bluuebunny/crossref_metadata_2025 huggingface dataset:
Under Deposit Corrosion in Steam Generators: Towards Understanding Critical Deposit Thresholds
Authors: Ramesh Abitha , Puolamaa Milla E , Laycock Nick , Barnes Andrew , Thyagarajan Aarthi , Abdullah Aboubakr M , Stitt Camilla , Ryan Mary P.
Published: February 2020

Most significant industrial facilities operate large steam systems, including multiple steam generators. The steam produced may be used for power generation by steam turbines or for heating various equipment items and is usually critical to the overall operation of the plant. Each steam generator will typically contain hundreds of carbon steel tubes: the failure of such tubes by unpredicted corrosion represents a common cause of plant downtime, significant lost production, and an ongoing safety risk.

The mechanism of UDC in these systems is not well-understood, and this is in part because of the experimental challenges of studying such systems [1-3]. However, some clear parametric observations have been made and it is now established that very low (ppb) levels of dissolved ferrous ions and micro-scale particles of magnetite are produced by flow-assisted corrosion in the steam generator feed-water systems, and that these are then deposited on to the heat transfer surfaces. Together with the presence of only trace (ppb) levels of bulk chloride contamination, these deposits can lead to extraordinarily rapid corrosion. Characteristic features of the damaged material include: the porous structure of the deposit layer; the presence of high local chloride concentrations within the deposits; and formation of a complex ‘multi-duplex’ layer of corrosion product that exhibits approximately linear growth kinetics.

According to EPRI guidelines [4], 35 mg.cm-2 represents a critical threshold for deposit thickness after which interventional maintenance should be initiated. This nominal thickness is not based on mechanistic understanding and is often achieved in boilers within only a few years of operation, resulting in the need for expensive and time-consuming chemical cleaning to remove the deposits. Hence, it is necessary to better understand the various stages in the formation of these layers to improve prediction of UDC and help reduce conservatism in maintenance without compromising on safety.

In this presentation, we will present a study of field-retrieved samples that were examined with optical and electron microscopy techniques, coupled with phase and chemical analyses. This will be compared with model experiments where deposits are formed under laboratory-controlled conditions [1], including both new and literature data. We will discuss these data in terms of a model for UDC in steam generators, with emphasis on the critical deposit thickness and the particular role of chloride in the formation of the characteristic multi-duplex scales.

References

Robertson, J. and Forrest, J.E., 1991, Corrosion Science, 32(5/6), 521-540.

Howell, A.G., 2006, NACE – 06458, NACE international publication.

Dooley, R.B. and Bursik, A., 2010, Boiler and HRSG tube failures - Hydrogen Damage, 12(2), 122-127.

Dooley, R.B., 2005, EPRI Technical Report, 1-154.
Finite Element Modelling of Microelectrode Arrays of Mg and AA2024 Galvanic Couple
Authors: Moraes Carolina Vicente , Kelly Robert G.
Published: February 2020

Aerospace aluminum alloys, such as AA2024-T3, are susceptible to microgalvanic corrosion and pitting due to its heterogeneous microstructure. Thus, they require additional corrosion protection methods. Magnesium rich primer coatings (MgRP) have emerged as an effective alternative to highly toxic chromate-based coatings. MgRP systems consist of an organic resin loaded with Mg pigment. The organic resin provides barrier protection, while metallic Mg pigment serves as a sacrificial anode by galvanic coupling with more noble Al alloy. The distance over which an active corrosion system can protect a defect exposing a metal surface is named galvanic throwing power and it is an important parameter used to evaluate the effectiveness of this type of protection method. Microelectrode array (MEA) is a technique commonly used to determine the galvanic throwing power. In this technique, wires of the metals of interest are mounted in a non-conductive matrix and the galvanic current distribution over the wires is measured. The wire diameter and the distance between the wires are important factors that affect the accuracy of MEA. While thin wires can provide finer spatial resolution, the experimental setup is challenging, and edge effects can decrease the representativeness of the measurement.

Finite element analysis (FEA) is a tool used to predict both spatial and temporal potential and current distributions in electrochemical systems related to metal dissolution and cathodic reactions. FEA also can be used as an experimental design tool. In this work, FEA was used to assess important parameters and predict an optimal combination of wire diameters and distance between wires that result in higher accuracy of MEA.

COMSOL Multiphysics (ver.5.4) was used to perform the finite element simulations. Potentiodynamic polarization scans of AA2024 and pure Mg immersed in 0.9 M NaCl solution were performed to generate E - i curves that were used as the electrochemical boundary conditions. Laplace equation was used to describe the current distribution that resulted from the galvanic coupling. The effect of the spacing between the wires and their diameters on the current distribution was studied. The results were compared to a reference solid plate configuration, where the two metals were in electrical contact.
Charge Injection at Metal-Polymer Interfaces a First-Principles Study
Authors: Kamal Deepak , Chen Lihua , Li Zongze , Nasreen Shamima , Cao Yang , Ramprasad Rampi
Published: February 2020

