bluuebunny/crossref_metadata_2025 huggingface dataset:
Modification of Sacrificial Polymers for Low-Cost MEMS Packaging
Authors: Phillips Oluwadamilola , Kohl Paul A
Published: February 2020

Packaging of microelectromechanical systems (MEMS) is vital to maintaining device performance and minimizing the impact of environmental threats. Packaging accounts for a substantial portion of the total cost of the MEMS device. In the approach taken here, the movable  MEMS component is encapsulated by a sacrificial polymer in order to protect the device during processing. The component is then packaged in a traditional way, such as by overmolding on a substrate or lead-frame packaging. Thermal decomposition of the sacrificial polymer releases the MEMS device either during or after component packaging. A thermally decomposable sacrificial material, polypropylene carbonate (PPC) and overcoat material BCB (benzocyclobutene) was used for protection of the MEMS device during packaging. PPC decomposition products permeate through the overcoat to leave an air cavity. Control of the thermal decomposition of polypropylene carbonate is an integral part of the process because the MEMS device needs to be released at a critical point in the process.

In this study, the thermal decomposition temperature of the PPC was modified by kinetically inhibiting the thermal decomposition via end-capping. Reacting the hydroxyl-end group of polypropylene carbonate with chemical moieties such as organohalides and mono/difunctional acids alters the thermal stability of these materials. Furthermore, additives such as metal halides and multifunctional alcohols can also alter the thermal decomposition PPC.  In this presentation, the status of these modified polymers in this cavity-forming MEMS packaging process will be discussed.
The Electrodeposition of Crystalline Gallium Antimonide Using Electrochemical Liquid-Liquid Solid Deposition (ec-LLS)
Authors: DeMuth Joshua James , Maldonado Stephen
Published: February 2020

The growth of crystalline III-V semiconductor material from aqueous solutions has maintained a challenging task in the field of semiconductor electrodeposition. Electrochemical liquid-liquid solid deposition (ec-LLS) is a method in which an applied potential is used to grow crystalline semiconductors from a liquid metal electrode/solvent.1 In this study crystalline gallium antimonide (c-GaSb) films were electrodeposited from both Sb­2O3 and SbCl3 precursors in aqueous electrolyte via ec-LLS at mild temperatures (40o-90oC) and ambient pressure. The electrodeposition of c-GaSb films has been previously attempted2,3 but the deposits contained large amounts of excess antimony and required post-deposition annealing steps. However, in the present study c-GaSb films with stoichiometric amounts of Ga and Sb were obtained without any post-deposition annealing. In addition, the growth conditions were varied and the effects on the grain size, texture and composition of the resultant films were examined using X-ray diffraction, energy-dispersive X-ray spectroscopy and Raman spectroscopy. The results showed that the temperature, precursor concentration and pH were the most significant parameters that influenced the crystalline quality and composition of the as-grown films.      

References:

(1)    Fahrenkrug, E.; Gu, J.; Maldonado, S. J. Am. Chem. Soc.,2013, 
135
, 330-339

(2)    McChesney, J et al., Optical Materials, 1996, 6, 63-67

(3)    Musiani, M et al., J. Appl. Electrochem., 1989, 20, 868-873
Solid State Reaction to Form Metal Oxide Heterostructure Nanowire
Authors: Chen Yi-Hsuan , Huang Chun-Wei , Chan Jui-Yuan , Huang Yu-Ting , Wu Wen-Wei
Published: February 2020

ZnO nanostructure has been investigated extensively due to its fascinating functional properties. ZnO heterostructure especially attracts a lot attention owing to various kinds of applications such as light-emitting device, resistive random-access memory, and solar cell. In this study, we deposited few nanometer of Al onto ZnO nanowire by electron beam evaporator, and successfully transformed ZnO nanowires into Al2O3/ZnO axial heterostructure. This reaction was occurred through solid state reaction at 700˚C in ultrahigh vacuum transmission electron microscope (UHV-TEM). We directly observed diffusion process during heating; in addition, the analysis of the kinetic behavior was carried out through the in situ video. The structure and composition were also identified by energy dispersive spectrometry (EDS) and Cs-corrected STEM. This research provide a method to fabricate a new type of one dimensional Al2O3/ZnO axial heterostructure, which may be applied in opto-electrical device and nanosensors.
Solid Polymer Electrolytes Based on Chitosan and Europium Triflate
Authors: Silva M. M. , Alves R. , Donoso J. P. , Magon C. J. , Silva I. D. a. , Pawlicka Agnieszka
Published: February 2020

The solid polymer electrolytes (SPEs) have been extensively studied since the pioneering work of Wright and Armand et al[1, 2]. Previous studies were focused on poly(ethylene oxide) (PEO) and lithium salts [3]. However recent research aimed at developing SPE based on natural polymers, which are interesting due to their natural abundance, low price and environmentally friendly nature [4].

Chitosan is a natural polymer obtained from chitin and it has been largely investigated due to its biodegradability, non-toxicity, absorption properties and biocompatibility.

In this presentation are described the preparation and characterization of novel systems from chitosan and europium (III) trifluoromethanesulfonate salt. The transparent samples were characterized by thermal analysis (DSC and TGA), impedance spectroscopy and electron paramagnetic resonance (EPR). The Chitosan55.04%Eu(Trif)3 sample showed the best ionic conductivity of 1.52×10-6 and 7.66×10-5 S∙cm-1 at 25ºC and 80ºC, respectively. The thermal analysis revealed that the degradation started at around 120 - 145ºC and the weight loss ranged from 15 to 40%. The EPR analysis showed a broadening of the EPR resonance lines with increasing europium contents in the chitosan membranes due to the magnetic dipole–dipole coupling and spin-spin exchange between the Eu2+ions.

