bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Low Temperature Epitaxial SiGe:P in View of Source/Drain Application for 5nm Technology Node and Below
Authors: Hikavyy Andriy Yakovitch , Porret Clement , Vohra Anurag , Ayyad Mustafa , Douhard Bastien , Loo Roger
Published: December 2020

After a long period of research and development high mobility Ge-based materials are being introduced as channel materials of pMOS transistors targeting 5nm node and below [1, 2]. Due to an aggressive scaling, transistors source/drain (S/D) areas are reduced dramatically along with the channel, which has a strong impact on epitaxial layers quality, strain introduction in the channel, contact resistivity, parasitic capacitances, etc. Although standard S/D materials such as SiGe:B and Si:P are being intensively used by the semiconductor industry, other options are being investigated in order to improve the contact resistivity. In the case of Ge based n-MOS transistors SiGe:P attracts attention since it allows a defect free growth on the Ge starting surface, the introduction of tensile stress in the Ge channel and comparably low Rc if sufficiently doped.

In this contribution we focus on SiGe:P growth at a very low temperature of 400oC in view of Ge-based devices processing and further 3D device integration which require a considerable reduction of thermal budget. We show that maximum achievable active P concentration (~1e20cm-3) of as grown layers strongly depends on the Ge concentration with the optimal Ge concentration below 45%. For higher Ge concentrations achievable active P concentration is lower. However, it can be significantly improved by means of post epi laser annealing which eventually allows to vary Ge concentration in a broad range of 30 – 70%. Finally, we will demonstrate a selective epitaxial growth, obtained by applying a cyclic deposition and etch routine using Cl2 as an etchant gas (Fig.1).

[1] E. Capogreco et al
., Symposium on VLSI Technology, 2019, pp. 94

[2] G. Yeap, et al., IEDM 2019, pp. 879

Fig.1. Maximal P active concentration as a function of Ge concentration in SiGe grown at 400oC (left), SiGe:P selectively grown in the Source/Drain areas of a Ge finFET device (right).

Figure 1
(Invited) Strain Engineering of Si/Ge Heterostructures on Ge-on-Si Platform
Authors: Sawano Kentarou , Youya Wagatsuma , Alam Md. M , Omata Kaisei , Niikura Kenta , Shibata Shougo , Hoshi Yusuke , Yamada Michihiro , Hamaya Kohei
Published: December 2020

Si/Ge heterostructures with high Ge contents have attracted increasing interests for last few decades because of their various high potential applications in the microelectronics industry. Strain engineering is an additional key technology not only for electronic devices with enhanced carrier mobilities but also for photonic devices since efficient light emission can be made possible via strain-induced direct band transition. In addition to the conventional (100) orientation, Si/Ge with a (111) orientation is very attractive owing to the higher electron mobility and applicability to spintronic devices via lattice matched epitaxial growth of high-quality ferromagnetic materials.

As well known, however, it is a challenging issue to grow high-quality Ge-rich SiGe layers on the Si platform due to the large lattice mismatch between Si and Ge. Hence, strain engineered Si/Ge heterostructures with high Ge contents have to be created on Ge-on-Si virtual substrates, whereas strain states and crystallinities of the SiGe are expected to be highly influenced by those of the Ge-on-Si. Here, we show recent studies on heteroepitaxy of various Si/Ge heterostructures on Ge-on-Si with various surface orientations and discuss their strain states, stabilities, critical thickness and crystal qualities. Furthermore, their applications to optoelectronic and spin devices are overviewed.
(Invited) Low-Temperature Growth of Strained Germanium Quantum Wells for High Mobility Applications
Authors: Bedell Stephen W. , Hart Sean , Bangsaruntip Sarunya , Durfee Curtis , Ott John A. , Hopstaken M , Carroll Malcolm S. , Gumann Pat
Published: December 2020

The extremely high hole mobilities attainable in strained germanium quantum wells (QW) provide a unique pathway to develop novel devices in the emerging field of quantum electronics. A major challenge associated with the growth of Ge QW structures using the industrial standard reduced-pressure chemical vapor deposition (RP-CVD) technique is the incorporation of unintentional impurities in the growing film. We will show that a compromise exists between the growth conditions that minimize the various impurities (mainly O and Si) and the abruptness of the QW. The purity of the incoming gas plays a central role in this compromise and will be discussed.
Enhancing the Kinetics Using Lithium-Powder Electrode As an Anode in Lithium-Oxygen Batteries
Authors: Lee Seung Taek , Yoon Woo Young
Published: December 2020

