bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Electrodeposited POLY(3,4-ETHYLENEDIOXYTHIOPHENE) (PEDOT) for Invasive Recording and Stimulating Neural Electrodes
Authors: Bodart Côme , Rossetti Nicolò , Cicoira Fabio
Published: February 2020

Neural electrodes are the best medical technique to alleviate the symptoms of neurodegenerative diseases and to explore of our brains. However, their efficiency is limited by several constraints: their small dimensions lead to high impedance and their rigid and metallic nature coupled with the destructive insertion procedure leads to inflammatory responses in the body that further increases the impedance. Conducting polymers are soft and organic materials that possess a mixed electronic-ionic conductivity, and are ideal candidates for biotic-abiotic interfaces. They are regularly used as coatings for neural electrodes due to their enhancement of electrochemical properties and their believed biocompatibility. The dominant technique to deposit conducting polymers on neural microelectrodes is electropolymerization. Extensive work as being performed on the optimization of the parameters of this deposition method. Still, electrodeposited conducting polymers coatings suffer from poor adhesion on most of their substrates. Besides this issue, there is a lack of long-term in vivostudies confronting conducting polymer coatings to electrical stimulation conditions used in medical applications.

In this work, we investigated the influence of the processing solvent for electropolymerization on the stability and the adhesion of conducting polymer coatings. After having defined a precise deposition procedure providing us with stable coatings, we investigated the usefulness of these coatings for in vivodeep brain stimulations.

Poly(3,4-ethylenedioxithiophene) (PEDOT) was electropolymerized in three different solvent: acetonitrile, propylene carbonate and water, on platinum-iridium microelectrodes. The coated microelectrodes were subjected to different stability tests: sonication, passive ageing, steam sterilization, and electrical stimulations in vitro. We found out that acetonitrile and propylene carbonate provided the most resistant PEDOT coatings. Still, all of PEDOT coatings processed in the different solvents were stable enough to be used in a medical context. We therefore implanted PEDOT-coated stimulating microelectrodes in rats and applied daily stimulation all the while monitoring the impedance of the microelectrodes. We observed that electrical stimulations decreased the impedance of both the PEDOT-coated microelectrodes and the uncoated control microelectrodes. The decrease in impedance was more important for the control microelectrodes than for the PEDOT-coated ones, which questions the relevance of PEDOT coatings for deep brain stimulation purposes and indicates that more work is required to obtain a performant conducting polymer coating for stimulating neural electrodes.
(Invited) Halide Vapor Phase Epitaxy for b- and a-Ga2O3 Power Electronics Devices
Authors: Leach J. , Udwary K , Rumsey J , Dodson G , Splawn H , Evans K
Published: February 2020

Monoclinic b-Ga2O3 and rhombohedral a-Ga2O3 have recently emerged as promising materials for “ultrawide” bandgap electronics for next-generation high voltage lateral and vertical power switching devices, thanks to their large bandgaps (4.9eV and 5.3eV, respectively), high expected critical breakdown fields (8MV/cm and 10MV/cm, respectively), and their correspondingly large high voltage and high frequency Baliga figures of merit (FOMs). These large FOMs ultimately translate to higher efficiencies for high power (>1kW) switching devices, which will enable more compact, higher performing power electronics systems. In order to realize the high voltages required for the most demanding applications, further development of epitaxial growth techniques which can produce thick Ga2O3 films is required. Halide vapor phase epitaxy (HVPE) is a scalable and inexpensive growth technique which currently appears to be well positioned to address such a need. Kyma Technologies has developed a low-cost HVPE reactor for the growth of thick Ga2O3 films which boasts high growth rates and smoothness while simultaneously being able to be lightly and controllably doped with Si and free of carbon. The reactor has been configured to grow both b-Ga2O3 and a-Ga2O3, and in this talk we will outline our recent growth results from both. Effects of substrate preparation, epi-readiness, and growth conditions on epilayer quality as well as on the corresponding Schottky barrier diode device performance will be presented.
Size Effects on the Cross-Plane Thermal Conductivity of Transparent Conducting Indium Tin Oxide (ITO) and Fluorine Tin Oxide (FTO) Thin Films
Authors: Olson David , Rost Christina , Gaskins John , Szwejkowski Chester , Braun Jeffrey , Hopkins Patrick E
Published: February 2020

Visibly transparent and electrically conductive oxides are attractive for a wide array of applications. Indium tin oxide (ITO) and fluorine tin oxide (FTO) are a subset of the larger transparent conducting oxide family, and possess transmittance in the visible spectrum as well as high electrical conductivity. Even though their unique optical and electrical properties have been thoroughly examined, the thermal transport properties, namely thermal conductivity in the cross-plane direction, have received much less attention. In this paper, using a series of ITO and FTO thin films comprising a range of thicknesses and grain sizes, we characterize the cross-plane thermal conductivity using time-domain thermoreflectance. We determine the heat capacity of the FTO films from simultaneous measurements of volumetric heat capacity and thermal conductivity on an 396 nm thick FTO film. We show that size effects have a considerable influence on the thermal conductivity from both the perspective of grain boundary and thin film scattering.
Highly Efficient Hydrogen Evolution of Platinum Via Tuning Interfacial Dissolved-Gas Concentration
Authors: Luo LONG , Zhao Xu , Ranaweera Ruchiranga
Published: February 2020

