bluuebunny/crossref_metadata_2025 huggingface dataset:
Redox Flow Batteries Utilizing Aqueous-Soluble Organic Electrolytes
Authors: Hollas Aaron , Wei Xiaoliang , Li Bin , Nie Zimin , Murugesan Vijayakumar , Wang Wei , Reed David , Sprenkle Vincent
Published: February 2020

Grid-scale battery storage devices have garnered increased attention for their ability to balance the intermittency of ever-expanding renewable energy deployment and to mediate periods of peak power demand. The redox flow battery has emerged as a viable alternative to traditional solid state batteries. With decoupled electrode and electrolyte storage vessels, the redox flow battery offers design flexibility where capacity and power may be independently tuned. The current state-of-the-art flow battery systems utilize vanadium-based electrolytes, however, the high cost of vanadium has hindered wide-scale deployment.1 The use of organic molecules as electrolyte materials has emerged as a potentially lower cost alternative.2,3

Presented will be our recent efforts in developing aqueous-soluble organic molecules as electrolyte materials for redox flow batteries. Structurally related molecules have undergone rational design to affect solubility and redox potential via the introduction of varying substituents on the parent molecule. Promising candidates have been incorporated into a full flow cell and undergone flow cell optimization. An exemplary candidate, when coupled with the benchmark ferri/ferrocyanide catholyte, delivers an OCV of 1.35 V at 50% SOC and achieves stable cycling over extended periods (Figure 1).

References

Zhang, M.; Moore, M.; Watson, J.S.; Zawodzinski, T.A.; Counce, R.M. J. Electrochem. Soc.
2012, 159, A1183.

Park, M.; Ryu, J.; Wang, W.; Cho, J. Nat. Rev. Mater.
2016,
2, 16080.

Soloveichik, G.L. Chem. Rev.
2015, 115, 11533.

Figure 1
Influence of Ni on the Activity of Co-Mo Electrocatalyst for Ethanol Oxidation
Authors: Kalu Egwu Eric , Chaitree Wasu
Published: February 2020

Ternary as-deposited Co-Ni-Mo electrocatlyst on carbon support was investigated for the ethanol oxidation, and its activity was compared to that of bimetallic Co-Mo electrocatalyst. All electrocatalysts were prepared by electroless deposition method on carbon substrate support (CCS) made active for electroless deposition with Pd-ink. The effects of electroless deposition time, electro-oxidation temperature (30-60°C), and amount of nickel species were studied. The result showed that CoNiMo/CCS was highly active in alkaline ethanol solution (0.5M NaOH+1 M EtOH) for ethanol oxidation. The electroless deposition time, and temperature effect on the performance of the catalysts will be discussed. Although minor amount of Pd (< 50 μg/cm2) was used to make the carbon substrate active for electroless deposition, the results obtained showed that the Pd, was not utilized in ethanol oxidation. Therefore, the catalytic activity observed for the reaction is attributed to Co, Ni, and Mo, in the catalyst and not from Pd. Furthermore, the amount of nickel species affected the reaction performance significantly. Additionally, the peak current densities for the electrocatalyst with the presence of Ni species was higher than those from the bimetallic Co-Mo eletrocalalyst. This suggests that the nickel has a positive influence in the catalyst activity. Overall, this study provides a promising novel and effective non-noble Co-Ni-Mo electrocatalyst with an onset potential of -0.7 V (vs. Ag/AgCl) for electrooxidation of ethanol.
Synthesis of Active Bimetallic Catalysts for Direct Methanol Fuel Cells
Authors: Tavakoli Mehrabadi Bahareh Alsadat , White Rembert D. , Regalbuto John R. , Weidner John W. , Monnier John R.
Published: February 2020

The direct methanol fuel cell (DMFC) uses methanol as fuel and has significant advantages over hydrogen-fed proton exchange membrane (PEM) fuel cells for mobile applications, particularly in terms of fuel storage and supply. Platinum (Pt) catalysts are effectively able to catalyze the oxidation of methanol to carbon dioxide in this system. However, one of the main challenges of making DMFCs commercially feasible is that the surface of Pt sites become rapidly poisoned by strongly adsorbed carbon monoxide (CO) that is produced during the oxidation process, limiting the overall rate of methanol oxidation. Studies have shown that bimetallic catalysts composed of platinum (Pt) and a second metal (i.e., Ru or Ni) are more active for the oxidation of methanol compared to catalysts composed of only Pt. Results suggest the Ru or Ni component provides sites that chemisorb H2O in the moist environment which reacts with strongly adsorbed CO on an adjacent Pt site to form easily desorbed CO2 [1]. In this study, we focus on the preparation of nanometer sized Pt-Ru and Pt-Ni particles supported on carbon by using the methods of strong electrostatic adsorption (SEA) and electroless deposition (ED).

The method of SEA has been used to prepare ultra-small Pt nanoparticles with high dispersions and a narrow size distribution. Catalysts prepared by SEA were then used as seed nuclei for addition of a secondary metal (Ru or Ni) using Electroless Deposition (ED). These compositions form bimetallic surfaces where Pt and Ru (or Ni) are in intimate contact to facilitate the interaction of adsorbed CO with adsorbed H2O to form CO2 during evaluation for methanol oxidation. These bimetallic catalysts show higher activity towards methanol oxidation than the analogous, commercial catalysts. Finally, the catalysts have been characterized by XRD, STEM, and temperature programmed methods to confirm the compositions of the bimetallic particles.