Lithium-oxygen battery(Li-O2 battery) is a promising candidate for use in large-scale storage systems such as electric vehicles and energy storage system. Li-O2 battery has a significantly higher theoretical energy density than conventional Li-ion batteries by using lithium metal anode which has the lowest electrochemical potential(-3.04V versus the standard hydrogen electrode) and unlimited cathode active material. However, Li-O2 battery still suffers from drawbacks such sluggish ORR/OER kinetics at the cathode, dendrite growth on the lithium metal anode and the decomposition of the electrolyte. In ORR/OER process, lithium oxide intermediate, LiO2 is generated at the cathode/electrolyte interface. It induces a high discharge/charge overpotential, which reduces round trip efficiency. And also due to its high reactivity, it makes side product reacting with electrolyte. Due to sluggish ORR/OER kinetics, LiO2 residues in the electrolyte for a long period thereby increases overpotential and reacts with electrolyte severely. It was previously reported that lithium powder electrode inhibits dendrite growth by reducing the effective current density. Also it has a capability to use more Li than conventional lithium foil electrode. In this study, lithium powder electrode(LPE) was applied as an anode in Li-O2 battery. It is proposed that lithium powder electrode not only inhibits dendrite growth on anode but also increases lithium ion diffusion thus promoting the ORR/OER kinetics at the cathode. By Cyclic voltammetry(CV) and Linear sweep voltammetry(LSV), it was confirmed that lithium powder increased kinetics of the cathodic reaction and also lithium ion diffusion coefficient was calculated using Randles-sevcik equation. The result showed that lithium powder enhances lithium ion diffusion at the cathode by increasing the electrochemically active surface area when comparing with lithium foil electrode. The morphology and chemical reaction after cycling was investigated by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). Fourier-transform infrared spectroscopy(FT-IR) and X-ray photoelectron spectroscopy(XPS) also demonstrated that side product on cathode of LPE used Li-O2 battery was reduced. Consequently, LPE used Li-O2 battery(2800mAh/g) exhibited higher discharge capacity than lithium foil electrode(LFE) used Li-O2 battery(2200mAh/g) and much better cycle performance. In conclusion, the larger electrochemically active surface area of LPE enhances the lithium ion diffusion thereby promotes ORR/OER kinetics and reduces LiO2 residual time. As a result, improved kinetics and reduced residual time of LiO2 contribute to the higher discharge capacity, better cycle performance and decreased side reaction product.
(Invited) Design of Solid Polymer Electrolytes with Poly(Ethylene Oxide) Backbone for Lithium Batteries Operated at Room Temperature
Authors: Nguyen Hanh Thi Tuyet , Subramani Ramesh , Pham Minh-Nhat , Teng Hsisheng
Published: December 2020

Replacing organic liquid electrolytes with all-solid polymer electrolytes (SPEs) remedies various safety problems related to lithium ion batteries (LIBs). This work focuses on the design of SPE membranes with a backbone of poly(ethylene oxide) (PEO), containing no solvent, ionic liquid, oligomer, or semisolid additives, for LIBs operated at room temperature. Despite their ability in dissociating the lithium salt and Li+-ion coordination, PEO-based SPEs exhibit poor ionic conductivity at room temperature because their polymer chains tend to crystallize. Instead of adding inert fillers to suppress the crystallization tendency, this work employs functional linkers, such as silsesquioxanes, isocyanates, and triglycerides, to crosslink the PEO-based chains and produce a three-dimensional polymer network. These crosslinkers serve as hubs to facilitate effective Li+-ion motion. A low glass transition temperature and a low activation energy for ion conduction confirm the high segmental mobility of the polymer chains. When incorporated with a porous PVDF membrane, the SPEs exhibit high mechanical, chemical, and electrochemical stability, showing an ionic conductivity of ~ 10−4 S cm−1 and a stable potential of >5 V (vs. Li/Li+) at room temperature. The resulting Li|SPE|LiFePO4 batteries deliver discharge capacities of >155 and >135 mAh g−1 (based on LiFePO4) at 0.1 and 1 C-rates, respectively, at room temperature with an excellent charge-discharge cycling stability (>300 cycles).
(Invited) Cubic Garnet Solid Electrolyte with Superior Air Stability
Authors: Hwang Bing-Joe , Abrha Ljalem Hadush
Published: December 2020

Garnet kind of solid electrolytes have attracted extensive attention due to their good ionic conductivity, safety and stability towards Lithium (Li) metal anode. However, the stability problem during synthesis and storage results in high interfacial resistance and prevents them from practical applications. Hence, finding the causes of degradation and being able to prepare a garnet stable in air and with less interfacial resistance are important. Here, we synthesized air-stable dual-doped ((Ga, Nb)-LLZO) cubic phase garnet with best ionic conductivity (9.4 mS cm-1), using an enhanced sol-gel method. The unique characteristics towards air stability of the (Ga, Nb)-LLZO cubic garnet is attributed to the Ga, Nb doping at the Li and Zr sites respectively and the inherited synergy of the dopants. Doping Ga at the Li site enhances the stability in air, because Ga is less reactive than Li. The influences of CO2 and H2O were investigated, separately. The (Ga, Nb)-LLZO is found to form less LiOH and Li2CO3 and they can be significantly reduced or removed after drying treatment. To confirm the stability of our garnet, electrochemical test of Li//Li symmetric cell was also performed in comparison with previously reported garnet. The dual-doped (Ga, Nb)-LLZO cubic phase garnet shows less polarized and stable plating/striping than the reported garnet. This may open a new direction for the realization of garnet based solid electrolytes with lower interfacial resistance and stable in air.
(Invited) Various Strategies Using Protective Coating Layers for High-Performance Lithium Metal Batteries
Authors: Park Soojin
Published: December 2020

Recently, a consensus has been reached that using lithium metal as an anode in rechargeable Li-ion batteries is the best way to obtain the high energy density necessary to power electronic devices. Challenges remain, however, with respect to controlling dendritic Li growth on these electrodes, enhancing compatibility with carbonate-based electrolytes, and forming a stable solid–electrolyte interface layer.

