Thin Electrolyte Layer Research Articles

Optimization of Lithium Content and Sintering Additives in Tape Cast Lithium Garnet Electrolyte Sheets

The lithium garnet (LLZO) remains one of the most promising electrolyte materials for producing solid state batteries. Tape casting is one method for producing the thin ceramic electrolyte layer required for a high-performance solid state battery. Processing of LLZO is complicated by several factors including lithium volatilization, abnormal grain growth and phase instability. Many of these issues are exacerbated in tape cast sheets by the sheets’ higher surface area to volume ratio, when compared to pellet processing methods. We report on an environmentally friendly aqueous tape casting process for LLZO using methylcellulose as a binder and compare final sheet properties to other, solvent-based, options. Solids loading, binder content, dispersant composition, and wetting agent type are varied to improve ease of casting and enhance properties of the as-cast tape. Lithium content in sintered LLZO sheets is controlled by the inclusion of excess Li2CO3 as lithium source in the ceramic tape itself and by a novel method of producing a lithium-saturated furnace atmosphere. Sintering time and temperature are optimized, and rapid thermal processing is investigated as a method of reducing lithium loss. Al2O3 and MgO are examined for use as sintering additives. Characterization of LLZO sheets is performed with XRD, EIS and SEM. Li2CO3 and sintering additive levels are optimized for ionic conductivity and density. The optimization effort improved the conductivity and density of 100µm thick sintered sheets to greater than 3x10-4 S/cm conductivity and 90% density. Figure 1

(Invited) All-Solid-State Batteries Using Li7La3Zr2O12 Garnet Electrolyte Framework

All-solid-state batteries (ASSB) using LLZO (variants of Li7La3Zr2O12) garnet solid electrolyte with lithium metal anode potentially offer higher energy density and improved safety. Rational design of cell architecture as well as manufacturing scalability are key aspects to consider as the technology readiness level advances. A thick composite cathode layer attached to a thin solid electrolyte layer is desirable to obtain superior energy densities. Furthermore, the architecture within the composite cathode may be engineered to contain directional conduction paths of lithium ions or electrons for enhanced rate capabilities.Here, we demonstrate a functioning bulk-type LLZO based all-solid-state battery with a practical form factor incorporating the above described design concepts. Freeze-tape-casting (FTC), a scalable and environmentally friendly ceramic processing method, is used to construct 3D porous LLZO scaffolds composed of vertical arrays of LLZO walls. The thin solid-electrolyte layer is fabricated by tape-casting (TC). By sintering the stacks of FTC and TC green tapes, porous/dense bilayers and porous/dense/porous trilayers of LLZO frameworks are obtained. An ASSB was constructed using a porous/dense bilayer by infiltrating LiNi0.6Mn0.2Co0.2O2 cathode powder and carbon black into the porous layer and adhering lithium metal foil to the dense side. We find it crucial to introduce a plastic crystal based soft solid electrolyte to the porous layer to electrochemically connect all cathode components, obviating the need for co-sintering to establish contact. The soft nature of the plastic crystal based solid-electrolyte may be able to accommodate the volume change of the cathode material as it cycles. In this device, which contained no liquid component, the initial discharge capacities were similar to those observed in a lithium ion battery configuration using the same cathode powder at C/10 rates.

Design and Performance of a Full Functional Electrochemical Cell for Lab Scale in-Situ GI-XRD Instruments