References

Ehteshami, S.M.M. and S.H. Chan, A review of electrocatalysts with enhanced CO tolerance and stability for polymer electrolyte membarane fuel cells. Electrochimica Acta, 2013. 93: p. 334-345.
Carbon Deposition Diagnostics for Reliability and State-of-Health Assessment of SOFC
Authors: Ploner Alexandra , Hagen Anke , Hauch Anne
Published: February 2020

The possibility of Solid Oxide fuel cells (SOFCs) to not only operate on hydrogen but hydrocarbon based fuels is certainly beneficial compared to other fuel cell technologies. Yet, the use of carbon-containing fuels can lead to electrochemical deactivation of the cell if carbon deposition occurs 1.Various studies were dedicated to understand the influence of different operation conditions to prevent this detrimental failure to occur. However, even though the thermodynamic limit offers a good guideline for SOFC operation, studies on specific operation conditions are still controversial 2

, 3. Therefore, recent research activities are focusing on the development of online-monitoring tools to prevent destructive failure and maintain fault free conditions 4.

Our recent study investigates the evolvement of carbon deposition in an anode-supported single cell under operation with a steam/methane fuel. Cell voltage monitoring, temperature monitoring and additionally employing in situ electrochemical impedance spectroscopy (EIS) in combination with the distribution of relaxation time (DRT) method allowed state-of-health assessment of the cell. The electrochemical examination is furthermore complemented by post-mortem investigations. ‘Failure’ was simulated by operating the cell on methane without steam. Via time-dependent EIS and DRT measurements, it was possible to correlate the onset of carbon deposition for the individual layers within the SOFC anode with different frequency ranges which will be presented at the meeting.

Furthermore, a recovery possibility via the set back to nominal operating conditions (to simulate a close-to-real approach) is evaluated with the same methodology. The cell voltage measurement during the performed experiment is shown in Figure 1.

Figure 1 Cell voltage for the cell operated under steam reforming conditions and methane.

Our findings have the potential to utilize EIS characteristics for recognizing carbon deposition in anode-supported cells in due course to counteract fatal failure of the SOFC and are a promising method to ensure safe operation of SOFC under steam-reforming conditions for industrial purposes.

Boldrin, P. et al., Chem. Rev.
2016,
116, 13633-13684.

Kuhn, J. & Kesler, O., J. Power Sources
2015,
277, 443-454.

Kuhn, J. & Kesler, O., J. Power Sources
2015,
277, 455-463.

Sinha, V. & Mondal, S., Int. J. Dynam. Control
2017.

Figure 1
Impact of Size, Shape and Location of Reference Electrodes on Measuring Anode Potential
Authors: Kim Sun Ung , Pande Vikram , Viswanathan Venkatasubramanian , Christensen Jake
Published: February 2020

Lithium plating is a major cause of degradation and in turn capacity fade in lithium-ion batteries. The driving force for lithium plating is dependent on the surface overpotential at the negative electrode. Surface overpotential can be measured by introducing a reference electrode and measuring the potential difference between the anode and the reference electrode. However to minimize this prediction error under different charging conditions, it is important to design a stable and accurate reference electrode. Lithium reference electrodes have been widely used as they give a constant reference potential and are relatively easy to make. The stability and accuracy of a reference electrode depends on the charging rate; the size, shape, and location of the reference electrode; and corrosion reactions occurring at the reference electrode. In this work, we built a 2D electrochemical model to understand the trends in accuracy of prediction of surface overpotential for reference electrodes of different sizes and shapes placed at different locations and including corrosion reactions to explore their stability.
Performance of Treatment of Oil-Sands Produced Water By Electrocoagulation
Authors: Shu Tianpei , Fuladpanjeh-Hojaghan Behzad , Yasri Nael , Nightingale Michael , Trifkovic Milana , Roberts Edward P.L.
Published: February 2020

In Alberta, Canada, the oil-sands industry plays an important role in the local economy, however the industry is the largest water consumer and has a significant impact on the environment. Only 20% of the available bitumen can be extracted by surface mining, while the rest can be produced by in-situ methods. For in-situ methods, steam is typically injected into the reservoir to reduce the bitumen viscosity, allowing the bitumen to be pumped to the surface along with water. In order to avoid hardness and silica in the produced water from fouling the steam generators, water treatment processes are needed. The treatment of this produced water is challenging as it contains dissolved silica, a high level of hardness and complex organics. Our research has shown that electrocoagulation (EC) is a viable technology to remove a large variety of contaminants. This technology applies the concept of electrochemistry by using sacrificial metal electrodes in an electrochemical cell to produce metal hydroxide coagulants that can efficiently remove contaminants by either adsorption or charge neutralization [1].

In this study, a continuous flow-through cell was designed to remove the contaminants from produced water and synthetic produced water following the same inorganic compositions as the produced water. Mild steel and aluminum were evaluated as electrode materials for the EC treatment process. The results show that EC was very effective for removal of dissolved silica in both real and synthetic produced water. More than 90% of the silica was removed using a charge loading of less than 1000 coulomb of charge per liter of water treated, which corresponds to less than ten minutes of treatment under the experimental conditions used. The effect of design and operating parameters including: water flowrate, current density, dissolved oxygen concentration, and electrode spacing will be reported.