 

ACKNOWLEDGEMENTS

 

We are grateful to the Fundação para a Ciência e Tecnologia (PestC/QUI/UI0686/2013,  POPH/FSE for a grant  SFRH/BD/97232/2013 (R. Alves)) for financial support of this work. The authors are also grateful to, FAPESP, CNPq and CAPES for financial support. M. M. Silva acknowledges CNPq, for the mobility grant provided by this institution.

 

REFERENCES

[1] P. V. Wright, British Polymer Journal 7 (1975) 319.

[2] M. B. Armand. J. M. Chabagno, M. J. Duclot, In Fast Ion Transport in Solids; Vashishta, P., Mundy, J. N., Shenoy, G. K., Eds.; North-Holland: Amsterdam, The Netherlands, 1979, p 131.

[3] P. K. Varshney, S. Gupta, Ionics 17 (2011) 479-483.

[4] I. S. M. Noor, S. R. Majid, A. K. Arof, D. Djurado, S. C. Neto, A. Pawlicka, Solid State Ionics 225 (2012) 649-653.
Bioinspired Metal Organic Naostructures for Electrcatalysis
Authors: Grumelli Doris , Wurster Benjamin , Hötger Diana , Gutzler Rico , Kern Klaus
Published: February 2020

Electrochemical conversions at fuel cell electrodes are complex processes. Oxygen reduction and oxidation reactions (ORR and OER, respectivelly) have considerable overpotential limiting the efficiency. Effective and inexpensive catalytic interfaces are therefore essential for increased performance. Taking inspiration from enzymes, earth- abundant metal centers embedded in organic environments present remarkable catalytic active sites. We present here strategies for effectively mimicked these catalytic centers by using two- dimensional metal- organic coordination networks self- assembled on electrode surfaces. Networks consisting of an aromatic ring backbone with specific functional groups (carboxylic, pyrimidine, pyridine or cyano groups) coordinated to single Fe, Co or Cu atoms on Au(111) catalyze effectively ORR or OER and reveal distinctive catalytic activity. The results demonstrate the high potential of surface- engineered metal- organic networks for electrocatalytic conversions. Specifically designed coordination complexes at surfaces inspired by enzyme cofactors represent a new class of nanocatalysts with promising applications in electrocatalysis.
Oligothiophene-Graphene Ensembles
Authors: Tagmatarchis Nikos
Published: February 2020

The rise of graphite exfoliation pumping up graphene’s chemistry brings significant impact towards the preparation of novel hybrid materials combining the exceptional mechanical and electronic properties of graphene sheets with those of photoinduced charge transfer from organic chromophores interacting with the carbon nanostructure. Applications including charge transfer processes demand both defect-free graphene sheets and robust chemical procedures for the chemical or supramolecular grafting of the desired organic molecules onto the sp2-honeycomb lattice of graphene. Covalent chemistry of graphene leads to strong interactions between the organic material and the graphitic skeleton, however, introduces defects at the anchoring sites, thus acting as insulators. On the other hand, when supramolecular interactions are utilized to integrate organic moieties to graphene, the resulted hybrids although may suffer from the weaker π-π interactions and the subsequent release part of the organic units to the solution, the extended aromatic lattice of graphene sheets remains intact and undisrupted, as no bond formation takes place, thus allowing for ballistic transport of charges with negligible loss of energy.

Oligothiophenes in general and terthiophenes in particular, are readily accessible organic chromophores with interesting electronic properties. The stiff skeleton of oligothiophenes and the presence of the sulfur atom generate a stable π-conjugated chain, which can interact through multiple π-π stacking forces with the sp2 graphene lattice.

In this frame, the ease of oligothiophenes chemical manipulation allows the preparation of oligothiophene-graphene ensembles showing enhanced solubility in organic solvents. The latter is justified due to the insertion of alkyl groups at 3' and 4' position of the thiophenes ring. Herein, the preparation of oligothiophene-graphene ensembles will be presented, followed by their full characterization through Raman and IR spectroscopy, TEM imaging and TGA analysis. Notably, our first data from the newly formed materials, based on electronic absorption, photoluminescence and electrochemistry, indicate the interaction of the organic units and the carbon allotrope under light irradiation.

Partial financial support from GSRT/NSRF 2007-2013 through action “Postdoctoral support” project GRAPHCELL PE5(2126) is acknowledged.
Electric Field Tunable Band Gap in Bi-Axially Strained Graphene/Hexagonal Boron Nitride Super-Lattice
Authors: Masood Khalid Ibne , Alam Md. Hasibul , Khosru Quazi D. M.
Published: February 2020

In this work, we have reported the tunable band gap of single-layer graphene (SLG) on hexagonal boron nitride (h-BN) monolayer arranged in B3 super-lattice form, as a function of an external electric field perpendicular to the super-lattice plane and an applied external bidirectional stress from the first principle Density Functional theory (DFT). Graphene with its intrinsic high electron mobility poses itself very promising for electronic device application, but absence of band gap and substrate induced mobility degradation limits its application in logic transistor. To reduce the effect of substrate related performance degradation graphene placed on h-BN has been reported in literature. Three super-lattice structures of this bilayer system have been proposed in literature where B3 is reported to have the greatest intrinsic band gap opening among the three but this is not sufficient for logic transistor. To tailor the band gap perpendicular electric field and biaxial stress was applied in this work. It was observed that band gap increases (65.45 meV – 84.5 meV) from compressive to tensile biaxial strain (-5% to +5%) when no electric field was applied. With the application of 5×109 V/m external electric field a band gap of 144.5 meV was found which is promising for logic FET. However, tensile stress and external electric field causes degradation in Fermi velocity and produces higher electron effective mass.

