bluuebunny/crossref_metadata_2025 huggingface dataset:
Alleviation of Internal Microstrain in Ni-Rich Ncma Cathode through Microstructure Tailoring
Authors: Ryu HoonHee , Lee Jin Wook , Sun Yang-Kook
Published: November 2022

Lithium–ion batteries (LIBs) became mainstream power sources for a wide variety of electronic devices and electric vehicle applications. The cost and overall performance of LIBs are primarily dictated by the cathode, which is the heaviest and most expensive component in an LIB. To achieve the recommended threshold for future EVs, Ni-rich, Li[NixCoy(Mn or Al)1−x−y]O2 (NCM or NCA) materials above Ni 90% have become strong cathode candidates because of their high reversible capacities, close to their theoretical values, and relatively low material cost owing to their low Co content. To address the poor durability of Ni-rich NCM cathodes, the introduction of Al into an NCM cathode (NCMA) is a practical strategy to stabilize the host layered structure; consequently, outperforming both NCM and NCA cathodes with the same Ni content. However, the loss of capacity owing to the electrochemical inactivity of Al limits the fraction of the Al dopant that can be introduced. This also limits the usefulness of Al–doping in improving the cycling stability of Ni–rich NCMA cathodes which exhibit rapid capacity fading resulting from the high concentration of unstable Ni4+ species in the deeply charged state. In this presentation, we report microstructure-tailored NCMA of which the core is encapsulated by a buffer layer. Similar to tempered glass, where a steep thermal gradient during quenching produces different states of stress in the surface and the bulk material, the proposed hybrid cathode structure suppresses the formation of microcracks by creating a non-uniform spatial distribution of the microstrain within the cathode particle, thereby improving its long-term cycling stability.
Decomposition Pathways of EC and Effects of Additives: Accounting for Liquid, Gas, and Solid Phase Reactions during the First Charge
Authors: Kerber Brian M , Guillot Sarah Lucienne , Usrey Monica Lee , Zhou Liu (Amy) , Du Peng , Peña-Hueso Adrián
Published: November 2022

The majority of lithium-ion batteries (LIBs) utilize carbonate-based electrolytes, due to the good lithium solvation, electrochemical stability, and electrode passivation.1 Studies regarding decomposition pathways and other reaction mechanisms2-4 of carbonates in LIBs are abundant in the literature but few attempt to quantify total losses of these solvents. Quantitative measurement of solvent loss from the electrolyte would significantly inform the comprehensive picture of electrolyte reaction mechanisms in the cell. Furthermore, this approach allows for the study of any effects additives may have on carbonate solvent decomposition. For example, organosilicon (OS) additives have been shown to reduce gassing and improve high temperature cycling in carbonate-based LIBs,5 but their quantitative impact on EC decomposition is not known.

In this poster, we detail our methodology for quantitatively tracking and characterizing different forms of ethylene carbonate (EC) decomposition in a LIB pouch cell as well as the effects of organosilicon additives on these reactions. This study focused on the loss of EC after the first charge when the majority of SEI formation occurs. Liquid phase composition, including both EC and its decomposition products, was quantified by NMR analysis (1H and 19F) of extracted electrolyte using internal standards (LiPF6 and 1,4-bis(trifluoromethyl)benzene). Gas phase decomposition was characterized by a combination of the Archimedes method (to quantify gas volume) and GC-MS analysis (to determine gas composition). Finally, the impact of OS additives on the decomposition pathways of EC was examined. Inclusion of OS molecules reduces EC decomposition during the first charge, predominately by reducing the amount of liquid phase decomposition.

1Xu, K. Chem. Rev.
2004, 104, 4303-4417.

2 Campion, C.; Li, W.; Lucht, B. Thermal Decomposition of LiPF6-Based Electrolytes for Lithium-Ion Batteries. Journal of the Electrochemical Society
2005, 152, A2327.

3 Seo, D.; Chalasani, D.; Parimalam, B.; Kadam, R.; Nie, M.; Lucht, B. Reduction Reactions of Carbonate Solvents for Lithium Ion Batteries. EC Electrochemistry Letters
2014, 3, A91-A93.

4 Xing, L.; Li, W.; Wang, C.; Gu, F.; Xu, M.; Tan, C.; Yi, J. Theoretical Investigation on Oxidative Stability of Solvents and Oxidative Decomposition Mechanism of Ethylene Carbonate for Lithium Ion Battery Use. J. Phys. Chem. 2009, 113, 16596-16602.

5 Guillot, S.L.; Usrey, M.L.; Peña-Hueso, A.; Kerber, B.M.; Zhou, L.; Du, P.; Johnson, T. Reduced Gassing in Lithium-Ion Batteries with Organosilicon Additives. J. Electrochem. Soc.
2021, 168, 030533-030543.
Dynamics of Lithium Microstructure at Lithium Metal and Graphite Anodes Probed with in Operando Pulse EPR
Authors: Szczuka Conrad , Ackermann Jörg , Schleker P. Philipp M. , Jakes Peter , Eichel Rüdiger-A. , Granwehr Josef
Published: November 2022

Lithium microstructure formation is the limiting factor preventing the application of lithium metal anodes and, to some degree, fast-charging of graphite anodes, because of enhanced cell degradation and risks of short-circuits. To improve mechanistic understanding and develop prevention strategies, a complementary analytical tool set is necessary.