A facile perfluorooctanesulfonate (PFOS)-modulation strategy was developed to precisely control the dissolved-gas concentration at electrode/gas/electrolyte interface for enhanced hydrogen evolution reaction (HER). With PFOS modulation, lowered dissolved-hydrogen concentrations at catalytic interface and sufficient exposure of surface active area can be achieved. Accordingly, relative to pure Pt, the PFOS-modulated Pt possesses remarkable HER performance.
MoS2/NiS2 Composites for Efficient Hydrogen Evolution Both in Acidic and Alkaline Media
Authors: Hu Jue , Zhang Chengxu
Published: February 2020

The growing concern about global warming, environmental pollution and energy security has raised the demand for clean energy resources in place of fossil fuel. Cost-efficient generation of hydrogen from water-splitting through electrocatalysis holds tremendous promise for clean energy (1, 2). Central to the electrocatalysis are efficient and robust electrocatalysts composed of earth-abundant elements, which are urgently needed for realizing low-cost and high-performance energy conversion devices. Transition metal compounds (TMCs) are a group of attractive noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER). Earth-abundant MoS2 has emerged as a promising hydrogen evolution reaction (HER) catalyst with high activity and durability, but it is kinetically retarded in alkaline media . Extensive efforts have been devoted to improving the HER activity of MoS2 in acid (3), but little attention has been paid to simultaneously enhancing its HER performance both in acid and base. This work demonstrates a dramatic enhancement of HER kinetics both in acidic and alkaline media by hybridizing vertical MoS2 with another earth-abundant material, nickel disulfide (NiS2). Field-emission SEM image shows that the MoS2/NiS2 composite is composed of a film-like structure of NiS2 cover on the edge surfaces of the MoS2 sheets (Figure 1a). As shown in Figure 1b, the XRD peaks observed at 2θ=14.1°, 32.9° and 58.8° of the MoS2/NiS2 sample can be indexed to 2H-MoS2 crystal (JCPDS No. 75-1539), and peaks at 2θ=31.4°, 45.1° and 53.4° indexed to (200), (220) and (311) facets of the NiS2, respectively (JCPDS No. 88-1709). The synthesized MoS2/NiS2 composite exhibits a much lower HER overpotential both in acidic and alkaline media than that of bare MoS2 and NiS2 catalysts (Figure 1c and d).

Figure caption

Figure 1. (a) FESEM image of the MoS2/NiS2 composite. (b) XRD patterns of the NiS2 and MoS2/NiS2 samples, together with the standard pattern of 2H MoS2 (JCPDS 75-1539) and NiS2 (JCPDS 88-1709). (c) Polarization curves of bare MoS2, NiS2 and MoS2/NiS2 composite catalysts in 0.5 M H2SO4 solution at a scan rate of 5 mV/s. (d) Polarization curves of bare MoS2, NiS2 and MoS2/NiS2 composite catalysts in 1 M KOH solution at a scan rate of 5 mV/s.

References

D. Strmcnik et al., Improving the hydrogen oxidation reaction rate by promotion of hydroxyl adsorption. Nat. Chem.
5, 300-306 (2013).

Y. Jiao, Y. Zheng, M. T. Jaroniec, S. Z. Qiao, Design of electrocatalysts for oxygen- and hydrogen-involving energy conversion reactions. Chem. Soc. Rev.
44, 2060-2086 (2015).

J. Hu et al., Engineering stepped edge surface structures of MoS2 sheet stacks to accelerate the hydrogen evolution reaction. Energy Environ. Sci.
10, 593-603 (2017).

Figure 1
Coherent-x-Ray Imaging of Nanoparticle Alloy Electrodes and Catalysts
Authors: You Hoydoo , Liu Yihua , Cha Wonsuk , Ulvestad Andrew
Published: February 2020