Figure 1
MoS2 Devices Using Pencil Circuits
Authors: Tiruparkadal Parthasarathy Vedhikha , Berry Vikas
Published: February 2020

As a semiconducting analog of two-dimensional (2D) graphene, MoS2 monolayer is a three-atom-thick layered transition-metal dichalcogenide, composed of a stratum of molybdenum atoms sandwiched between two layers of sulfur atoms. MoS2’s physical, chemical and opto- electrical properties can be tuned over a wide range by changing its interface and chemistry, opening potential for next generation two-dimensional flexible electronics. Here, we have developed several electronic circuits on paper using MoS2 and graphite (from pencil) and have studied electrical, capacitive and optoelectrical properties of the flexible composite. Via this process, we envision the evolution of on-demand device fabrication by writing prescribed or innovative ‘scripts’ on paper by combining art and science. Further, such 2D circuitry will evolve into writable, accessible, cost-effective (and disposable) electronics.
Mxene-Based Membranes As Novel Materials for Ion Separation
Authors: Ren Chang E. , Alhabeb Mohamed , Hatzell Kelsey B. , Ling Zheng , Mahmoud Khaled , Gogotsi Yury
Published: February 2020

Advanced separation membranes can provide drinkable water via an energy-efficient and facile way in reverse or forward osmosis systems. Recently, two dimensional (2D) graphene oxide (GO) membranes have shown good selectivity to inorganic salt ions and rejection of organic molecules. However, there is a need for further increase in selectivity, improvement in mechanical properties and resistance against fouling. Herein we present a new class of 2D metal carbides, MXenes, as a promising membrane material selective to metal ions. MXene films display a range of physical properties that make them ideal for separation membranes including flexibility, high mechanical strength, hydrophilic surfaces, and high electrical conductivity. Through the preparation method of vacuum-assisted filtration, MXene membranes can be made with thicknesses ranging from hundreds of nanometers to tens of micrometers. Like GO, the MXene membranes have layered structure with nanochannels permeable for ions, molecules, gases and water. Here we report on selectivity of micrometer-thick MXene membranes towards different cations (Li+, Na+, K+, Mg2+, Ca2+, Ni2+and Al3+) with Cl- anions. Permeation rates were shown to rely on the hydrated radius of ions with a critical point around 4.0 Å and on charges of cations, which demonstrates better selectivity than GO membranes with similar thickness. To improve the mechanical stability of MXene membranes, MXene /polymer composite membranes were prepared which showed equal or even better selectivity. Analysis of the effects of interlayer spacing of MXene and negative charge on MXene surfaces on the permeation of ions is provided.
Direct Formation of Monolayer Graphene on SI-Based Dielectrics
Authors: Nguyen Phong , Berry Vikas , Seacrist Mike
Published: February 2020

Graphene – a one atom thick planar sheet of carbon atoms – possesses a distinct combination of properties including ultrahigh carrier-mobility, ultrafast photodetection, sensitivity, tunable spintronics, strong/tunable optical absorption, carrier controlled interband/optical-transition, and quantum interference. To incorporate it into the semiconductor industry, direct growth of wafer scale, high-quality, monolayer graphene on silicon-based dielectrics (SiO2 and Si3N4) is desired for the next step towards graphene electronics. In this talk, we show that thin copper (Cu) film on SiO2 or Si3N4 dielectric (electron beam evaporation) can be employed for direct growth of high-quality graphene via chemical vapor deposition (CVD) process. Here, precursor methane (CH4) gas is diffused through Cu grain boundaries to the interface between Cu and selected Si based dielectric, where it is catalytically dissociated into active carbon species at elevated temperature. Further, optimization of the process parameters (temperature, CH4/H2 flow rate ratio, and total pressure) leads to the formation of a uniform continuous, large-area graphene monolayer directly on top of the chosen dielectric. Raman spectroscopy and selectrive area electron diffraction (SAED) are employed for graphene’ structural characterization. The Raman D-peak, G-peak, and 2D-peak occur at characteristic ~1350 cm-1, ~1600 cm-1, ~2700 cm-1 respectively. The ID/IG ratio (~ 0.25 ) corresponds to a graphene cyrstalline sp2 domain size of 17 nm. The I2D/IG ratio (~1.4) confirms the formation of graphene monolayer. Moreover, SAED measurements show single hexagonal pattern, and a d-spacing of 2.44, which also validates the formation of monolayer graphene on chosen dielectric. The electrical properties of the produced graphene will also be presented. Our patented method allows us to achieve high quality wafer sized graphene on silicon based insulating substrate without the need of graphene transfer.
Inkjet Printed Graphene Electrodes for High-Performance Supercapacitors
Authors: Yu Hye-Ryeon , Choi Yu-Song , Cheong Hae-Won
Published: February 2020