The long term insulating behavior of polymers critically depend on the polymer-metal interfaces. Injection of charged particles (electrons/holes), from the electrodes (metals) to the dielectric at these interfaces are precursors to dielectric aging which culminates in breakdown of the dielectric. The probability of this charge injection is decided by the energy difference between the fermi level of the electrode and the edges of valence and conduction bands of the dielectric. For a given polymer-metal interface, this primarily alignment depends on the dipole moments created by various features at the interface. Here, using calculations based on density functional theory (DFT), we look closely at some common interface features developed during physical vapor deposition of Al and Au on poly-propylene (PP), poly-styrene (PS), and Polyethylene Terephthalate (PET), surfaces and their effects on the charge injection behavior. On comparing our results with the experimental values, we see that adding defects on the interface bring the computed values of charge injection barriers closer to the experimental values, suggesting the presence of various defects at the interface. We also observe that by controlling the concentration of interface defects, we can align the fermi-level of the metal in the middle of the bandgap of the dielectric which potentially minimizes charge injection and impede the process of aging and breakdown.
Dependency of Multi-Level-Cell Behavior on Thickness of Top MgO Tunneling Barrier in Double Pinned Structure Perpendicular Spin-Torque-Transfer Magnetic Random Access Memory
Authors: Jun Han-Sol , Park Miri , Jung Sunhwa , Choi Jin-Young , Ashiba Kei , Baek Jong-Ung , Shim Tae-Hun , Park Jea-Gun
Published: February 2020

These days dynamic-random-access-memory (DRAM) fabrication to scale down under 10-nm is complex which leads to high cost [1]. On the other hand, perpendicular spin-transfer-torque magnetic random access memory (p-STT MRAM) cell has a possibility of high-density integration with feature size of 4F2. Therefore, p-STT MRAM is the most powerful candidate of new memory instead of DRAM. In hence, p-STT MRAM requires high tunneling magnetoresistance (TMR) ratio greater than 150%, enough thermal stability (Δ=KuV/kBT) above 75 for a ten-year retention-time, and low switching current (J
C0 ~ 1 MA/cm2) must be achieved for low power consumption [2-4]. However, the thermal stability is hard to maintain when the cell size is scaled down to 10 nm because the small volume of free layer leads to the changes of direction of spin by thermal agitation [5].

In this study, we designed a p-MTJ spin-valve with a double pinned structure to realize two-bit operation to overcome a larger scaling limit. We calculated four resistance states using relationship between the two different TMR of each MTJs. In particular, if the TMR of MTJ1 is half of MTJ2 and ratio of parallel resistance(Rp2/Rp1) is 0.8-0.9, the difference of each resistance state is equal. (see Fig. 1(b)) The TMR is mainly dependent on thickness of MgO tunnel barrier; therefore, we fabricated the p-MTJ spin-valve with a different thickness of MgO tunnel barrier (0.90 nm-1.35 nm) of MTJ1. Finally, we confirmed that the R-H curves match the four resistance states of p-MTJ with double pinned structure with our predicted results, and interval of resistance state is uniform when the thickness of top and bottom MgO are 1.36 nm and 1.10 nm as shown in Fig. 1(c). This implies that the double pinned p-MTJ spin-valve may be suitable for terabit integration compared to that of the single-bit operating p-STT MRAM memory cells.

In the end, we report dependency of MLC behavior on thickness of top MgO tunneling barrier in double pinned structure pSTT MRAM. In addition, we present the MLC behavior of pSTT-MRAM with double pinned structure and show the thickness of top MgO for uniform resistance state.

Acknowledgements

This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No.2017R1A2A1A05001285) and Brain Korea 21 PLUS Program in 2014.

References

[1] K. C. Chun et al., IEEE J. Solid-st. Circ. 48, 598 (2013)

[2] J. G. Park et al., IEEE Int. Electron Devices Meeting, IEDM 2015–February, 19.2.1-19.2.4 (2015)

[3] Y.Huai et.al., IEEE International Magnetics Conference, AB-07 (2015)

[4] H.-S. P. Wong et. al., “Stanford Memory Trends,” (2015)

[5] Shouzhong Peng, et al., IEEE MAGNETICS LETTERS,
volume 8 (2017).

Figure 1
Novel Degradation Model of Igzo TFT on High Drain Bias Stress
Authors: Kim Kihwan , Seo Miseon , Choi Byoung-deog
Published: February 2020

In this paper, the TCAD degradation model of IGZO using spatial distribution (X, Y) of physical parameters is proposed for the first time and is confirmed according to various channel length, active thickness, and bias stress conditions that agree with actual measurements. Oxygen vacancy in the presence of 2+ ionized states (VO
2+) in IGZO is stable. However, when band bending is severe, the electrons are captured, and the structural transition occurs as a neutral VO in the meta-stable state. This process is assumed to be a mechanism of IGZO degradation at high drain bias stress, and the electric field (>0.5M V/cm) and electron concentration (>1x1010 cm-3) in the channel are considered as the main factors of degradation and are modeled using the mapping function provided by Silvaco. Fig.1 show that the flow of development of degradataion model using TCAD.

Based on the oxide degradation mechanism, the following mathematical model was proposed to determine the number of electrons captured by the electric field, Ɛ(X,Y) and the electron concentration n(X,Y) at each position in the oxide film according to equation 1. Here, ƐC and nc represent the critical electric field and electron concentration at which the deterioration starts, respectively, and 0.5 M V/cm and 1x1010 /cm3. ƐC represents the minimum energy required for metastable transition to the metastable state, and nc is a threshold value that rapidly increases the probability of occurrence of this event. These parameters can be very important physically, but they are now empirically derived from the measurement results.