Herein, we suggest a groundbreaking solution to these challenges consisting in the preparation of a Li2TiO3 (LT) layer that can be used to cover Li electrodes via a simple and scalable fabrication method. Not only does this LT layer impede direct contact between electrode and electrolyte, thus avoiding side reactions, but it assists and expedites Li-ion flux in batteries, thus suppressing Li dendrite growth. Other effects of the LT layer on electrochemical performance were investigated by scanning electron microscopy, electrochemical impedance spectroscopy, and galvanostatic intermittent titration technique analyses. Notably, LT layer-incorporating Li cells comprising high-capacity/voltage cathodes with reasonably high mass loading (LiNi0.8Co0.1Mn0.1O2, LiNi0.5Mn1.5O4, and LiMn2O4) showed highly stable cycling performance in a carbonate-based electrolyte. Therefore, we believe that our approach based on the LT layer can boost the realization of high energy density lithium metal batteries and next-generation batteries.

Furthermore, functional organic protective layers are helpful to suppress the dendritic growth of Li metal. We would like to introduce two different polymer systems including ferroelectric poly(vinylidene fluoride) fiber mats and elastic polymer, poly(styrene-b-butadient-b-styrene) copolymer for this purpose.
(Invited) Device-Algorithm Codesign for Efficient Neuro-inspired Computing with Resistive Memory Devices
Authors: Kuzum Duygu , Shi Yuhan , Oh Sangheon
Published: December 2020

Resistive memory arrays offer an attractive solution to minimize off-chip data transfer and parallelize on-chip computations for hardware implementation of neural networks. In this talk, I will present a hardware/software co-design approach employing novel quantization and pruning methods based on switching characteristics resistive memory devices. I will discuss several aspects of neuro-inspired computation including energy efficiency, robustness and parallelism. I will share our recent results on pruning and quantization with PCM and subquantum CBRAM devices. I will conclude my talk with challenges and future directions towards towards resistive memory-based neuro-inspired systems that can autonomously learn and process information in power-limited settings.
A Low-Current and Analog Memristor with Ru As Mobile Species
Authors: Yoon Jung Ho
Published: December 2020

The switching parameters and device performance of memristors are predominately determined by their mobile species and matrix materials. Devices with oxygen or oxygen vacancies as the mobile species usually exhibit a great retention but also need a relatively high switching current (e.g., >30 µA), while devices with Ag or Cu as cation mobile species do not require a high switching current but usually show a poor retention. Here, Ru is studied as a new type of mobile species for memristors to achieve low switching current, fast speed, good reliability, scalability, and analog switching property simultaneously. An electrochemical metallization-like memristor with a stack of Pt/Ta2O5/Ru is developed. Migration of Ru ions is revealed by energy-dispersive X-ray spectroscopy mapping and in situ transmission electron microscopy within a sub-10 nm active device area before and after switching. The results open up a new avenue to engineer memristors for desired properties.
Welcome Remarks - H06: Nonvolatile Memories and Artificial Neural Networks
Authors: Shingubara Shoso
Published: December 2020

Welcome to H06: Nonvolatile Memories and Artificial Neural Networks! Take a moment to listen to welcome remarks from the lead organizer, Shoso Shingubara.
Electrochromic Alarm System with Computer Vision in Smart Contact Lens
Authors: KIM Moobum , Jung Im Doo , Kim Yeongae , Yun Jeonghun , Gao Caitian , Lee Hyun-Wook , Lee Seok Woo
Published: December 2020

Recent advances in smart healthcare system using IoT are becoming mandatory with continuous and real time healthcare monitoring system. This system can give signal to the user by sound or stimulation when health condition become severe. As one of them, smart contact lens can be used to monitor vital signals from glucose level of the tear related to diabetes1 and intraocular pressure related to glaucoma2. However, previous researches about smart contact lens used wireless communication for signal transfer which need external receiver and antenna inside. Moreover, research that deals with data transmission to the user by image visualization on the contact lens has not been yet published. Herein, we have demonstrated electrochromic alarm system which uses color change to give direct signal transfer to the user by electrochemical reaction with ions in tear. This system showed clear color change with curved shape in limited spaces. Also, diverse intensities and frequencies of color change were controlled by the various voltages and duration of voltage application to this system. In addition, various color changing patterns can be shown to the user by controlling the duration of voltage application and Morse code was used to transfer words to the user in specific purpose. With the help of computer vision, color changing patterns were detected and interpreted. We believe that our electrochromic alarm system with diverse patterns suggest new method for direct data transmission to the user with the help of computer vision. Also, it can be integrated into smart contact lens with battery and various sensors.

References

D. H. Keum, S.-K. Kim, J. Koo, G.-H. Lee, C. Jeon, J. W. Mok, B. H. Mun, K. J. Lee, E. Kamrani, C.-K. Joo, S. Shin, J.-Y. Sim, D. Myung, S. H. Yun, Z. Bao, S. K. Hahn, Wireless smart contact lens for diabetic diagnosis and therapy. Sci. Adv. 6, eaba3252 (2020).

J. Kim, M. Kim, M.-S. Lee, K. Kim, S. Ji, Y.-T. Kim, J. Park, K. Na, K.-H. Bae, H. K. Kim, F. Bien, C. Y. Lee, J.-U. Park, Wearable smart sensor systems integrated on soft contact lenses for wireless ocular diagnostics. Nat. Commun. 8, 14997 (2017).