A wide variety of supercapacitors has been developed for many high-power energy storage application. Especially, flexible supercapacitors with thin electrodes are being needed for powering flexible electronics for military applications. In this study, the inkjet-printed graphene electrode is investigated for high-performance thin film supercapacitors. In order to make the ink for printing, graphene flakes ware dispersed in a solvent and then printed onto a metal foil. The electrodes were inkjet-printed with the various graphene flake size and the film thickness. After the printing, the electrodes were dried to remove solvent. These electrodes were sealed together with the electrolyte and separator, and then assembled into a coin cell. The microstructures of the printed graphene electrodes were analyzed by SEM, TEM and XRD. The electrochemical performances were also investigated.
What Is Different about Hydrothermally Synthesized Îµ-LiVOPO4?
Authors: Chung Youngmin , Wen Bohua , Omenya Fredrick , Chernova Natasha , Kharki Khim , Wiaderek Kamila M , Chapman Karena W , Chupas Peter J , Whittingham M. Stanley
Published: February 2020

e-LiVOPO4 is a multi-electron intercalation cathode with theoretical capacity of 330 mAh/g. It could be practically realized if both high-voltage Li removal and low-voltage Li insertion processes could run reversibly over many cycles. In this work, we have investigated ε-LiVOPO4 synthesized by hydrothermal (HT) reaction and then ball-milled with carbon for the electrode preparation. This material shows high initial capacity around 300 mAh/g (Fig. 1) which holds for about 10 cycles, but then gradually decays. The electrochemical curve of the HT e-LiVOPO4 is more sloping in comparison to that of the solid state (SS) synthesized material, which shows distinct steps typical of two-phase reactions. We have used high-resolution x-ray diffraction, pair-distribution function analysis (PDF), ICP, TEM, thermogravimetric analysis with mass-spectroscopy (TGA-MS), and magnetic measurements to understand the distinctions of the HT e-LiVOPO4. The bulk structure of HT and SS products is essentially the same: triclinic with very similar lattice parameters. The particle size is large for both HT (5μm) and SS (1μm) products, therefore high-energy ball-milling with carbon was used to achieve good electrochemistry. Distinct differences were found in TGA-MS and magnetic tests. TGA-MS reveals about 1wt.% of water loss at 300 °C for the HT product, indicating structural water or hydroxyl incorporation into the structure. Magnetic test shows antiferromagnetic transition at 14 K in the SS product in agreement with previous reports, while the HT product becomes ferrimagnetic at 11 K, which points toward structural defects in the HT sample. High-resolution x-ray diffraction and pair-distribution function analysis results will be discussed to reveal fine structural differences between HT and SS products and the effect of ball-milling on the structure. Also, similar data for the cycled samples will be presented to address the issue of capacity fading. This work was supported as part of the North East Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0012583.

Figure 1
Functionalized Multi-Walled Carbon Nanotubes As Supporting Matrix for Enhancement Oxidation of Fucose on Gold Nanoparticle-Based Catalyst
Authors: Huong VU THI , Yoshikawa Hiroyuki , Hoa Le Quynh , Toake Hitoshi , Tamiya Eiichi
Published: February 2020

Biomass extracted from brown macro-algae promises as a future renewable energy because of non-toxicity, natural availability, greenhouse gas free, and do not interfere with the human food chain. Here, we first present the extraction of energy from brown macro-algae via direct oxidation of fucose using anodic catalytic composite material of gold nanoparticles (AuNPs) sintered on functionalized multi-walled carbon nanotubes (f-MWCNTs). The combination of AuNPs/f-MWCNTs showed super catalytic activity on fucose oxidation in compare to AuNPs and f-MWCNTs only. The oxidation peak of fucose shifted to more negative peak by using AuNPs/f-MWCNT/C in compare to Au/C electrode only, while almost there is no peak can be observed in the case of f-MWCNT/C electrode. The direct fucose fuel cell performance by using AuNPs/f-MWCNT/C electrode as the anode resulted in power density of 1.923 mW cm-2, is much more higher than 0.658 mW cm-2 of AuNPs/C and 0.028 mW cm-2 of f-MWCNT/C. A small air - fucose fuel cell using 1 cm2 anode can run a LED lamp. Furthermore, a fuel cell using 16 cm2 anodic electrode modified by AuNPs/f-MWCNT with 3 mL fuel solution can keep a small fan running for at least 3 hours. The results from this research open possibility for practical application of our fuel cell with high efficiency on conversion of energy from brown macro-algae biomasses.
High Energy Density Capacitor By Plasma-Treated ALD BaTiO3 Thin Films
Authors: An Jihwan , Prinz Fritz B.
Published: February 2020

Atomic layer deposition (ALD) is a modified chemical vapor (CVD) deposition tool, which is suitable for depositing high quality thin films or locally modifying the surface properties. Due to its advantages such as conformality, low pin-hole density, and the easiness of composition/doping control, ALD can used for engineering wide variety of thin film devices.

