bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanostructured Graphene-Supported Pt-NiTiO3 Catalyst for the Oxygen Reduction Reaction for Alkaline Direct Alcohol Fuel Cells Applications
Authors: Hernández Ramírez Anayantzin , Rodriguez-Varela F.J. , Sánchez-Castro Ma. Esther , Kalasapurayil Kunhiraman Aruna , Karthikeyan Palanisamy , Manoharan Ramasamy
Published: February 2020

The catalytic activity for the ORR of graphene-supported Pt-NiTiO3 (Pt-NiTiO3/G) catalyst was evaluated in 0.5 M KOH. NiTiO3 nanoparticles were synthesized via a wet-chemical method. XRD analysis confirmed the formation of crystalline NiTiO3 nanoparticles with a size of ca. 25 nm. Then, nanostructured 20% Pt-NiTiO3/G catalyst (Pt:NiTiO3 ratio of 1:1) was obtained by the microwave assited polyol method. The titanate-based catalyst showed a high cataytic activity for the ORR in 0.5 M KOH electrolyte. It also showed enhanced tolerance to methanol and ethanol, compared to Pt/C and Pt/Gr catalysts. The results suggest that Pt-NiTiO3/G electrocatalyst is a good candidate for Alkaline Fuel Cells applications.
Leveraging Local pH Gradients to Optimize Electrochemical Lanthanum Accumulation
Authors: Medina Adan , Babauta Jerome T. , Beyenal Haluk
Published: February 2020

Lanthanum accumulation on a polarized unmodified electrode has been shown to be under local pH control. Cyclic voltammograms in unbuffered aqueous solutions have shown that the local pH varies up to 10 pH units compared to the bulk solution, while buffered solutions vary ~ 6 pH units. This is due to lanthanum’s theoretical deposition potential being well outside the working region of water, resulting in the consumption of proton-equivalents during water electrolysis. Previous work has shown that high pH induces lanthanum to become insoluble and thus unavailable for electrochemical reactions. The large background current from water electrolysis hides lanthanum’s electrochemical response during cyclic voltammetry experiments, so the electrochemical quartz crystal microbalance (eQCM) was used to track the frequency shift resulting from attached mass on the surface of carbon-coated QCM electrodes. Varying levels of buffering agent (acetate buffer) resulted in modulation of the onset deposition potential as well as the length of the stable film region during anodic stripping. This shows that bulk parameters (pH, buffer strength) can be used to determine the potentials at which lanthanum will deposit and strip on unmodified carbon electrodes.
Agglomeration in Porous Silicon Prepared from Si-Nanowires Structures
Authors: Velez Victor H. , Sundaram Kalpathy B
Published: February 2020

Silicon nanowires (SiNW’s) arrays prepared by electroless etching method are attractive due to their significant light absorption properties across the visible spectrum [1]. Typical silicon nanowires grown by electroless etching is shown in Figure 1a. Following this preparation of silicon nanowires, these samples are etched in an electrolytic HF and ethanol solution to produce porous silicon quantum confined structures. Mechanical behavior of materials at nanoscale is different due to their quantum confinement effect. When porous silicon nano-structures are prepared from SiNWs obtained through electroless process, they may have a tendency to become thin. Ultimately these nano-structures may collapse and form bunches on the surface [2], as shown in Figure 1b. However, bunched silicon nanowires structures may be desirable in some applications but may not be for some others. In order to avoid bunching of SiNWs, it may be necessary to reduce the surface tension during the growth of nanowires [3].

                                (a)                                                                                                      (b)

Fig 1. Cross-section images of silicon nanowires (a) grown by electroless etching, (b) Porous silicon structures prepared from SiNWs.

SiNW’s were grown by eletroless etching in a solution of hydrofluoric acid (HF) and silver nitrate (AgNO3) at room temperature [4]. The prepared nanowires were then etched in an electrolytic solution containing HF and ethanol to make porous Si quantum confined structures. Reflectance and photoluminescence studies are performed on this structures

Figure 1
Improvement of Quantum Efficiency of the Nanosized Phosphors Using a Flux
Authors: Ha Jungmin , Wang Zhenbin , Novitskaya Ekaterina , Hirata Gustavo , Graeve Olivia A , Ong Shyue Ping , McKittrick Joanna
Published: February 2020

Micron-sized phosphors have been widely researched for a near UV-LED by the mean of the convenient solid-state method. The phosphors with micron-sized tend to show good quantum efficiency oriented from their large crystallite size, but present high light-scattering and decrease packing density on the LED device, causing low resolution. Therefore, integration of the phosphors for a near-UV LED package has particles size requirements in order to overcome the issue from bulk size phosphors. The scatter effect in visible and UV radiation region will be negligible when the radii of phosphors particles are less than ~400 nm. However, phosphors with nano-size particles have poor quantum efficiency comparing to phosphors with micron sized particles.