Figure 1
Investigating Liquid Water Transport in Different Pore Structure of Gas Diffusion Layers for PEMFC Using Lattice Boltzmann Method
Authors: Sepe Mitchell , Satjaritanun Pongsarun , Hirano Shinichi , Zenyuk Iryna V. , Shimpalee Sirivatch
Published: December 2020

Proton exchange membrane fuel cells (PEMFC) require a gas diffusion layer (GDL) and micro porous layer (MPL) to aid in the transport of liquid fuel to the catalyst layer. The GDL needs to remain saturated to assist in the chemical reaction at the catalyst layer. The mass transport through the gas diffusion media is essential to the operation of the PEMFC system. Previously, to observe the liquid flow through gas diffusion media, X-ray CT scans were used. X-ray CT scans have limitations in the resolution capability. When applying a microporous layer to a GDL sample, X-ray CT’s have difficulties capturing the saturation at the micro scale level. In this work, direct modeling using the Lattice Boltzmann Method (LBM) [1-3] was applied to micro X-ray CT scans of commercial carbon paper gas diffusion media geometries. The LBM, combined with computational fluid dynamic modeling techniques, can accurately predict liquid saturation at the macro and micro scale, which provides more insight into the mass transport phenomena through the GDL. Three injection cases, seen in Figure 1, were investigated using different samples. The rib and channel wall boundary were created to represent the effect of the flow-field area inside the PEMFC. Liquid water flow through samples with and without MPL’s were studied. The primary focus of this work is to understand the transport of liquid water through the gas diffusion media, determine which injection case results in the most liquid saturation, and if the addition of an MPL increases or decreases saturation levels inside the GDL. Figure 2 shows an example of the predictions of water evolution inside sample EP40-T, without the addition of a MPL. The sample was ran at all three injection cases. When comparing each case, a dual injection point with a land and channel orientation, case 3, resulted in the most liquid present inside the sample. This work will be extended to include the effect of non-uniform wettability of GDL on water transport and saturation.

References:

P. Satjaritanun, J. W. Weidner, S. Hirano, Z. Lu, Y. Khunatorn, S. Ogawa, S. E. Litster, A. D. Shum, I. V. Zenyuk, S. Shimpalee, Journal of The Electrochemical Society, 164, (2017) E3359-E3371.

P. Satjaritanun, S. Hirano, A. D. Shum, I. V. Zenyuk, A. Z. Weber, J. W. Weidner, S. Shimpalee, Journal of The Electrochemical Society, 165, (2018) F1115-F1126.

P. Satjaritanun, S. Hirano, I. V. Zenyuk, J. W. Weidner, N. Tippayawong, S. Shimpalee, Journal of The Electrochemical Society, 167, (2020) 013516.

Figure 1
An Assessment of Novel Graphene Foam and Graphene-Based Microporous Layers for Polymer Electrolyte Fuel Cells: Fabrication and Characterisation.
Authors: Lee Florence Cecilia , Ismail Mohammed S , Ingham Derek B , Hughes Kevin J , Ma Lin , Lyth Stephen Matthew , Pourkashanian Mohamed
Published: December 2020

Polymer Electrolyte Fuel Cells (PEFC) are electro-chemical energy conversion devices capable of providing sustainable transport, stationary and portable solutions, owing to their high-power density and fast start-up time. However, water management remains one of the largest barriers limiting fuel cell efficiency and the wide scale deployment of PEFC. The microporous layer (MPL) of PEFC is widely acknowledged as a crucial, performance enhancing component; increasing cell efficiency and durability, largely by the improved management of liquid water and two-phase flow.

The purpose of this research is to develop a greater understanding of how composition affects MPL microstructure and morphology, and ultimately identifying strategies to improve fuel cell efficiency. Here we present the fabrication and characterisation of novel MPLs produced from graphene-based materials. Graphene-based materials are a highly promising MPL material, due to their unique physical structure and their excellent electric and thermal conductivity. MPLs were produced from graphene-based materials and compared to conventional carbon black. The graphene-based materials studied were; graphene foam, derived from pyrolysis of sodium ethoxide (GF); graphene nanoplatelets (GN); and multi-wall carbon nanotubes (CNT). The synergetic effect of carbons with different aspects was also studied by the fabrication of composite MPLs mixed with conventional carbon black. Analysis of the performance enhancement and water management capabilities of the MPLs was conducted through microstructural and physical ex-situ characterisation, and polarisation measurements at 100% and 20% relative humidity (RH).

Detailed analysis of the physical characteristics, morphology and microstructure provides an insight into how MPL architecture can be optimised to facilitate mass transport and negate flooding issues whilst maintaining membrane hydration. Thus, graphene-based materials hold the potential to optimise the MPL’s ability for reactant, heat and electron transport, over a range of operating conditions, and so improving overall cell efficiency.
Distribution of Water Molecules inside Proton Exchange Membrane in Transient State during Fuel Cell Operation Monitored By Operando Time-Resolved CARS Spectroscopy
Authors: Nishiyama Hiromichi , Takamuku Shogo , Iiyama Akihiro , Inukai Junji
Published: December 2020

On the performance and stability of proton exchange membrane fuel cells (PEMFCs), the distribution of water inside the membrane during the power generation has a direct, profound influence, especially for the automotive applications. In this study, coherent anti-Stokes Raman scattering (CARS) spectroscopy was applied to investigating the distribution of water and its chemical states inside the membrane with high spatial (10 μm φ (area) ×1 μm (depth)) and time (0.5 s) resolutions during the power generation.