Figure 1
(Invited) Challenges and Opportunities for High-K Dielectrics for Advanced Technology Nodes
Authors: Tapily Kandabara , Clark Robert D. , Consiglio Steven , Niimi H , Triyoso D. , Wajda Cory S. , Leusink Gert J.
Published: February 2020

The relentless downscaling of the semiconductor device feature sizes has resulted in tremendous technological advances such as mobile/portable electronics, internet of things (IOT) just to name a few. New device engineering and dielectric materials with engineered properties are becoming essential in overcoming the issues seen in scaled CMOS devices such as short channel effects (SCE). Mobile device, automotive, IOT, big data, and machine learning will be the growth drivers of the semiconductor industry for the next decades to come. These applications will not be successful without new materials, novel processing and integration schemes. There have been several innovations recently in reducing power such as FinFETs, nanosheets, and nanowires. However, the power supply voltage has not significantly scaled below ~1V due to the physical limitation in transistor operation known as Boltzmann limitation which dictates the inability of scaling down the voltage require to increase the transistor drive current by a decade also known as the subthreshold swing (SS) below 60mV/decade. One solution investigated by device makers and foundries is ferroelectric FET (FeFET). The ferroelectric material acts as a transformer boosting the input voltage hence overcoming the Boltzmann limitation or SS below 60mV/decade. Several scaling boosters are being studied to enable further device performance improvement such as self-aligned gate contact, fully self-aligned via, negative capacitance. In this presentation, applications and challenges associated with implementing high-k dielectrics will be discussed.
Controlled Electrochemical Synthesis of Ag Nanoparticles and Their Morphology-Dependent Performances on Catalysing Hydrogen Evolution Reactions
Authors: Ma Yue , Rosillo-Lopez Martin , Cai Xiaosheng , Hadzifejzovic Emina , Foord John S.
Published: February 2020

Hydrogen evolution reaction (HER) is one of the most critical reactions in fuel chemistry to produce clean and sustainable hydrogen gas as a renewable energy source. Nowadays, HER has always been catalysed with costly Pt or Pd metal1. To reduce the cost but still maintain a satisfactory performance, studies on Pt/Pd free catalysts for HER have never ceased. In the present work, we explore the electrodeposition of three morphologies (polyhedral, dendritic, and spherical) of Ag nanoparticles on boron-doped diamond electrodes (BDDEs) in various electrochemical conditions including deposition potential and deposition time. Specifically, by varying the deposition potentials of the single-stepped electrochemical deposition, a morphological change from polyhedral to homogeneous dendritic Ag was observed. The high deposition potential would drive the formation of dendritic Ag, which is a thermodynamically unfavourable structure with high surface energy. On the other hand, a two-stepped deposition mechanism was performed to synthesize spherical Ag nanoparticles. This two-stepped mechanism, which was used in synthesising small Au nanoparticles with high coverage by F. Bottari et al., contains a nucleation step at a more negative potential, and a growth step at a less negative potential.2 The sizes of each type of Ag nanoparticles were confirmed by Scanning Electron Microscopy (SEM), and the surface compositions were verified by X-Ray Photoelectron Spectroscopy (XPS). The current densities for HER catalysis were investigated using Linear Sweep Voltammetry (LSV), and a connection between morphologies and catalytic activities was drawn. All three types of Ag modified BDDEs showed better catalytic performance compared to that of drop-coated colloidal Ag-BDDE with comparable coverage and bare BDDE. Notably, spherical Ag-NP modified BDDE with an average particle diameter of 75nm has the highest percentage of pure elemental silver and showed the best performance as well as high stability in HER catalysis, which can be a less expensive yet efficient alternative for Pt/Pd containing catalysts.

References:

Walter, M.; Warren, E.; McKone, J.; Boettcher, S.; Mi, Q.; Santori, E.; Lewis, N. Chemical Reviews2010, 110, 6446-6473.

Bottari, F.; De Wael, K. Journal of Electroanalytical Chemistry 2017, 801, 521-526.
Electrochemical Nanostructuring of Electrodeposited Cu2o Thin Film for Efficient Hydrogen Reduction
Authors: Singh Akhilender Jeet , Das Chandan , Aggarwal Garima , Balasubramaniam Kavaipatti Ramanathan
Published: February 2020

Cu2O is an intrinsic p-type semiconductor with a direct bandgap of 2 eV and its conduction band edge lies 0.7 V negative of hydrogen reduction potential which makes it a promising photocathode for water splitting. This study emphasizes the modification of the surface of Cu2O thin films to facilitate the separation of photogenerated charge carriers as well as increase the electrode-electrolyte contact area. Mesoporous Cu2O is realized by holding a thin film of electrodeposited Cu2O at a positive potential (0.4 V ‒ 1 V vs. Ag/AgCl) in buffered Na2SO4 (pH 5) . The treated films are found to have mesoporous structure with 10-30 nm thick flakes on its surface. No phase change is observed in electrochemically treated Cu2O thin films although the XRD intensities of all peaks are slightly lower indicating material loss. This morphological conversion is attributed to Cu2O dissolution in acidic media as trace copper ions are detected in the solution. The modified Cu2O photocathode can lead to a better device performance due to increased surface area and improved charge transport.