Contributing to non-invasive in operando techniques, we present pulse electron paramagnetic resonance (pEPR) with a practical sampling rate of 100 microseconds, providing a global view on lithium microstructure formation and evolution.[1] pEPR experiments offer an estimate of the dimension and size distribution of the morphology that is in line with post-test SEM characterization. For lithium metal anodes, the sampling rate is sufficient to observe dynamic morphology changes that evolve for several seconds after fresh lithium deposition, attributed to surface smoothening, comparable to recently observed heating-induced healing of dendrites.[2] For graphite anodes, lithium plating can be followed at C-rates up to 18C. Quantitative measurements reveal an exponential increase of deposited lithium mass upon galvanostatic charge. The plating onset is pinpointed to the characteristic voltage drop well below 0 V vs. Li/Li+.[3] After stopping the charge at intermediate states of charge, the partial intercalation of lithium can be monitored at OCV, identifying two kinetic domains and the amount of remaining dead lithium.

[1] C. Szczuka, J. Ackermann, P. Philipp, M. Schleker, P. Jakes, R.-A. Eichel, J. Granwehr, Commun. Mater.
2021, 2, 20.

[2] L. Li, S. Basu, Y. Wang, Z. Chen, P. Hundekar, B. Wang, J. Shi, Y. Shi, S. Narayanan, N. Koratkar, Science.
2018, 359, 1513–1516.

[3] C. Uhlmann, J. Illig, M. Ender, R. Schuster, E. Ivers-Tiffée, J. Power Sources
2015, 279, 428–438.

Figure 1
Silver Grafted Ti3C2-Mxene Nanocomposite As Novel Anode Materials for Lithium-Ion Batteries
Authors: Abdul Quddus Khadija , Tariq Hanan Abdurehman , Shakoor Abdul , Al-Qaradawi Siham , Kahraman Ramazan
Published: November 2022

Dependence on fossil fuels for energy is a huge obstacle in the current age due to their unreliability, rising costs, and impact on the environment. The aforementioned issues can be resolved by developing energy storage systems (ESS) such as lithium-ion batteries (LIBs). The proposed synthesis focused on the synthesis of Ag-Ti3C2 (Ag-MXene) nanocomposites, which was followed by studying the physical characteristics and electrochemical performance of the material. The MXenes are resistant to oxidation, have outstanding thermal and electrical conductivity, high electrochemical efficiency, composition flexibility, and a large specific surface area. This Ag-Ti3C2 (Ag-MXene) was synthesized by first synthesizing MXene from MAX (M=Ti, A=Al, X=C) using mixed acid method followed by the reduction of silver nitrate. It is challenging to coat Ag nanoparticles due to the narrow space between MXene layers, so an appropriate synthesis route was developed. XRD proved the presence of pure Ag nanoparticles on Ti3C2 layers with sharp peaks showing its crystalline nature. Homogenous distribution of Ag particles of size ≈ 50nm on Ti3C2 and its morphology was illustrated by SEM images. TGA revealed the improvement in thermal stability of Ti3C2 with the use of Ag. Along with this, the electrochemical properties of both Ag-Ti3C2 and Ti3C2 anodes in lithium ion batteries were examined using testing methods such as galvanostatic charge/discharge, cyclic voltammetry, and rate capability. Ag-Ti3C2 nanocomposite outperformed pure Ti3C2, providing greater performance and enhanced cycle efficiency. After 100 cycles at a current density of 0.1C, Ag- Ti3C2 nanocomposite had excellent cyclic stability and a highly reversible potential of around 523 mAhg-1.The rate capability was also improved to up to 180 mAhg-1 at 10C. These beneficial properties were caused by the unique morphology of the proposed material. Furthermore, carefully coated Ag-Ti3C2 and Ti3+ layers produce high conductivity in MXene layers and the Li+ ions can readily diffuse to the electrode through coated MXene layers.
Hydro-to-CathodeTM Customizable Cathode Materials Made from Recycled Elements
Authors: Liu Yadong , Deng Haixia , Gratz Eric , Wang Yan
Published: November 2022

With the explosively growth of battery usage from consumer electronics to electric vehicles, and large scale on/off-grid renewable energy storage, a large quantity of spent batteries that once powered those devices has been generated and will accelerate within the next decade and beyond. To avoid tons of spent batteries ending up in landfills, which would be hazardous wastes and could cause severe environmental pollution, we developed a highly cost-effective and energy-efficient technology “Hydro-to-Cathode” to recover the precious elements (Li, Ni, Mn, Co, etc.) from the spent batteries and make them into new cathode materials and batteries to power new devices.

Without extracting and separating the elements in the leached solution like the traditional hydrometallurgy approach does, Ascend Elements starts directly with the impurity-removed and adjusted solution to make high quality precursor for cathode materials. By controlling the conditions of precursor reactions and sintering process, we can make cathode materials with a wide range of particle sizes (2~16 µm), single crystal/polycrystalline, porous or dense intraparticle structure, and different compositions, including LiNi1/3Mn1/3Co1/3O2 (NMC 111), LiNi0.5Mn0.3Co0.2O2 (NMC 532), LiNi0.6Mn0.2Co0.2O2 (NMC 622), LiNi0.8Mn0.1Co0.1O2 (NMC 811), LiNi0.83Mn0.06Co0.11O2 (Ni 83), and LiCoO2 (LCO). The recycled cathode materials show as good as, or even better performance than cathode materials made from newly mined salts. Our unique Hydro-to-CathodeTM process significantly reduces the steps and costs to recover and recycle cathode materials from spent batteries.
4.7 Kv Reverse Breakdown Voltage Ultra-Thin Double-Layered NiO/β-Ga2O3 p-n Junction Rectifiers
Authors: Li Jian-Sian , Chiang Chao-Ching , Xia Xinyi , Yoo Timothy Jinsoo , Ren Fan , Kim Honggyu , Pearton Stephen J
Published: November 2022