Figure 1 shows a schematic illustration of the measurement system. Two laser lights, pump light (ω
1: 532 nm) and Stokes light (ω
2: 550-700 nm), were set coaxial and irradiated to the membrane inside the single fuel cell having a glass window in the middle on the cathode-side endplate1. The CARS light emitted was separated by filters and introduced into a spectrometer. Five measurement locations were set from the membrane surface (0 μm) of the cathode side through the membrane to that of the anode side separated by 5μm. Each spectrum was recorded every 0.5 s at each location during the current-density jump from 0.1 to 1.0 A cm−2. The number of water molecules per sulfonic acid group,λ, was quantified using spectral information from a calibration curve created in advance2.

Figure 2 shows the number of water molecules per sulfonic acid group, λ, at five locations of the membrane with the ohmic resistance and the cell voltage during the current-density jump. Upon the jump, the cell voltage dropped abruptly but increased slowly and reached a steady state, whereas the ohmic resistance of the cell decreased abruptly and increased immediately to reach a steady state after the current density jump. Upon the jump, the λ value at 0 μm overshot with a peak at 4.5 s and reached a steady state at 7.0 s. At other locations, a gradual increase in λ was observed corresponding to the electro-osmosis drag and the back diffusion of water. The results of the analysis under conditions other than those in Fig. 2 will also be reported.

Nishiyama et al. J. Phys. Chem. C 2020, 124, 18, 9703–9711

Hara et al. Electrochim. Acta 2012, 82, 277-283

Figure 1
Structured Electrodes for PEM Fuel Cells
Authors: Rahman MD Azimur , Holby Edward F. , Ahmed Towfiq , Chuang Po-Ya Abel , Komini Babu Siddharth , Kort-Kamp Wilton J.M. , Spendelow Jacob S
Published: December 2020

Slow reaction rates for oxygen reduction reaction (ORR) is one of the major barriers for improving PEMFC performance. Optimizing electrode structures for enhanced transport properties can improve high current density performance of PEMFCs. Conventional porous electrodes are fabricated by coating or spraying techniques with minimal control of its micro-structure, rendering random and tortuous transport pathways (Fig. 1a left). As a result, proton transport through the ionomer and oxygen diffusion in primary and secondary pores are sub-optimal and often become a performance limiting factor depending on the cell’s operation conditions. Therefore, a carefully designed electrode micro-structure should significantly improve proton and oxygen transport. In this work we developed structured electrodes (Fig. 1a right) for Platinum based PEMFCs where different components of the electrode serve a dedicated function (i.e., transport of proton or oxygen). These electrodes are highly ordered to reduce transport losses associated with tortuosity and non-percolation. In addition, the structural attributes are controlled on multiple length scales to minimize transport resistance and improve the PEMFC performance. For design optimization and to improve the fundamental understanding of the transport mechanism in the electrode, we developed a state-of-the-art multi-physics electrode model to perform parametric study. The model accurately accounts for ORR kinetics, agglomerate structure, proton transport in bulk membrane and thin film ionomer, oxygen diffusion in the pores, heat transfer, as well as vapor and liquid phase water transport in the electrode. By varying geometric and cell operating conditions, we conducted more than 12,000 simulations using COMSOL Multiphysics to identify critical electrode design parameters that enable fast reaction and improved transport phenomena. Results from our continuum scale simulation show significant performance improvement for structured electrodes compared to conventional electrodes (Fig. 1b). The performance improvement is due to the reduced proton and oxygen transport resistances. Altogether, our findings unveil structured electrodes as a new resource for efficient charge and mass transport, and as a promising material design platform towards obtaining reliable PEMFCs with enhanced energy conversion performance.

Figure 1
Fabrication and Evaluation of Catalyst Layers in Polymer Electrolyte Fuel Cells: A Comparison of Decal and Inkjet Printing Techniques
Authors: Shimizu Yuki , Murata Ryosuke , Kokogawa Riho , Suzuki Takahiro , Tsushima Shohji
Published: December 2020

In polymer electrolyte fuel cells (PEFCs), an enhancement of oxygen transport with excess water removal in membrane electrode assemblies can lead to better cell performance especially in high current density operation. Controlling porous structure in the catalyst layers is of great concern, satisfying these demands as well as achieving less precious catalyst loading and reduction of overpotential that are necessitated for automobile application of PEFCs. Depositing and engineering the catalyst layers have been gathering much attention intensively in these two decades [1-2]. Porous electrodes in PEFCs are generally fabricated by either coating or spraying the electrode slurry on substrate materials. Mixing, coating and drying processes of the slurry inherently affect the structural formation of the porous electrode and thus cell performance [3].

In this study, we focused our attention on the inkjet printing technique as a versatile method to control catalyst layer structure. Catalyst layers (CL) with micro-grooves, which potentially provide liquid water channels in the electrodes, were fabricated by adjusting an electrode slurry injectable from a single capillary nozzle in a printing device (Fig.1). Catalyst layers made by a decal transfer technique were also prepared for comparison. The catalyst layers prepared by each method were controlled to gain the same amount of contents, i.e. platinum, ionomer and carbon, within 5% variation.

