013, 13, 3817-3823.

[6] Chiu, Y.-H.; Chang, K.-D.; Hsu, Y.-J. J. Mater. Chem. A 2018, 6, 4286-4296.

[7] Chiu, Y.-H.; Hsu, Y.-J. Nano Energy 2017, 31, 286-295.
On/Off Ratio Improvement of Carbon Nanotube Thin Film Transistors By Combining Asymmetric Gate Design and Chemical Doping
Authors: Huang Qi , Xia Jiye , Zhao Jie , Liu Fang , Liang Xuelei
Published: February 2020

Carbon nanotubes are regarded promising building blocks for the future nanoelectronics. High performance transistors and integrated circuits based on semiconducting CNT thin films, e.g., CMOS type 4-bit adder, CNT computer, flexible sensor etc., have been reported. These progresses demonstrate the CNT transistor technology is being pushed to practical application. For real circuits applications, high Ion/Ioff ratio with low Ioff for a transistor are required in high speed and low power consumption integrated circuits. However, the switching behavior of most reported CNT thin film transistors are not good enough. Due to the intrinsic ambipolarity of CNTs, the Ioff values are usually higher than hundreds of nano Ampe and the Ion/Ioff ratio is decreased to less than 102 at relatively high source/drain bias voltages (e.g. 1V). Though the switching behavior of the FETs based on individual CNTs can be improved by either special design of the device geometry or chemical doping, these methods do not work well in CNT thin film transistors. In this work, we improved the performance of CNT thin film transistors by combining the asymmetric gate design and chemical doping. In this way, the Ioff was suppressed while the Ion was increased at the mean time. Thus the Ion/Ioff ratio was increased by ~2 orders of magnitude when compared with normally designed top-gate device. Moreover, the devices showed better subthreshold swing (SS) and the threshold voltage (Vth) was closer to zero than normal devices. These improvements are benefit to more complicated circuits design, and our method is applicable for the emerging nanodevices.
(Invited) Interfacing Graphene with III-Nitrides for Power Device Applications
Authors: Yakimova Rositsa , Kovacs Andras , Kakanakova Anelia , Giannazzo Filippo , Pecz Bela
Published: February 2020

Full performance of GaN power devices is not attained yet due to their self-heating. Towards solving this issue Silicon Carbide is a common substrate for growth of GaN and AlGaN epitaxial layers. In spite of the superior thermal conductivity of SiC compared to e.g. Sapphire or Silicon, thermal management of GaN based devices is still a challenge.

This talk will review recent research appraising the benefits of graphene integration with III-N for high power electronics. The merits of graphene as a 2D carbon made material are well demonstrated. We will present, from a material perspective, the recent progresses in the growth of high quality GaN layers on graphene templates. The latter are obtained via sublimation epitaxy on SiC and this process and the graphene quality will be also discussed in the view of template design and its role in the subsequent CaN and AlN deposition. Furthermore, the possibility and the advantage of templated growth of novel 2D Nitrides will be discussed, both from experimental and theoretical point of view of their formation mechanism.

In order to gain full understanding of the new structure formation results from HRTEM and STEM characterization will be shown.

Finally, strategies to use graphene for thermal management in high-power AlGaN/GaN transistors will be discussed.

References

A. Kovacs et al. Graphoepitaxy of highquality GaN layers on graphene/6H-SiC, Adv. Mater. Interfaces 2, 1400230 (2015).

F. Giannazzo et al. Phys. Status Solidi A 214, No. 4 (2017)
Multi-Scale Characterization of Lithium Ion Battery Cathodes
Authors: Almar Laura , Joos Jochen , Weiss Michael , Costard Janina , Weber André , Ivers-Tiffée Ellen
Published: February 2020

Optimizing the performance of the Lithium ion batteries requires further understanding of the relationship between the electrode microstructure and the electrochemical performance. Advanced microscopy methods like focused ion beam-secondary electron microscopy (FIB-SEM) and X-ray tomography have been lately used to characterize the battery electrodes [1,2]. However, the study of the complex morphology of the electrodes is not a trivial task, since relevant details take place at different length scales. One single technique is thus meaningful up to a certain extend but not enough to achieve information of the battery as a whole [3].