In this study, we present a double-layer NiO/β-Ga2O3 p-n heterojunction diode, which exhibits high performance with breakdown voltage, on-resistance and turn-on voltage. β-Ga2O3 has been attracting great attention as one of the excellent materials for next-generation high-performance electronics, owing to its high Baliga’s figure-of-merit (BFOM), carrier mobility, critical breakdown field strength and low-cost, simple growth methods. β-Ga2O3 based unipolar devices, especially Schottky barrier diodes, have been developed rapidly; however, the lack of p-type doping in Ga2O3 remains a challenge for bipolar devices, which can more generally be utilized in practical applications. One of the possible strategies is to introduce a p-type material to construct p-n junctions with n-type β-Ga2O3. The NiO turns out to be a feasible p-type material that has a wide bandgap, adjustable doping concentration, intrinsic p-type conductivity and diverse deposition techniques to form a uniform film, such as sputtering, PLD and thermal oxidation. In this study, we fabricated the diodes from depositing Ti/Au for the back Ohmic contact metal and annealing at 550℃ in N2, followed by sputtering two NiO layers with different doping concentrations by tuning the ratio of Ar/O2. The Ni/Au contact metal was deposited onto the NiO layer after annealing at 300℃ under O2 ambient. Compared to typical NiO thicknesses of 300 to 500 nm, we turned to another trend with ultra-thin layers of NiO. The top layer NiO thickness is 10nm while the bottom layer of NiO thickness varies from 10 to 80 nm. Through the design of the ultra-thin (20 nm) double-layer NiO structure, the breakdown voltage (Vb) is substantially improved to 4.7 kV and demonstrates the on-resistance (Ron) of 11.3 mΩ·cm2, which leads to a figure-of-merit (Vb
2/Ron) of 2 GW/cm2. The high Vb is attributed to the structure of both the double-layer and the guard-ring designs. From the TCAD simulation, the peak of the electric field locates at the edge of the diodes. Increasing the doping concentration of NiO layer contact with Ni/Au can reduce the electric field on the edge of the Ohmic contact. On the other hand, the low doping concentration of the NiO contact with β-Ga2O3 can effectively move the electric field crowding on the edge to the inside of devices. In addition, the extension guard ring can also spread the electric field crowding. This work provides a desirable design strategy for p-n heterojunction, which has the highest breakdown voltage among all Ga2O3-based p-n diodes.

Figure 1
(Invited) Approach to Oxide Tfts with High Mobility & Stability
Authors: Hosono Hideo
Published: November 2022

Thin film transistors (TFTs) with the channel of amorphous oxide semiconductors (AOSs) represented by amorphous Indium-Gallium-Zinc Oxide (a-IGZO) are now applied to drive pixels of the state-of the art display based on high mobility, good homogeneity, easy fabrication and optical transparency [1]. Recently, larger mobility TFTs are highly demanded for emerging applications such as ultra-high vision and memories. However, there is a critical obstacle to be overcome, i.e., an empirical trade-off rule in oxide TFTs between mobility and stability. Higher mobility TFTs possess less stability to various types of stress (negative bias-thermal stress instability, NBTS, positive bias-thermal stress instability, PBTS, and negative bias-illumination stress instability, NBIS). The Elucidation of origin for this trade-off rule and new approach are required to realize high mobility and high stability TFTs.

We clarify that the origin of this trade-off through comparison in TFTs between IGZO with low mobility and high stability and ITZO with high mobility and low stability. A critical phenomenon was noted during the conventional TFT fabrication; CO-related impurity donates electrons to Indium-Tin-Zinc Oxide (ITZO) with high mobility under the negative bias stress condition but such CO-related impurity effect is negligible in IGZO with lower mobility than ITZO [2]. This finding may be understood by considering that large difference in ECBM determines the transfer of electron generated by adsorbed CO-related species on the back surface of ITZO [3]. Based on this model and this finding, we successfully fabricated the most stable ITZO TFT with a high mobility of 70 cm2/Vs by eliminating CO-related impurity and further passivation; NBTS (-20V, 60 oC, 3600 s, ΔVth: -0.02 V), PBTS (+20 V, 60 oC, 3600 s, ΔVth: 0.12 V) and NBIS (-20V, 15000 lx, 3600s, ΔVth: -1.33 V).

[1] Hosono, H., & Kumomi,K., (ed), Amorphous Oxide Semiconductors: IGZO and Related Materials for Display and Memory (Wiley, 2022); Hosono, H. (2018). How we made the IGZO transistor. Nature Electronics, 1(7), 428-428.

[2]Shiah, Y. S., Sim, K., Ueda, S., Kim, J., & Hosono, H. (2021). Unintended Carbon-Related Impurity and Negative Bias Instability in High-Mobility Oxide TFTs. IEEE Electron Device Letters, 42(9), 1319-1322.