Porous structure and cell polarization of each catalyst layer were examined. A two-stage ion-beam method using ion milling and focused ion beam (FIB) [4] was applied to analyze the spatial distribution of both ionomer and pore in the catalyst layers as shown in Fig.1. In this technique, a relatively wide cross-section of the CL was firstly formed by a broad ion beam and then, the ionomer impregnated in the CL was removed selectively by a focused ion beam. It was revealed that the electrode thickness was affected by fabrication methods, presumably due to mixing and coating processes. Cell performance shows its variation, depending on fabrication methods and this suggests an optimized electrode structure for further cell performance improvements.

Acknowledgements

This work was supported by JSPS KAKENHI Grant Number 18H01383.

References

[1] A. Strong, C. Thornberry, S. Beattie, R. Chen, S. R. Coles, J. Fuel Cell Sci. Technol., 12(6), (2015), 064001.

[2] M. Breitwieser M. Klingele S. Vierrath R. Zengerle, S. Thiele, Adv. Energy Mater., 8, (2018), 1701257.

[3] T. Suzuki, S. Tsushima, S. Hirai, Int. J. Hydrogen Energy, 36(19), (2011), 12361.

[4] T. Suzuki, T. Koyama, S. Tsushima, ECS Trans., 80(8), (2017), 419-423..

Figure 1
A Computational Fluid Dynamics Analysis of Heat Transfer in an Air-Cooled Proton Exchange Membrane Fuel Cell with Transient Boundary Conditions
Authors: Lind Alexander , Yin Chungen , Berning Torsten
Published: December 2020

In recent studies, it was found that the current density and power density in air-cooled proton exchange membrane fuel cells is limited by heat transfer. The air that serves as both reactant and coolant has a low thermal conductivity which leads to an early onset of membrane overheating at current densities that are typically in the range of 0.3 - 0.4 A/cm^2. In addition, the stoichiometric air flow ratios are in the regime that lead to laminar flow while it is known that turbulent flow leads to higher heat transfer rates and more efficient cooling. It has therefore been suggested to place a turbulence grid before the entrance of such an air-cooled fuel cell, and first experiments have shown that both the current density and power density can be increased while keeping the fan power constant.

In order to further improve the heat transfer, it has been suggested to induce pulsating flow to the air stream by sinusoidally varying the fan power as function of time. In this numerical study, a turbulence grid was placed before the entrance of a single air-cooled fuel cell channel with varying distances, and the velocity inlet of the air was varied periodically as function of time. One finding is that the choice of the numerical turbulence model is crucial in this analysis. Results indicate that the best distance between the grid and the cathode inlet is the closest at 2.5 mm which is in good agreement with prior experiments. The transient effects are small but show an additional cooling effect.

Figure 1
Feasibility Studies of Pulsed Oxidation Mitigation of CO Poisoning in Polymer Electrolyte Fuel Cells
Authors: Sarma Paran Jyoti , Gardner Christopher L , Chugh Sachin , Sharma Alok , Kjeang Erik
Published: December 2020

Operation of low temperature polymer electrolyte fuel cells (PEFCs) require up to 99.97% purity hydrogen with CO concentrations mandated to be below 0.2 ppmv by ISO 14687-2 standards [1]. The production and application of such high purity hydrogen increases the fuel price and overall cost of fuel cell operation due to the requirement of additional pre-purification measures. Indian Oil Corporation is the largest producer of reformate hydrogen with up to 99.9% purity in India. It contains traces of methane, carbon monoxide and carbon dioxide as some of the major impurities. This low-cost hydrogen could conceivably be used in PEFCs subject to operando mitigation of CO poisoning with the aid of techniques such as pulsed oxidation [2] and air-bleeding [3] to deliver satisfactory performance [4]. However, the long term impacts of these techniques and their feasibility in terms of overall efficiency and cost must be carefully assessed.

In this work, we present a detailed investigation of the pulsed oxidation technique to mitigate the effect of CO poisoning in long term PEFC operation. A single cell PEFC with an active area of 25 cm2 and Pt-Ru as the anode electrocatalyst is subjected to 80 ppm CO fuel at a nominal operating current density. Pulsed oxidation operation for 4000 cycles showed a consistent performance recovery up to 90% compared with pure hydrogen potentials. Performance governing parameters such as average potential, peak potential and droptime are presented to show changes in cell performance and pulsed oxidation efficiency. A one-dimensional transient model is developed to detect variations in cell potential and surface coverages of species during poisoning and its pulsing process. The model results show up to 26 % increase in the overall efficiency of the cell with and without the application of pulsing process as a function of bleed rates (anode flow). The technical and economic feasibility of operating a PEFC with impure hydrogen with pulsing is demonstrated.

Acknowledgement: This work was supported by Indian Oil Corporation (R&D) and Simon Fraser University under the SFU-IOCL joint PhD program in clean energy.

[1] B. Shabani, M. Hafttananian, S. Khamani, A. Ramiar, A.A. Ranjbar, J. Power Sources. 427 (2019) 21–48.