Crystallizing and densifying thin films to increase their relative permittivities are critical issues in fabricating high information density dynamic random access memory (DRAM) capacitors. The high process temperature (> 600 ° C) is usually necessary for thin film crystallization and densification, which could be detrimental to other components of DRAM. In this manuscript, we report a simple and novel method to simultaneously increase the dielectric constant and decrease the leakage current density of atomic layer deposited BaTiO3 thin films using post-deposition remote oxygen plasma treatment while keeping the process temperature low (250 °C). The dielectric constant increases from 53 (as-deposited) to 122 (plasma-treated) and the leakage current density decreases by one order of magnitude. The dielectric constant of the plasma-treated BaTiO3 film is one of the highest values ever reported for ultra-thin (5 nm thick) films. We ascribe such improvements to the crystallization and densification of the film induced by high-energy ion bombardments on the film surface during the plasma treatment. We think that plasma-induced crystallization presented in this work may have an immediate impact on fabricating and manufacturing DRAM capacitors due to its simplicity and compatibility with industrial standard thin film processes [1].

Acknowledgment 

             We thank Manufacturing Technology Center, Samsung Electronics for financial support

References

[1] J. An, et al., ACS Appl. Mater. Inter. 6 (13), pp 10656–10660 (2014)
Hydrocarbon Membrane for Vanadium Redox Flow Batteries
Authors: Kim Haekyoung
Published: February 2020

With the expanding need for large electrical energy storage systems in connection with renewable energy sources, flow batteries, have been enormously considered due to their high flexibility in upgrade and low cost associated with scale-up. Of all the flow batteries, vanadium redox flow battery (VRFB) use of same element in both half-cell solutions that overcomes the inherent issue of cross contamination by diffusion of different ions across the membrane. Together with the absence of any toxic emissions, the vanadium redox flow battery has demonstrated its uniqueness in terms of safety and long life cycle. Typical charge-discharge reactions of a VRFB involve two vanadium redox couples, V(II)/V(III) and V(IV)/V(V), in the negative and positive half-cells, respectively. In a fashion similar to most batteries, electrons are transferred between the two electrodes through the external circuit during the charge and discharge processes. In a VRFB, the ion exchange membrane is a key component as an ionic conductor and separator: it not only provides an ionic conduction pathway between the two electrolytes but also prevents mixing of the negative and positive electrolytes. The crossover of ions through the membrane, with the diffusion of vanadium ions from one half-cell to the other due to the concentration gradients between the two electrolytes, will result in self-discharge and thus the loss of the chemical energy.

In this study, in order to improve membrane selectivity, hydrocarbon based polymer membranes were synthesized and fabricated for VRFBs. Sulfonated polysulfone membranes (PATS-XX) were characterized in terms of ionic conductivity and permeability with degree of sulfonation. PATS-35 exhibited the ionic conductivity of 0.06 S/cm, which showed 40% lower permeability than Nafion 115 membrane. VRFB cell with PATS-35 exhibited higher coulombic and energy efficiency than that with nafion 115 membrane. The results of VRFBs with blended PATS-xx membrane will be discussed and compared with that with Nafion membrane.
In Operando Electrochemical-Acoustic Time-of-Flight Analysis: Correlating Physical Dynamics within Batteries to States of Charge and Health
Authors: Hsieh Andrew , Bhadra Shoham , Hertzberg Benjamin Joseph , Gjeltema Peter J , Steingart Daniel A
Published: February 2020

Recently, advances in the mechanical understanding of electrochemical energy storage devices, based investigations of stress/strain, have yielded significant improvements in battery materials, designs, and management systems. To date, however, the field has lacked a non-invasive method for monitoring these complex mechanics within in practical cells. Here, we demonstrate a simple electrochemical-acoustic model and experiment as the basis for a potentially universal in operando, field-deployable tool for determining the mechanical evolution, state-of-charge (SOC) and state-of-health (SOH) of any closed battery. This technique, which we call Electrochemical Acoustic Time of Flight (EAToF) analysis, was tested against several off-the-shelf lithium ion and alkaline batteries and a general phenomenon was observed: that the behavior of sound passing through the cells correlated strongly to its SOC and SOH. Regardless of the chemistry, the density distribution within a battery must change as a function of its SOC, and the bulk moduli of the anode and cathode change as well. These shifts, in turn, directly influence the behavior of sound passing through the cells. Overall, a one- or two-point acoustic measurement can be related to the interaction of a pressure wave at multiple discrete interfaces within a battery, which in turn provides insights into state of charge, state of health, and mechanical evolution/degradation. This work, which is unique to the literature, provides new physical insights into the physical dynamics within batteries. With this EAToF technique, we propose a framework relating changes in sound speed within the cell, via changes in electrode densities and moduli, to SOC and SOH measurements in a manner that can be readily embedded into battery management systems.

Figure 1
Influence of Convection and Material Properties in Vanadium Redox Flow Batteries
Authors: Houser Jacob , Mench Matthew M. , Pezeshki Alan , Clement Jason T. , Aaron Douglas
Published: February 2020

Substantial work has been done recently to improve performance of all-vanadium redox flow batteries (VRFB) as a viable large scale energy storage system1.  Prototype systems have been installed in small numbers to demonstrate their feasibility.  There still exists a lack of understanding of the processes and design tradeoffs which exist in these systems, particularly regarding the relationship between mass transport, performance, realized capacity accessed, and parasitic pressure losses through the system.    Despite the literature available regarding this particular chemistry, a thorough analysis of the design tradeoffs and their impact on system optimization is still lacking.

Flow field design is one such area where an opportunity for optimization exists for mass transport and system pressure drop.  Such optimization can be experimentally explored, as well as computationally2.  This combined experimental and computational study that will be presented will show that optimal flow field design is not simply related to the architecture, but is instead a more complex interplay between architecture, electrode properties, electrolyte properties, and operating conditions. The results of this study should be useful to design engineers seeking to optimize VRB systems through enhanced performance and reduced pressure drop.