References:

[1] D. Moussa, M. El-Nass, M. Nasser, and M. Al-Marri. "A comprehensive review of electrocoagulation for water treatment: Potentials and challenges." Journal of Environmental Management, vol. 186, pp. 24-41, 2017.
Electrosynthesis of Near-Neutral Ferrate Species for Drinking Water Treatment Using a Recirculating Batch Reactor
Authors: Bonakdarpour Arman , Cataldo Macarena , Mohseni Madjid , Wilkinson David P.
Published: February 2020

High oxidation state iron species of ferrates (e.g., Fe (VI), Fe (V) and Fe (IV)) are very promising oxidants and are in particular excellent candidates for water treatment applications. Their advantages include, for instance, a higher redox potential (+2.2 V vs. SHE) than the commonly used ozone oxidant (+2.07 V vs. SHE), no production of carcinogenic and harmful disinfection by-products (DBPs – produced with disinfectants such as chlorine) and decomposition into benign ferric hydroxides which form excellent coagulants. Ferrates are known to remove many different types of pollutants, including organic matter such as biofilms, algae, and coliforms, and inorganic matter such as cyanide, heavy metals, and radionuclides, and bio-contaminants like viruses and chlorine-resistant bacteria. One approach in production of ferrates is oxidation of Fe3+-containing solutions using an inert anode electrode. The oxidation reaction can be expressed by:

Fe3+ + 4H2O → FeO4
2- + 8H+ + 3e- E0 = -2.2 V vs. SHE

On-site production of ferrates for drinking water treatment by electrochemical means avoids a number of challenges with respect to transport and storage of chemical ferrates and also allows for direct integration of the electrochemical process with the treatment chain. In earlier papers on electrochemical ferrates, we have reported on a novel analytical method of ferrate quantification, degradation of ferrate and production of ferrates in small batch-type reactors [1-3].

Here we present a semi-batch (2 L) reactor which includes recirculation, temperature control, lower cell resistance, excellent mixing, provision for the use of ion exchange membrane, and in-situ pH control. The reactor uses boron doped diamond (BDD), Fe (III) solution and can be operated with or without an ion exchange membrane. The impact of several variables including current density (5 - 15 mA cm-2), pH (5 - 9), concentration of the dissolved iron salts on the production of ferrates temperature (15 - 30 oC) and operation with/without membrane have been studied and will be presented. Current efficiencies of as high as 90% were reached for the first 20 minutes of operation using a 30 mM of Fe (III) feed and a current density of 45 mA cm-2. The recirculating reactor results were successfully interpreted by a simple model which considered first order kinetics for Fe (VI) generation.

References

[1] M. Cataldo Hernandez, A. May, A. Bonakdarpour, M. Mohseni, D.P. Wilkinson, Can J. Chem, 95 (1) 2016.

[2] M. Cataldo Hernandez, M. Stewart, A. Bonakdarpour, M. Mohseni, D.P. Wilkinson, Accepted for publication in the Canadian Journal of Chemical Engineering.

[3] M. Cataldo Hernandez, R. Govindarajan, A. Bonakdarpour, M. Mohseni, D.P. Wilkinson, Accepted for publication in the Canadian Journal of Chemical Engineering.

Figure 1
Enhanced Performance of Compact Electrolytic Cells through Optimization of Cell Structures and Components to Produce Chemicals from Brine for Use in Sequestration of Carbon Dioxide
Authors: Ha Heung Yong , Kim Jaewon , Park Su-Ryeon , Lee Ki Bong
Published: February 2020

In recent decades, CO2 capture and utilization (CCU) strategy has been actively promoted because of the potential of CO2 to be used as a feedstock for producing useful organic and inorganic substances such as methanol, formic acid, and carbonates through biological, thermal, photochemical and electrochemical methods.

In this study, we report a development of compact continuous-flow electrochemical cells for an energy-efficient electrochemical splitting of brine (aqueous NaCl) to produce alkali (NaOH) and hydrochloric acid (HCl) that would be used to convert carbon dioxide into carbonate minerals at a subsequent stage. Cell structures and types of polymer electrolyte membranes (PEMs) have been explored for constructing energy efficient electrochemical cells in terms of reaction rates and caustic (Faradaic) efficiencies (CE). Two types of cell designs representing a first version (design 1, namely one-membrane cell) and an advanced version (design 2, namely two-membranes cell) are investigated.

The one-membrane cell consisted of a membrane sandwiched between an anode and a cathode. A feedstock comprised of a NaCl solution and H2 gas was supplied to the anode side while pure water was supplied to the cathode side. Upon applying a voltage of 1.5V between the two electrodes, the electrolytic reactions proceeded to produce HCl at the anode and NaOH and H2 at the cathode. In the case of two-membrane cells, two-membranes were used and a separator plate was placed between the two membranes and the NaCl solution was fed to the separator plate while H2 gas was fed to the anode.