Bragg coherent diffraction imaging (BCDI) studies of silver nanoparticles revealed a new dissolution mechanism that has not previously been observed.1 We find that a long incubation time, ~30 sec, before start dissolution reaction when the particle starts from the pristine state. During the incubation period, however, electrochemical potential-induced pressure nucleates a dislocation loop within the nanoparticle that eventually exposes to the surface. Only then, rapid dissolution is activated at the surface sites. This result points to an important connection between structure and stability of silver in an electrochemical environment and demonstrates the potential of BCDI to elucidate this relationship. Understanding silver dissolution process is important in studying dealloying process of binary alloys. Dealloying is a selective dissolution of one element in an alloy resulting in a porous, strained structure often with new properties, such as highly active electrocatalysts.2 In the past, the pore formation during dealloying has been visualized using electron microscopy and the dealloying-induced strain has been studied at the ensemble level using x-ray diffraction.3 However, the information on lattice strain, which has been unavailable, could play an integral role in understanding and controlling properties and activities for a variety of applications. In our BCDI studies, 3D strain distributions of individual nanoparticles and thin film grains of silver-gold alloys were investigated during dealloying in nitric acid.4 Isolated particles exhibit dramatic changes in their shapes as expected (See the graphical abstract). Our results (not shown) also demonstrate that significant local strains occur as a result of dealloying. The same dealloying process was used for nanoscale grains of a thin film instead of the isolated nanoparticles. The results show that isolated nanoparticles are significantly more strained than the grain embedded in the film texture,4 primarily because strain can be relieved via grain boundaries in the case of the single grain. These observations demonstrate that the unique capabilities of BCDI techniques. We also have begun working on alloys under catalytic environment where the compositions and shapes of alloy nanoparticles are highly sensitive to gas and temperature environment. We will present some preliminary results as time permits in my presentation.

Liu, Y., et al., Nano Letters (2017) 17 (3), 1595

Erlebacher, J., et al., Nature (2001) 410 (6827), 450

Yang, R. Z., et al., Journal of Physical Chemistry C (2011) 115 (18), 9074

Cha, W., et al., Advanced Functional Materials (2017) 27 (25)

Figure 1
Enhanced Electrochromic Properties of a Nickel Oxide-Alanine Film
Authors: Wang Ke-Hsuan , Ikeuchi Hayato , Kawai Takeshi
Published: February 2020

Electrochromic materials can change their color under the application of an electrical voltage. The color change accordingly upon charge insertion/extraction, which induce in the material a process of redox reaction. Electrochromic materials are expected to serve an important role in efficient energy applications to control the brightness of light. High optical contrast, fast switching speed, and good cycling durability are required for an electrochromic material to function as a practical material in a device. These properties are influenced by the morphology of the electrochromic film and the associated changes in local ionic diffusion.

In this work, we report a facile and cost-efficient preparation of electrochromic materials which are formed by assembly of nano-sized clusters of nickel oxides by electrodeposition integrating amino acids. Electrodeposited films were characterized using Raman spectroscopy, in situ X-ray absorption fine structure spectroscopy, and atomic force microscopy to determine the electronic and structural changes in the films during coloration. These results indicate that the structure of the nickel oxide films in their oxidized state is similar to γ-NiOOH, regardless of kinds of integrated amino acids, although the grain size of the films is dependent on kinds of integrated amino acids. The different grain size results in significant differences in electrochromic performance. The film made of small grain size exhibits the best electrochromic performance. This study demonstrates that a suitable integration of amino acid is essential to enable sustained electrochemical activity, reactive site formation, and functional stability.

Figure 1
9 Kw VRFB Experimental Facility: High Current Polarization Tests and Energy Analyses
Authors: Guarnieri Massimo , Trovo' Andrea , Alotto Piergiorgio
Published: February 2020

A Vanadium redox flow battery test facility of industrial size (IS-VRFB) has been recently built at the Energy Storage and Conversion Laboratory of University of Padua in order to investigate the performance potential of scaling-up from small-scale single-cell bench experiments. The facility is built around a 40-cell 600-cm­
2 active-area stack and two 550-litre tanks. The facility is provided with advanced electronic bidirectional power supply, multi-physics instrumentation and data acquisition and control system. This paper reports on the experimental results obtained so far. Two working modes were tested, i.e. fast and steady-state discharge, representative of real operative conditions, such as primary frequency regulation and peak shaving, respectively. During discharge tests at SOC=0.9 on a passive load, currents as high as 400 A (665 mA cm­–
2) where measured at a specific flow rate of 20.5×10–3 cm s–1, with a steady state value in excess of 350 A (of 583 mA cm–2). Maximum power exceeded 9 kW (370 mW cm–2 per cell), with a steady state value approaching 8 kW (330 mW cm–2 per cell). Energy losses measurement showed a round trip efficiency (RTE) in excess of 70%. This performance required a proper programming of the control strategies provided by the system supervisor.

References

Alotto, M. Guarnieri and F. Moro, “Redox flow batteries for the storage of renewable energy: A review,” Renew Sus. Energ Rev. 29, (2014): 325–335.

Guarnieri, A. Trovò, A. D’Anzi, P. Alotto, “Developing vanadium redox flow technology on a 9-kW 26-kWh industrial scale test facility: design review and early experiments”, Appl Energy, 230 (2018) 1425-1434. DOI: 10.1016/j.apenergy.2018.09.021.

Trovò, G. Marini, A. Sutto, P. Alotto, M. Giomo, F. Moro, M. Guarnieri, “Standby thermal model of a vanadium redox flow battery stack with crossover and shunt-current effects”, Appl Energy, 240 (2019) 893-906.

Trovò, A. Saccardo, M. Giomo, F. Moro, M. Guarnieri, “Thermal modeling of industrial-scale vanadium redox flow batteries in high-current operations”, J Power Sources, in print.