1.  D.S. Aaron, Q. Liu, Z. Tang, G.M. Grim, A.B. Papandrew, A. Turhan, T.A. Zawodzinski, M.M. Mench,  Journal of Power Sources, 206  450-453 (2012).

2.  T. Jyothi Latha and S. Jayanti, J. Appl. Electrochem., 44, 995 (2014).

Figure 1
Optical Gain Optimization of Al0.8Ga0.2N-Delta-GaN Quantum Well Laser in Ultraviolet Spectra Using Genetic Algorithm
Authors: Polash Md. Mobarak Hossain , Alam M. Shah
Published: February 2020

In this work, AlGaN based quantum well laser has been designed with delta layer and characterized the designed laser structure. After the characterization, Genetic Algorithm process has been performed over optical gain to optimize it. In this design, AlN has been used as barrier material, Al0.8Ga0.2N has been utilized as active region material and GaN layer has been used as delta layer. For optimization, well width, delta layer width and barrier width have been taken as the variable for which genetic algorithm has performed the optimization process. Characterization of the designed laser shows good agreement with previously published works. Optimization of optical gain for both TE and TM gain also exhibits good improved result than previously published works. From characterization, it is found that the designed laser structure gives peak optical gain of 3589.5 cm−1 and peak spontaneous emission rate of 12.94×1028 s-1cm-3eV-1 at 246.89 nm for 5×1019 cm-3 carrier density. From optimization, it is obtained that optimum TE optical gain is found 6479.1 cm-1 for 11 Å of QW along with 7 Å delta layer at 279 nm wavelength and optimum TM gain is found found 116.95 cm-1 for 20 Å of QW along with 3 Å delta layer at 289.8 nm wavelength. In this work, electronic characterization has been performed with 6 band k.p Hamiltonian for valence subband calculation including valence band mixing effect, strain effect due to lattice mismatch, spontaneous and piezoelectric polarization. For conduction subband calculation, single band Hamiltonian has been solved with strain and polarization effect.

Figure 1
Operando Imaging of Electrochemical Phase Transitions in LiNi0.8Co0.15Al0.
05O2
secondary Particles
Authors: Yu Young-Sang , Kim Chunjoong , Liu Yijin , Cabana Jordi
Published: February 2020

The observation in dynamic conditions of electrochemical transformations relevant to energy storage creates the opportunity of identifying design rules that directly reflect the veiled electrochemical reaction mechanisms which are controlled by kinetics under load. Under the intrinsic limitations of ex-situ methods, opening the circuit to harvest multiple samples of interest at the different stages of reaction can lead to relaxation of the materials to a different, thermodynamically stable state. In addition, these operandoobservations must occur at multiple scales, but are particularly critical at the individual cathode particle level, where incomplete reactions and failure are prone to occur.

In this study, we focused on LiNi0.8Co0.15Al0.05O2 (NCA)-based cathode materials, which are one of the leading candidates for use in high energy density Li-ion batteries for electric vehicle applications. This material offers high storage, but still presents limitations vis-à-vis capacity loss and concurrent increases in impedance. We adopted operando 2D full field transmission X-ray microscopy (FF TXM) coupled with X-ray absorption near edge spectroscopy (XANES) to follow the chemical and microstructural evolution at the secondary particles of NCA with sub-30 nm spatial resolution. Chemical phase maps from quantitative analysis of pixel-by-pixel X-ray absorption near edge structure spectra and morphological information of optical-density images at the post-absorption-edge region were obtained at the different state of charge as shown in Figure 1. As a result, this work successfully revealed the existence of kinetically-induced inhomogeneities during the electrochemical phase transition, and their morphological consequences, within a secondary particle, at nanoscale spatial resolution during an electrochemical reaction. We believe the rich insight provided by high resolution spectro-microscopy could inform the design of optimized architectures and the projection of performance using continuum models.

Figure 1. A. Charge galvanostatic profile of operando Li metal half cell with an NCA composite cathode. The cell charged to capacity of 350 mAh·g-1 with cycling rate of C/15 (C was defined as the current density to achieve the theoretical capacity in 1 hour). Chemical maps were obtained at different state-of-charges (SOCs), labeled as 1 ~ 9, indicated as blue outlined circles. B. A map of white line peak positions for a secondary particle at SOC 5. Higher white line peak position indicates more oxidazed area.

Figure 1
Surface Composition and Oxygen Transport Properties of LSCF: From Bulk Ceramics to Devices
Authors: Druce John , Téllez Helena , Ishihara Tatsumi , Kilner John A.
Published: February 2020

The exchange of oxygen between the gas phase and a mixed conducting ceramic, and its subsequent solid state diffusion, is key to the operation of electrochemical energy conversion devices such as Solid Oxide Fuel Cells (SOFCs) and Solid Oxide Electrolysers (SOECs), as well as dense membranes for oxygen separation. Indeed, it is often the surface reaction that determines the overall performance in such applications. However, whilst the mechanisms of oxygen diffusion in the bulk of these materials are generally well understood in terms of the defect chemistry and crystal structure, such an atomistic description of the surface exchange reaction still eludes us.