            In this work, flux effect on quantum efficiency is studied in nano-sized phosphors. Blue colored CaMgSi2O6:Eu2+ phosphors were synthesized by a co-precipitation method and NH4F, NH4Cl, or H3BO3 was added as a flux. Flux is typically used in the solid-state reaction to help diffusion of atoms in the bulk materials, not nano-sized materials. The crystallite size is increased from ~20 nm to ~40 nm, but particles size is unchanged (~ 50 nm) with the addition of a flux in the materials, confirmed by X-ray diffraction, Dynamic Light Scattering analysis, and Scanning Electron Microscopy. The emission wavelength of CaMgSi2O6:Eu2+ is 458 nm under 350 nm as an excitation wavelength. The intensity of emission wavelength is about twice increased when 5wt% NH4F is added as a flux in the phosphors materials comparing to the phosphors without a flux, indicating the improvement of quantum efficiency. This study shows the potential of flux that could improve quantum efficiency in the nano-sized phosphors. This work is supported by the National Science Foundation, Ceramics Program Grant (DMR-1411192).
Magneto-Photoluminescence and Giant Magneto-Resistance in Self-Assembled Vertically-Aligned (ZnO)0.5:(La0.7Sr0.3MnO3)0.5 Nanopillars
Authors: Pan Wei
Published: February 2020

A great deal of research has been carried out in perovskite rare-earth manganites. Among them, La0.7Sr0.3MnO3 (LSMO) is of particular interest due to its colossal magnetoresistive effect. So far, studies in LSMO have mainly been focused on its bulk magnetic transport properties. Much less work has been carried out in LSMO nanostructures. In fact, to our knowledge, there is no report on exploring low temperature photoluminescence (PL) measurements and the magnetic (B) field dependence in LSMO.

In this talk, I will first report our recent results of magneto-photoluminescence in La0.7Sr0.3MnO3 nanopillars embedded in a self-assembled vertically aligned epitaxial (ZnO)0.5:(La0.7Sr0.3MnO3)0.5 nanocomposite film in the ultra-violet regime at magnetic (B) fields up to 12T. We have observed that at low B fields the PL intensity is nearly constant. As the B field is further increased over a characteristic value, which depends on sample temperature, the PL intensity decreases sharply and eventually quenches at higher magnetic fields. In the second part, I will present our recent results on giant magneto-resistance in LSMO nanopillars.
(Invited) XAFS of Rare Earth Elements in Amorphous Silicon Alloys: What Do We Know about the Local Structure?
Authors: Tessler Leandro R. , Bosco Giacomo Ferreira
Published: February 2020

X-ray absorption spectroscopy (both XANES, X-ray Absorption Near-Edge Spectroscopy and EXAFS, Extended X-ray Absorption Fine Structure) is a powerful tool to determine the chemical environment of selected elements in solids. It is particularly well suited to study rare earth elements in amorphous silicon alloys. In this paper we review the technique and results obtained for different rare earth elements, especially Er, Eu and Tb.

Whenever possible, the rare earth elements coordinate to any oxygen present in subcoordinated envitronments that vary with the host and can be very distorted. The details of the environment depend on the technique used to prepare the samples. Annealling above 400C makes the coordination evolve towards oxide-like 6-fold environments.

Europium is a special case. It may assume either 2+ or 3+ oxidation states.  The X-ray absorption peaks associated with the core electrons binding energy can be used to estimate the relative concentration of each. Annealling in oxidizing atmospheres can modify the Eu3+/Eu2+ ratio, affect the atomic surroundings and change the luminescence spectrum.

In general, efficient luminescence of the 3+ ions is associated with low coordination oxygen environments. This environment does not change significantly at the  relatively low annealling temperatures (up to 300C) that maximize the photoluminescence. The reason for the increase of the luminescence intensity with annealling not a modification of the local environment of the rare earth ions.
Calibration of a Circular HV Magnetron Sputtering Source for in-Situ RE Doping of Ecr-PECVD Si-Based Thin Films
Authors: Miller Jeremy William , Wojcik Jacek , Bradley Jonathan D. B. , Mascher Peter
Published: February 2020

Rare-Earth doped silicon based luminescent materials have become an attractive solution in some key areas of technological development. For instance, in the field of silicon photonics there is a drive to replace electronic on-chip components with photonic counterparts [1-2]. One of the major challenges thus far has been to provide the monolithic integration of an efficient reliable electrically driven light source. Such an element could also be used for solid state lighting, and avoid expensive III-V compounds that cannot be fully integrated into electronic drivers in a CMOS line [3].

In-situ doping of Eu3+ions in silicon oxides and oxynitrides fabricated by electron-cyclotron-resonance plasma enhanced chemical vapour deposition (ECR-PECVD) is performed. Doping is achieved by using a Circular High Vacuum Magnetron sputtering source attached to the ECR-PECVD tool. The doping concentration is varied by varying the distance of the sputtering source to the target. The hot matrix composition is varied through varying oxygen and nitrogen gas flows. The effects on the doping concentrations of the sputtering source distance to target is determined through Rutherford Backscattering Spectrometry and Variable Angle Spectroscopic Ellipsometry. Preliminary luminescence measurements are discussed.

[1] Jalai, B., and Fothpour, S. “Silicon photonics,” Journal of Lightwave Technology 24, 4600-4615(2006)

[2]Liu, A. Jones, R., Liao, L., Samarah-Rubio, Rubin, D., Cohen, O. Nicolaescu, R., and Paniccia, M., “A high-speed silicon optical modulator based on a metaloxide-semiconductor capacitor,” Nature 427, 615-618 (2004)

[3] Ponce, F.A., Bour, D.P., “Nitride-based semiconductors for blue and green light-emitting devices”, Nature 386 (6623), 351-359 (1997)
Impact of Conjugated Mechanical and Electrical Stimuli on Interfacial Adhesion and Electrical Contact
Authors: Zade Vishal , Martini Ashlie , Lee Min Hwan
Published: February 2020