Figure 1
Understanding the Interplay between Electrolyte Velocity Distribution and Current Distribution in Vanadium Flow Battery Electrode
Authors: Ertugrul Tugrul Yavuz , Houser Jacob , Daugherty Michael , Aaron Douglas , Mench Matthew M.
Published: February 2020

Vanadium redox flow batteries (VRFBs) are considered a promising candidate among grid-scale energy storage technologies due to their flexibility and scalability, high coulombic efficiency, and long cycle life. However, system costs and relatively low energy and power density compared to other electrochemical energy storage devices are major challenges to commercialization. At the cell level, mass transport losses are one of the major contributors to performance losses; this mechanism is associated with inadequate delivery of active species to electrode surfaces. Improving flow field design and electrode structure or simply increasing flow rate can mitigate mass transport losses. However, due to parasitic pumping losses, optimization is not straightforward. As yet unpublished research in our lab has shown that increased convection improves mass transport of the active species through the porous electrode and it is possible to achieve better electrochemical performance with lower pressure drop in convection-dominated VRFB cells. In this study, the impact of convection on electrochemical performance is investigated using computational fluid dynamics (CFD) model and in-situ localized current distribution diagnostics. Polarization curve analysis and pressure drop measurements are also used to support the conclusions. Experiments and simulations are conducted on strip cell architecture with varying channel depths (0.25, 0.50, 1.00, 2.50 mm) and flow rates (10-50 ml min-1). The simulation domain includes both channel and porous electrodes seen in Figure 1. Conservation of mass and momentum are solved to obtain velocity and pressure distributions. It is found that there is a strong relationship between electrolyte velocity in the electrode and electrochemical performance. Similar electrolyte velocity distribution (in the electrode) predicted for two configurations: 1 mm channel depth at 40 mL min-1 flow rate and 0.50 mm channel depth at 10 mL min-1 have similar polarization curves and current distributions down the channel. However, the model predicts very different velocity distributions for these configurations in channel. Higher velocity distribution predicted for 1 mm configuration has also higher pressure drop than 0.5 mm configuration. The results of the computational and experimental study as related to the trade-off between pumping power requirements and electrochemical performance in VRFBs will be discussed in this talk.

Figure 1
Mixtures of Ionic Liquid and Organic Electrolyte with Improved Safety and Electrochemical Performance with Nanostructured Silicon-Anode for Li-Ion Batteries
Authors: Pandey Gaind P. , Meda Lamartine , Li Jun
Published: February 2020

The present rechargeable lithium-ion battery systems commonly use small amount of electrolytes based on suitable lithium salts (generally LiPF6) and organic solvents (generally alkylcarbonates, such as EC, DMC), which represent a major concern for device safety due to the flammable and volatile nature of these organic liquids. The use of these organic carbonates electrolytes allows the realization of high-performance batteries, but due to its flammability, their use also poses serious safety risks and strongly reduces the battery operative temperature range. Therefore, alternative electrolytes have been proposed and tested in the last decade [1].

Ionic liquids doped with a lithium salt are alternative electrolytes for lithium-ion batteries that offer some advantages compared to organic carbonates based liquid electrolytes. Ionic liquids display a low vapor pressure which leads to nonflammability. The main drawback of ionic liquid-based electrolytes is the low lithium-ion conductivity due to relatively high viscosity of ionic liquids. A lot of research has been devoted to developing ionic liquids with low viscosity. However, so far, these ionic liquids could be obtained only at the expense of lower thermal and/or electrochemical stability. In recent years, mixtures of organic carbonates-based electrolytes and ionic liquids have been proposed as a solution to overcome the lithium-ion transport limitations of ionic liquid-based electrolytes while improving safety due to a lower flammability than that of organic carbonates electrolytes [1, 2].

Herein, we report the results of physical-chemical and electrochemical investigations performed on mixed electrolytes based on an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSI), and organic electrolytes (LiTFSI in EC/DMC) with nanostructured silicon-anode for lithium-ion batteries. The ionic conductivity, lithium-ion transference number, viscosity and electrochemical stability windows of all different ionic liquid content mixtures were investigated and compared with carbonates-based electrolyte. The specific capacity and cycling stability of the nanostructured silicon-anode were investigated at different C-rates at room temperature. A reversible capacity of 3480 mAh g-1 (of Si) at C/10 and 1600 mAh g-1 at 5C is obtained with cells having electrolyte mixture with a composition of 1:1. This study indicates that safety and electrochemical performance of the Si-anode for Li-ion battery can be improved by using mixed ionic liquid and carbonates-based electrolytes.

[1] A. Guerfi, M. Dontigny, P. Charest, M. Petitclerc, M. Lagacé, A. Vijh, K. Zaghib, J. Power Sources 195 (2010) 845-852.