Whilst 18O isotopic tracer diffusion experiments coupled with SIMS analysis have been used for more than 30 years to study the kinetics of oxygen exchange and transport in candidate mixed conductors, relatively little attention has been paid to the characterization of the realistic surface composition of such materials; despite the great attention which is paid to the bulk chemistry, it is often assumed that the surface is a simple termination of the bulk. More recently, it is becoming apparent that the surface and near-surface composition after high temperature treatment is often radically different from the bulk.

Some of this recent work has been facilitated by the availability of new tools to probe the surface composition. Our group in particular has been applying Low Energy Ion Scattering (LEIS) spectroscopy, which is uniquely capable of determining the elemental composition of the single outer atomic layer of a material (i.e. the very same atomic surface that interacts with oxygen in the gas phase).

In this contribution we will use the commonly used perovksite La0.6Sr0.4Co0.2Fe0.8O3-d (LSCF) to illustrate how LEIS and SIMS can contribute to our understanding of the relevant surface composition, complementing the existing understanding of the bulk properties of this commonly used electrode material. Starting from studies of surface segregation and restructuring in dense ceramic pellets after heat treatments similar to sintering conditions, we will then show how compositional changes can also occur at targeted device operating temperatures (around 500 ºC). Finally, we will show how laterally resolved LEIS analysis can be applied to understand compositional changes and interdiffusion occurring in the very outer atomic surfaces of LSCF microelectrode – YSZ electrolyte electrochemical half cells.
Modeling and Optimization of the Nano-Particle Infiltrated Electrode of a Solid Oxide Fuel Cell
Authors: Chen Mei-Na
Published: February 2020

Recently, nano-particle infiltrated electrode has shown its advantages in many aspect. Although there are many experimental studies on it, the theoretical design of the nano-particle infiltrated electrode which is also very important is still lacking. In this paper, the processes of electrochemical reactions, electronic and ionic conductions and gas transports in the nano-particle infiltrated electrode of the solid oxide fuel cell are discussed in detail. A corresponding multi-physics model is also obtained which can be verified by the experimental I–V relations. This model is further used to systematically examine the effects of various microstructure parameters on the performance of the nano-particle infiltrated electrode. This comprehensive study can finally give the optimization design of the nano-particle infiltrated electrode.
Theoretical Study of Inorganic Carbonaceous Species Reaction with the Surfaces of BaTiO3(001)
Authors: Rivera Rocabado David Samuel , Ishimoto Takayoshi , Quang-Tuyen Tran , Shiratori Yusuke , Koyama Michihisa
Published: February 2020

Due to the variety of component elements and their high chemical stability at elevated temperatures, various perovskite oxide materials have been used to replace catalyst containing precious metals as oxidation catalysts or oxygen-activated catalysts (1). Additionally, because of their oxygen mobility through the material the C accumulation is not promoted. Such is the case of the resistance towards C deposition of Ni/BaTiO3-Al2O3 when employed as catalyst for low temperature dry reforming of CH4 (2). During the CH4 reforming, the C deposition is caused mainly due the CH4 decomposition or the CO disproportionation reaction that will lead to the formation of CO2 and C. On the other hand, one of the drawbacks of some perovskite materials such as BaTiO3 is that in the presence of CO2 the formation of a localized stable carbonate phase on the surface is possible (3). This carbonate phase will affect not only the catalytic activity of the material, but also may influence in its electronic properties. In this study the density functional theory (DFT) will be employed to analyze from a theoretical point of view the interaction of CO2 and the CO disproportionation reaction on the surfaces of BaTiO3(001). Our first approach with the BaO-terminated surface revealed that the CO molecule chemisorbs on the surface O atom. Additionally, if another CO molecule from the gas phase will interact with the already adsorbed CO molecule (Eley-Rideal reaction mechanism), the formation of trioxydehydroethene showed high spontaneity and the least stable but still probable to occur is the formation of CO2 and C that chemisorbs on top of an O atom (disproportionation reaction).  Moreover, for the CO2 reaction with the BaO-terminated surface, the formation of CO3 anion showed to be quite stable. Furthermore, the CO2 reaction and CO disproportionation reaction will be also analyzed for the TiO2-terminated surface.

References

J. T. S. Irvine, in Perovskite Oxide for Solid Oxide Fuel Cells, T. Ishihara, Ed., p. 167, Springer, Fukuoka (2008).

X. Li, Q. Hu, Y. Yang, Y. Wang, and F. He, Appl. Catal. A, 413– 414, 163, (2012).

M. Wegman, L. Watson, A. Hendry, J. Am. Ceram. Soc., 87, 371 (2004).
Simulation and Prediction of 3-D Microstructural Evolution and Long Term Performance of Ni-YSZ Anode
Authors: Wang Xin , Atkinson Alan
Published: February 2020