The one-membrane cells show initial reaction rates as high as 400 mA/cm2 at an applied voltage of 1.5V. The reaction rate, however, drops rapidly due to the degradation of the anode catalyst by hydrochloric acid that is produced at the anode side during the reaction. On the other hand, the two-membranes cells show very stable performance over 200 hours though their reaction rates are kept below 80mA/cm2 at an applied voltage of 1.5V. In addition, we have tested various types of fluorine-based and hydrocarbon-based polymer electrolyte membranes. While two-membranes cells display definitely higher CEs than their counter parts, some membranes show comparable CEs even in a one-membrane cell. Therefore, development of PEMs suitable for this electrolytic cells is crucial in improving the cell performance. Optimization of the operating conditions, cell structures and types of membranes have been further carried out to enhance the reaction rates while maintaining the CEs high.

In conclusion, the two-membranes cells are estimated superior to the one-membrane cells because of their stability over long run though their reaction rates are somewhat lower than the latter.
Optimization of Mechanical Properties of Nickel-Cobalt Coatings from Sulphamate Baths
Authors: Karakaya Esra , Başkan Mertcan , Erdogan Metehan , Karakaya Ishak
Published: February 2020

Nickel-cobalt alloys are important coating materials due to their magnetic properties [1-2],

wear resistance [3-4] and electrocatalytic properties [5]. Their deposition from sulfamate

electrolytes has many advantages including low internal stress, homogenous deposition at

high current densities, high current efficiencies and higher hardness as compared to the

conventional Watts electrolyte [6]. A statistical experimental design was used to study the

effects of boric acid and nickel chloride concentrations, bath temperature and applied current

density on nickel coatings in sulphamate baths. After the optimization of the electrolyte

composition, effects of pH and Co additions to the electrolyte were investigated. The coating

thickness and its distribution were measured by XRF techniques. Microhardness, surface

morphology and internal stress of coatings were also determined. It was found that Co

addition to the electrolyte and operation at higher pH yielded deposits of higher Co content

and enhanced hardness up to a certain point.

References

[1] A. Karpuz, H. Kockar, and M. Alper, J. Mater. Sci. Mater. Electron., 24 (2013) 3376-3381.

[2] G. Chatzipirpiridis, E. Avilla, O. Ergeneman, 50 (2014) 10-12.

[3] L. Xuewu, X. Yunhua, Q. Yi, and S. Lilong, Integr. Ferroelectr., 152 (2014), 144-151.

[4] L. Wang, Y. Gao, Q. Xue, H. Liu, and T. Xu, Appl. Surf. Sci., 242 (2005) 326-332.

[5] C. Hu, C. Tsay, and A. Bai, Electrochim. Acta, 48 (2003) 565-572.

[6] M. Saitou, S. Oshiro, and S. M. Asadul Hossain, J. Appl. Electrochem., 38 (2008) 309-313.
Carbonization Temperature As a Key Factor for Ultrahigh Performance Activated Carbon from Polyaniline for Capacitive Deionization
Authors: Zornitta Rafael Linzmeyer , Nogueira Francisco Guilherme E. , Ruotolo Luis Augusto Martins
Published: February 2020

Capacitive deionization (CDI) has been considered a reliable technology used to provide water with low salt concentration and low energy consumption. However, there are still some drawbacks to overcome concerning the choice of the electrode material. Carbon electrodes are extensively used for CDI electrodes since they provide a stable material with high pore volume and good conductivity. However, it is been challenging to find a low-cost symmetric CDI electrode with high salt adsorption capacity (SAC), fast electrosorption kinetics and good energy efficiency. Recently, our group published a paper reporting the use of activated carbon derived from polyaniline (PAC), a low-cost precursor, with high SAC and good electrosorption kinetics. It was demonstrated that the use of different polyaniline (PAni) dopants have a strong influence on the activate carbon properties and, consequently, the electrode performance for CDI. In the present research, it was explored the use of PAC electrodes varying the carbonization temperature before the activation. It was observed a strong dependence of the specific surface area (SSA) and pore size distribution (PSD) on the carbonization temperature. When low temperatures (500 °C) were employed during carbonization (PAC500), the BET SSA was 3653 m²/g and pore volume of 2.50 cm³/g was obtained while at higher carbonization temperatures (850 °C) this value was much lower (2362 m²/g of SSA and 1.26 cm²/g of pore volume for PAC850). The BET SSA obtained in this work is among the highest values reported in literature. The explanation for this high value is probably ascribed to the reactivity of the low temperature carbonized PAni with KOH. Indeed, when PAni was carbonized in temperatures lower than 500 °C all the material was consumed during the activation step, indicating a strong reactivity of the precursor with KOH. These values of SSA and pore volume resulted in an outstanding performance as symmetrical electrodes for CDI. The capacitance of PAC500 and PAC850 measured in a NaCl 0.2 M solution were 213 F/g and 162 F/g, respectively. These impressive values are result of the high SSA and pore volume of PAC materials. Finally, the CDI desalination carried out in batch operation mode also showed an outstanding SAC performance for symmetric electrodes, achieving 22 mg/g for PAC500 and 15 mg/g for PAC850. Moreover, 85% and 76% of electrode saturation was reached after 5 minutes of electrosorption for PAC500 and PAC850, respectively, indicating very fast electrosorption kinetics. This work present a very promising electrode material for CDI and shows how important is the carbonization temperature for PAC electrodes.