[3] Shiah, Y. S., Sim, K., Shi, Y., Abe, K., Ueda, S., Sasase, M., Kim,J., & Hosono, H. (2021). Mobility–stability trade-off in oxide thin-film transistors. Nature Electronics, 4(11), 800-807.
2D MoS2 Pattern from Sol-Gel-Processed Precursors Using Jet Printer for TFT Application
Authors: Choi Woon-Seop , Can Thi Thu Thuy
Published: November 2022

Molybdenum disulfide (MoS2) is one of the most studied layered TMDCs due to its excellent optical, electrochemical, and electrical properties. Monolayer MoS2 is a semiconductor with a direct band gap of 1.8 eV, but it has an indirect band gap in its bulk form, and make it possible to use 2D materials in the next generation of switching and optoelectronic devices.

Many research groups have attempted to synthesize MoS2 with different methods to make good MoS2 quality. Mechanical exfoliation has been known as an uncomplicated way for flakes extracted from single crystals. However, several restrictions that method had to come up with were small and random flake size then extreme difficulty in the alignment for device fabrication. Chemical vapor deposition (CVD) have been used to prepare MoS2 thin layers in large scale. Nevertheless, this method demanded vacuum, the use of Mo or MoO3 thin films as precursors included in four-step CVD process for reduction and sulfurization resulted in expensive MoS2 films. Solution based methods, by contrast, is promising for large area formation of controllable MoS2 film with simple equipment, time-saving at low cost. No report has been published using jet printing technology from MoS2 precursor solution but our group.

Therefore, the goal of this research was to develop a new drop-on demand printing method for MoS2 atomic layers based on sol-gel synthesis method. We developed a unique solution process to obtain large-size and uniform MoS2 atomic layers without CVD. The sulfurization process is omitted to simplify the entire process, and wafer-scale and larger-scale synthesis of MoS2 can be achieved by simple thermal treatment. The atomic layers of the synthesized MoS2 were identified as 2 layers, 3 layers, and 5 layers for MoS2 concentrations. MoS2 patterns were made with highly uniform coverage using electrohydrodynamic (EHD)-jet printing for the first time. The EHD jet-printed MoS2 TFTs show good electrical properties of 19.4 cm2 V-1 s-1.
(Invited) Highly Active Metal Pyrites Catalysts for a Low-Cost, High-Performance Polysulfide/Ferrocyanide Redox Flow Battery
Authors: Dong Yifan
Published: November 2022

Polysulfide is a promising redox couple employed in various aqueous redox flow batteries (RFB) for large scale electrochemical energy storage due to its high solubility and low cost. However, polysulfide has much lower rate constant in comparison with other commonly used redox couples in RFB. Therefore, efficient electrocatalysis is a key to achieving high performance for polysulfide-based RFB. Here we first systematically investigated the electrocatalytic activity of various pyrite phase metal disulfides (FeS2, CoS2, NiS2) as thin film electrodes towards polysulfide redox reactions under steady state condition. Then we further demonstrated a high-performance polysulfide/ferrocyanide RFB using optimized high surface area NiS2 nanostructures grown on carbon paper as the electrode. The NiS2/carbon paper electrode showed a high exchange current density of 9.3 mA cm-2 and was able to achieve a current density of 38.6 mA cm-2 at an over potential of 100 mV. An aqueous polysulfide/ferrocyanide RFB employing NiS2/carbon paper as anode and plain carbon paper as cathode was further evaluated by constant current cycling test and electrochemical impedance spectroscopy to demonstrate high charging-discharging cycling performance and low charge transfer impedance.
(Invited) Stretchable Sensing Devices Combining Ionic Liquids and Soft Electrodes
Authors: Ota Hiroki
Published: November 2022

In recent years, a variety of ultra-flexible devices have been proposed. Their applications include wearable devices and soft robots. Among ultra-flexible devices, the devices with stretchablity is attracting attention as next-generation sensing devices. In such devices, ionic liquids can be used as a sensing material. Ionic liquids are polymers in a liquid state and their structure can be easily altered, For example, ionic liquids can be developed reactive to temperature, humidity, light, gases, and many other factors. Furthermore, since they are in a liquid state, they are durable against device stretching. In this study, we report on a stretchable sensing device using ionic liquids. In particular, by using liquid metal and CNT(Carbon nanotube) as electrode materials, we propose a super-stretchable device and a super-flexible device with transparency and high breathability.

 liquid metal was used as electrode, and ionic liquids as a sensing material. Equivalent circuit of the sensors were established based on Nyquist plot The sensor showed stable sensitivity to temperature without hysteresis as shown with a 0.039/°C increase in conductivity, which is quite high compared to other reports. We also show proof of concept for humidity, oxygen gas, and optical sensings using four kinds of ionic liquids, 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][Otf]), 1-Butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMPYR][NTf2]) and 1-butyl-3-(4-phenylazobenzyl)imidazolium bis(trifluoromethanesulfonyl)amide ([Azo][NTf2]) for optical sensing. The sensitivity of each ionic liquid to humidity and oxygen differed depending on the ionic liquid. For each type of stimuli, the sensing can be optimized by choosing the proper ionic liquid. In addition, using [Azo][NTf2], we demonstrate optical sensing and memory in this study.