This work was performed in an effort to fundamentally understand how nanoscale contacts between materials evolve due to coupled stresses, specifically those arising from mechanical and electrical stimuli. To investigate the stress response of contact between these materials, atomic force microscopy (AFM) experiments was performed with the AFM tip-substrate interface subjected to normal mechanical loading and electric current, individually and in combination. Experiments to study the effect of coupled external stresses on metal/metal and metal/graphite interfaces are largely based upon AFM. We chose this experimental tool because the AFM tip mimics the contact of a single nanoscale asperity which provides a means of studying the very complex process by which a contact area evolves with stress. AFM is also advantageous for this study because 1) a predefined force can be applied to the tip-substrate interface enabling measurement of forces down to the pN level; 2) multiple characteristics of an interface can be measured simultaneously under various external stimuli at the nanoscale; and 3) measurements can be made in a non-vacuum environment unlike other nanoscopic equipment. After creating a nanoscale contact by bringing a metal-coated AFM probe or all-metal probe into contact with a sample, coated with either a metal or a graphitic layer, mechanical and/or electrical stresses are applied to the tip-substrate interface. Then the resulting adhesion force and electrical contact resistance are measured. These measurements are used not only to understand how stresses couple to affect the size of nanoscale material interfaces but also to explore limits of continuum contact area expressions for predicting contact evolution and to identify atomic-scale metrics for characterizing nanoscale contacts.

Research supported by the US AFOSR (Grant # FA9550-15-1-0256).
Fabrication and Characterization of Tungsten Oxide Nanostructures Using Thermal Evaporation
Authors: Sung Po-Heng , Lu Kuo-Chang
Published: February 2020

We report an efficient and simple method to synthesize tungsten oxide nanostructures, including high quality and quantity nanowires, through thermal evaporation of WO3 powders without catalyst. The thermal evaporation processing was conducted in a three zone horizontal tube furnace over temperatures ranging from 300 to 800℃, where multiple substrates were placed at different temperature zones to form distinct nanostructures, such as films, nanorods and nanowires. The temperature of each zone was measured by a thermal couple. Processing parameters, including pressure, temperature, type of gas and flow rate, were varied and studied in terms of their influence on the morphology, aspect ratio and density of the nanowires. The morphologies of the products were observed with scanning electron microscopy. High resolution transmission electron microscopy and x-ray diffraction studies were conducted to further identify the chemical composition, crystal structure and growth direction of the nanostructures. Additionally, the growth mechanism has been proposed. Furthermore, we investigated the doping effect on physical properties of the nanostructures. Since tungsten oxide has lots of interesting properties, including chromism, optical and field emission, the research at nanoscale here supports the development of promising potential applications for sensors, light-emitting diodes and field emitters.
Anodically Grown TiO2 Nanotube Arrays Used As Substrates for Thermal Dewetting of Pt Show Significantly Enhanced Photocatalytic H2 Generation with Minimal Co-Catalyst Amounts
Authors: Nguyen Nhat Truong , Altomare Marco , Schmuki Patrik
Published: February 2020

TiO2 nanostructures have recently attracted much attention due to their wide range of applications, such as photocatalysis, photovoltaics (dye-sensitized solar cell, photo-electrochemistry) and gas sensing. Particularly, electrochemically formed TiO2 nanotube arrays were shown to exhibit improved photocatalytic activity compared to other TiO2 nanostructures, this being ascribed to their directional electron transport and orthogonal charge carrier separation.1 The advantage of an electrochemical growth of the TiO2 nanotube layers is not only the simplicity of the process, but also the possibility of controlling the tube geometry (length, diameter, wall thickness) by selecting suitable anodization parameters (applied voltage, anodization time, temperature, fluoride concentration). Nevertheless, TiO2 alone is not effective in photocatalytic H2 generation: it requires the presence of noble metal co-catalysts (Pt, Au, Pd).2,3 Among the various noble metals, Pt is the most effective co-catalyst: it enables an efficient electron transfer at the semiconductor interface by providing a favorable solid state junction to TiO2 and it enhances the hydrogen recombination reaction.

There are several well explored methods to decorate Pt onto TiO2 nanotubes, mostly leading to a decoration of the full tube length with nanoparticles (the most frequently used up to date is photodeposition).

With our contribution we show a different approach: we decorate only the outermost surface of anodic TiO2 nanotubes with very thin Pt films (nominally few nm-thick) by using a simple plasma sputtering technique.4 Then, by a controlled thermal treatment, the Pt films are dewetted at the mouth of the tubes into arrays of Pt nanoparticles that are as small as of few nm. This site-selective deposition (only at the tubes top) allows for minimizing the amounts of costly noble metal co-catalyst, while at the same time leads to a significantly enhanced photocatalytic H2 generation compared to tubes that carry along their full length a classic Pt nanoparticle decoration.

[1] K. Lee, A. Mazare, P. Schmuki, Chem. Rev.
2014, 114, 9385–9454.

[2] N. T. Nguyen, J. Yoo, M. Altomare, P. Schmuki, Chem. Commun.
2014, 50, 9653–9656.

[3] N. T. Nguyen, M. Altomare, J. Yoo, P. Schmuki, Adv. Mater.
2015, 27, 3208–3215.

[4] N. T. Nguyen, M. Altomare, J. E. Yoo, N. Taccardi, P. Schmuki, Adv.
Energy Mater.
2015, doi: 10.1002/aenm.201501926. 