In-situ XRD may support electrochemical measurements by delivering analytical information about electrochemical processes. Since structural changes at the electrode/electrolyte interface are of specific interest, measurements are done usually in small angle reflection mode geometry. The surface sensitive grazing incidence – XRD (GI-XRD) in-situ technique allows the detection of short-lived electrode reaction products or products sensitive to ambient atmosphere exposure. This method finds applications for quite a number of investigations of electrochemical processes including corrosion, film growth and deposition, reconstruction of superficial regions, ion insertion battery materials, etc. The common cell designs for lab scale XRD equipment use thin electrolyte layers to avoid unacceptable beam intensity loss through water. The use of synchrotron radiation would reduce this shortcoming to some extent but is much less accessible.In 1986, Fleischmann et al. presented an in-situ XRD thin layer cell in reflection as well as in transmission mode, where a X-ray transparent Mylar foil was used as window material [1]. However, this geometry restricts the positioning of counter and reference electrodes and therefore has unfavorable current density distribution, has very small electrolyte volume, is vulnerable to side reactions with gas evolution and does not allow high flow rates for the solution. Thus, the general applicability is limited.In our proposed in-situ cell design for GI-XRD, the electrochemical cell is fully functional, avoiding all of the above mentioned drawbacks [2]. The solution of this issue is the "backside-illumination" (or "inverse" illumination) of a thin film working electrode applied on a thin polymer foil as a support by the X-ray beam at a small incident angle. On the opposite side a conventional electrochemical cell with reference electrode and counter electrode and sufficient solution volume can be used. The big advantage of this design is that the X-ray only has to penetrate the foil and the thin layer of electrode material resulting in high signals from the region of interest. It is used with a conventional laboratory X-ray source and does not need high intensity synchrotron radiation. With this cell design, problems with bulk solution resistance, inhomogeneous current-density distribution, insufficient bath agitation or gas evolution as side reaction are eliminated.In this contribution, details of the cell design, analysis of current density distribution within the thin current collector and the electrochemical cell, results of calibration measurements and measurements on copper as an example for a galvanic deposition/dissolution process are presented.[1] M. Fleischmann, A. Oliver, and J. Robinson, ‘In Situ X-ray diffraction studies of electrode solution interfaces’, Electrochimica Acta, vol. 31, no. 8, pp. 899–906, (1986)[2] S. Reither, W. Artner, A. Eder, S. Larisegger, M. Nelhiebel, C. Eisenmenger-Sittner, G. Fafilek, ‘On the In-Situ Grazing Incidence X-Ray Diffraction of Electrochemically Formed Thin Films’, ECS Transactions, 80 (10) 1231-1238, (2017) 10.1149/08010.1231ecst Figure 1

(Corrosion Division Morris Cohen Graduate Student Award Address) A Systematic Study of Critical Parameters Affecting the Galvanic Corrosion between Al Alloy and Stainless Steel in Atmospheric Condition