[2] R.-S. Kühnel and A. Balducci, J. Phys. Chem. C 118 (2014) 5742-5748.
Outstanding Low-Temperature Performance of Structure-Controlled Crumpled Graphene Battery Anode Based on Surface-Controlled Charge Storage Mechanism
Authors: Lee Michael J , Lee Byeongyong , Lee Seung Woo
Published: February 2020

There is a critical impediment to the practical use of Li-ion batteries (LIBs) at low temperature conditions owing to the sluggish diffusion-controlled intercalation mechanism. Moreover, the metallic Li-plating issue on the graphite anode surface at low temperature results in the capacity deterioration and short circuits due to the dendrite growth. The promising strategy to resolve these hindrances is the transition of the charge storage mechanism from the diffusive intercalation to the surface-controlled capacitive charge storage mechanism that has fast charge storage kinetics. Herein, we assembled the structure-controlled 3D crumpled graphene electrode. We employ an aerosol drying process to synthesize the structure-controlled 3D crumpled graphene electrode by controlling the stacking process of graphene sheets. We first identify the key processing parameters that can control the stacking process of the graphene sheets, assembling structure-controlled 3D crumpled graphene with superior charge storage performance. Then, we quantitatively evaluate the portion of the surface-controlled and the diffusion-limited charge storage mechanisms of the graphene anodes as a function of potential and temperature. Based on this approach, the 3D structure of the graphene assembly is further optimized to maximize the low-temperature charge storage performance through the effective utilization of the surface-controlled charge storage mechanism.
Computational Study of K/Mg Adsorption on (110) MO2 (M= Mn, Ti, V) Surfaces
Authors: Maenetja Khomotso P , Ngoepe Phuti E
Published: February 2020

The metal air battery use free oxygen from the air to react with metal ions on the surface of the air (oxygen) electrode, which is much lighter than conventional cathodes used in Li-ion batteries. However, the fundamental challenge that limits the use of metal air battery technology is the ability to find a catalyst that will catalyse the formation and decomposition of discharge products during charging and discharging cycle i.e. oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Density functional theory (DFT) study is employed in order to investigate the surfaces of, (Rutile) R-MnO2, TiO2 and VO2 (MO2) which act as catalysts in metal-air batteries. Adsorption and co-adsorption of metal (K/Mg) and oxygen on (110) β-MO2 surface is investigated, which is important in the discharging and charging of K/Mg–air batteries. Due of the size of the supercell, and assuming that oxygen atoms occupy bulk-like positions around the surface metal atoms, only five values of (gamma) Γ are possible if constraint to a maximum of 1 monolayer (ML) of adatoms or vacancies: Γ= 0 surface is the stoichiometric surface, Γ= 1, 2 are the partially and totally oxidised surfaces, and Γ=-1, -2 are the partially and totally reduced surfaces. The manganyl, titanyl and vanadyl terminated surface are not the only surfaces that can be formed with Γ= +2, oxygen can be adsorbed also as peroxo species (O2)2-, with less electron transfer from the surface vanadium atoms to the adatoms than in the case of manganyl, titanyl or vanadyl formation. The Mg orientation between two bridging oxygen and in-plane oxygen (bbi) orientation is much more stable for the three metal oxides, thus Mg generally prefers to adsorb where it will be triply coordinated to two bridging oxygens and one in-plane oxygen atom. However, K prefers to position itself between the two in-plane oxygens and a bridging oxygen on the surface.
Effect of Hydroxyapatite Coatings on Photocatalytic Characteristics of Titanium Dioxide Photoanode
Authors: Nay Wunn Htoo , Morita Motoaki , Motoda Shinichi
Published: February 2020

The photocatalytic n-type semiconductor characteristics of titanium dioxide (TiO2) has been under study for decades. We have studied the effect of dye sensitizing on TiO2 electrode with seawater as the electrolyte. In that study, we found that only the hydroxyapatite (HAp) coating used for the purpose to increase the binding ability between dye and TiO2 improved the capability of TiO2 electrode. However, the mechanism of HAp coating is unclear. In order to make it clear and to improve the effect of HAp coating on TiO2 electrode, this study is conducted by preparing different types of HAp paste for coating on TiO2 electrode.

Screen printing method was used for TiO2 layer and both manual and screen printings were used for HAp (Ca10(PO4)6(OH)2) coating for comparison. Type 329J4L stainless steel was used as a substrate for TiO2 electrode. The surface of the substrate was cleaned with ultrasonic cleaner and then the surface was passivated with HNO3 solution for 30 minutes. Double layers of TiO2 were screen printed on the substrate. The first layer was screen printed and heat treated at 150 ºC for 60 minutes. The second one after printed was heat treated at 550 ºC for 30 minutes. HAp was coated on TiO2 doubled layer. HAp paste was heat treated after printed. HAp paste was prepared from HAp powder. The powder was mixed with carboxymethyl cellulose (CMC) in various ratios. Water and alcohols are added to the mixture and well stirred to be a paste. Different types of HAp paste were prepared by changing the ratios of the components of the paste. The finishing was performed to get the electrodes ready for measurements in artificial seawater.