Figure 1
A Mathematical Model of Reduction Potentials of Lanthanide Alloys Correlation with Atomic Radius and Electronegativity Based on the Hume-Rothery Rules
Authors: Yan Yongde , Wang Chunqi , Wang Pu
Published: February 2020

To achieve closed nuclear fuel cycle and sustainable development of nuclear energy, efficient pyroprocessing of spent fuel becomes one of the major concerns in Generation IV nuclear energy [1]. Molten salt based electrolysis is a promising method in future pyroprocessing technology. As neutron poison, lanthanides are the typical detrimental elements that encumber the realization of the so-called partitioning & transmutation (P&T) strategy, and thus must be separated from actinides [2]. Therefore, investigating the electrochemical properties of actinides and lanthanides is of pivotal importance. In fact, in light of the chemical similarity of trivalent actinides and lanthanides, the chemistry of actinides can be revealed somewhat through exploring the lanthanide elements which are more readily obtained [3, 4].

In this work, it was found that the reduction potentials of Cu(Ni, Al, Zn)-rich Cu(Ni, Al, Zn)-Ln alloys manifest an evident “Bimodal Effect”. Hume-Rothery rules pointed out that the main factors affecting the formation of alloy solid solution of two metal elements are: 1) the difference of the atomic radius of the solvent and the solute metals, and 2) the electronegativity difference between the solvent and the solute metals. By fitting the data of reduction potentials, differences of the atomic radii and electronegativity differences, a formula was built up, which provides a useful and reliable approach for predicting related important reduction potentials of actinide alloys. The result of multiple linear regression analysis (Fig. 1) indicated that the good reliability of forecast and goodness of fit.

Acknowledgments

This paper is funded by the International Exchange Program of Harbin Engineering University for Innovation-oriented Talents Cultivation.

References

[1] S. V. Perumal, B. P. Reddy, G. Ravisankar, K. Nagarajan, Actinides draw down process for pyrochemical reprocessing of spent metal fuel, Radiochim. Acta 103 (2015) 287–292.

[2] K. O. Kim, J. K. Kim, A study on artificial rare earth (RE2O3) based neutron absorber, Appl. Radiat. Isot. 105 (2015) 52–59.

[3] S. Vandarkuzhali, N. Gogoi, S. Ghosh, B. P. Reddy, K. Nagarajan, Electrochemical behaviour of LaCl3 at tungsten and aluminium cathodes in LiCl–KCl eutectic melt, Electrochim. Acta 59 (2012) 245–255.

[4] B. Y. Kim, D. H. Lee, J. Y. Lee, J. I. Yun, Electrochemical and spectroscopic investigations of Tb(III) in molten LiCl–KCl eutectic at high temperature, Electrochem. Commun. 12 (2010) 1005–1008.

Figure 1
Theory of Ionic Liquids in the Bulk and at the Interface
Authors: Schammer Max , Horstmann Birger , Latz Arnulf
Published: February 2020

Theoretical studies and simulations are efficient means for the evaluation of materials and for improving the design of electrochemical devices [1]. Here, we present a thermodynamically consistent transport theory of ionic liquids. Our approach is based on a continuum framework and rigorous physical assumptions and we derive a set of coupled transport equations for the ions, charge and heat, based on modeling methodologies for lithium-ion batteries [2]. It describes the bulk phase of ionic liquid electrolytes. In addition, we incorporate microscopic interactions into our transport theory.

Upon this framework we model a zinc-ion battery with a mixture of ionic liquid and water as electrolyte, described experimentally in Ref. [3]. The battery is simulated along one dimension and good agreement with the experimental observations is found (see Figure, left). We integrate the particle nature of the medium into our transport theory. Near electrified interfaces, this leads to crowding and overscreening [4] for neat ionic liquids (see Figure, right). Recently, we have examined the influence of a minor additive species (Ag[TFSA]) on the interfacial structure of the neat ionic liquid Pyr[TFSA] in a joint experimental/theoretical study [5]. Our theory predicts the minimal minor salt concentration which is needed to destroy the layered structure. The theoretical predictions are in good agreement with experimental observations.

This work was supported by the Federal Ministry of Education and Research via the project “Zinc/Air Battery with Advanced Materials for Storage of Renewable Energies and Grid Balancing” (LUZI).

References:

Clark, A. Latz, B. Horstmann, Batteries, 4 (2018), 5. doi:10.3390/batteries4010005.

Latz et al., Beilstein Journal of Nanotechnology, 6 (2015), 987–1007. doi:10.3762/bjnano.6.102.

Endres et al., ACS Applied Materials and Interfaces, 8 (2016), 12158–12164. doi:10.1021/acsami.6b01592.

Bazant, et al., Physical Review Letters, 106 (2011), 046102. doi:10.1103/PhysRevLett.106.046102.

Hoffmann, M. Schammer, F. Endres et al., Physical Chemistry Chemical Physics, 20(2018),

Figure 1
In-Situ Seiras Observation of Co Electrodeposition in an Ionic Liquid: Correlation between the Reaction and Interfacial Restructuring
Authors: Motobayashi Kenta , Shibamura Yuhei , Ikeda Katsuyoshi
Published: February 2020

Room temperature ionic liquids (RTILs), promising electrolyte materials for various electrochemical applications, requires molecular level description of their structures at the interface where electrochemical reactions occur. Recently, our studies using surface-enhanced infrared absorption spectroscopy (SEIRAS) that can selectively probe solid/liquid interfaces revealed that the first ionic layer is so rigid that a certain overpotential is required to change the adsorbed ions [1]. Therefore, the rigid first ionic layer possibly inhibits redox species from adsorption onto the electrode surface, which is the initial step of electrochemical reactions; however, no direct experimental evidence for such inhibition has been reported. For uncovering the correlation between electrochemical reactions and interfacial structures of RTILs, we measured electrochemical current and SEIRA spectra simultaneously during potential scans under reaction conditions of Co electrodeposition.