< Transparent and Breathable Ion Gel-based Sensors using CNT> highly transparent, ultra-flexible, and gas-permeable polymer thin-film sensors using ion gels as the sensing material, which demonstrated the capacity for selective detections, were proposed. Particularly, simultaneous and independent sensing of temperature and humidity was demonstrated in this study. The sensors were fabricated using a simple spray coating method on a thin silicone rubber film (around 25 µm thickness). Owing to their thin-film shape, they showed more than 80% visible light transmittance and a higher gas permeability of 58.7 g/m2 h than the human transepidermal water loss. Simultaneous and independent detection of temperature and humidity was achieved with a high sensitivity of 15.9%/°C and 2.5%/percentage of relative humidity, respectively, using two types of gels with ionic liquids.

These results suggest that the easily modifiable nature of ionic liquids contribute to the development of stretchable electronics.
Wireless Self-Powered High-Performance Integrated Nanostructured-Gas-Sensor Network for Future Smart Homes
Authors: Song Zhilong , Fan Zhiyong
Published: November 2022

The accelerated evolution of communication platforms including Internet of Things (IoT) and the 5th generation (5G) wireless communication network makes it possible to build intelligent gas sensor networks to monitor the chemical safety of our surroundings and personal health in real time. However, this application scenario requires a very challenging combination of characteristics of gas sensors including small formfactor, low-cost, ultra-low power consumption, superior sensitivity, and high intelligence. Herein, we demonstrate self-powered integrated nanostructured-gas-sensor (SINGOR) systems and a wirelessly connected SINGOR network for the first time. The SINGOR features ultra-high sensitivity to H2, formaldehyde, toluene, and acetone with the record low limits of detection (LOD) of 10 ppb, 2 ppb, 1 ppb and 1 ppb, respectively, obtained under room temperature sensor operation. Therefore, ultra-low power consumption of 68.6 μW at sensor level and 1.71 mW at the system level has been achieved. As the result, an individual SINGOR system can be self-driven by indoor light with a Si solar cell. Furthermore, each SINGOR consists of an array of nanostructured sensors powered by machine learning algorithm and thus a SINGOR has the capability of gas pattern recognition and classification. And multiple SINGOR systems are wirelessly connected together to form a sensor network for smart home application demonstrations. Intriguingly, the sensor network has successfully demonstrated flammable gas leakage detection and alarm function when they are deployed in multiple rooms. And when the SINGOR network is deployed in one single room, it can achieve gas leakage localization with satisfactory precision. These successes open up the possibility of using nanostructured-gas-sensor network for wide range applications including smart home, smart building and future smart city.
(Invited) Triboelectric Nanogenerator as a New Energy Solution for Biomedical Applications
Authors: Kim Sang-Woo
Published: November 2022

As main topics, this presenter will report transcutaneous ultrasound energy harvesting using triboelectric technology. Implantable medical devices (IMDs) are designed to perform or augment the functions of existing organs by using monitoring, measuring, processing units, and the actuation control. Conventional IMDs are powered with primary batteries that require frequent surgeries for maintenance and replacement. Therefore, IMDs require a new reliable and safe powering system to avoid the need for frequent surgeries. Recently my group demonstrated that ultrasound was used to deliver mechanical energy through skin and liquids and demonstrated that a thin implantable vibrating triboelectric nanogenerator (TENG) is able to effectively harvest it. Ultrasound TENG (US-TENG) was triggered with an applied ultrasound. As the second topic, the presenter will deal with our very recent demonstration of a commercial coin battery-sized high-performance inertia-driven TENG (I-TENG) based on body motion and gravity. In a preclinical test, we demonstrate that the encapsulated device successfully harvested energy using real-time output voltage data monitored via a Bluetooth low-energy information-transmitting system. Finally the presenter will report a self-powered disinfection system for the rapid disinfection of air-transmitted bacteria and viruses based on a highly efficient nanowire-assisted electroporation mechanism powered by vibration-driven TENGs that harvest mechanical vibration energy.
Photothermal Lasing-Assisted Synthesis of 2D Metal-Organic Framework and Its Application to Memory Device
Authors: Han Seung Woo , Lee Chang Taek , Shin Moo Whan
Published: November 2022

Resistive random access memory (RRAM) has attracted as candidate in the next generation of non-volatile memory device due to its low power consumption, fast write/erase speed, and high CMOS compatibility 1–3. At present, among various materials, metal-organic frameworks (MOFs) are significantly attracting attention as promising materials for data storage applications due to their advantages of highly ordered pores, large surface area, tunable structure, and subsequent controllable function 4–6. However, it is difficult to apply MOF to RRAM, because synthesis time is generally long and additional step is needed to form the MOF into a thin film. Therefore, there is a need for a new method for synthesizing MOF in the form of a thin film simply and fast. In this work, we simply and fast synthesized a 2D MOF nanosheets, Cu(BDC), in the form of thin film using laser process. The dissolved ligand (terephthalic acid) in the N,N-dimethylformamide (DMF) is dropped on the Cu thin film and then irradiate the laser beam on the active spot. Photon energy of laser is absorbed in the Cu metal film, which generate the photothermal effect. This photothermal effect oxides the Cu atom into Cu ion and the oxidized Cu ions are used as metal source of Cu(BDC). This process simply and quickly transforms the Cu thin film into a Cu(BDC) thin film that can act an active layer of RRAM. The suggested method not only is finished in minutes, but also does not needed additional process step of transferring the MOF onto the thin film. The fabricated 2D MOF based-RRAM shows a typical bipolar switching behavior. Our device also exhibits a high on/off ratio (>103), low set/reset voltages (1 V > in SET and -0.5 V > in RESET), and long retention (1×104
s). Therefore, our research suggests a simple and rapid synthesis method of MOFs in the form of a thin film by using laser process and demonstrates applicability 2D MOF fabricated by laser process for the non-volatile memory device.