Connections between dissimilar materials are frequently encountered in complex structures involved in the aerospace industry. In a typical aircraft structure, one of the most common couples encountered is that of an aluminum-alloy-based airframe component and noble fasteners such as stainless steel. When this type of galvanic couple is exposed to a atmospheric marine environment, it can develop cracks that pose increased risk and require costly maintenance and repair. In this work, a complementary modeling and experimental approach is applied to systematically investigate the effect of electrolyte layer thickness, solution chemistry and materials surface properties on the electrochemical and corrosion distributions in the galvanic coupling between AA7050 and SS316L, and capture the underlying mechanism of the dependence of corrosion distributions on each external variable.To validate the robustness of our modeling approach, a Laplace-Equation based modeling coupled using mathematically-fitted electrochemical kinetics from experiment as boundary conditions was applied to simulate galvanic corrosion between Zn plate and SS 316 rods under thin layer electrolyte conditions. The modeling results were compared with experimental results from a four-day modified B117 test. It shows that: electrolyte layer thickness (WL)=3,500~4, 000 \U0001d707m would be the appropriate WL range formed on the sample surface during modified B117 salt fog testing; the robustness of Laplace-Equation based modeling is highly dependent on the boundary conditions, experimentally-determined electrochemical kinetics as boundary conditions can truly reflect the electrochemical response of anode/cathode to the surrounding solution environment, which in turn yields the simulated results mostly close to experimental measurement.In the study of the effect of electrolyte layer thickness, the total cathode current capacity of a surface on the electrolyte film thickness and cathode size in a galvanic couple to support the corrosion of AA7050 was accessed. The total cathode current capacity was studied over the range of WL thickness from full immersion conditions (where the total cathode current scales directly with cathode size) to the thin film regime in which the WL is the diffusion boundary layer thickness. In order to fully assess the transition from thin film to thick film condition, an understanding of the natural convection layer thickness is required. For the conditions studied here, the natural convection boundary layer was found to be close to 800 um. The WL thickness, cathode length and electrochemical kinetics interact to create four regimes of total cathode current as a function of WL thickness.In the study of the solution chemistry, the effect of Al3+ on the electrochemical and galvanic corrosion distributions between SS316L and AA7050was emphasized as it represents the major dissolved metal species from AA7050. It is found that Al3+ accelerates the hydrogen evolution reaction (HER) kinetics due to enhanced proton diffusivity, with the effect being observed not only on Al alloys, but also on Pt and stainless steel. The cation study for the galvanic couple indicates that Al3+ is also galvanic corrosion accelerator.The effect of oxide film properties on the cathodic kinetics of stainless steel were investigated because cathodic kinetics can significantly affect the degree of galvanic corrosion based on mixed potential theory. The study focused on the oxygen reduction reaction (ORR) and was studied by electrochemical (potentiodynamic polarization, cyclic voltammetry, potentiostatic test, and electrochemical impedance) techniques and x-ray photoelectron spectroscopy surface analysis. This study shows that the kinetics of ORR on stainless steels is determined by a combined effect of oxide film composition, film thickness, and resistivity.This work has improved the fundamental understanding of the effect of several pertinent variables on the galvanic-coupling induced localized corrosion of Al alloy, provided an approachable modeling means to predict corrosion distribution at given conditions in a timely fashion as well as develop corresponding corrosion mitigation strategies, and complemented continuum/meso-scale atmospheric corrosion modeling studies in this field. Acknowledgements The financial support from the Office of Naval Research (ONR) via Grants No. N00014-14-1-0012 and No. N00014-17-1-2033, the Sea-Based Aviation Program, and William Nickerson, Program Manager is gratefully acknowledged. The assistance of my advisor, Prof. R. G. Kelly is gratefully acknowledged. Helpful technical discussions with Profs. S. J. McDonnell, J. R. Scully, and J. T. Burns (University of Virginia), Dr. Jayendran Srinivasan (the Ohio State University), Dr. Piyush Khullar (Medtronic), Dr. Veronica Rafla (SpaceX) and Mr. Victor Yang (University of Virginia) are also acknowledged.

On the local corrosion in a thin layer of electrolyte separating two materials: specific aspects and their contribution to pad-to-disk stiction in automobile brake system

The stiction phenomenon which results in the adhesion of the brake pad to the disc brake of a vehicle has been investigated from a corrosion point of view. Asbestos-free organic pad that contains copper associated with a cast iron disc was investigated and compared to a model system which consisted in a ceramic pad (chemically inert) associated with the same cast iron disc. The whole system was described as a thin-layer cell of electrolyte and was studied using different electrochemical methods including polarization curves and impedance spectroscopy. The influence of the cell geometry was pointed out, but the corrosion of the system is enhanced due to the presence of copper in the pad. Indeed, the copper dissolves from the pad and redeposits on the disc. This was confirmed by scanning electron microscopy observations and Raman spectroscopy. A mechanism taking into account the thin-layer geometry was then proposed to account for the role of metallic additive (in this case copper) on the corrosion of the disc.

Solid-State Lithium-Sulfur Battery Based on Composite Electrode and Bi-layer Solid Electrolyte Operable at Room Temperature

We report a unique solid-state lithium-sulfur cell based on a bilayer electrolyte and composite solid-state cathode. The bilayer electrolyte that contains a layer of mixed conduction membrane and a layer of polymer electrolyte eliminates the use of organic flammable liquid electrolytes and separators. The sulfur electrode is also a unique composite of sulfur with ionically-conducting intercalating nano-particulate material. Unlike many other solid-state batteries, this cell can be cycled at room temperature to utilize 85% of the active material at the sulfur electrode. The low internal resistance of the cell is comparable to that of a liquid electrolyte based lithium-sulfur cell. Impedance studies indicate that the low internal resistance results from the high ionic conductivity of the intercalating nano-particulate materials and the thin layer of polymeric electrolyte. While the volume changes at the cathode result in loss of inter-particle contact with repeated cycling, the addition of alumina to the polymer layer improved the capacity retention. This unique solid-state cell configuration opens a new pathway towards a safer high-energy lithium battery.