Figure 1
High-Energy-Density, Long-Life Lithium-Sulfur Batteries
Authors: Manthiram Arumugam
Published: February 2020

The current lithium-ion technology is based on insertion-compound cathodes and anodes, which limit the charge-storage capacity and energy density. Also, transition-metal ions with multi-electron redox reactions generally encounter a large step in the voltage profile on going from one redox couple to the other. To increase the energy density, much attention is being paid in recent years towards conversion-reaction electrodes, such as sulfur and oxygen as they offer two-electron transfer per sulfur or oxygen atom. However, the Li-S cells suffer from low electrochemical utilization and poor static (high self-discharge) and dynamic (short cycle life) stabilities, arising from the low electronic conductivity of both the end members S8 and Li2S, migration of dissolved polysulfide intermediates from the cathode to the anode, large volume changes during charge/discharge, and poor cycle life and dendrite formation with the lithium-metal anode.

To overcome the above difficulties, this presentation will focus on both novel electrode architectures as well as innovative cell designs. Specifically, the presentation will focus on approaches to enhance the electrochemical utilization of sulfur, suppress the migration of dissolved polysulfides to the anode, stabilize the lithium-metal anode surface, and utilize Li2S as a cathode. For example, novel cell configurations with a microporous carbon paper interlayer between the cathode and the separator, as well as polymeric separators coated with unique carbon architectures to trap and reutilize the migrating ploysulfides and enhance the electrochemical utilization, will be presented. Particularly, attention will be paid to the increase in the sulfur content (wt. %) and sulfur loading (mg/cm2) and the challenges associated with it to make the energy density of lithium-sulfur cells well above that of the currently available lithium-ion cells. In addition, additives to form a stable solid-electrolyte (SEI) layer in situ on a lithium-metal anode will be presented. Also, additives to lower the activation barrier during the first charge of Li2S cathode will be discussed.
Molten Sulfides: From Thermoelectricity to Electrochemical Extraction
Authors: Allanore Antoine
Published: February 2020

Sulfides are the second most abundant compounds after oxides, hosting metals essential for energy application and storage such as copper, lead or zinc. The extraction of those commodity metals provides access to energy critical elements such as silver, molybdenum, rhenium or indium, as by-products. There is however an interest in reconsidering metal extraction methods from sulfides. In particular, methods that prevent SO2 emissions during processing or that can integrate with the power grid are of appeal. In addition, new extraction techniques with the potential to selectively recover one critical elements independently of the existing smelters are needed to reshape the existing supply chain and allow more recycling. Sulfides are known to electrochemists for their use in sodium polysulfide-based batteries, but little is discussed about their unique properties in the molten state. The presentation reports recent results obtained for both semiconducting and partially ionic melts. The semi-conductor properties prove valuable for high temperature thermoelectricity while the ionic nature of certain sulfides enables to conduct metal extraction by electrolysis. The results prove that a path toward high-temperature electricity harvest or usage thanks to molten sulfides is possible. They also reveal the need for dedicated experimental and modeling efforts to accelerate the rate of generation of thermodynamic and physical chemical data for molten sulfides.
Materials Engineering Using Nano-Fibrous and Molecular Cellulose
Authors: Wang Howard
Published: February 2020

Cellulose is the most abundant natural polymer on earth, and widely used in everyday-life products from building construction to clothing to paper. Fundamental understanding of molecular solutions of cellulose is the key to realize advanced technologies beyond cellulose fibers. It has been previously reported that certain ionic liquid and organic solvent mixtures dissolve cellulose. In this study, the tertiary phase diagram of cotton linter microcrystalline cellulose, 1-Ethyl-3-methylimidazolium acetate (EMIMAc), and dimethylformamide (DMF) mixtures has been determined using primarily optical cloud point method and small angle neutron scattering (SANS).  The mechanism of cellulose dissolution in tertiary mixture has been investigated by combining quasielastic and small angle neutron scattering (QENS and SANS).  As SANS data show that cellulose chains take Gaussian-like conformations in homogenous solutions, which exhibit characteristics of having an upper critical solution temperature, the dynamic signals predominantly from EMIMAc molecules indicate strong association of EMIMAc with cellulose in the dissolute state.  Data indicate that a molar ratio of EMIMAc to cellulose repeating unit greater or equal than 3 is necessary but not sufficient in forming one-phase homogeneous solutions.  Clustering of cellulose chains occurs at low EMIMAc/DMF or EMIMAc/cellulose ratio, or at low temperatures.  The mechanism of cellulose dissolution in tertiary mixture is discussed, and the potential applications of molecular cellulose are demonstrated.
Study of HF-Free Pulse Reverse Electropolishing of Nb Surface with an Alkaline Electrolyte
Authors: Tian Hui , Taguchi Junji , Reece Chalies E , Namekawa Akihiro , Saeki Takayuki , Hayano Hitoshi
Published: February 2020