Figure Caption

Figure (a) Schematics of synthesis of metal-organic frameworks (MOFs) using laser process. (b) Scanning electron microscopy (SEM) image of Cu(BDC) thin film surface. (c) Transmission electron microscopy (TEM) image of single Cu(BDC) nanosheet. (d) Current-voltage (I-V) curve for 2D MOF based-RRAM device. (e) Retention tests of 2D MOF based-RRAM device.

Figure 1
(Excellent Student Presentation Award) Confined Conducting Filaments in Resistive Random Access Memory By Al2O3 Nanodome-Shaped Arrays (NDSAs) Via Glancing-Angle Deposition
Authors: Shen Ying-Chun , Chueh Yu-Lun
Published: November 2022

Resistive random access memory (RRAM) is vital to neuromorphic computing applications. However, filamentary RRAM cells are affected by transitions from abrupt switching to analog switching. In this study, we develop Al2O3 nanodome shaped arrays (NDSAs) by glancing angle deposition technology (GLAD) to geometrically confine the conducting filaments (CFs), for which conducting atomic force microscopy (C-AFM) was performed to analyze positions and dimensions of filaments. For the Pt/HfO2/75 % Al2O3 NDSAs/TiN device, the dimension of the CFs can be restricted to 10-12 nm, whereas for the Pt/HfO2/TiN device, the CFs were formed with the dimension of ~50 nm. The device first yielded multiple weak CFs that subsequently transformed into stronger and larger CFs when the coverage of Al2O3 NDSAs was reduced to 55 % while Pt/HfO2/75 % Al2O3 NDSAs/TiN device exhibited synaptic features with more linear potentiation and depression, demonstrating the analog switching. The controllable coverages of Al2O3 NDSAs render the geometric design more promising as a memristor for future applications in neuromorphic computing.
(Invited, Digital Presentation) The Challenges of Overcoming Defects in GaN Hemts for Operation in Extreme Environments
Authors: Setera Brett , Christou Aristos
Published: November 2022

GaN high electron mobility transistors (HEMTs) are known to contain a high density of crystal defects. The material properties of GaN such as high breakdown voltage, carrier mobility, critical electric field strength, and higher thermal conductivity than Si, make it an ideal candidate material for use in power switches in extreme environments. In high power environments (>1.5kV), vertical GaN device geometry is emerging as an effective technique to improve performance, but the more mature lateral GaN HEMT technology is being consistently improved upon to increase breakdown voltage and overall performance in the high-power regime. In high temperature environments, GaNs wide bandgap helps in preventing unwanted thermal generation of carriers, but devices also experience increased gate-leakage current and ohmic contact resistance degradation at high temperatures. The role of defects in these limiting factors of GaN HEMT performance in extreme high power and high temperature environments is reviewed.
Investigating Oxygen Reduction Reaction Using a Multiscale Modeling Approach for Polymer Electrolyte Membrane Fuel Cell
Authors: White Zakar , Litster Shawn
Published: November 2022

Cathode catalyst layer (CCL) modeling is an important tool in elucidating the coupled transport-reaction phenomena and optimizing electrode architectures for greater efficiency, power density, and durability and thereby, reducing fuel cell costs. State-of-the-art catalyst use a high surface area carbon black (HSC) that supports platinum (Pt) nanoparticles, where some of the Pt particles reside on the carbon surface and a significant fraction of particles are found in the nm-scale pores of the carbon support. Within the electrode, the catalyst in bound by a polymer electrode binder (i.e., ionomer) that coats the external surface of the catalyst but does not penetrate the internal pores that are filled with liquid water due to capillary condensation. The contact of ionomer with Pt is known to reduce electrocatalytic activity due to site-blocking by the ionomer anion as well as increase the oxygen transport resistance. There is very little prior work on modeling the distinct performance of the internal Pt and the external Pt in contact with the ionomer. Most prior attempts to model CCLs with HSC catalyst supports at the MEA-scale and cell-scale have used an uncoupled approach, that separately considered the transport to the internal and external Pt particles, not considering the combined flux of oxygen through the ionomer film. Thus, the prior uncoupled model could potentially underestimate the oxygen concentration drop through the ionomer film. Here, we have adopted a numerical model of the catalyst that simultaneously considers the transport to the internal and external Pt as well as the different transport properties in the water and ionomer domains in single primary particle of the catalyst. The single spherical catalyst support model is upscaled to a 3D fuel cell model using a parametric linear regression fitting to model the local source/sink terms in the CCL. This multi-scale model is then applied to study the impact of the catalyst morphology.