Figure 1
Profiled Anode Supported Solid Oxide Fuel Cells for Low Cost Stacks for Stationary Applications
Authors: Kluczowski Ryszard , Swieca Adam , Kawalec Michal , Kupecki Jakub , Krauz Mariusz , Naumovich Yevgeniy , Blesznowski Marcin , Zurawska Agnieszka , Skrzypkiewicz Marek , Motylinski Konrad
Published: February 2020

This work presents the results of elaboration of technology dedicated to fabrication of anode supported solid oxide fuel cells (AS-SOFC) with profiled surface of the anode. Profile on anode support was designed as channels which allow to facilitate the fluxes of gaseous components to and from electrochemical reaction zone due to the decreased thickness on Ni-YSZ composites between ribs. Additionally profiling of the anode increases the active area and allows elimination of the profiled or corrugated interconnectors. At state-of-the-art, in order to collect current from the surface of AS-SOFC and to ensure proper distribution of the fuel flow, interconnects are made from special heat-resistant alloys with precise milled or stamped channels. Profiled anode supports will allow to distribute gaseous fuel and replace dual-side profiled interconnects by cheaper ones without introduction of additional treatments or parts.

In order to produce anode support with profiled surface without necessity of additional machining process of anode surface, the ceramic injection molding method (CIM) was used. This method significantly shortens the production time of the anode supports for AS-SOFCs, reduces its costs in comparison to commonly used techniques and is generates negligible amount of process waste material. This technique makes it possible to manufacture complex three dimensional ceramic components with tight dimensional tolerances. Cost-intensive post-processing can frequently be avoided, which allows high-scalable mass production of ceramic elements.

The mold for injection of anode support was designed to make an anode support of 50x50 mm with 1.4 mm of thickness. The profile consisted of 18 channels was fabricated along of one side of the support. Dimensions of each channel were 0.6 mm of depth and 1.5 mm of width (Fig. 1). The geometry of channels defined using numerical simulations and then adjusted to the technological requirements of CIM. Using this mold the anode supports consisted of NiO/8YSZ 66/34 wt.% with porosity of 25 vol.% were injected (Fig. 1). The screen printing method was used to print 3 µm thick NiO anode contact layer, 7 µm thick NiO/8YSZ 50/50 wt.% anode functional layer, 4 µm thick 8YSZ dense electrolyte, 1.5 µm thick Gd0.1Ce0.9O2 barrier layer and the 30 µm thick La0.6Sr0.4Fe0.8Co0,2O3–δ cathode with porosity 25 vol.%. Sintering conditions were adjusted to avoid the deformation of the anode

support.

Fig.1.

Schematic drawing of the profiled anode support (left) and the anode with fuel channels (right)

Fabricated AS-SOFCs were characterized by the microstructural analysis and electrochemical performance was measured.

Figure 1
In Situ TEM Observation of Dynamic Switching Behaviors in Vrram
Authors: Wu Min-Ci , Chen Jui-Yuan , Wu Wen-Wei
Published: February 2020

Resistive random access memory (RRAM) is considered as a promising candidate for the next-generation nonvolatile memories (NVM) due to its high storage density, reduced power consumption, and fast switching speed. Transition metal oxides are widely utilized to RRAM as insulator, which exhibit stable structure, high endurance and retention, and shrinking ability under several nanometers.

In order to realize higher endurance and stability while reducing the size, knowing the mechanism of filaments formation and the interaction between adjacent nanodevices are essential. In this work, three-dimensional vertical RRAM (VRRAM) array architectures were built to access and organize data, which are expected to high density application potential. In our simple MIM structure, ZnO is the insulator, and Ag and Pt are served as active electrode and inert electrode, respectively. Each electrodes intersection contains two types of RRAM devices (Ag/ZnO/Pt, Pt/ZnO/Pt). By utilizing in-situ transmission electron microscope (TEM), we could observe the dynamic switching behaviors of two neighboring devices and realize the interaction between them. While the devices sizes scale down to few nanometers scale, the evolution of different types of filaments provides important information to improve the stability and performance of the devices.
Observing Electrochemical Switching Behaviors in Crossbar Core-Shell Ni/NiO Nanowires Memristor
Authors: Ting Yi-Hsin , Chen Jui-Yuan , Huang Chun-Wei , Huang Ting-Kai , Hsieh Cheng-Yu , Wu Wen-Wei
Published: February 2020

The crossbar structure of resistive random access memory (RRAM) is the most promising technology for the development of ultra-high-density devices for future nonvolatile memory. However, only a few studies have focused on the switching phenomenon of crossbar RRAM in detail. The main purpose of this study is to understand the formation and disruption of the conductive filament occurring at the crossbar center by real-time transmission electron microscope (TEM) observation. Core-shell Ni/NiO nanowires were utilized to form a cross structure, which restricted the position of the conductive filament to the cross-center. A significant morphological change could be observed near the crossbar center, which resulted from the out-diffusion and backfill of oxygen ions. Energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS) demonstrated that the movement of the oxygen ions led to the evolution of the conductive filament, followed by redox reactions. Moreover, the distinct reliability of the crossbar device was measured via ex situ experiments. In this work, the switching mechanism of the crossbar core-shell nanowire structure is beneficial to overcome the problem of nanoscale minimization. The experimental method shows high potential to fabricate high-density RRAM devices, which could be applied to 3D stacked package technology and neuromorphic computing systems.