Chemical etching or electropolishing of Nb superconducting radio-frequency (SRF) cavities to achieve a clean and smooth internal surface require the removal of the passive Nb2O5  film. Typically, an aggressive chemical, such as hydrofluoric acid is included in the solution to accomplish this. The problem with using HF is that it is dangerous both to people and to the environment.  As an alternative, in order to depassivate the surface, cathodic pulses may be interspersed between anodic pulses which passivate the Nb surface forming Nb2O5 film, in place of or in conjunction with off-times. Use of such cathodic pulses eliminates the need for HF and/or fluoride salts or other chemicals to actively remove the surface oxide. A present understanding of a pulse reverse electropolishing of Nb in alkaline electrolyte-sodium hydroxide will be reported. In this study, 10~30 % concentration of NaOH has been used as the electrolyte. In order to better understand the mechanism of a pulse reverse electropolishing of Nb with sodium hydroxide, and optimize the process parameters for Nb cavity process,  the effect of cathodic pulse duration and amplitude, off time, and anodic pulse duration have been systematically studied, the surface of Nb samples have been characterized chemically and morphologically. We expect the results will enable application of this safer and greener process to future accelerator projects using Nb SRF cavities.
In Search of an Alternative Solar Grade Silicon Production By Electrochemical Reduction of SiO2
Authors: Akpinar Bengisu , Ergul Emre , Erdogan Metehan , Karakaya Ishak
Published: February 2020

Silicon plays an important role in fabrication of solar cells and solar chips.  Metallurgical grade silicon (98 to 99 % Si) demands further purification such as zone refining [1, 2], metallothermic reduction [3] and Siemens process [4] to convert it to solar grade. A promising method, based on direct electrochemical reduction of oxides by FFC Cambridge Process [5], was adopted to form silicon from porous SiO2 pellets in molten CaCl2 and CaCl2–NaCl salt mixture [6]. The contamination of silicon powder by iron and nickel originating from stainless steel cathode was reported to disqualify the product from solar applications. SiO2 pellets, sintered at 1300oC for 4 hours, were sandwiched between pure silicon wafer plates to minimize contamination of silicon. The promising results indicated a potential alternative method of direct solar grade silicon production for expanding solar energy industry.

[1] P.R. Mei, S.P.Moreira, E.Cardoso, A.D.S.Cortes, F.C.Marques, “Purification of metallurgical silicon by horizontal zone melting”, Sol. Energ. Mat. Sol., 98 (2012), 233-239.

[2] P. Siffert, E.F. Krimmel, eds. Silicon: Evolution and future of a technology. Berlin,Springer (2004).

[3] K. Yasuda, T.H. Okabe, “Solar-grade silicon production by metallothermic reduction”, JOM,62 (12) (2010), 94-101.

[4] Siemens & Halske: BRD Patents 1.102.117 and 1.140.1594 filed 1954, issued 1956

[5] G.Z. Chen, D. J. Fray, T. W. Farthing, “Direct Electrochemical Reduction of Titanium Dioxide to Titanium in Molten Calcium Chloride”, Nature, 407 (2000), 361-364.

[6] E. Ergül, İ. Karakaya, M. Erdoğan, “Electrochemical decomposition of SiO2 pellets to form silicon in molten salts” Journal of Alloys and Compounds, 509 (2011), 899-903.
(Invited) The Influence of Flux Changes on Semiconductor Nucleation and Crystal Growth from a Liquid Metal Electrode
Authors: Maldonado Stephen
Published: February 2020

This presentation will discuss the latest findings in regards to the concept of mediating nucleation and growth of a solute crystal inside a liquid metal electrode through heterogeneous electrochemical reduction reactions at the electrolyte/electrode interface. The focus will be to compare/contrast experimental and modeling data that pertain to the flux conditions that favor and inhibit nucleation and crystal growth steps. Two systems will be discussed. First, conditions that favor large-grain crystal growth from a bulk liquid pool electrode will be discussed. Second, flux conditions that permit a single crystal to grow from a microscopic liquid metal droplet will be presented. The possibility of using AC amperometry in both systems to initiate and affect crystal growth will also be discussed.
Simulation of Transport Properties in Gas Diffusion Layer of PEMFC Using Lattice Boltzmann Method
Authors: Kim Jongsung , Lee Sungho , Yim Chulho , Hwang Inchul
Published: February 2020

Gas diffusion layer (GDL) in fuel cell plays an important role of passage for reactant transport and water removal between the bipolar plate and the electrode. In the present work, effective transport physical properties of gas diffusion layer in proton exchange membrane fuel cells (PEMFC) are deduced using lattice Boltzmann simulation, which is applicable for both GDL substrate with a pore size of 10~100 micrometer and MPL with 10~100 nanometer pore size. We also use GDL microstructure scanned using high resolution X-ray computed tomography and compressed under realistic levels with virtual material design tool. Liquid water saturation in the GDL is considered in the simulation because the blockage of pores by water has a strong influence on its effective gas transport properties. The deduced properties can be applied to fuel cell performance program and its influence on cell performance be measured.
A Combined Aging and Abuse Study of Li-Ion Cells
Authors: Juarez Robles Daniel , Chen Chien-Fan , Jeevarajan Judith A. , Mukherjee Partha P.
Published: February 2020

Lithium-ion batteries have been powering a wide range of electrical and electronic devices, from consumer products and medical equipment to automotive systems and space applications. Some highly publicized failures of products powered by lithium ion cells, such as laptops, cellphones and electronic toys, have been reported recently. A portion of these failures has been linked to overheating of the battery resulting in fire and explosion. Overall, these incidents have catalyzed a great deal of research and design activities aimed at trying to understand the causes of such failures and help guide safer cell designs.