The potential measurement, polarization and power density measurements against platinum counter electrode were performed by a potentiostat in dark and irradiated conditions. The irradiation used for the experiments is a Xenon lamp with 150 W and calibrated wavelength range from 250 nm to 800 nm. The lamp was calibrated so that the light intensity produced became approximately 10.5 mW/cm2. The surfaces of the electrodes before and after measurement were analysed and compared by Scanning Electron Microscope (SEM). The study is in progress and the preliminary showed that screen printing of HAp on TiO2 electrode showed higher photopotentials than manual printing or without printing. The variations in HAp paste constituents also affected the performance of TiO2 electrodes.
A Tri-Electrode Configuration for Zinc-Air Batteries Using Poly(acrylic acid) to Enhance Cycling Performance
Authors: Tran Wendy , Chung Hyun-Joong , Ivey Douglas G
Published: February 2020

Zinc–air batteries (ZABs), which employ oxygen from air for the reduction reaction or discharging, have several benefits, such as high energy density, operational safety, environmental compatibility and low cost. Primary ZABs are a mature technology; however, rechargeable battery design and structure need to be optimized to achieve better cycle life. Two different configurations for a tri-electrode, rechargeable battery with poly(acrylic acid) (PAA) have been developed in this work; i.e., a planar cell and a sandwich cell. Charge-discharge cycling tests at 5 mA-cm–2 show that the sandwich cell is more suitable for ZABs than the planar cell. Various additives for the PAA, such as cross linking agents and ZnO, have also been evaluated using the tri-electrode design. The addition of ZnO to the oxygen reduction reaction side of the battery enhances the cycling performance of ZABs, i.e., the battery can withstand at least 100 cycles at 5 mA cm–2 with initial efficiency of 62%.
Design of Preferentially Faceted Zinc to Improve the Rechargeability of Alkaline Batteries
Authors: Faegh Ehsan , Ng Benjamin , Hayman Dillon , Mustain William E.
Published: February 2020

Rechargeable Zinc-based batteries have attracted a growing interest due to their intrinsic high safety as well as the low environmental impact and low cost of Zinc. However, there still exists some major obstacles in achieving these low cost secondary cells, including shape change during repeated charge/discharge (dendrite formation) and limited reversibility of the Zinc electrodes. Traditional Zinc anodes are formed from large, polycrystalline particles with limited control over the morphology. Many studies have looked to improve morphology control of Zinc through the design of Zinc nanostructures 1, 2, but the future implementation of these nanomaterials is hindered by the high rate of corrosion for Zinc nanostructures 3, 4 as well as the expense and scalability of manufacturing such nanostructures. Therefore, there is a need to develop a scalable synthesis method that allows for the creation of large monocrystalline particles with controlled shape.

In this work, we report a facile electrolytic method to synthesize micron-sized preferentially faceted, hexagonal-shaped Zinc particles. Using a three-electrode electrochemical cell, the charge and discharge behavior of these Zinc particles were studied in alkaline (6M KOH) and mildly acidic (1M ZnSO4) aqueous electrolytes. It was confirmed that the dendrites form during cycling the Zinc particles in KOH electrolytes, however, using ZnSO4 electrolytes no dendrite formation was observed, and the particles were able to retain their hexagonal structures ever after cycling for than 100 times at 1C.

References

M. Chamoun, B. J. Hertzberg, T. Gupta, D. Davies, S. Bhadra, B. Van Tassell, C. Erdonmez, and D. A. Steingart, NPG Asia Materials,
7 (4), e178 (2015).

T.-H. Wu, Y. Zhang, Z. D. Althouse, and N. Liu, Materials Today Nano, 100032 (2019).

E. Faegh, T. Omasta, M. Hull, S. Ferrin, S. Shrestha, J. Lechman, D. Bolintineanu, M. Zuraw, and W. E. Mustain, Journal of The Electrochemical Society,
165 (11), A2528-A2535 (2018).

Y.-D. Cho and G. T.-K. Fey, Journal of Power Sources,
184 (2), 610-616 (2008).
Carbon-Free NiCo2O4-Based bifunctional Air Electrode for Metal-Air Battery Application
Authors: Zhu Jiahong
Published: February 2020

The air cathode of an alkaline rechargeable metal-air battery typically contains carbon as the catalyst support. Unfortunately, carbon can be severely attacked by the highly reactive oxygen generated from the oxygen evolution reaction (OER) during charging, which limits the battery cycle life. To overcome this obstacle, it is imperative to develop carbon-free bifunctional air electrodes that exhibit improved stability and durability under charging and discharging. In this work, NiCo2O4 powders with a crystallite size from 5 to 190 nm were synthesized for preparation of carbon-free air electrodes for rechargeable metal-air battery cathode application. The unsupported, bifunctional, NiCo2O4-based electrodes exhibited reduced overpotentials for both oxygen evolution and reduction, compared to the carbon-based electrode. As the NiCo2O4 crystallite size decreased, the cycle life of the carbon-free electrode increased drastically, reaching over 100 successive, 0.5-h charge/discharge cycles at a current density of ±50 mA.cm-2 in a 6 M KOH electrolyte when the 5-nm spinel powder was utilized.
Effective Shielding of Sodium Polysulfides Using Two-Dimensional Ceramic Based Polymer Membrane for Ambient Temperature Sodium Sulfur Battery
Authors: Ramaprabhu Sundara , Ajay Piriya Vijaya kumar Saroja , Rajamani Arunkumar , M Kamaraj
Published: February 2020