By a correlative approach the central issues arising during post-processing the image data can be investigated: (1) segmentation of the carbon (carbon black-binder) domain limited by the lower X-ray tomography resolution, (2) reliability of the small volume fractions of the active material and/or other large features taken by FIB-SEM tomography and (3) impact of inner porosity, fissured texture or agglomerated particles, which demand a high resolution technique, in the transport properties.

In this work, LiNixMnyCo1-x-y (NMC) cathodes are characterized by correlation of both FIB-SEM and X-ray tomography. Relevant microstructural information of each individual phase (i.e. active material, carbon, and pore phases) is determined with their respective volume fraction, surface area, particle size distribution and tortuosity at the different relevant length scales.

In addition, the electrochemical performance of the cathodes is studied by impedance spectroscopy (EIS) combined with distribution of relaxation times (DRT) depicting information about the ohmic resistance (R0), charge transfer (e-) at the interface cathode/current collector (RCC), charge transfer (Li+) at the interface cathode/electrolyte (RCT) and the ionic and electronic transport [4].

As a whole, the possibilities, limits and prospects of both microstructural characterization methods will be critically discussed along with the impact on the results.

References

M. Ender, J. Joos, T. Carraro, E. Ivers-Tiffée, J. Electrochem. Soc.
159 (2012) A972-A980.

P.R. Shearing, L.E. Howard, P.S. Jorgensen, N.P. Brandon, S.J. Harris, Electrochem. Comm., 12 (2010) 374-377.

R. Moroni, M. Börner, L. Zielke, M. Schroeder, S. Nowak, M. Winter, I. Manke, R. Zengerle, S. Thiele, Sci. Rep., 6 (2016) 30109.

J. Illig, J.P. Schmidt, M. Weiss, A. Weber, E. Ivers-Tiffée, Journal of Power Sources, 239 (2012) 670-672.

Figure 1
(Invited) Status of Fuel Cell Systems R&D
Authors: Takeuchi Norimitsu
Published: February 2020

Current status of fuel cell systems research and development for automobile application will be reported in this presentation. Fuel cell vehicles (FCVs) are expected as the one of electric motor driven vehicles and will be adapted to passenger vehicle to heavy duty tracks in advantage of cruising range with hydrogen tanks than battery electric vehicles. Fuel Cell systems still has some tasks for mass commercialization. Some approaches of improvement of fuel cell system performance, durability and reliability are developed and discussed in this presentation.
Development of a Hydrogen Contaminant Detector
Authors: Banas Charles Joseph , Yilmaz Abdurrahman , Aponte Bryan , Bonville Leonard J. , Pasaogullari Ugur , Hesler Gregory , Molter Trent M.
Published: February 2020

As fuel cell vehicles (FCV) are introduced and commercialized, durability remains a critical characteristic towards competing with the lifecycle of conventional vehicle engines1. Reforming and electrolysis still remain as the dominant production processes for the foreseeable future for the hydrogen fuel. Coupled with transportation, storage, and delivery into FCVs, numerous sources of contamination are possible to introduce impurities into hydrogen fuel, which can enter into and poison the fuel cell, leading to rapid degradation of performance.

In this work, we detail the development of an electrochemical hydrogen contaminant detector (HCD) designed to measure the quality of hydrogen fuel dispensed at the filling station against the specifications outlined by the SAE J27192. Specifically, the role that mass transport plays in the sensor response is discussed. The sensor consists of a two-electrode system, for hydrogen oxidation and evolution in the fueling system environment, which consist of a low surface area platinum and platinum-rhodium alloy couple. A Nafion electrolyte coats the tip of the HCD to conduct protons between the electrodes.