This material is based upon work supported by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office, Award Number DE-EE0008822.
Characterizing the Pore Network of Diffusion Media at the Pore Size Scale
Authors: Bozzetti Michele , Berger Anne , Girod Robin , Gasteiger Hubert Andreas , Tileli Vasiliki
Published: November 2022

Water management by gas diffusion media and electrodes is a fundamental aspect of the performance of electrochemical cells including proton exchange membrane (PEM) fuel cells. In these devices, product liquid water blocks part of the available space for reactants flow, leading to mass transport losses and lowering of the performance1. Pores saturation has been observed with different experimental techniques for GDL substrates, however a detailed saturation process at the pore size scale of the microporous layer (MPL) is necessary. Previously, it was suggested that large pore network domains are responsible for an enhanced water evacuation2, however, possible existence of narrow size constrictions could still limit water evacuation. In this work, we detail the benefits of three-dimensional imaging of the pore network at the typical MPL pore size scale, i.e. the sub-micrometre scale, which is achieved by focused ion beam scanning electron microscope (FIB-SEM) nanotomography.

Two different MPL designs were analysed: an acetylene black based MPL, named Li100, and a vapor grown carbon fiber (VGCF) based MPL, the latter showing better performance under high relative humidity conditions2,
3. FIB-SEM tomography volumes in Fig. 1a-b were used to observe the relative distribution of larger pore domains and narrower pore constrictions. By removing narrower sized pores from the network and analysing the connections of large pore domains, we show the existence of a characteristic size for pore constrictions below which the pore network is well connected. This characteristic size is depicted by the red line in Fig. 1c-d, which plots the fraction of connected pores as a function of their minimum size. Constrictions size values for the two MPL designs were further validated with mercury intrusion experiments, since constrictions affect all the intrusions by capillary pressure, such as water flow in hydrophobic MPLs.

The calculated parameters, which are representative of the connections between large pore domains, open up new perspectives on the prediction of gas diffusion under realistic conditions. The approach allows evaluation of the effects of alternatively removing larger and narrower pore domains, to understand the saturation-driven tortuosity in different MPL structures.

J. Shen, L. Xu, H. Chang, Z. Tu, and S. H. Chan, Energy Conversion and Management, 207, 112537 (2020).

C. Simon, D. Kartouzian, D. Müller, F. Wilhelm, and H. A. Gasteiger, Journal of The Electrochemical Society, 164, F1697–F1711 (2017).

C. Simon, J. Endres, B. Nefzger-Loders, F. Wilhelm, and H. A. Gasteiger, Journal of The Electrochemical Society, 166, F1022–F1035 (2019).

Figure 1
Pairing Gas Diffusion Media for High-Power PEMFC Operation
Authors: Garsany Yannick , Carter Rachel Elizabeth , Sassin Megan B. , Bethune Keith , Gould Benjamin
Published: November 2022

Proton exchange membrane fuel cell (PEMFC) water management and current density are highly sensitive to the gas diffusion media (GDM) used at both the anode and the cathode. As the gas and mass transport requirements vary at each of these electrodes, the optimal properties for the respective GDM contrast. Utilizing different GDM at the anode and cathode, in an asymmetric GDM pairing, maximizes current densities in a broad range of operating conditions compared to symmetric pairings comprising the same GDM at the anode and cathode. The optimal asymmetric GDM pairing features a highly permeable anode GDM with a high porosity and thick microporous layer (MPL, 80 µm) that is homogeneous in through-plane flux. Alternatively, the cathode GDM is less permeable and has a thinner and less porous MPL (20-45 µm) with a broad flux distribution. Net water drag measurements show that this asymmetric GDM pairing facilitates water retention at the anode and water expulsion from the cathode to realize lower oxygen transport resistance and up to 73% higher current density than PEMFCs with symmetric GDM pairings. Symmetric GDM pairings are insufficient at removing product water from the PEMFC cathode, resulting in greater cathode water saturation. As a result, more product water must back-diffuse across the membrane to be removed from the anode at the expense of significantly greater oxygen transport resistances and concomitantly lower current and power densities than the asymmetric GDM pairing. GDM are characterized by X-ray computed tomography (CT) and scanning electron microscopy (SEM) to reveal differences in MPL carbon type, average pore size, pore character, porosity, pore connectivity, tortuosity, and spatial flux distribution that govern PEMFC gas transport and water management.
Visualization of Combustion in Polymer-Electrolyte-Membrane Fuel Cell - Mechanism on Abrupt Change from Moderate to Accidental Scale-
Authors: Ngo Manh , Ito Kohei , Nakajima Hironori , Karimata Takahiro , Saitou Tomoko
Published: November 2022

This study is focused on elucidating the catalytic combustion phenomenon in proton-exchange membrane fuel cells. A visualization cell and an infrared (IR) camera are used to capture the thermal behavior under combined chemical and mechanical accelerated stress conditions in situ. A 3.4 cm2 catalyst coated membrane (CCM) embedded in the cell is subjected to a relative humidity (RH) cycling test at atmospheric pressure and a cell temperature of 80 °C under open-circuit voltage (OCV) conditions. The temperature distribution on the gas diffusion layer surface at the cathode is captured using a high-transmittance glass window (ZnS window). Continuous IR imaging revealed a hot spot at ca. 500 RH cycles, suggesting the existence of a pinhole in the degraded CCM and the occurrence of catalytic combustion there. The occurrence of the hot spot coincides with the time at which the electrochemical indicators detect membrane failure, i.e., hydrogen crossover rate, OCV. Furthermore, the post mortem analysis revealed a 105-micrometer diameter pinhole, the position of which matched that of the hotspot. An accidental combustion during the durability test could cause the formation of a pinhole. This pinhole is responsible for the rapid increase in the hydrogen crossover rate as well as the significant decrease in the OCV at 500 RH cycles until the end of the durability test.