The development of high energy density batteries is an essential requirement for the large-scale energy storage applications and the balance between cost as well as performance will drive a way to meet the energy needs. Focusing on low cost energy storage devices, sodium is widely available in the Earth’s crust (23600 ppm). The coupling of low cost sodium anode and sulfur cathode can lead to cost effective high energy density sodium sulfur battery. But the conventional sodium sulfur batteries are operated at a higher temperature of above 300 °C. Since the operating temperature far exceeds the melting points of sodium and sulfur, the problem of corrosion prevails and may bring safety issues. So, the operation of battery at room temperature will turn to improved safety and high energy density. Since solid electrolytes cannot conduct sodium ions at ambient condition, the ambient temperature sodium sulfur battery has to move towards the use of liquid electrolytes. But the dissolution of sodium polysulfides formed during the discharge process is highly soluble in liquid electrolytes and reduces the durability of the battery. Preventing the dissolution of sodium polysulfides by chemical binding towards the cathode is an effective strategy for obtaining the high energy density and durable sodium sulfur battery. This study employs a two-dimensional porous ceramic polymer membrane for suppressing the shuttling effect. The presence of boron and nitrogen in white graphite helps in chemical binding of higher order sodium polysulfides and helps to attain a reversible specific capacity of 1027 mAh g-1 at a current density of 50 mA g-1. The electrochemical impedance study validates the control of polysulfide shuttling using the porous ceramic membrane. This method provides a new technique of controlling the polysulfide shuttling and can lead to the development of room temperature sodium sulfur battery.
Anodic Oxide Growth on Heat-Treated Titanium
Authors: Tsuchiya Hiroaki , Kamimura Yuka , Fujimoto Shinji
Published: February 2020

It has been reported that self-organized nanotubular oxide layers are formed on various metals and alloys by anodization in fluoride containing electrolytes. In particular, the nanotubular structure of TiO2 has been extensively studied due to a wide range of application of TiO2. To tune the properties of the layers, the optimization of anodization condition has been carried out. However, in such trials, the chemical aspects of anodization condition have been mainly focused, that is, only few works has reported the metallurgical aspects of the condition. In the present work, we examined the effects of heat-treatment on anodization behavior and resulting morphology of the TiO2 architecture.

Specimens were cut from pure titanium sheets (purity; 99.5 %). The specimens were encapsulated into a silica quartz tube where the vacuum level was controlled less than approximately 2x10-5 torr. The specimens in the silica tube were heat-treated under several conditions. After the heat-treatments, the surface of the specimens was ground with SiC abrasive papers and then mirror-finished with diamond pates and colloidal silica suspension. The specimens were anodized at 50 V in a mixture of ethylene glycol, water and ammonium fluoride. After the anodization, the surface and cross-sectional morphology of resulting oxide layers was observed.

Under an optimized heat-treatment condition examined, the specimen consisting of large grains in millimeter range was obtained. The anodization of the specimen revealed that its current behavior was similar to that obtained on as-received specimen. In addition, the obtained structure of anodic oxide layer on the heat-treated specimen was also similar to that on as-received specimen, that is, nanotubular structure was obtained. However, the thickness of the nanotubular oxide layer and the ordering of nanotubes were clearly different. Higher thickness of nanotubular oxide layer was obtained and improved ordering of nanotubes was found on the heat-treated specimen. These results indicate that the substrate property could affect not only the growth but also arrangement of nanotubes.
Corrosion of Directed Energy Deposited Cantor Alloy in Molten KNO3-NaNO3 for Solar Thermal Applications
Authors: Moon Jeremy , Summers Kodi , Melia Michael Anthony , Kustas Andrew , Argibay Nicolas , Schindelholz Eric John , Chidambaram Dev
Published: February 2020

High entropy alloys (HEA) with 4-5 component elements are being considered for various applications including nuclear and solar thermal energy generation due to desirable mechanical properties and corrosion resistance.

Advanced heat transfer systems in both nuclear and solar thermal energy generation are being designed to utilize molten salts as the working fluid, allowing for a significant increase in hot-leg temperatures leading to increased efficiency. The use of additively manufactured HEAs may be beneficial to these systems but corrosion properties of HEAs have not yet been established for many of the common molten salt systems. Additionally, the unique microstructure of HEA components produced via additive manufacturing can potentially alter the corrosion properties of the component relative to a cast or forged microstructure. This study will focus on CoCrFeMnNi HEA Cantor alloy prepared via an additive manufacturing pathway using directed energy deposition (DED); this method will allow for the development of complex geometries not available through traditional manufacturing methods.