[2] P. J. Sarma, C. L. Gardner, S. Chugh, A. Sharma, E. Kjeang, J. Power Sources (2020)

[3] L-Yu Sung, B-Joe Hwang, K-Lin Hsueh, W-Nien Su, C-Chung Yang, J. Power Sources 242 (2013) 264-272

[4] C.L. Gardner, D. Mehta, S. Chugh, E. Kjeang, J. Electrochem. Soc. 166 (2019) F3123–F3135

Figure 1
Understanding the Charge Storage Mechanism of Redox-Active Ionic Liquid Based Supercapacitors
Authors: Wang Yanyu , Rochefort Dominic
Published: December 2020

Redox-active ionic liquids are emerging as promising new electrolytes for supercapacitors, which provide higher capacitance and energy density than organic or ionic liquid electrolytes. The fundamental studies of charge storage mechanism in supercapacitors are of critical importance for the development and applications of devices. Solid-state NMR (SS-NMR) methodology that has the ability to give atomic information on local environments within electrodes has been recently developed to study the charge storage mechanism of supercapacitors at molecular level. The charge storage mechanisms in supercapacitors with organic or ionic liquid electrolytes have been studied by SS-NMR. However, there is until now no research on supercapacitors with redox-active electrolyte published. Therefore, the study of charge storage mechanism in supercapacitors with redox-active electrolyte are highly required. In this context, we employed SS-NMR techniques combined with electrochemical dilatometry measurements that are associated with charge induced strain of electrode to investigate in depth the charge storage during charging process in supercapacitors with redox-active ionic liquid electrolyte. It is revealed that the charging process of supercapacitors with redox-active ionic liquid electrolyte EMIM FcNTf/ACN is driven by different charge regimes for different voltages, that is, co-ion desorption at low voltage range and subsequently counter-ion adsorption at higher voltage range. The electrochemical dilatometry measurements show macroscopic change of the electrode during charging and further confirm the proposed mechanism obtained from SS-NMR. The results give a detailed picture of the charge storage mechanism of supercapacitors with redox ionic liquid electrolyte, providing new insights on the charge storage of supercapacitors.
Electrochemical Study of the Effect of Prussian Blue As a Mediator in a Solid-State Supercapacitor
Authors: Qiao Xiaoyao , Wang Yuchen , Zhang Chen , Yan Zhiwei , Akin Mert , Mansour Azzam N. , Zhou Xiangyang
Published: December 2020

In the present study, electrochemical, X-ray photoelectron spectroscopy (XPS), and In-situ X-ray absorption spectroscopy (XAS) measurements were performed to investigate the charge/discharge process in a solid-state mediator supercapacitor (SC) or redox electrolyte SC. Prussian blue (PB) was synthesized using a wet chemistry method. A solid-state asymmetrical supercapacitor was fabricated with the configuration of (active carbon) /polymer electrolyte membrane/ (active carbon + PB). A KCl saturated Ag/AgCl reference electrode was inserted in the cell to monitor the potentials of the positive and negative electrodes during the charge/discharge process. Both electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements indicated that the supercapacitor had a capacitor-like behavior. Upon negative polarization of the PB-containing electrode the specific capacitance of the SC was increased 80% while upon positive polarization, there was much less enhancement of the specific capacitance. The potentials of the two electrodes versus the reference electrode were displaced proportionally with increasing the voltage of the cell. The XPS results indicated that the potassium concentration in PB is 0.5 atomic % suggesting that iron ions had valence close to +3, which is consistent with the measured XPS binding energy of the Fe 2p3/2 line and the X-ray absorption Fe K-edge energy when compared with the appropriate reference compounds. This indicated that instead of a nominal chemical formula KFeFe(CN)6, the formula was actually closer to K0.07FeFe(CN)6. In-situ XAS results (Figure 1) confirmed that upon positive polarization of the PB-containing electrode there was only small degree of redox activity occurring. On the other hand, upon negative polarization of the PB-containing electrode there was significant redox activity occurring due to reduction of Fe3+ to Fe2+. The XAS results also confirmed that the redox activity is completely reversible between cycles 4 and 5.

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High Rate Capability of Tungsten Oxide Coated Graphite Anode for Lithium-Ion Battery
Authors: Ma Donghyeok , Chung Dong Jae , Choi Seong Hoon , Kim Hansu
Published: December 2020

On increased demands for electric vehicles (EV), Lithium-Ion Batteries (LIBs) face new challenge in terms of fast charging. Graphite, successfully implemented as anode material in current LIBs, shows prominent limitation during fast charging process. As resolving such a problem, many researchers have been suggesting the alternative of graphite materials. In this presentation, we present fast charging capability of graphite anode by coating tungsten oxide layer by means of sol-gel reaction. The tungsten oxide coated graphite showed high performance at a high rate without compromising reversible capacity. The tungsten oxide coated graphite anode showed 90.3% of capacity retention at a rate of 5 C (1800 mA g-1) compared to reversible capacity obtained at a rate of 0.2 C (72 mA g-1). This result showed that the tungsten oxide coated graphite can provide a way to overcome the limitation in term of rate capability. More detailed microstructure and electrochemical properties of tungsten oxide coated graphite material will be discussed in the presentation.
A Method to Optimize 3D Microbatteries
Authors: Miyamoto Kaito
Published: December 2020

The rapid development of information technology (IT) since the end of the 20th century and the technological progress of sensors and devices have familiarized the concept of the Internet of Things (IoT). So far, the miniaturization of the sensors and devices has significantly contributed to the rapid growth of the IoT ecosystem. However, compared with such technological progress on the sensors and devices, the miniaturization technology of the power sources for the off-grid operation of the electronics has not been well established, which hinders further prevalence of the IoT. Especially, for the integration with microelectronics, the high areal energy density is recognized as one of the key properties for such power sources.