Baseline performance is measured on clean hydrogen, which rapidly degrades when the impurities are presented. Experimental response of the HCD to carbon monoxide is presented3. A thin Nafion film, provides rapid response within 30 seconds, but quickly degraded and delaminated off the electrode surfaces. Development of more durable Nafion electrolyte film is discussed which shows much slower response time due to increased thickness. The effect of relative humidity, alternate electrolytes and high-pressure on the HCD response are also presented.

References

1) U.S. Drive Fuel Cell Tech Team Roadmap, https://www.energy.gov/eere/vehicles/downloads/us-drive-fuel-cell-technical-team-roadmap (2017).

2) SAE International Surface Vehicle Standard J2719TM, http://standards.sae.org/j2719_201511/ (2015).

3) C.J. Banas, L.J. Bonville, U. Pasaogullari and T.M. Molter, ECS Trans., 80(8), 497-507 (2017).
Upscaling the Production of High Temperature Polymer Electrolyte Membrane Fuel Cells – an Assessment of Reproducibility, Performance and Durability
Authors: Bodner Merit , García Héctor R. , Steenberg Thomas , Vassiliev Anton , Alfaro Silvia M. , Avcioglu Gökçe S. , Hjuler Hans Aage
Published: February 2020

With the globally growing market for renewable energy carriers and converters, the scale of material production is increasing, making it necessary to reevaluate processes and parameters of materials. Even though improvements are without doubt still necessary, fuel cells have a high probability to live up to the requirements of the market regarding power density, lifetime, scalability, costs and system simplicity that have to be met in order to enable a broad commercialization.

Especially high temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) have clear advantages over other available systems at a comparable technological readiness level. The - in comparison to low temperature polymer electrolyte fuel cells (LT-PEMFCs) - elevated operation temperature increases the tolerance of the platinum electrocatalyst towards gas contamination. This enables a simpler system setup, as extensive gas purification becomes obliterated. Furthermore, the higher temperatures allow a more efficient use of the produced heat, contributing to the overall efficiency [1],[2].

The upscaling of the production of electrodes and membranes for high temperature polymer electrolyte membrane fuel cells, as well as the membrane electrode assembly (MEA) manufacturing post new challenges on product reliability. The choice of production method defines the scalability as well as the product reproducibility.

Different coating processes are feasible for high throughput electrode production, all requiring specific ink properties to ensure sufficient loading and homogeneity. In order to assess the reproducibility and scalability, electrodes based on commercial catalysts are manufactured by spraying, casting and with a slot die process. Electrodes are evaluated in regard to their reproducibility, performance and durability. A new non-destructive method for quality control is introduced. Continuous X-ray scanning of the electrodes allows to determine the Pt loading and distribution over large areas.

Performance and durability are determined during operation with wet reformat, mimicking the gas composition of a methanol reformer. The latest results show degradation rates as low as 1 µV h-1, calculated from after the initial 50 h up to 3000 h at 0.4 A cm-2 (Figure 1). The results and experience are used to assess process requirements and scalability.

[1] Q. Li, D. Aili, H.A. Hjuler, J.O. Jensen (Eds.), High Temperature Polymer Electrolyte Membrane Fuel Cells: Approaches, Status and Perspectives, Springer, Switzerland (2016).

[2] G. Schuller et al., Journal of Power Sources, 347, 47 (2017).

Figure 1
(Invited) Advancement of Thin, Reinforced Membranes for High-Performing, Long-Lasting Proton Exchange Membrane Fuel Cells
Authors: Redmond Erin L. , Maruyama Masashi , Liu Wen K. , Cleghorn Simon
Published: February 2020

After decades of research and development, commercialization of proton-exchange membrane fuel cell (PEMFC) vehicles is now a reality, and several production scale vehicles have been launched. GORE-SELECT® Membranes (GSMs) enable the Toyota Mirai (2015), Honda Clarity (2016), and Hyundai Nexo (2018)1. However, mass deployment of PEMFC vehicles is hindered by lack of hydrogen infrastructure and higher cost than internal combustion engines2. W. L. Gore and Associates, Inc. (Gore) is committed to supplying the fuel cell market with the highest performance and most durable membranes to support the lowest $/kW system. One approach to simultaneously increase power density and decrease membrane cost (by reducing material content) is to use thinner membranes, ca. 10 µm or less.