To understand the corrosion of additively-manufactured HEAs, a sample of DED-manufactured Cantor alloy was exposed to a 40/60 weight percent mixture of molten KNO3-NaNO­3 at 500 °C. This environment is relevant to solar thermal power plants. Accelerated corrosion testing using potentiodynamic polarization was carried out. Also, the sample subsequently underwent 50 hours of exposure to the molten salt. The sample surface was analyzed with x-ray diffraction, x-ray photoelectron spectroscopy, and focused ion beam milling coupled with scanning electron microscopy/energy dispersive spectroscopy. The molten salt electrolyte was analyzed post-exposure via inductively-coupled plasma – optical emission spectroscopy. Cantor alloy exposed to this nitrate salt mixture developed an oxide film with small, densely packed, vertically oriented fin-shaped grains and an inhomogeneous composition profile through its depth. The results of these studies will be discussed.

Acknowledgments: The authors thank Zachary Karmiol, research scientist at Materials Characterization Nevada, for technical input. One of the authors, JM, acknowledges the Graduate Research Fellowship from the US National Science Foundation. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1447692.
(Invited) Advanced Techniques for the Study of Elementary Mechanisms of Oxide Formation and Growth on Co-Al-W Model Alloys at High Temperatures
Authors: Virtanen Sannakaisa
Published: February 2020

γ′-strengthened Co-base superalloys, based on the Co-Al-W system and its modifications, show high potential for use at high temperatures, with promising mechanical properties. A challenge remaining is the high-temperature oxidation behavior, as oxidation resistance above 800 °C is relatively poor as compared for instance to corresponding Ni-based superalloys. This is due to hindered formation of continuous, protective Al2O3 oxide layer. The presentation will discuss elementary mechanisms in the early stages of oxidation of Co-Al-W model alloys. A special focus of our studies is to clarify the role of the γ/γ'-microstructure in the formation and growth of oxide scales. In situ oxidation experiments in SEM, ex situ high-resolution TEM, and further surface analytical techniques were employed to determine critical factors and mechanisms of high-temperature oxidation of this alloy system. The results demonstrate the key role of the ratio of elemental fluxes (diffusion of oxygen and aluminum) on the formation of protective alumina scales.
On the Development of a Flow-Type Electrochemical Microcell
Authors: Summers Kodi , Kaehr Bryan J. , Schindelholz Eric John , Chidambaram Dev
Published: February 2020

Localized corrosion is one of the most challenging and important fields in corrosion science. While there are a number of methods for studying corrosion at small scales, a majority of these methods involves immersion of a sample into an environment of interest, exposing them for prescribed amount of time, and then analyzing the sample’s surface post-exposure. Methods that have been studied include (i) the use of electrochemical techniques during immersion to understand transient processes that initiate and those that propagate localized corrosion behavior such as scanning reference electrode technique (SRET), and (ii) using electrochemical microcells or scanning droplet cells to perform electrochemical analysis of sample surfaces without the need to immerse an entire sample into an environment. The downside of these techniques is either that the entire sample must be sacrificed for the analysis or that the analysis area is still too large to truly isolate localized corrosion processes. In this study, we demonstrate a novel approach to the development of a flow-type electrochemical microcell that provides the necessary resolution to study localized corrosion while being completely customizable. Additionally, results on various samples will be presented showing the applicability of the system as well as verification of performance.

Acknowledgement: This work was performed under the auspices of the US Nuclear Regulatory Commission (NRC) under contract NRC-HQ-84-16-G-0033. Ms. Nancy Hebron-Isreal serves as the program manager.
Explanation of the Electrochemical Behavior of Salt Film in Pit Growth
Authors: Li Tianshu , Scully John R. , Frankel Gerald S.
Published: February 2020

A unifying framework has recently been developed to describe the critical conditions for pit growth stability and salt film formation 1-3. It was shown that a salt film is not required for pit stabilization; it is just a consequence of a pit achieving diffusion-controlled growth. A salt film can form on the surface of both metastable and stable pits when the maximum pit dissolution current density, i
diss,max, exceeds the diffusion-limited current density, i
lim.

In this work, the unifying framework is further expanded to establish a mathematical model describing the electrochemical behavior of salt film after it precipitates, i.e. the situation when i
diss,max > i
lim. It can be mathematically shown that the main function of a salt film during diffusion-controlled pit growth is to accommodate the extra potential of (E
max - E
sat) by regulating its thickness to adjust the actual potential at the pit surface to E
sat and thus restricting the anodic dissolution current density at the diffusion-limited value 4. Therefore, the salt film will respond to any changes of the applied potential, temperature, pit depth, and perforation radius of the pit cover.

This new model can explain the current peak observed during the downward potential scan of a 1D pit at the transition point from diffusion-controlled region to charge-transfer-controlled region. According to this new model, the current peak results from the supersaturation generated by thinning of the salt film during the downward scan. The model predicts that the amplitude of the current peak decreases with decreasing scan rate, which is in agreement with the experimental results from 1D artificial electrode, providing strong support for the validity of the new model.

Acknowledgments: This work was supported as part of the Center for Performance and Design of Nuclear Waste Forms and Containers, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0016584.

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