SEIRA spectra recorded for a polycrystalline Au electrode in neat [C3mpy][TFSA] (Fig.1) during potential scans showed hysteretic potential dependence, indicating the requirement of a certain overpotential for anion-cation exchange in the first ionic layer in analogy with the other RTILs [1]. SEIRA spectra for a Au electrode in [C3mpy][TFSA] containing 0.1 M Co(TFSA)2 indicated that the anion-cation exchange starts at -0.8 V vs Pt during a negative-going scan. Simultaneously observed CV shows the onset potential of Co electrodeposition at the same potential as shown in Fig. 1. It suggested that the anionic first layer prevent Co2+ from adsorption onto the electrode and thus electrodeposition did not start, and partial mixing of the first ionic layer triggered the adsorption and reduction of Co2+. This is the first direct observation of the correlation between electrochemical reactions and potential-induced interfacial restructuring of RTILs.

[1] K. Motobayashi et al., Electrochem. Commun. 100, 117 (2019).
Solvation Properties of Silver and Copper Ions in a Room Temperature Ionic Liquid: A First-Principles Study
Authors: Pham Tuan Anh , Horwood Corie , Maiti Amitesh , Peters Vanessa N. , Stadermann Michael
Published: February 2020

Understanding the behavior of metal ions in room temperature ionic liquids (ILs) is essential for predicting and optimizing performance for technologies like metal electrodeposition; however, many mechanistic details remain enigmatic, including the solvation properties of the ions in ILs and how they are governed by the intrinsic interaction between the ions and the liquid species. Here, we utilize first-principles molecular dynamics simulations to unravel and compare the key structural properties of Ag+ and Cu+ ions in a common room temperature IL, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate. We find that, when compared to Cu+, the larger Ag+ shows a more disordered and flexible solvation structure with a more frequent exchange of the IL species between its solvation shells. In addition, our simulations reveal an interesting analog in the solvation behavior of the ions in the IL and aqueous environments, particularly in the effect of the ion electronic structures on their solvation properties. This work provides fundamental understanding of the intrinsic properties of the metal ions in the IL, while offering mechanistic understanding and strategy for future selection of ILs for metal electrodeposition processes.
Electrochemical Precipitation of Struvite in Acidic Environment: Pure Magnesium Vs. AZ31 Alloy Anode
Authors: Kékedy-Nagy László , Herring Andrew M. , Pollet Bruno G. , Greenlee Lauren F.
Published: February 2020

Nutrient recovery from phosphorus-rich wastewater streams is essential to reduce environmental impacts and to improve the sustainability of fertilizer production globally. One potential approach is to recover phosphates by electrochemical precipitation of struvite, also known as magnesium ammonium phosphate hexahydrate (MgNH4PO4*6H2O). Struvite is considered a premium grade, slow-release fertilizer, which is a potentially marketable product for the fertilizer industry. The effect of pure-Mg versus AZ31 magnesium alloy as the only source of magnesium on anodically-driven struvite precipitation was investigated in a single-cell electrochemical batch reactor with no pH adjustment, in acidic environment. The results showed an elongated needle-shaped pattern with smooth sharp edges which indicates a high-quality pure struvite and a particle size of ca. 30 µm in length, ca. 6.5 µm in width. In a 6 h batch experiment, the pure-Mg anode out-performed the AZ31 alloy by producing a 4.5-fold greater mass of struvite, next to a 2.8-fold higher current density. The measured magnesium dissolution rates were 1.2 mg cm-2 h-1 for the pure-Mg and 0.8 mg cm-2 h-1 for the AZ31 magnesium alloy anode, respectively. Overall, in this electrochemical reactor setup, the pure-Mg anode showed a better performance towards the electrochemical struvite precipitation.
Modeling of Industrial Electroplating Processes with Comsol Multiphysics in Order to Optimize Treatment of Complex Parts
Authors: Fedi Baptiste , Canals-riclot Jef , Hihn Jean-Yves
Published: February 2020

Electroplating processes are widely used on several aeronautical applications to confer functional properties (electrical conductivity, tribological, anti-corrosion). In this industrial context, it is possible to keep the desired properties by respecting specifications such as thicknesses and coating composition for alloys. However, it is well-known that phenomena intrinsic to electrochemical processes create heterogeneities, especially on complex geometries like landing gears.

Industrially, the treatment of these disparities is part of the know-how of the workshops, and they are balanced by complex auxiliary tools in order to obtain a more uniform local current densities distribution, and therefore coating thickness. The development of these specific anode shapes is time-consuming and depends strongly of an empirical know-how. The numerical simulation of electrochemical processes is developed at Safran Tech in collaboration with Institute Utinam to optimize the development of plating tools at industrial scale with ComsolÒ Multiphysic software. The global objective is to improve the reliability of the existing systems, and moreover to enhance the innovation by facilitating new coatings integration. This is crucial in the context of tightening of environmental REACH regulations, such as the substitution of cadmium by zinc-nickel.