The electrochemical performance of SOFCs degrades over the operation time due to a number of factors. The electrochemical activity of the anode is one of these changing parameters due to microstructure coarsening. The change in microstructure of a Ni cermet anode is mainly due to the mobile Ni phase at high temperatures and can be accelerated by the presence of water vapour. The reduced triple phase boundary (TPB) density caused by coarsening leads to degradation of electrochemical performance of the anode. In order to manufacture SOFCs with long- lasting high performance and predict their useful lifetime, it is necessary to understand and predict the microstructural evolution of the anode under different operation conditions. In this contribution, we will demonstrate that the evolution of a 3D real microstructure of a Ni-YSZ anode can be simulated and predicted using our newly developed cellular automaton approach. For this simulation, the YSZ is assumed to be immobile while the mobility of Ni is by the route of evaporation-condensation. In the model the surface energy of Ni and the YSZ/Ni interface energy are simulated based on a new concept of material structural imbalance. The 3D microstructures of anodes subjected to different aging conditions are reconstructed experimentally using focus ion beam (FIB) slice and view. It is shown that the simulation results fit the experimental results very well.  Using these short time experimental observations as a calibration of the model, we demonstrate that it is feasible to predict the long time microstructure evolution of the Ni-YSZ anode and hence its long term performance and lifetime.
Density Functional Theory Study of Dopant Effect on Sintering in the Anode of Solid Oxide Fuel Cell
Authors: Xu Jingxiang , Higuchi Yuji , Ozawa Nobuki , Kubo Momoji
Published: February 2020

Sintering of Ni nanoparticles in a Ni/YSZ porous anode of a solid oxide fuel cell (SOFC) during the long-term operation take places easily due to the high operation temperature, which leads to the degradation of the Ni/YSZ porous electrode. In previous studies, we developed a multi-nanoparticle modeling methodology that can consider the effects of the properties of the porous structure such as porosity and YSZ nanoparticle framework, etc., for investigating the sintering process in the porous structure and revealed that the porous structure plays a critical role in suppression of the sintering [1,2]. Moreover, the porous structure is determined by the framework consisting of many nanoparticles. Thus, the design of the framework structure that can effectively prevent the sintering during the operation is demanded. For this purpose, the investigation of the YSZ nanoparticle size effect on the framework structure and its effect on the sintering is needed, because the framework structure is determined by the nanoparticle size, nanoparticle ratio and so on. However, the mechanism of different sintering behavior by changing the size of YSZ nanoparticle has not been revealed. In this study, we investigated the effect of YSZ nanoparticle size on the sintering of Ni nanoparticles in the Ni/YSZ porous structure by using our multi-nanoparticle sintering simulation based on the large-scale molecular dynamics simulation method. Our results show that Ni nanoparticles make contact with each other and the sintering proceeds by the growth of the contact area between the Ni nanoparticles. Then, we quantified the degree of sintering and found that the degree of sintering in the Ni/YSZ model with the large YSZ nanoparticles compared to Ni nanoparticles is larger than that with the small YSZ nanoparticles compared to Ni nanoparticles. In the Ni/YSZ model with the large YSZ nanoparticles compared to Ni nanoparticles, the framework of large YSZ nanoparticles generates the large pore. The Ni nanoparticles are easy to move in the framework structure, and the sintering of Ni nanoparticles takes place easily. On the other hand, the framework of small YSZ nanoparticles generates the small pore in the Ni/YSZ model with the small YSZ nanoparticles compared to Ni nanoparticles. The framework of small YSZ nanoparticles restrains the movement of the Ni nanoparticles. Thus, the sintering of Ni nanoparticles is inhibited in the Ni/YSZ model with the small YSZ nanoparticles compared to Ni nanoparticles. 

[1] J. Xu et al., J. Phys. Chem. C 117 (2013) 9663.

[2] J. Xu et al., ECS Trans. 57, (2013) 2459.
Permeability of Gases in the Anode of an Anode Supported SOFC
Authors: Geagea Maya , Genov Ivaylo , Stoynov Zdravko , Vladikova Daria , Chesnaud Anthony , Thorel Alain
Published: February 2020

In the high current density regime, the performance of SOFCs is limited by concentration overpotentials, which are particularly significant at the anode side where a competition occurs between incoming hydrogen and outgoing water. In standard SOFCs where the anode is made of YSZ and Ni, this becomes crucial when the demand for reactants exceeds the capacity of the porous cermet anode to supply them by gas diffusion mechanisms. A delicate compromise should be found between maintaining a high level of activation in the anode, i.e. high density of triple phase boundaries (TPB), favored by a distribution of small interconnected pores with high tortuosity and small grains size, and high gas permeability, favored by a distribution of large interconnected pores with low tortuosity, while the percolation of both electronic and anionic conductivity phases is maintained.

The present work aims at determining experimentally anodes gas permeability as a function of the experimentally determined percolation, tortuosity and volume fraction of the pores, assuming that the diffusion of gases is described by the Darcy Law. Anodes with varying porosity ensured by different quantities of the pore former were obtained by cold pressing and sintering. SEM image analysis, mercury intrusion porosimetry and permeability measurements for different gases were performed. The obtained results show that permeability increases with the volume fraction of the pore former. However, non-linearity as a function of the gases molecular weight is observed and discussed as a function of the mean free path and thus of possible mixed Darcy and Knudsen diffusion.
Sunfire Industrial SOC Stacks and Modules
Authors: Strohbach Thomas , Mittmann Frank , Walter Christian , Schimanke Danilo , Geipel Christian
Published: February 2020

In the past years, sunfire has increased its product portfolio and production depth. Four product classes (single stacks and stack modules for SOFC and SOEC) are tackling several markets (off-grid, on-grid, mobile). A ceramic center and a new production facility were inaugurated. The R&D activities are strongly driven by market requirements. With the new SOC stack electrolysis operation is introduced aside fuel cell operation. Furthermore, an increase in power density and a reduction of cost was achieved under the constraint of using standard industrial materials. Latest results of SOC single stack testing like I-V curves and reversible operation will be presented. The engineering and testing of stack modules in the power range >25kW will be also shown.