Quantitative study of the corrosion evolution and stress corrosion cracking of high strength aluminum alloys in solution and thin electrolyte layer containing Cl-

Stress corrosion cracking (SCC) behavior of 2024-T351 and 7075-T651 in solution and thin electrolyte layer (TEL) are investigated by electrochemical and mechanical testing, surface observation, and hydrogen detection. Corrosion in TEL is more severe than that in solution as indicated by the higher corrosion coverage fraction, deeper corrosion attacks, serious local exfoliation, and higher hydrogen uptake content. SCC susceptibility of 2024-T351 in TEL is higher than that in solution, while the 7075-T651 is the opposite. Corrosion-induced hydrogen dominates the degradation in TEL environment, while the synergistic effect of stress, corrosion, and hydrogen controls the elongation loss in solution.

Alternately stacked thin film electrodes for high-performance compact energy storage

High mass loading of active materials is crucial to improve the performance of electrochemical energy storage devices. However, high mass loading inevitably increases internal resistance, hinders electron conduction and ion diffusion, and ultimately leads to poor energy storage performance. Herein, a new type of supercapacitors with alternately stacked electrode configuration for high-performance compact energy storage is proposed, and fabricated by alternately stacking highly conductive MXene films as electrodes, and using a thin layer of gel electrolyte as an ionic carrier and a separator. The supercapacitor with 33-layer alternately stacked electrodes can achieve a high areal capacitance of 10.8 F cm −2 at the scan rate of 2 mV s −1 , and reach a record volumetric energy density of about 10.4 mWh cm −3 in an aqueous gel electrolyte system, much higher than that of the supercapacitor with two-electrode configuration under the ultra-high loadings of the active materials. The novel design of the electrodes towards next-generation energy storage devices, not limited to supercapacitors, would offer distinctive opportunities for the energy storage systems with high mass loadings of active materials, to achieve high areal and volumetric energy densities. A newly-structured supercapacitor with alternately stacked MXene films as electrodes and gel electrolyte as a separator for compact energy storage is demonstrated. This structure can shorten the ion transport path, and increase the mass loadings of active materials without sacrificing performance. A high areal capacitance about 10.8 F cm −2 and a high volumetric energy density up to 10.4 mWh cm −3 have been achieved. • A new-structured supercapacitor with alternately stacked MXene film electrodes is firstly introduced. • Alternately stacked configuration of the supercapacitor increases the mass loading of active materialwithout sacrificing power performance. • Alternately stacked configuration results in an enhanced volumetric energy density and an ultra-high areal capacitance. • Alternately stacked configuration offers insight into the improvement of energy storage performance at the device scale.

The mechanism of vortex instability in electromagnetically driven flow in an annular thin layer of electrolyte

A circumferential flow of a conducting fluid in an annular channel can be created by the action of a Lorentz force arising as a result of the interaction between an applied vertical magnetic field and a radial electric current flowing through the electrolyte. Quite unexpectedly, experiments revealed that a robust vortex system appears near the outer cylindrical wall in such flows. McCloughan and Suslov (J. Fluid Mech. 887:A23, 2020) (McCS) reported comprehensive linear stability results of such a flow for variable Lorentz forcing. Here we complement that study by investigating the flow structure as a function of the channel aspect ratio. Remarkably, despite the completely different physical nature of parametric dependences, dynamic in McCS and purely geometric here, we show that in both scenarios vortices appear on a background of a steady axisymmetric flow at the boundary between two counter-rotating toroidal structures and have a similar energy distributions. The two studies demonstrate the robustness of the mechanism responsible for the vortex formation: Rayleigh's inviscid centrifugal instability aided by radial shear in the boundary layer near the outer cylindrical wall.