Modeling industrial electroplating processes by a secondary current distribution model is evaluated in terms of thickness prediction by a comparison with experimental results at a laboratory scale pilot. It has been emphasized that the main limitation are due to the failure to take full account of mass transport induced by convection.

The study also participate to the development of good practice for auxiliary tools design, and the simulation demonstrate invaluable assistance in industrial operations.

Figure 1
Water Splitting in Brine: Engineering Electrolytes for Active, Stable, and Tunable Photoelectrochemical Cells
Authors: Mu Linchao , Tarpeh William Abraham
Published: February 2020

Solar-driven water splitting is a promising source of renewable energy, but faces several obstacles to widespread implementation, including photoelectrocatalyst activity, stability, and control. While current remedies focus on improving catalysts themselves (e.g., fabricating protective layers, modifying surfaces for higher activity), engineering electrolyte remains an underutilized strategy for tuning properties of photoelectrochemical cells (PECs). The goal of this project is to leverage aqueous chemistry to increase activity, stability, and control of photoelectrocatalysis. We demonstrate that saline waters increase activity (as cathodic H2 and anodic O2 production) through increased conductivity, and employ varying concentrations of NaCl electrolyte. To increase stability, we add aqueous buffer species such as carbonate, acetate, and ammonia to resist extreme pH changes that can degrade electrodes. We investigate tunability of PEC performance by changing electrolyte pH, organic content, and silica concentrations. Ultimately, we investigate mechanistic impacts of aqueous species in a TiO2/MoS2 PEC (standard photoelectrodes) through experiments with synthetic electrolytes of controlled composition; we also aim to establish proof-of-concept for photoelectrocatalytic energy production in desalination brines, an underutilized waste stream.
A Rational Asymmetric Hollow Fiber Membrane for Oxygen Permeation
Authors: Ren Chunlei , Gan Yun , Yang Chunyang , Lee Myongjin , Xue Xingjian
Published: February 2020

A typical oxygen permeation hollow fiber membrane fabricated by phase inversion‐based extrusion process demonstrates heterogeneous porous microstructures, in which the surface layer with relatively low porosity is used as a separation layer after sintering. It is usually not convenient to control the thickness of separation layer. And a high sintering temperature is needed to densify the separation layer, which in turn could destroy the desired porous microstructures in other portion. This paper studies a novel process to fabricate multilayer asymmetric hollow fiber membrane with a rational design using 67 vol. % Gd0.2Ce0.8O2−δ−33 vol. % La0.6Sr0.4Co0.2Fe0.8O3−δ (GDC‐LSCF) as a model material system. The phase inversion‐based extrusion process in open literature is employed to fabricate a hollow fiber substrate featuring radially well‐aligned microchannels open at the inner surface. Built upon the hollow fiber substrate, a thin dense separation layer and porous surface catalyst layer at shell side are then fabricated through dip‐coating and sintering process alternatively. The oxygen permeation flux of the fabricated hollow fiber membrane reaches 2.68 mL/cm2/min at 900°C under Ar/air gradient, the highest performance of the membranes with GDC‐LSCF material system in open literature. The innovative fabrication process is able to readily control the thickness of functional layers while decreasing sintering temperatures.
A Novel Three-Dimensional Desalination System Utilizing Honeycomb-Shaped Lattice Structures for Flow-Electrode Capacitive Deionization
Authors: Cho Younghyun , Kim Dong Kook
Published: February 2020

Capacitive deionization (CDI) technology has attracted a great deal of attention over the past few decades due to its high energy efficiency (less than 1 kWh/m-3) compared to conventionally utilized reverse osmosis (2–4 kWh/m-3) and distillation based (50–80 kWh/m-3) desalination technologies. However, due to a couple of issues including cost and requirement for a disruptive discharging step, it has been regarded as a challenging task to perform large-scale desalination of seawater by the CDI process. Herein, we report a novel design for a 3D desalination system utilizing porous lattice scaffolds. It can desalinate water as salty as sea water (35 g/L) with desalting efficiency comparable with conventional flow-electrode-based CDI (FCDI). By coating of ion exchange membranes and a graphene layer inside each channel of the lattice structures, honeycomb-shaped desalination cells could be realized. First, the desalination performance of the new design was investigated in batch mode. It exhibited comparable desalting performance while maintaining typical advantages of FCDI systems, such as low energy consumption and no need of a discharging step. Furthermore, since the porous structures involve channels for ion transportation and act as a structural scaffold, the cell architecture is remarkably compact and it can be readily scaled-up by varying the number of unit cells and its configuration, allowing great increase in the salt removal capacity. We scaled-up the desalination system to a 3 × 3 cell, which showed desalination efficiency four times higher than that of a 1 × 3 cell. Such facile build-up of the unit cell structure and versatile design of cell configuration provide strong potential for further scalability. We also determined that this system can be operated successfully in continuous mode, indicating that neither a distinct discharging step nor substitution of inflow and effluent are required. Because there is opportunity for much more improvement of desalting performance in terms of the electrode materials, resistance at the interface, and conductivity of the current collecting layer of this system, we expect that our approach has opened a new door in the field of desalination research.
(Keynote) Beta Alumina – Prelude to a Revolution in Solid State Electrochemistry
Authors: Whittingham M. Stanley
Published: February 2020

In 1971 Bob Huggins and I presented a paper at NBS, titled as above*. Little did we realize how prophetic our title would be. The remarkable ion transport properties of the beta alumina family not only led to searches for other ion conducting solids, but also to the use of mixed conducting materials as electrodes for electrochemical cells and shortly thereafter to the use of mixed conducting intercalation compounds for rechargeable lithium batteries.