As one of the promising candidates for such IoT-enabled power sources, lithium-ion microbatteries have attracted attention. Especially, the three-dimensional design of the microbattery at full cell level has been investigated in order to improve the areal energy density while maintaining high power density. The benefit of the geometrical modification is the lowering of the internal resistance due to the reduction of the ion transport distance without reducing the battery capacity. Indeed, the recent advancement of a variety of 3D manufacturing technologies has allowed the realization of the 3D microbattery. However, the 3D electrode structure is limited to simple shapes such as interdigitated plate or cylindrical electrodes and, therefore, the battery performance is restricted by such electrode shapes. To design the 3D battery architecture beyond the interdigitated configuration, the 3D battery optimization method at the full cell level is vital. Also, the 3D battery optimization method is crucial from the point of view of industrial demand since there are a variety of IoT devices that have different functions, and it is demanding to optimize the battery following the requirements of each IoT device by hand. However, there are no reports regarding the 3D battery optimization methods at the full cell level.

In this talk, we propose a novel battery optimization system at the full cell level, which consists of an automatic geometry generator and performance simulators. The geometry generator designs the full cell based on the random sampling by only receiving the size and the resolution of the 3D battery cell as the input data. For compatibility with the geometry generator, as one of the performance simulators, we newly propose the transmission line model, the so-called 3D porous electrode model, to compute the internal resistance of the 3D battery quickly. To demonstrate the effectiveness of our approach, the tradeoff frontier for the internal resistance and capacitance is created by plotting 200,000 data points as shown in Fig. 1 (a). From the figure, we successfully find new battery geometry (Geometry D in Fig. 1 (b)), which has both higher power and energy densities than the interdigitated plate configuration (Geometry C in Fig. 1 (b)).

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Renewable Flexible Supercapacitors Based on Lignin Electrodes and Electrolytes
Authors: Park Jeong Hee , Rana Harpalsinh H. , Kim Junsu , Park Ho Seok
Published: December 2020

Lignin which is the second most abundant natural polymer is found to be the most promising candidate for environmentally benign energy storage materials because of its high carbon content, favorable functionality, biodegradability and economic feasibility. Also, the valorization of lignin (to produce something useful like materials, energy or chemicals) is considered as an effective way to minimize our reliance on depletion non-renewable energy sources and to explore novel feedstock for energy storage/conversion device. Therefore, in the quest for renewable and highly efficient energy storage devices, we have prepared lignin-based porous freestanding electrodes and chemically crosslinked hydrogel electrolytes. Ultimately we have fabricated all-solid-state flexible supercapacitor exhibiting a maximum energy density and power density of 4.49 Wh kg-1 and 2.63 kW kg-1, respectively by integrating the lignin-PAN nanofiber electrodes and lignin hydrogel electrolytes. Our approach of using wood biomass based renewable materials for the flexible energy storage devices is expected to contribute to the expansion of sustainable chemistry.
Area-Perimeter Relation for Si-Based Anode Materials Using Cross-Sectional SEM Analysis
Authors: Qin Si
Published: December 2020

Silicon is one of the promising anode materials for next generation high energy density batteries due to its high theoretical capacity. However, its large volume expansion during lithiation hinder its practical application. Here, we report a relation of cross-sectional area and particle perimeter of lithiated silicon using cross-sectional SEM analysis in order to discuss volume expansions and surface degradations of Si-based materials.

The silicon electrodes were prepared by a mixture of Si-based materials, conductive materials and binders in a weight ratio of 80:10:10. After gently fabricating cross-sectional electrodes with an ion-milling, cross-sectional SEM images before and after lithiation were obtained. A software, ImageJ was utilized to process the SEM images and calculate length of X-axis and Y-axis, cross-sectional areas and particle perimeters.

Figure 1 shows SEM images of a Si-based electrode before and after lithiation. Si expanded uniformly with X-axis and Y-axis expansion ratio of 128%. The cross-sectional area was the expansion ratio of 165%. Since volume expansion is uniform, volume should be calculated by setting to 3 power of X-axis (or Y-axis) or 3/2 power of cross-sectional area. According to the above data, we achieved similar volume expansion rates those were 210% (calculated by X-axis) and 214% (calculated by cross-sectional area). With this method, expansion rate of graphite was shown to be 112%, which is similar to previous Schweidler’s report (113%) [1]. Figure 2 shows processed images of high resolution SEM before and after cycling in order to calculate precise perimeter of Si-based material. The perimeter after the initial lithiation increases to 1.2 times larger than the pristine electrode, which is equivalent to the volume expansion. However, a perimeter after cycling is 3 times larger and it could be caused by a surface erosion. It suggests that the perimeter relates the surface erosion with SEI formation, not only the volume expansion.We will demonstrate the detailed results of cross-sectional SEM analyses on several other Si-based materials.

References

[1] S. Schweidler, L. d. Biasi, A. Schiele, P. Hartmann, T. Brezesinski, and J. Janek, J. Phys. Chem. C 2018, 122, 8829.

Figure 1