In this work, the degradation mechanisms in commercial 18650 lithium ion cells, due to long term cycling under nominal-use charge discharge cycling as well as under electric vehicle drive cycling, are studied. In addition, studies were carried out after subjecting the cells to overcharge and external short circuit testing on fresh as well as cycled cells.  During the external short test, the cells were subjected to a low resistance load (50 mΩ). Actual results indicate that for a very short time the cell experiences a very high current causing a rise in the cell temperature (>70 oC). In the overcharge test, the cell is charged up at a constant C-rate until the test is stopped due to either an abnormal event or the cell protection activation. Preliminary results have shown lithium metal deposition, as expected, in the negative electrode once that the intercalation rate has been overcome by the diffusion rate. Also, cell temperature has shown a significant increment during the overcharge process. Finally, the electrodes and electrolyte from the cycled cells were subjected to a similar analysis to understand the degradation mechanisms in long term use as well as to understand their behavior under abuse conditions after long term use. Understanding what causes this temperature rise and its effect on the electrodes could provide some information about how to prevent thermal runaway in cells and batteries used in various applications for long periods.

The cells under these tests have been characterized by conducting a Destructive Physical Analysis (DPA). The study is being accomplished through charge/discharge cycling, internal resistance measurement, capacity fading, and impedance spectroscopy. Cell temperatures are monitored in all the experiments. The morphological changes are studied by extracting the electrodes from the abused cells and analyzing them by microscopy and spectroscopy techniques. This analysis will help to obtain the changes in the electrochemical properties of the cell as well as its morphology.
Solid Electrolyte Interphase Formation and Failure Mechanisms in Lithium Ion Batteries: In Situ and in Operado AFM Imaging
Authors: Kumar Ravi , Tokranov Anton , Huang Zhuangqun , Li Chunzeng , Xiao Xingcheng , Mueller Thomas , Sheldon Brian W.
Published: February 2020

The lifetime and performance of lithium-ion batteries depend significantly on the formation and evolution of the solid electrolyte interphase (SEI) layer. A stable SEI is necessary for utilization of high specific capacity anode materials such as Si which goes through huge volume changes (upto ~400%) during cycling. In this study we report in situ atomic force microscopy (AFM) investigation on the formation and failure mechanisms of SEI layer using patterned Si island structures. Due to the shear lag effect [1], these patterned Si islands go through lateral expansion and contraction. This puts the SEI layer on the top of the island in tension and compression during lithiation and delithiation, respectively. We performed the studies in a glovebox at the environment with < 1 ppm O2 and H2O. In addition, the unique PeakForce tapping mode was used to image the extremely fragile SEI layer, which is very challenging for conventional AFM modes in organic solvent. Our in situ studies show for the first time the in operando cracking of SEI layer and its evolution during cycling. To understand the mechanics of the SEI layer, the critical strain at which this cracking starts to evolve was derived from a progression of the AFM images. This observation will be complemented with coin cell data on comparison of irreversible capacities of continuous film and patterned island samples which differ in their mode of deformation. We are also using Scanning electrochemical microscopy (SECM) to detect local electrochemical differences at stable and unstable SEI sites. Our comprehensive studies not only provide a new in-depth understanding of the in
operando SEI formation, evolution and its mechanical response, but also offer guidance to tailor passivation layers for optimal battery performance.

Reference:

[1] Tokranov et. al. ACS Appl. Mater. Interfaces, 2014, 6, 6672
Solvation and Solid Electrolyte Interphases in Sodium Ion Batteries
Authors: Cresce Arthur v. , Russell Selena M , Allen Joshua L. , Rogers Reginald , Xu Kang , Peng Jing , Gobet Mallory , Greenbaum Steven
Published: February 2020

High capacity sodium ion batteries, with the capacity to rival mid-range lithium ion batteries, are developing a solid presence in the field of energy storage research. Sodium ion batteries, at a material level, offer a unique opportunity to apply lessons learned in the study of lithium ion battery behavior. Most important of these is the formation of the solid electrolyte interphase layer at the anode, which shields the electrolyte from continuous decomposition. In lithium ion batteries, the formation of the solid electrolyte interphase is highly dependent (though not exclusively) on the solvation condition of the Li+ ion as it interacts with the surface of the anode. Previous work has shown that the solution behavior of the Na+ ion closely mirrors its alkali metal cousin Li+ in a variety of competitive binary solvent systems, such as ethylene carbonate and dimethyl carbonate. We hypothesize that similar rules of interphase formation will be observed in a Na-ion battery system, and the interphase will serve a similar function. This work will describe the connection between the solvation of Na+ in binary solvent electrolytes, and how this affects the structure and chemistry of the interface at the anode. We will focus on hard carbon, which has sufficient Na+ capacity to support a variety of developing cathode chemistries.

Figure 1
Molecular Basis of Active Material-Blocking By Intrinsically Microporous Polymer Membranes in All-Organic Flow Batteries
Authors: Helms Brett A. , Ward Ashleigh L. , Frischmann Peter D. , Chenard Etienne , Sevov Christo S. , Gavvalapalli Nagarjuna , Baskin Artem , Prendergast David , Sanford Melanie S , Moore Jeffrey S
Published: February 2020

All-organic flow batteries are poised to meet cost and performance targets for grid-scale electrochemical energy storage. One of the outstanding challenges in these systems concerns unwanted active material crossover, where small organic charge-storing (charge-releasing) molecules are allowed to traverse a non-selective membrane separating the positive and negative electrode compartments. Crossover leads to a shuttling process that both reduces energy ecfficiency and contributes to capacity fade. I will discuss our recent progress in understanding the molecular basis of active-material crossover for redox-active organic molecules across microporous polymer membranes with controlled pore size and pore chemistry. These membranes are based on a modular platform, namely polymers of intrinsic microporosity, or PIMs. These membranes uniquely feature sub-nanometer pores and are highly permeable. Using them, it now becomes possible to tailor both the membrane and the redox-active organic molecules to minimize the impact of crossover on cell performance.
Investigation of Nano Carbon Materials with Incorporation of Catalyst As Air-Cathode Materials for Sodium-Air Batteries
Authors: Wu James J. , Peng Zhenmeng
Published: February 2020