The studies at Stanford identified several key parameters that control the ionic conductivity of such ions as Na+, Ag+, Cu+, Li+, K+, Tl+and NO+. These parameters include the ionic size, the lattice spacing (diffusion path size), the defect concentration, defect type and diffusion mechanism. Later, similar studies on the WO3, MoO3, TiO2and VOPO4materials, all of which exist in several different structures with varying molar volumes, show the criticality of matching the diffusion path size to the mobile cation. The learnings from these studies will be described.

*NBS Special Publication 364, Washington DC: U.S. Department of Commerce and National Bureau of Standards, 1972, 139-154
(Invited) Progress in Solid State Ion Conductors- Have You Made Any Significant Impact?
Authors: Thangadurai Venkataraman
Published: February 2020

Currently, solid state (ceramic) ion conductors are being considered to replace conventional liquid and gel electrolytes in numerous electrochemical energy technologies such as batteries due to their high voltage and chemical-thermal stabilities. There are several family of inorganic crystalline and amorphous compounds discovered as fast ion conductors since 1950. However, their application in modern devices are limited today. Only a few solid ion conductors have been used in commercial electrochemical technologies. This talk will report milestones in solid state ionics, including Professors Huggins’s key contributions.
Understanding and Engineering Interfacial Transport in K-β′′-Alumina at Room Temperature
Authors: Baclig Antonio C , McConohy Geoff , Kong Nathan , Chueh William C
Published: February 2020

Aided by Prof. Huggins’s contributions1, the research and development of sodium beta-alumina solid electrolytes led to the commercialization of the molten sodium-sulfur battery, used today for grid-scale energy storage. Sodium-sulfur and ZEBRA batteries typically operate above 300 °C, and recent efforts have explored lowering the operating temperature to 100-200 °C2–4. The melting point of sodium is 98 °C, but its alloy with potassium (Na-K) has a eutectic melting point of -13 °C and is a liquid metal at room temperature with a capacity in the liquid region of 580 mAh/g (using K). Na-K has seen recent attention for batteries with organic electrolytes5 as well as for flow batteries using K-β′′-alumina 6, since polycrystalline sodium beta-alumina is not compatible with Na-K.

A key challenge in using beta-alumina at low temperatures is transport through the interfaces. We discuss transport through the interfaces in a Na-K — K-β′′-alumina — aqueous potassium ferrocyanide (model posolyte) battery. On the Na-K — K-β′′-alumina interface, although Na-K does not wet K-β′′-alumina at room temperature, we find a form of reactive wetting, given certain conditions, that nearly eliminates the interfacial resistance between Na-K and K-β′′-alumina. On the aqueous posolyte — K-β′′-alumina interface, we find that ion exchange of hydrogen/hydronium species and K+ increases the interfacial resistance substantially over time, but this can be greatly decreased through modifying the solution chemistry.7 Understanding and engineering the interfaces of beta-alumina may enable novel applications of this amazing fast ionic conductor at low temperatures.

References

Whittingham, M. S. & Huggins, R. A. J. Chem. Phys.
54, 414 (1971).

Lu, X. et al.
Energy Environ. Sci.
6, 299–306 (2013).

Lu, X. et al.
Nat. Commun.
5, 4578 (2014).

Li, G. et al.
Nat. Commun.
7, 10683 (2016).

Xue, L. et al.
Adv. Mater.
28, 9608–9612 (2016).

Baclig, A. C. et al.
Joule
2, 1287–1296 (2018).

McConohy, G. et al.
Solid State Ionics
337, 82–90 (2019).
(Invited) A Critical View on the Application of Distribution of Relaxation Times
Authors: Boukamp Bernard Abraham
Published: February 2020

Electrochemical Impedance Spectroscopy (EIS) has been an important tool in Solid State Ionics since the sixties of the 20th century. Evolving from graphical analysis to fully automated Complex Nonlinear Least Squares analysis (CNLS), it has contributed to a better understanding of charge and mass transfer and storage processes in solid state devices, e.g. batteries, sensors, fuel cells etc. In many cases the use of an Equivalent Circuit (EqC) gave access to important materials parameters. Due to the increasing complexity of e.g. electrodes, it is not always simple to find an appropriate EqC. The transformation of the impedance spectra to a distribution of relaxation times in the τ-domain has gained increased attention over the last decades, as it is seen as a model independent representation. The main problem, however, is that this transformation is an ill-posed inverse problem. Various methods (e.g. FFT, Tikhonov Regularization, Max Entropy) have been designed to provide the distributions, but they all require adjustment of a ‘smoothing’ parameter. In this presentation the advantages and limitations of the use of a DRT will be presented with selected practical examples.
(Invited) “Decrepitation” and Mechanical Degradation: In Situ Investigation to Understand Chemo-Mechanical Stability in Batteries
Authors: McDowell Matthew T
Published: February 2020