Figure 1
Monte Carlo Model of Ion Conduction in Non-Arrhenius Glasses
Authors: King Clarence C , Beckman Scott P
Published: February 2020

Ion conducting glasses are promising for use as electrolytes in all-solid-state batteries, which have the potential to both have higher volumetric energy density and overall safety than liquid electrolyte batteries. There are multiple studies that report non-Arrhenius conductivity in highly ionic conductive glasses. Although there are several theories proposed to explain this phenomena, as of yet, none of these have been verified.

Here we develop and deploy a Monte Carlo model of ion conduction to compare and contrast the theories of non-Arrhenius conductivity in glasses. In this relatively simple model ions hop between sites according Boltzmann statistics. The ions’ motion is coupled in the short range by geometrical factors, e.g., the network of interstitial sites and their occupancy, and in the long range by Coulomb interactions.

We further demonstrate that this model can be used to simulate the macroscale charging and discharging behavior of batteries. For these battery simulations, regions identified as cathode, electrolyte, and anode are identified. A jellium background charge is used in the electrolyte to maintain charge balance and used in the anode and cathode to account for the oxidation and reduction of the ions. This model accounts explicitly for the change in entropy during cycling and implicitly the overpotential that develops due to ion accumulation at the interfaces.
Quantum–Continuum Modeling of Pd-Au(111) Surface Alloys Under Electrochemical Conditions
Authors: Weitzner Stephen Eric , Dabo Ismaila
Published: February 2020

Bimetallic surface alloys often exhibit enhanced electrocatalytic performance due to ligand, ensemble, and bifunctional effects that arise from the presence of different transition metals along the catalyst surface. Segregation, dealloying, and poisoning events are common modes of catalyst deactivation that are difficult to suppress, limiting the durability of bimetallic catalysts in harsh environments. Efforts to estimate the stability of these novel catalyst formulations under operational conditions via first principles techniques is challenging due to the critical influence of solvation, surface electrification, and finite temperature effects. In this talk, we present a quantum-continuum model of the electrode-solution interface [Weitzner & Dabo, npj Comp. Mater. 3, 1 (2017)] that directly accounts for the influence of the electrochemical environment and pair this model with a recently developed voltage-sensitive cluster expansion technique to perform semi-grand canonical Monte Carlo simulations of the interface [Weitzner & Dabo, Phys. Rev. B (in press)]. We apply this method to study the voltage-dependent stability of Pd-Au(111) surface alloys under realistic electrochemical conditions and discuss the role of environmental effects on the durability of the catalyst.
(Invited) Multiscale Analysis of the Polysulfide Shuttle Effects at the Li Metal Anode and Cathode Morphology Evolution in Li-S Batteries
Authors: Balbuena Perla B , Mukherjee Partha P , Pol Vilas G.
Published: February 2020

Lithium-sulfur batteries are sought as promising candidates for electric vehicle technologies. The soluble polysulfide (PS) migration from cathode to anode and their posterior decomposition at the Li-metal anode side, and the low electronic conductivity of the main discharge products Li2S2 and Li2S are among the main challenges. Here we use a multiscale modeling approach to evaluate and characterize these issues. Reactivity of the electrolyte at the bulk and at the anode surface and the transport mechanisms of the soluble polysulfides are studied with density functional theory and ab initio molecular dynamics. The composite carbon-sulfur cathode is modeled at the atomistic and mesoscopic levels and the effects of changes of morphology during reaction are investigated through the analysis of battery performance. The carbon-sulfur composite properties are compared to those resulting of a novel pressurized autogenic synthesis route. Finally, the important effects of precipitation modes and low electronic conductivity of the insoluble Li2S2 and Li2S species on charge reactions and cathode capacity are also evaluated with a multiscale modeling approach.
(Invited) How to Deal with Electrode Heterogeneity in Cell-Level Battery Modeling
Authors: Wheeler Dean R.
Published: February 2020

As shown in Fig. 1, typical porous electrodes (in this case for a Li-ion anode) clearly have heterogeneity on the µm and smaller length scales. In addition, it has been shown that there is heterogeneity on mm length scale for even commercial quality electrodes [1]. This heterogeneity is a consequence of the particle-based manufacturing processes [2]. Furthermore, this heterogeneity is undesirable as it essentially requires that the electrodes be overdesigned to achieve adequate minimum performance.

The commonly accepted Newman-type model of the full-cell sandwich essentially averages over local heterogeneities in porous electrodes in order to make the system “macrohomogeneous.” The resulting model allows for uniform pathways for electrons and ions. Homogenization of the microstructure greatly decreases the computational cost of the model while retaining the essential physics of transport and reaction within the electrodes.

In this presentation I will discuss how one can measure heterogeneities as well as average values of electronic and ionic conductivities [1,3]. These can be compared to empirical correlations such as the Bruggeman equation. Our group has considerable experience in this area.

With respect to modeling, I will discuss strategies for dealing with heterogeneities in the context of Newman-type models. This can include using multiple particle types [4] as well as effective medium theories that allow one to average local values of physical properties to generate an overall or effective medium property. Lastly, I will discuss what effect such averaging has on predictions of the battery model.