Thin membranes facilitate high performance systems by means of higher proton conductance and faster water transport properties, yet durability remains a challenge. Gore is uniquely positioned to deliver high-strength reinforcement layers for the most mechanically durable thin membranes at high volume with superior uniformity. Expertise in engineering fluoropolymer composites has allowed Gore to develop thin membranes that mechanically outlast thicker membranes while exceeding performance, Figure 1. The remaining challenge to address is chemical durability. Higher gas permeance of thin membranes can result in increased radical generation through multiple mechanisms3. As shown in Figure 2, Gore is working to increase the selectivity of protons relative to gas crossover, which is critical for maintaining performance while extending chemical lifetime. Additionally, chemical degradation can be mitigated through advanced additive strategies.

In this talk we discuss Gore’s understanding and advancements of thin membrane technology culminating with the introduction of new state-of-the-art membranes that break the cost / performance trade-off.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the contribution of the Electrochemical Products team of W. L. Gore and Associates, Inc.

REFERENCES

W. L. Gore & Associates, (2018) https://www.gore.com/news-events/press-release/gore-s-fuel-cell-technology-helps-power-latest-hyundai-fuel-cell-vehicle.

D. L. Greene and G. Duleep, Status and Prospects of the Global Automotive Fuel Cell Industry and Plans for Deployment of Fuel Cell Vehicles and Hydrogen Refueling Infrastructure, Oak Ridge, Tennessee, (2013).

M. Zaton, J. Rozière, and D. J. Jones, Sustain. Energy Fuels, 1, 409–438 (2017).

Figure 1
Stability of Perfluoro Bis(Sulfonyl)Imide-Based Ionomers in Fuel Cell Membranes and Electrodes
Authors: Yandrasits Michael , Lindell Matthew , Hamrock Steven , Komlev Andrei , Peppin Daniel M. , Haugen Gregory M , Fort Eric , Kalstabakken Kyle
Published: February 2020

Perfluoro bis(sulfonyl)imides have potential for use in next generation ionomers for proton exchange membrane fuel cells. It is well known that these functional groups are strong acids and can be used to make membranes with excellent proton conductivity. Until now, there has been very little published work studying the long-term durability of these ionomers. In recent years, 3M has developed several imide-based ionomers, most notably a perfluoro imide acid (PFIA). Membrane electrode assemblies (MEAs) prepared using this ionomer have been run in the U.S. Department of Energy specified open circuit voltage (OCV) hold accelerated test. The purpose of this test is to stress the chemical stability of the membrane until a breach is detected. PFIA-based membranes, with mechanical supports and peroxide scavenging additives, will routinely exceed the 500-hour DOE target without crossover failure. However, a suppression in the OCV value has been observed in the first few hundred hours and, later, the cell resistance is observed to increase during this test. The first observation indicates a poisoning effect due to small molecule fragments on one or both electrodes. The resistance increase suggests a loss in protogenic groups and thus decreasing conductivity. Several techniques have been employed to better understand the origins of these observations. MEAs made with three membranes allows for the center layer to be subjected to the in-cell OCV test conditions and then separated at the end of life for analyses by FTIR, 19F NMR, and AC impedance measurements. Analysis of the effluent water by liquid chromatography - mass spectroscopy (LC-MS) is used to search for ionomer fragments. These methods have been employed to study the PFIA ionomer in both the membrane and electrode. In addition, an ionomer containing only the bis(sulfonyl)imide functional group has been studied. A complicated picture is emerging regarding the chemical stability of this class of imide-based ionomers and membranes.
Tuning Architecture in Polybenzimidazole Reinforced Membranes
Authors: Zaton Marta , Donzel Nicolas , Cavaliere Sara , Rozière Jacques , Jones Deborah J.
Published: February 2020