Mechanical degradation and fracture have long been recognized as challenges that have impeded development of large-volume-change electrode materials that exhibit stable cycling behavior. Bob Huggins (along with Bill Nix) was among the first to quantify mechanical fracture and “decrepitation” or fracture processes in alloying anode materials, predicting that fracture during electrochemical reaction should be dependent on particle size, among other variables [1]. In recent years, our understanding of how reaction processes relate to mechanical degradation in battery materials has advanced significantly, and in situ/operando experimental techniques have been key for this progress. Here, I discuss my group’s recent efforts in understanding chemo-mechanical degradation in battery materials. First, in situ transmission electron microscopy (TEM) experiments are presented in which individual nanocrystal electrode materials are observed to react with various alkali ions (Li+, Na+, and K+). For FeS2 nanocrystals, the reaction with all three ions involves conversion to form a mixture of phases, along with volume expansion. Despite larger volume changes during reaction with Na+ and K+, only reaction with Li+ was observed to cause fracture. This surprising result was found to be due to the shape of the reaction front as it evolves during reaction, with sharp corners during lithiation resulting in stress concentration and fracture. In addition to this work, other in situ TEM investigations of reaction processes in metal alloying anode nanocrystals have revealed the importance of the mechanical properties of the native oxide in determining transformation pathways during electrochemical cycling. Finally, our research on chemo-mechanical degradation at interfaces within solid-state batteries will be briefly discussed. This work points to the necessity of understanding and controlling chemo-mechanical phenomena in high-capacity battery materials for developing next-generation battery materials.

[1] R. A. Huggins, W. D. Nix “Decrepitation Model for Capacity Loss During Cycling of Alloys In Rechargeable Electrochemical Systems” Ionics, 2000, 6, 57.
Electrochemical Dewatering of Cellulosic Nanomaterials
Authors: Vijapur Santosh H. , Hall Timothy D. , Taylor E. J. , Inman Maria , Snyder Stephen , Nelson Kim
Published: February 2020

Cellulosic nanomaterials exhibit great potential in various applications due to their unique properties, abundant availability, and low production cost. Although cost effective to produce it is costly to ship, primarily due to the excess of water (>95 wt.%) in growth media necessary to produce the cellulosic nanomaterials. Therefore, a need has been identified by cellulosic material providers to develop energy-efficient, dewatering or drying of cellulosic nanomaterials, “as cellulosic nanomaterials are not economical to ship long distances while containing significant water content”. Moreover, the dewatered or dried cellulosic nanomaterials should be readily re-dispersed in water without any changes in its functional properties.

Faraday Technology in collaboration with AVAPCO, answer this need by developing an economical manufacturing method and apparatus for electrochemical dewatering of cellulosic nanomaterials including cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs). Specifically, our innovation is directed towards dewatering of CNCs and CNFs, not drying. AVAPCO has indicated that dewatering to 20-30 wt.% solids would be the end product for numerous applications such as cosmetics and paper processing. Using innovative reactor designs, we demonstrated the feasibility of a cost-effective, industrially viable, and energy efficient ElectroDewatering approach capable of generating 20 wt.% final solids, that was rehydrated under vortex and confirmed for re-dispersibility. Material properties (structure, particle size) were maintained by the dewatered cellulosic nanomaterials. Implementing sophisticated electric fields, we reduced energy use by 50% compared to conventional constant voltage approaches at similar or higher dewatering performance. Specifically, this talk will discuss the results of these advancements.

Acknowledgements: The financial support of DOE Contract No. DE-SC0018787 is acknowledged.
Pulse Reverse Current Cr+3 Deposition for Wear Applications
Authors: Hall Timothy D. , Taylor E. J. , Inman Maria , Snyder Stephen , Xu Jing , Radhakrishnan Rajeswaran
Published: February 2020

Faraday Technology Inc. is a research, development and engineering firm developing electrochemical innovations based has pulse/pulse reverse electrolytic principles [1]. One of Faraday’s current activities is directed towards the development of an innovative functional REACH compliant chrome plating process based on a trivalent chromium electrolyte to replace hexavalent chromium plating. Hexavalent chromium plating has been used for many decades to provide hard, durable coatings with excellent wear and corrosion resistance properties. However, hexavalent chromium has come under increasing scrutiny due to the toxic nature of the bath, effects on the environment, and workers’ health. Faraday has demonstrated that the chrome coatings prepared using the FARADAYIC(R) Process have equivalent functional properties to the coatings produced with a hexavalent chromium bath. The data demonstrates equivalent or superior: 1) plating rate, 2) Knoop hardness, 3) current efficiency, 4) hydrogen embrittlement behavior, 5) adhesion, 6) corrosion resistance, 7) porosity, 8) thickness, 9) Taber Abrasion, Ball on Flat Reciprocating and Dithering wear resistance, and with no hexavalent chromium formation in the bath.

Therefore, this paper will discuss the 2013 EPA Green Chemistry Challenge Award winning work on the development of a REACH compliant functional trivalent chromium plating process from a single, simple-to-control trivalent-based electrolyte to replace hexavalent chromium plating. Furthermore, it will specifically discuss electrochemical deposition approaches to improve the wear index and microstructure of the coating.

Acknowledgements: This study is supported by the US Army (W911NF-11-2-0014) and private sources.

[1] E. J. Taylor “Adventures in Pulse/Pulse Reverse Electrolytic Processes: Explorations and Applications in Surface Finishing” J. Applied Surface Finsihing,
3(4), 178-189 (2008).