NASA’s future missions demand high energy density batteries. Current state-of-the-art lithium-ion batteries (LIBs) reach the specific energy capacity limits (<250 Wh/kg), thus new electrochemical storage technologies are needed to meet NASA’s future mission requirement of >400 Wh/kg. Battery chemistries with higher theoretical energy densities in particular, Li-metal based battery chemistries such as Li-air, are being actively pursued, but there remains a number of issues to be solved. The development of a new system based on sodium (Na)-air battery chemistry, with theoretical energy of 1600 Wh/kg and an equilibrium discharge potential of 2.3V, is an attractive and promising new system that has potential to achieve a rechargeable battery that meets NASA’s needs.  Being rich abundance on earth but having similar electrochemical properties as lithium, sodium has the potential to be a low cost replacement for lithium in electrochemical storage technologies.

Development of novel and optimized air cathodes will be crucial for improving capacity retention and cycle life of Na-air battery. The microstructure of carbon substrates and the catalytic oxygen reduction of the air-cathode play critical roles in the electrochemical performance in metal-air batteries. With the development and proper selection of air cathodes, the energy efficiency and energy density can be enhanced significantly. In this presentation, the results of air cathodes with nano carbon materials and incorporation with catalysts on oxygen reduction reactions will be presented, and the performance of these air-cathodes in the Na-air cells will be discussed as well.
Returning to Zinc to Meet the Challenges for Next-Generation Energy Storage
Authors: Parker Joseph F. , Chervin Christopher N. , Long Jeffrey W. , Nelson Eric S. , Rolison Debra R.
Published: February 2020

The number of battery chemistries that check the boxes of high specific energy (>100 W h kg–1), rechargeability, power performance, inherent safety, low cost, and worldwide abundance is a short list. While lithium-based batteries continue to permeate the energy-storage landscape, many safety and supply concerns remain. Aqueous-electrolyte batteries meet many of the requirements for next-generation energy storage devices, but depending on the chemistry (Pb acid, Ni–MH, Ni–Zn, Zn–Air) often fail when it comes to safety, specific energy, and/or rechargeability. The radar chart below reveals the advantages and disadvantages of several battery technologies and especially highlights that improvements to rechargeable Zn-based batteries will propel them to the forefront of the energy landscape. The historical hindrance to broader use of Zn-based batteries is the poor rechargeability of the Zn electrode, especially when formulated as a powder-bed electrode that is too prone to launch dendrites upon cycling, which then short-circuit battery operation. The U.S. Naval Research Laboratory has redesigned the Zn electrode into a monolithic, metallically interconnected three-dimensional sponge form factor that supports a more uniform current distribution, thereby allowing nearly complete utilization of the Zn active material (>90%; projecting to ~450 W h kg–1) and avoiding the local critical current density required to spawn dendrites upon cycling. We established the reversibility of our 3D Zn sponge electrodes by cycling in Ni–3D Zn coin cells with particular emphasis on suitability in next-generation electric and start–stop vehicles. The lessons derived from studying Ni–3D Zn deep cycling allow us to demonstrate preliminary cycling performance of 3D Zn–air cells and offer prescriptions on appropriate electrolytes, current collectors, cell-fabrication particulars, and the future of Zn-based batteries.

Figure 1
Half-Cell Electrochemical Performance and Cost-Benefit Analysis of Utilizing Hybrid Ionic Liquids in Zinc/Bromine Flow Batteries
Authors: Rajarathnam Gobinath Pillai , Vassallo Anthony
Published: February 2020

Ionic liquids (ILs) are typically employed as bromine sequestration agents (BSAs) in zinc/bromine (Zn/Br) flow batteries to facilitate charge/discharge operations. The present work builds upon previous investigations into alternative BSAs, and explores the hybrid utilization of 1-ethyl-3-methylimidazolium bromide ([C2MIm]Br) and the conventionally employed 1-ethyl-1-methylpyrrolidinium bromide ([C2MPyrr]Br) ILs in 5 different molar proportions (1:0, 3:1, 1:1, 1:3 and 0:1, respectively) within the Zn/Br electrolyte. The electrochemical performance and behavior of each solution in the zinc and bromine half-cells was studied via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Preliminary results from electrochemical investigations and a normalized cost-benefit analysis are presented, together with a discussion on the feasibility of using hybrid IL solutions in Zn/Br systems. On the basis of charge and current densities during forward and reverse CV scans (i.e. charging and discharging phases) for a system utilizing glassy carbon electrodes, pure [C2MPyrr]Br and [C2MIm]Br offer the best performance, including efficiencies, for Br and Zn half-cells, respectively. This trend is generally maintained during cost analysis for each half-cell. EIS showed that low charge-transfer resistance is a primary reason for good performance in both half-cells. Furthermore, lower double-layer capacitance and Warburg diffusion limitations are potentially linked to better performance in the Zn and Br half-cells, respectively. Hybrid IL mixtures generally produced higher impedances compared to solutions containing a single type of IL. Interestingly, a preliminary whole-system analysis suggests that pure [C2MPyrr]Br is most cost-effective during charging while pure [C2MIm]Br offers the best cost-benefit during discharge. The 1:1 mixture generally gave the worst electrochemical performance and lowest cost-benefit in both half-cells, suggesting that non-equimolar mixtures of these ILs might be better suited for Zn/Br systems. These findings warrant further investigation of the behavior and influence of hybrid IL formulations for BSA applications in the bulk electrolyte and at the electrode-electrolyte interface, as well as full-cell charge/discharge cycle testing. While this work focuses on Zn/Br batteries, the methods and findings presented are also potentially applicable to other types of RFBs which utilize pure or hybrid ILs for bromine sequestration.
(Invited) Unveiling the Mechanism of Magnesium Battery Cathode
Authors: Ling Chen
Published: February 2020