Many fuel cell membranes are highly heterogeneous systems comprising mechanical and chemical reinforcing components, including porous polymer sheets, nanofibers or nanoparticles, as well as radical scavengers or hydrogen peroxide decomposition catalysts. In the last 10 years, significant attention has been devoted to 1D nanomaterials obtained by electrospinning. Several chemistries and compositions ranging from aliphatic or aromatic polymers to metal oxides and phosphates and morphologies from nanofibers to nanotubes have been employed to prepare nanocomposite membranes. Despite the significant advances realized, further improvements in ionomer membrane durability under operation are still required. In particular, it is crucial to control the heterogeneity induced by the nanofiber component and to strengthen the interface between them and the matrix. Specific interactions can improve the fiber/matrix interface with overall improvement of dimensional and mechanical properties. This presentation will briefly review the different approaches to fuel cell membrane reinforcement based on electrospun polymers and describe our recent advances with polybenzimidazole reinforcement of PFSAs.
Fabrication of Reinforced Tri-Layer Proton-Exchange Membranes By Dual Fiber Electrospinning
Authors: Powers Devon , Wycisk Ryszard , Pintauro Peter N.
Published: February 2020

Dual nanofiber electrospinning was used to fabricate a series of tri-layer fuel cell membranes with high proton conductivity and low in-plane water swelling, using 825 EW perfluorosulfonic acid (PFSA) ionomer from 3M Company and poly(amide imide) (PAI) from Solvay S.A. The relative flow rates of the PFSA and PAI solutions, supplied from separate spinnerets (needles) during electrospinning, were adjusted to create three-layer mixed-fiber mats with different PFSA/PAI weight ratios. After electrospinning, the fiber mats were transformed into dense membranes by heating and compaction, where each layer consisted of a PFSA ionomer matrix with an embedded network of reinforcing PAI fibers. The surface layers of all membranes contained 95 wt.% PFSA and 5 wt.% PAI. The center layer, depleted in PFSA, contained either 75 wt.%, 60 wt.%, or 40 wt.% 825 EW PFSA, with a uniform or gradient PFSA/PAI composition. The thickness of the center layer (uniform or gradient composition) was adjusted so that the effective/average composition of the entire membrane was 80 wt.% PFSA and 20 wt.% PAI. The best tri-layer membrane had a total thickness of 17 μm and a PFSA/PAI gradient morphology middle layer. This membrane had a sheet resistance 30% less than a commercial Nafion 211 membrane with a 3-fold decrease in areal water swelling, as compared to Nafion and excellent mechanical properties (a stress at break of 20 MPa versus 22 MPa for neat Nafion 211).

Acknowledgements. The authors thank the US DOE (EERE Cooperative Agreement No. DE-EE0006362) for funding this work and Dr. Michael Yandrasits at 3M Co. for providing the 825 EW PFSA used in this study.
Reinforced Composite Polymer Membrane: Research and Application for Proton Exchange Membrane Fuel Cells
Authors: Kim Jin Young
Published: February 2020

A polytetrafluoroethylene (PTFE)-reinforced Nafion composite material is a cost effective alternative to a pure perfluorosulfonic acid (PFSA) membrane, which is often applied as membrane in proton exchange membrane fuel cell (PEMFC), simply by lowering the amount of expensive PFSA applied for the membrane production. The reduction in cost is an attractive factor, but it is still a challenge to produce the composite membranes as efficient as commercial membranes. Recent research and application activities with the reinforced composite membrane for PEMFC applications include impregnation of the PFSA ionomer into the PTFE support, improving proton conductivity, reducing gas permeability, and addition of radical scavengers. In this talk, our recent results from these activities will be presented.
Preparation of Pt3y Nanoparticles Supported on Carbon
Authors: Brandes Benedikt Axel , Cleemann Lars Nilausen , Li Qingfeng , Jensen Jens Oluf
Published: February 2020

The development of active and stable nanoparticles for the ORR is crucial for the success of hydrogen fuel cells and their application in a new energy environment. Platinum based alloy nanoparticles supported on carbon is still the most widely applied catalyst. Literature suggests that platinum alloys of the rare earth metals, including Pt3Y, imposes a superior activity and stability towards the state of the art catalysts [1].