Effect of external direct current electric field on the inhibition behavior of cyclohexylamine and sodium nitrite under thin electrolyte layers

The effect of external direct current electric field on the inhibition behavior of cyclohexylamine and sodium nitrite under simulated atmospheric environments with thin electrolyte layers was investigated by surface characterizations and electrochemical measurements. Results confirmed that the vertical electric field from top to bottom increased the inhibition efficiency of cyclohexylamine but decreased that of sodium nitrite. The opposite electric field weakened the inhibition efficiency of cyclohexylamine but enhanced that of sodium nitrite. Surface analysis indicated that the external vertical electric field can affect the migration of inhibitors under thin electrolyte layers.

Stochastic Analysis of Electron Transfer and Mass Transport in Confined Solid/Liquid Interfaces

Molecular-level understanding of electrified solid/liquid interfaces has recently been enabled thanks to the development of novel in situ/operando spectroscopic tools. Among those, ambient pressure photoelectron spectroscopy performed in the tender/hard X-ray region and coupled with the “dip and pull” method makes it possible to simultaneously interrogate the chemical composition of the interface and built-in electrical potentials. On the other hand, only thin liquid films (on the order of tens of nanometers at most) can be investigated, since the photo-emitted electrons must travel through the electrolyte layer to reach the photoelectron analyzer. Due to the challenging control and stability of nm-thick liquid films, a detailed experimental electrochemical investigation of such thin electrolyte layers is still lacking. This work therefore aims at characterizing the electrochemical behavior of solid/liquid interfaces when confined in nanometer-sized regions using a stochastic simulation approach. The investigation was performed by modeling (i) the electron transfer between a solid surface and a one-electron redox couple and (ii) its diffusion in solution. Our findings show that the well-known thin-layer voltammetry theory elaborated by Hubbard can be successfully applied to describe the voltammetric behavior of such nanometer-sized interfaces. We also provide an estimation of the current densities developed in these confined interfaces, resulting in values on the order of few hundreds of nA·cm−2. We believe that our results can contribute to the comprehension of the physical/chemical properties of nano-interfaces, thereby aiding to a better understanding of the capabilities and limitations of the “dip and pull” method.

Corrosion behavior of immersion silver printed circuit board copper under a thin electrolyte layer

The corrosion behavior of immersion silver printed circuit board copper (PCB-Cu-ImAg) under a thin electrolyte layer (TEL) was studied by electrochemical tests and surface analysis. The results showed that galvanic effect accelerated the corrosion of PCB-Cu-ImAg and reduced the protective effect of silver-coating. The reduction of TEL thickness not only promoted the corrosion of PCB-Cu-ImAg, but also strengthened the galvanic effect. At the beginning of exposure to TEL, the potential difference decreased, but the galvanic current densities increased with decreasing TEL thickness because of the significant decrease of the total resistance. Because of the continuous formation and accumulation of corrosion products, the galvanic current densities decreased in the later stage of exposure to TEL.

Corrosion behaviour of 2205 DSS in the artificial industrial-marine environment

ABSTRACT The corrosion behavior of 2205 duplex stainless steel (2205 DSS) was investigated by atomization tests, which was performed in an S-bearing thin electrolyte layer used as the artificial industrial-marine environment. Electrochemical methods and X-ray photoelectron spectroscopy (XPS), were conducted to reveal the protection properties and the composition evolution of the passive film. The results indicated that the corrosion time would weak the protectiveness of passive film, which was attributed to the accumulation of defects and metal sulfides in the passive film. The decrease of composition percentage of Cr2O3 made more negative effects on the protection properties of passive film than the increase of Cr(OH)3 and CrO3, whose formation was related to the adequate supply of oxygen and water molecules. The metal sulfides such as NiS and MoS2 formed during atomization tests reduced the content of alloy oxides in the passive film, and provided locations for the growth of defects.