This work was supported by the U.S. Department of Energy through the BMR program.

[1] Lanterman et al., J. Electrochem. Soc. 162, A2145 (2015).

[2] Forouzan et al., J. Power Sources 312, 172 (2016).

[3] Zacharias et al., J. Electrochem. Soc. 160, A306 (2013).

[4] Thorat et al., J. Electrochem. Soc. 158, A1185 (2011).

Fig. 1 SEM/FIB cross section of Li-ion anode showing local heterogeneity.

Figure 1
(Invited) Modeling Battery Performance Due to Volume Change in Porous Electrodes
Authors: Garrick Taylor R , Weidner John W.
Published: February 2020

In order to accurately predict the behavior of electrochemical devices, it is necessary to develop sophisticated models that take into consideration transport processes, electrochemical phenomena, mechanical stresses, and structural deformations on the operation of an electrochemical system. Many different models exist that can predict the electrochemical performance of these devices under a variety of operating and design conditions. In many of these models, the porosity of a porous electrode is often assumed constant since the volume changes seen during the intercalation reaction can be small. However, electrode materials developed in recent years show significant volume changes during intercalation, which are unable to be accurately predicted using these constant porosity models.

Porosity and dimensional changes in an electrode can significantly affect the resistance of the battery during cycling and can cause premature failure of the battery due to generated stresses. Previously[1-5], we have shown the ability to incorporate dimensional and porosity changes in a porous electrode into a model to predict volume changes in the active material of a single electrode during intercalation through the coupling of porous rock mechanics and porous electrode theory. Many assumptions were used to obtain an analytical solution, including the assumption of bulk strain, uniform porosity, and uniform concentration across the electrode.[2] This model was extended to look at design considerations[5] as well as non-uniformity within a single porous electrode coupled to a lithium metal reference.[4] Here, we present a model that removes some of these assumptions and illustrates the coupling of porous electrode theory and rock mechanics in order to predict stress, strain gradients, and porosity gradients across a porous electrode during cycling in a battery containing a blended anode undergoing volume change coupled to a Lithium Nickel Manganese Cobalt Oxide (NMC) cathode.[6] In this model, we will examine separator deformation, volume change during high charge rates, and consider pressure generated in the cell due to restriction in a battery module.

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Modeling of Lithium Sulfur Battery with Microscopically Consistent Parameterization
Authors: Chung Jui-Hui , Chen Hsun-Yi
Published: February 2020

Lithium sulfur (Li-S) batteries are considered a promising energy storage technology for that its theoretical specific capacity of 1.672 Ah g-1 is over five folds of currently commercialized lithium-ion batteries. The charge/discharge processes of Li-S batteries, however, involve complex reactions of sulfur species and are not yet fully understood. Physical models are crucial to elucidate these mechanisms occurring in Li-S batteries in assisting a multitude of experimental investigations.

However, previously developed models are usually overly simplistic and lack generality. The first one-dimensional Li-S model employed dilute solution theory including diffusion and migration, where transport properties base only on interactions between the solute and the solvent. In the case of multicomponent transport, ion pairing and ion association are important. Therefore, we integrate concentrated solution theory to the macroscopic model to incorporate effects of multi-valent states of sulfides.

Comparing our concentrated solution theory results to those of dilute solution theory, the discharge curves resembled one another, suggesting concentration polarization took little part in the overall potential loss under current parameterization. Thus, we investigate interrelated components of potential loss, namely the surface overpotential, ohmic potential drop, and concentration overpotential. Fig 1 shows that the modeled discharge rate capability is limited by the anode surface overpotential. This result is inconsistent with previous studies, where the low discharge rate has been explained in terms of mass transport limitation and slow charge transfer at the cathode due to precipitation of Li2S. We consider the lack of reliable parametrization is to blame for the inconsistency, and seek to resolve the parameter-prediction problems inherent in computational models.

To simulate multicomponent diffusion in concentrated solutions, we compute the full transport properties through the representation of Onsager coefficients matrix (Fig 2) and thermodynamic factors using equilibrium molecular dynamics (MD). In addition, we report a theoretical analysis of sampled-current voltammetry based on concentrated-solution to compute the exchange current density, which is not previously established. We emphasize the mathematical consistency among the formulation of modeling equations, experimental methods, and MD methods to achieve fidelity in simulations.

Figure 1
Drop-in Electrodeposition Processes for Void-Free, High Aspect Ratio Structures of Five Metals
Authors: Josell Daniel , Moffat Thomas P.
Published: February 2020

Superconformal electrodeposition processes enable void- and seam-free metal filling of high aspect ratio features from tens of nanometers to hundreds of micrometers in size. There are two known mechanisms underlying such processes: Curvature Enhanced Accelerator Coverage (CEAC) and S-shaped Negative Differential Resistance (S-NDR). Voltammetric measurements on planar substrates can quantify kinetics in models based on both mechanisms, enabling accurate, a-priori prediction of filling from a particular electrolyte in a particular size and aspect ratio feature. I will summarize the chemistries and associated mechanisms for superconformal Cu, Ag, Au, Co, and Ni feature filling, including experiment and model predictions, for processes that are drop-in compatible with those presently used for fabrication of Cu damascene and through silicon via interconnects.
(Electronics and Photonics Division Award Address) Technological Issues and Design Rules of Electrodes for High-Efficiency GaN-Based Light-Emitting Diodes
Authors: Seong Tae-Yeon
Published: February 2020