A number of partly successful attempts to synthesize Pt3Y have been made [2][3][4], but unfortunately, the synthesis routes lead to unacceptable particle sizes and distributions or the formation of undesired PtxY phases next to Pt3Y. In most cases, scaling up is an additional challenge.

Our synthesis approach shows promise to produce phase pure and small Pt3Y nanoparticles with a narrow particle size distribution.

The final sample was acid washed and subsequently studied by XRD, XPS, TGA and TEM. Its ORR performance has been measured using RDE.

The XPS results in figure 1a show that metallic/alloyed yttrium exists on the surfaced of the sample confirming that platinum has indeed alloyed with Yttrium and is stable towards the acid wash. However, some yttrium oxide can also be found. It might be located within the carbon support and protected against acid leaching. The XRD spectrum in Figure 1b suggest that almost pure phase Pt3Y nanoparticles have been formed. Only minor contributions of the patterns originating from Pt and Pt2Y can be observed. Using the Scherrer equation, one finds an average particle diameter of 7 nm. TEM images of the the Pt3Y sample are shown in figure 1c, while figure 1d shows a commercial Pt/C catalyst for comparison. The improvement of activity is not yet as high as anticipated, so further work is needed to understand that and to optimize the manufacturing process. The synthesis process cannot be disclosed in the abstract due to a patenting process, but it will be presented at the conference.

[1] Hernandez-Fernandez, P., Masini, F., McCarthy, D. N., Strebel, C. E., Friebel, D., Deiana, D., … Chorkendorff, I. (2014). Mass-selected nanoparticles of PtxY as model catalysts for oxygen electroreduction. Nature Chemistry, 6(8), 732–738. https://doi.org/10.1038/nchem.2001

[2] Knudsen, B. P. (2016). Synthesis of Platinum Rare Earth Alloy Catalysts for Fuel Cells.

[3] Kanady, J. S., Leidinger, P., Haas, A., Titlbach, S., Schunk, S., Schierle-Arndt, K., … Alivisatos, A. P. (2017). Synthesis of Pt3Y and Other Early-Late Intermetallic Nanoparticles by Way of a Molten Reducing Agent. Journal of the American Chemical Society, 139(16), 5672–5675. https://doi.org/10.1021/jacs.7b01366

[4] Cui, R., Mei, L., Han, G., Chen, J., Zhang, G., Quan, Y., … Han, Z. (2017). Facile synthesis of nanoporous Pt-Y alloy with enhanced electrocatalytic activity and durability. Scientific Reports, 7(December 2016), 1–10. https://doi.org/10.1038/srep41826

Figure 1
Nitrogen and Sulfur Co-Doped MWCNT/Rgo Composite As Highly Active Electrocatalyst for Oxygen Reduction Reaction in Alkaline Fuel Cell
Authors: Kruusenberg Ivar , Šutka Andris , Shainyan Bagrat A. , Käämbre Tanel , Villemson Karl Markus , Wang Pangpang
Published: February 2020

Recently a major effort in fuel cell research and development have been undertaken to displace platinum with platinum-free or even better, totally metal free catalyst materials. With the possibility of using heteroatom doped carbon-based materials as electrocatalysts for oxygen reduction reaction (ORR) instead of Pt, anion exchange membrane fuel cells (AEMFCs) have big advantage over other low-temperature fuel cells. Beside other carbon nanomaterials, carbon nanotubes and graphene have shown good electrocatalytic and catalyst supporting properties for different fuel cell cathode catalysts. Graphene and/or carbon nanotubtube doping with heteroatoms is a common strategy to increase the electrocatalytic activity of these materials towards the ORR [1]. Different heteroatoms, such as nitrogen, phosphorous, sulfur and boron have been studied as promising dopants to prepare electrocatalysts for ORR in alkaline media [2].