Fabrication of Compositionally Gradient Anode Functional Layer for Proton Conducting Fuel Cell at Intermediate Temperatures: A Preliminary Study

In this work, an anode-supported button cell was fabricated with compositionally gradient (CG) NiO-BaCe0.54Zr0.36Y0.1O2.95 (NiO-BCZY) anode functional layer (AFL). The button cell has a configuration of NiO-BCZY (50:50) | NiO-BCZY (30:70) | NiO-BCZY (10:90) | BCZY | LSCF. All powder materials were synthesized using a sol-gel method. Firstly, NiO-BCZY anode substrate was fabricated using dry-pressing method. Next, NiO-BCZY CG-AFL and BCZY electrolyte thin film were spin-coated on the anode substrate and lastly the La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode was spin-coated on the electrolyte thin film. The microstructure of the fabricated button cell with good adhesion between all the layers, thin and dense electrolyte layer, and gradient increase in density of materials from anode substrate to electrolyte were observed using Scanning Electron Microscopy (SEM). Cell’s performance in terms of resistivity was evaluated using Electrochemical Impedance Spectroscopy (EIS) and conductivity meter using four-point probe method. Values of ohmic (Ro) and polarization resistance (Rp) of the cell are 7.3 and 2.4 Ωcm2 at 700 °C, respectively. The lower resistance values obtained compared to our previous work on a conventional 3-layers BCZY-based single button cell (Ro = 9.6 and Rp = 7.8 Ωcm2 at 700 °C) confirmed the functionality of GC-AFL in enhancing the cell’s performance. This preliminary result shows that simple deposition technique of CG-AFL plays a significant role in the optimization of PCFC button cell designs and electrochemical performance.

Sr2+-doped rhombohedral LiHf2(PO4)3 solid electrolyte for all-solid-state Li-metal battery

Solid-state electrolytes in rechargeable all-solid-state Li-metal batteries, which have better safety and higher specific capacity than conventional rechargeable Li-ion batteries with liquid electrolytes, are limited by the low Li-ion conductivity of the solid electrolyte and the large electrolyte/electrode interfacial resistance. Here, we report a new rhombohedral NASICON structure Li1.4Sr0.2Hf1.8(PO4)3 with a high Li-ion conductivity of 1.62 × 10−5 S·cm−1 at 25 °C, and its conductivity can be improved to 3.4 × 10−5 S·cm−1 after the densification of the pellet by hot pressing. Li1.4Sr0.2Hf1.8(PO4)3 coated by a thin layer of polymer electrolyte showed a stable low-impedance dendrite-free plating/stripping process in a symmetric Li/Li cell for 100 h; moreover, the Li1.4Sr0.2Hf1.8(PO4)3 electrolyte had a small interfacial resistance in all-solid-state Li/LiFePO4 cell, which allows a high Coulombic efficiency and good cycling of the cell.

Windowless thin layer electrochemical Raman spectroscopy of Ni-Fe oxide electrocatalysts during oxygen evolution reaction

In-situ Raman spectroelectrochemistry is a powerful tool to understand the structures and reaction mechanisms of electrochemical interfaces yet usually suffers from a low sensitivity and detection efficiency. Herein, we develop a windowless thin layer electrochemical cell design to improve the detection efficiency of in-situ Raman spectroscopy for practical nanoscale electrocatalysts. This was achieved by perforating a hole in the optical window of the cell, which not only eliminates the refraction of light by the window but also induces a meniscus thin electrolyte layer on the working electrode, thus significantly improving the detection efficiency of Raman spectra. We successfully applied this method to conduct in-situ Raman spectroscopy of structural evolutions of two representative Ni-Fe oxide catalysts (layered double hydroxides and spinel oxides) during oxygen evolution reaction (OER) electrocatalysis. It was shown that both catalysts underwent surface transformation to oxyhydroxides and formed active oxygen species at OER relevant potentials. However, the extent of the surface transformation was much lower on the Ni-Fe spinel catalyst, accounting for its lower OER activity. We further show that adding a carbon support can promote the surface transformation of Ni-Fe spinel to oxyhydroxides, thus significantly increasing the electrocatalytic activities. The established windowless thin layer method provides a new way to conduct in-situ electrochemical Raman spectroscopy of a wide range of materials and may be also combined with surface-enhanced Raman spectroscopic methods.