Figure 1
An Innovative Approach to Design and Optimize Flow Field Pattern of Polymer Electrolyte Membrane Fuel Cell
Authors: Tsukamoto Takayuki , Takayama Tsutomu , Miyamoto Yuhei , Komiyama Keisuke , Yoneda Masakazu
Published: November 2022

To increase power density of polymer electrolyte membrane fuel cells (PEMFCs), further optimization and downsizing of cell and stack design are necessary.

To support cell and stack design, we have been developing a three-dimensional (3D) PEMFC simulator P-Stack [1]. P-Stack can estimate power generation performance in good agreement with experimental results, and can clarify relationships between the performance and internal states depending on cell designs, operation conditions, and material properties [1]. Although 3D PEMFC simulations are powerful means, preparing 3D model is very time consuming, thus it was difficult to explore various cell designs.

In the present study, we have developed a new modeling technology for PEMFC flow fields. In this technology (Figure (a)), flow fields of anode and cathode gases are drawn by lines in 2D canvas. Properties of the lines such as width, depth and wall angle are given, then it automatically generate 3D model for anode/cathode flow fields and bipolar plates, coolant flow field, seal, gasket and MEA. Power generation performance of the 3D model can be estimated by P-Stack continuously. In addition, the line properties, vertex positions, and the number of repeat can be parametrized, enabling the parametric study of cell design.

In this technology, pressure and flow rate distributions can be calculated by a network model based on Darcy’s law [1], without generating 3D model. As shown in Figure (b), the result is in good agreement with computational fluid dynamics (CFD) calculation of 3D model. Although the CFD calculation takes several hours using 32 parallel processes, the calculation of the network model is finished within several seconds using single process. In similar manner, it can calculate flow rate distribution of cells in the stacking axis. Since the execution time per one case is very short, it can be combined with optimization by genetic algorithm (GA).

In the presentation, we will talk about a result of the parametric study and optimization for more practical cell design. Influence of flow field design on power generation performance and internal states will be discussed.

References

[1] T. Tsukamoto, T. Aoki, H. Kanesaka, T. Taniguchi, T. Takayama, H. Motegi, R. Takayama, S. Tanaka, K. Komiyama, M. Yoneda, J. Power Sources 488 (2021) 229412

Figure 1
Multiwalled Carbon Nanotube-Filled Polymer Composites for Direct Injection Molding of Bipolar Plates
Authors: Kypta Chadwick J , Young Brian A , Santamaria Anthony , Hollinger Adam S
Published: November 2022

Fuel cell bipolar plates are commonly fabricated from graphite and stainless steel, however machining intricate channels into these materials can be a costly and time-consuming process. For this reason, we are exploring injection molding of polymer composite bipolar plates. Polymer composites offer the potential for lightweight, low-cost plates [1]. Several factors impact the ability of a polymer composite to conduct electricity. The geometry, filler weight percentage, dispersion, and the physical properties of the fillers are important in forming an electrical pathway through the composite. In this study, polymer composites based on nylon were injection molded with different weight percentages of conductive filler. Initially, carbon fiber was added to nylon at weight percentages ranging from 10 to 50%. Results show that the percolation threshold for carbon fiber in nylon occurs around 25 wt%. While carbon fiber loadings beyond 50 wt% would further increase conductivity, the increased viscosity of the polymer blends can inhibit proper injection molding.

Multiwalled carbon nanotubes were then added to the direct injection-molded nylon/carbon fiber composites to investigate the synergistic effects of multiple conductive fillers [2]. By introducing carbon nanotubes into the polymer matrix, the nanotubes act as a bridge between the carbon fibers. SEM images show that the MWCNTs fill the void between each fiber due to their smaller size and their ease of dispersion. This bridging creates more conductive pathways within the composite, thereby increasing the electrical conductivity. Samples with MWCNTs reached conductivities nearing the United States Department of Energy technical target for bipolar plate conductivity (> 100 S/cm).

Mighri, F.; Huneault, M. A.; Champagne, M. F., Electrically conductive thermoplastic blends for injection and compression molding of bipolar plates in the fuel cell application. Polymer Engineering and Science 2004,
44 (9), 1755-1765.

Zameroski, R.; Kypta, C. J.; Young, B. A.; Sanei, S. H. R.; Hollinger, A. S., Mechanical and Electrical Properties of Injection-Molded MWCNT-Reinforced Polyamide 66 Hybrid Composites. Journal of Composites Science 2020,
4 (4), 14.

Figure 1
High Volume Fuel Cell Stack Manufacturing
Authors: Swider-Lyons Karen , Ramani Manikandan , Carlstrom Chuck , Lawler John , Owejan Jon
Published: November 2022

Plug Power is a world leader in fuel cell stack and fuel cell systems manufacturing, with over 50,000 fuel cells in the field for materials handling and stationary power applications. Plug Power is using this success to develop new markets in range-extenders for delivery vans, heavy duty vehicles, and aerospace. The rapid growth of Plug Power’s fuel cell technology has brought new challenges with high volume manufacturing. An individual cell needs to be made in less than 5 seconds, and then sealed and stacked rapidly and reproducibly.

This talk will review some of the general approaches that Plug Power is taking toward high-volume stack manufacturing. We will also review two programs funded by the U.S. Department of Energy on high volume manufacturing, and novels ways toward low cost, high volume manufacturing.