Group III-nitride-based LEDs are of great technological importance because of their applications including display, solid-state lighting, automotive headlight, and water/air purification. For these applications, the attainment of high external quantum efficiency (EQE) of LEDs is essential. On the one hand, their applications necessitate the fabrication of different geometry LEDs, such as lateral-type, vertical-type, and flip-chip LEDs, which require different design rules of electrodes and current spreaders. To maximize the EQE, it is important to increase the light extraction efficiency (LEE). In addition, the improvement of current injection (by forming low contact resistivity) and current spreading is vital for the fabrication of high-efficiency LEDs. It is well known that lateral LEDs suffer from the light extraction limit due to the absorption of the metal contacts, such as n and p contacts, and bond pads. In addition, p-GaN has characteristic problems, which make it difficult to achieve device-quality ohmic contacts with the specific contact resistance lower than ~10–4 Ωcm2 because of the difficulty in growing a highly doped p-GaN and the absence of appropriate metals or conducting oxides having work function larger than that of p-GaN. Thus, for the formation of ohmic and reflective contacts to p-GaN, also serving as light extractor and/or current spreader, transparent conducting oxides (TCOs)-based and Ag-based schemes have been extensively investigated. In this talk, we present methods of enhancing current injection efficiency through the formation of transparent and reflective ohmic electrodes. Design rules are suggested to enhance current injection efficiency, such as the control of surface Fermi-level through surface treatment, barrier tunneling by forming interfaces with inhomogeneous Schottky barriers, the modification of Schottky barrier heights (SBHs), control of native defects in GaN surface regions. Furthermore, nanostructures, such as Ag nano-dots (NDs) and Ag nano-wires (NWs), are used to enhance the light output powers of GaN-based LEDs. Finally, on the basis of scanning transmission electron microscopy, X-ray photoemission spectroscopy, secondary ion mass spectroscopy and Auger electron spectroscopy results, possible ohmic formation and electrical degradation mechanisms are described and discussed.
A Defect Density Profile Extraction Method for GaN Epi-Wafers
Authors: Kataoka Hiroaki , Hoshii Takuya , Muneta Iriya , Wakabayashi Hitoshi , Tsutsui Kazuo , Iwai Hiroshi , Kakushima Kuniyuki , Yamamoto Taiki
Published: February 2020

Owing to the wide bandgap and high-mobility of GaN compared to that of Si, GaN power devices are expected to perform low on-resistance at high withstand voltage. However, due to the presence of defects in the crystal, GaN epi-wafers contain lots of traps sites which results in malfunction during the device operation; current collapse and so on [1]. As the defects are distributed in the whole epi-layer, it is difficult to extract the defect density profile from cyclic voltammetry. In this presentation, we propose a method to extract defect density profile in the GaN epitaxial wafer.

When a DC voltage (V) is applied to an Ohmic electrode connected to 2DEG at AlGaN/GaN interface, the entire epi-layer will depleted (t=0+) and a charge of Qcap
(=CcapV) will appear at both electrodes. At steady state (t=∞), the depletion layer shrinks back depending on the active defect concentration. The thickness of the depletion layer (z) can be extracted by the charges (Qdep
), which is the integral of current until the steady state is reached using the Cdep
=QdepV
-1 relation. Since we have the relation between V and z, the defect density profile at the position x, ρ(x), can be extracted using eq.1. Where q and ε are the elementary charge and the dielectric constant of GaN, respectively.

Figure 2 demonstrates the defect density profile extracted with the proposed method on AlGaN/GaN/buffer structure on a Si substrate. Here, buffer was used to reduce defect density. A distinctive change in the defect profile can be seen at x=4μm, which corresponds to the position where the epitaxial process has been changed.

In summary, a novel method to extract the defect density profile in the GaN epi-wafer has been proposed.

[1] T. Hashizume, etc., IEICE technical report, 104 (2004).

Figure 1
(Invited) Latest Progress on B-III-N Alloy Research and Working Principle of TMA Preflow on AlN MOVPE
Authors: Li Xiaohang
Published: February 2020

The B-III-N alloys have not been studied extensively as compared to conventional III-nitride AlGaInN alloys. However, due to the large and tunable bandgap, tunable lattice constant, and many other electronic properties, this emerging material system has enormous potentials for DUV-IR optoelectronics and power electronics devices. In this presentation, some of the latest research progress of the B-III-N alloys will be discussed, covering from epitaxial growth, microscopic characterization to electronic properties.

The TMA and NH3 preflow processes have been critical for the AlN MOVPE process on sapphire, in that they pre-condition the sapphire substrates for the Al-polar epitaxy. Although the mechanism of the NH3 preflow has been thoroughly studied and clear, that of the TMA preflow has been a bit mysterious. Some MOVPE scientists have hypothesized that the TMA preflow resulted one or more than one layers of Al or Al-rich layers on sapphire surface, which further leads to the growth of Al-polar AlN. I will present our model of the TMA preflow based on systematic electron microscopy studies.