Development of high-performance anode/electrolyte/cathode micro-tubular solid oxide fuel cell via phase inversion-based co-extrusion/co-sintering technique

A complete set of triple-layer (anode/electrolyte/cathode) hollow fiber for high temperature micro-tubular solid oxide fuel cell (MT-SOFC) consisting of nickel oxide (NiO) – yttria-stabilized zirconia (YSZ)/YSZ/lanthanum strontium manganite (LSM) – YSZ has been successfully fabricated in this study. A simplified fabrication technique of phase inversion-based co-extrusion/co-sintering has yielded a perfectly bounded sandwich structure with free-delamination and defect layers. The effect of co-sintering temperatures (1300 °C–1450 °C) on the morphologies, elemental distributions, electrolyte gas-tightness, mechanical strength, electrochemical performance and the impedance spectra test are well-inspected. The increase of co-sintering temperature has significant effects on the anode finger-like micro-channels shrinkage where the voids become very sharp-thin structure; and developing a thin gas-tight electrolyte layer. Whereas, rapid co-sintering rate (10 °C min−1) and large particle size of 3–5 μm (micron) of YSZ has hindered the formation of fully dense cathode layer resulting from higher co-sintering temperature. Correspondingly, with only 0.1116 Ωcm2 value of area-specific resistance (ASR), a maximum power density has increased from 0.34 W cm−2 to 0.75 W cm−2 with 1.05 V OCV at 700 °C when the co-sintering temperature ranging from 1400 °C to 1450 °C; which comparable with single-layer counterpart.

Electromagnetically generated vortex streets in a narrow channel

The understanding of fluid wakes is of fundamental importance in several technological applications. In this paper, we present an experimental and numerical study of vortex wakes produced by a traveling localized Lorentz force in a thin layer of electrolyte contained in a narrow channel. The experimental set up consists of an open rectangular container with two parallel electrodes placed along its longest walls and connected to a power source that supplies a uniform DC current to the fluid layer. A permanent magnet located underneath the container is moved with a constant velocity so that the interplay of the moving magnetic field and the applied transversal current generates a traveling Lorentz force that stirs the electrolyte and creates different vortex wakes according to the flow conditions. Attention is focused on the effect of lateral walls on the flow patterns, therefore, two containers of different width and magnets of different sizes were used to vary the blockage parameter. Numerical simulations using a quasi-two-dimensional model agree qualitatively with experimental visualizations. Further, flow transition maps built from experimental and numerical results are presented.

Trace Fe Incorporation into Ni-(oxy)hydroxide Stabilizes Ni3+ Sites for Anodic Oxygen Evolution: A Double Thin-Layer Study.

Iron incorporation is essential for the record activity of NiFe-(oxy)hydroxides to oxygen evolution reaction (OER), but the details of how Fe affects catalysis remain under active investigation. In this work, we present a double thin-layer strategy for finding unique and solid evidence for the role of Fe in the OER mechanism. A thin-layer catalyst of a few nanometers of thickness was deposited on a Ni substrate and a thin-layer electrolyte of 0.1 mm thickness was created using a thin-layer spectroelectrochemical cell. The OER activity, the catalyst composition, and the electrolyte species were investigated together as a function of the Fe deposition time. The results show that trace Fe incorporation favors the formation of β-NiOOH in the thin-layer catalyst and effectively suppresses the dissolution of NiOOH into the electrolyte. The results of double-potential step chronoabsorptometry and cyclic voltabsorptometry demonstrate the potential-dependent formation of a Ni3+ intermediate in the electrolyte and, more importantly, the dissolution suppression effect due to Fe incorporation. These findings link the role of Fe in OER catalysis to the increased insolubility of Ni3+ active sites and highlight the importance of paying close attention to the active-site stability of an electrocatalyst impaired by the electrolyte at a reaction potential.

In situ investigation of atmospheric corrosion behavior of copper under thin electrolyte layer and static magnetic field

The effect of static magnetic field on atmospheric corrosion behavior of copper under thin electrolyte layer is investigated through polarization curves, electrochemical impedance spectroscopy, EDS and SEM techniques. The influences of the intensity and direction of magnetic field on the corrosion behavior are discussed. Results show that: mainly pitting corrosion occurs to the copper; the magnetic field reduces the ability of ions to migrate from thin electrolyte layer to electrode surface, and inhibits the formation of CuO and soluble copper chloride. The mechanisms involved are proposed to explain the inhibition effect.