In this work the electrocatalytic activity of nitrogen and sulfur co-doped MWCNT/rGO was studied towards the ORR in alkaline media (0.1 M KOH) using the rotating disc electrode (RDE) method. The catalyst materials were prepared by doping of MWCNT/rGO with N and S via simple one-pot synthesis method using high-temperature pyrolysis in inert gas atmosphere. The resulting catalyst material exhibited excellent electrocatalytic activity towards the ORR in alkaline media. Catalyst samples were characterized also by transmission electron microscopy, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy methods. Fuel cell experiments were carried out using Fumatech Fumapem® FAA anion-exchange membrane and FAA ionomer. Methanol tolerance and long-term stability tests were performed.

The results revealed remarkable catalytic activity of nitrogen and sulfur co-doped carbon towards the ORR in alkaline media, as well good methanol tolerance. Composition analysis with different physical characterization methods confirmed that nitrogen and sulfur have been grafted onto the carbon support. RDE tests demonstrated highly improved catalytic activity in comparison with undoped MWCNT/rGO and fuel cell tests showed a great potential of N and S doped carbon as alternative cathode catalyst and catalyst carrier for anion exchange membrane fuel cells.

References

[1] S. Ratso, I. Kruusenberg, U. Joost, R. Saar, K. Tammeveski, Enhanced oxygen reduction reaction activity of nitrogen-doped graphene/multi-walled carbon nanotube catalysts in alkaline media, International Journal of Hydrogen Energy 41 (2016) 22510.

[2] J.-C. Li, P.-X. Hou, C. Liu, Small 13 (2017) 1702002.

Figure 1
Alkaline Stable Sustainion® Anion Exchange Membrane for Fuel Cells
Authors: Liu Zengcai , Sajjad Syed D. , Yang Hongzhou , Zhu Liang , Masel Richard I.
Published: February 2020

Anion exchange membrane fuel cells are of interest since they allow to use non-precious metal catalyst for both anode and cathode reaction. More than 2000 articles have been published on alkaline membrane fuel cells(1). There is one previous report indicating initial power densities of 1W/cm² but with no long term data(2). The best long term data shows a cell voltage decrease by about 25% over 800hr at a current density of 400mA/cm2 and 60°C.

Presently, Sustainion® 37 anion exchange membranes have demonstrate excellent stability in anion exchange membrane carbon dioxide (CO2) and water electrolyzer(3-6). Carbon dioxide electrolyzer runs at pH 6-8 with 10mM KHCO3 in anode(3), while water electrolyzer runs at pH close to 14 with circulating 1M KOH at both anode and cathode at 60C(4-6). Both alkaline CO2 and water electrolyzers have demonstrated 4000hr runs with only 1-6µV/hr increase in the cell voltage(3, 5).

Here we report our preliminary results for fuel cells with Sustainion® 43 anion exchange membranes as shown in Figure 1. In this data, Pt/C catalysts were used as both cathode and anode, and humidified H2 and O2 were fed to anode and cathode, respectively. The cell operated at 60 °C with back pressure of 1 atm. The maximum power density was 0.44W/cm² and the maximum current density was 2A/cm². These initial results suggest that Sustainion® 43 membranes could be useful for alkaline membrane fuel cells.

Figure 1 Cell voltage and power density as function of current density of the fuel cell with Sustanion anion exchange membrane and Pt/C for both anode and cathode. Back pressure: 1 atm; cell temperature at 60°C.

D. R. Dekel, Journal of Power Sources, 375, 158 (2018).

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Figure 1