Li-ion battery plays a dominant role in portable electronic devices. Yet in large scale applications the requirement remains to find new chemistry with improved performances such as energy density and power density as well as lower cost. Magnesium battery is one of such candidates,[1] as the bivalency of Mg2+ ion provides good potential to exceed the energy density of current Li-ion technology. Metal Mg has a volumetric capacity of 3833 mAh/cc, nearly twice that of Li. However, the great hurdle to realize a practical Mg battery lies in the lack of appropriate cathode that can marry metal Mg anode with good capacity, cyclability and rate capability.

In this talk, we will discuss the mechanism of magnesiation for several Mg battery cathodes. In comparison with Li-ion battery, we demonstrated that the chemistry of Mg battery cathode is more complicated. Even for classical intercalation-type Li-ion battery cathodes, the magnesiation can deviate from the intercalation reaction and follow the conversion pathway.[2-8] Hence the intercalation of Mg is not only challenged by the sluggish mobility of bivalent Mg2+ ions. Necessary consideration about the stronger structural deformation and side reactions is also essential for the discovery of cathode candidates. The effect of conversion reaction will be carefully examined and discussed in details. Finally, we conclude our talk by suggesting several methods to avoid the challenges brought by intercalation with given examples.[9-11]

Reference:

[1]. D. Aurbach, Nature, 2001, 407, 73

[2]. R. Zhang, et al. Electrochem. Commun., 2012, 23, 110

[3]. T. S. Arthur, et al. ACS Appl. Mater. Interfaces, 2014, 6, 7004

[4]. C. Ling, et al. Chem. Mater., 2012, 24, 3943

[5]. R. Zhang, et al. J. Power Sources, 2015, 282, 630

[6]. C. Ling, Chem. Mater., 2015, 27, 5799

[7]. C. Ling, et al. in preparation

[8]. C. Ling, et al. submitted

[9]. C. Ling, et al. Chem. Mater., 2013, 25, 3062

[10]. R. Zhang, Chem. Commun., 2015, 51, 1108

[11]. R. Zhang, Chem. Commun., 2015, 51, 1457
A Rocking-Chair-Type Magnesium Hybrid Supercapacitor
Authors: Yoo Hyun Deog , Han Sang-Don , Bayliss Ryan D , Gewirth Andrew A. , Genorio Bostjan , Burrell Anthony K. , Cabana Jordi
Published: February 2020

Supercapacitors can provide high rate capability and long-term cycleability, profited by their simple mechanism based on the adsorption and desorption of ions on the surface of electrodes. It is possible to charge or discharge supercapacitor cells in a minute for 10,000 cycles without notable degradation. Based on the high power characteristics, supercapacitors can augment the batteries or fuel cells for electric vehicles or heavy equipment. So far, most of supercapacitors have symmetric configuration with activated carbon electrodes as the positive and negative electrodes (Fig. 1a). And they follow Daniell-type mechanism, where the electrolyte is depleted of and replenished with ions upon charging and discharging, respectively (Fig. 1b). In this mechanism, electrolyte serves as an ionic reservoir, from which cations and anions are separated to negative and positive electrodes, respectively. As a result, sufficient volume of electrolyte is indispensable for the operation of supercapacitors. This leads to a limitation in energy density and an increase in the internal resistance as the starvation of the concentration of salts in the electrolyte decreases during operation.

Herein, we introduce a hybrid supercapacitor that follows ‘rocking-chair’-type mechanism for the first time. This hybrid supercapacitor is composed of magnesium metal and activated carbon as the negative and positive electrodes, respectively (Fig. 1c). Mg2+ ions are replenished at the negative electrode while they are adsorbed into the pores of the positive electrode upon the discharging of the cell (Fig. 1d). On the other hand, Mg2+ ions are released from the positive electrode while Mg metal is deposited on the negative electrode upon the charging of the cell. As a result, only a minimum amount of electrolyte is needed to operate the cell since the electrolyte serves as a medium of Mg2+ ions. The use of Mg metal electrode can increase the energy density of the cell significantly by virtue of the large volumetric capacity of 3832 mAh/cc and the low redox potential of -2.2 V vs activated carbon’s open circuit potential. Therefore, the ‘rocking-chair’-type magnesium hybrid supercapacitor can double the energy density of a supercapacitor, and the internal resistance can be kept constant during the operation of the cell. The electrochemical results show highly reversible reactions at the positive and negative electrodes thanks to newly-developed Mg2+ electrolytes. Charge-discharge cycles at rates up to 5 mA/cm2 were possible, whereas cycling tests showed 64% retention of the capacity after 400 cycles. Detailed studies of the mechanisms of degradation and evidence of the ‘rocking-chair’-type mechanism will be presented.

Figure 1