Alloy Cathode Research Articles

Synergy of Ru and Ir in the Electrohydrogenation of Toluene to Methylcyclohexane on a Ketjenblack-Supported Ru-Ir Alloy Cathode

An organic hydride system based on hydrogenation/dehydrogenation of toluene (TL)/methylcyclohexane (MCH) has been studied as a hydrogen storage technology. Electrohydrogenation of TL to MCH using a proton exchange membrane (PEM) electrolyzer is proposed as a candidate for the hydrogenation of TL in the organic hydride system. Recently, we reported that a Ketjenblack-supported Ru-Ir alloy (Ru-Ir/KB) cathode was effective for the reaction; however, electrohydrogenation mechanisms and catalyses of Ru and Ir in the electrohydrogenation have been unclear. In this paper, detailed characterization studies using transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS), and electrochemical studies using cyclic voltammetry (CV) and linear sweep voltammetry (LSV) for hydrogen evolution and kinetic studies for catalytic hydrogenation of TL by Ru-Ir/KB catalysts were conducted. On the ...

The effects of growth TiO2 nanotubes on forged Ti6Al4V alloy and selectivelaser sintered Ti6Al4V alloy surfaces for environment and medical applications

The paper describes the effect of growth TiO2 nanotubes on titanium surfaces by anodic oxidation forenvironmental and medical applications. The importance of the metallurgical state of TiAl6V alloy on the growing of TiO2 nanotubes by anodization will be highlighted. Starting from the possibility of obtaining the TiO2 nanotubes, the paper presents results on TiO2 nanotubes grown by electrochemical anodization method, using a solution containing HF 0,4% and having as electrodes, graphiteas cathode and titanium alloy specimens obtained by two technologies: by cold plastic deformation as well as by additive manufacturing process SLS, as anode. So, the nanotubes were produced by anodization and analysed by scanning electron microscopy. The aim of this paper is to compare the electrochemical formation of TiO2 on the surface of both specimens knowing that the titanium alloys and its oxides are used in many biomedicaland environmental applications, thus providing the importance of nanotubes and the fact that their properties open doors in these fields.

Electrochemical Behaviors of Eu (III) on the Liquid Binary Al-Ga Alloy Cathode

The objective of this work is to explore the electrochemical and electrodeposition behaviors of Eu (III) cation at the liquid binary Al-Ga alloy cathode. In addition, the co-reduction behaviors of Eu (III), Al (III) and Ga (III) were also systematically studied on a W electrode. The results indicated that Eu (III) can be reduced on the binary Al-Ga alloy cathode, and Eu (III), Al (III) and Ga (III) also can be co-reduced on the W electrode to form Al-Eu/Ga-Eu intermetallic compounds. At the same time, the isothermal section phase diagram of the Al-Ga-Eu ternary system at 773 K was also calculated. In addition, Al-Eu and Ga-Eu alloys were prepared by potentiostatic and galvanostatic electrolyses in the LiCl-KCl-EuCl3 melt. Finally, the electrodeposition products were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS).

Prospecting Stress Formed by Hydrogen or Isotope Diffused in Palladium Alloy Cathode.

The objective of this project is to take into account the mechanical constraints formed by diffusion of hydrogen or tritium in watertight palladium alloy cathode. To know the origin of these, it was necessary to discriminating the damaging effects encountered. Effectively, hydrogen and isotope induce deformation, embrittlement, stress corrosion cracking and cathodic corrosion in different regions of cathode. Palladium can be alloyed with silver or yttrium to favourably increase diffusion and reduce these constraints. Effects of electrochemical factors, temperature, cathode structure, adsorbed transient complex of palladium and porous material support are given to estimate and to limit possible damage.

A multi-cathode counter in a single-electron counting mode

We describe the operation of the multi-cathode counter developed by us. It has an aluminum alloy cathode and operates in single-electron counting mode. The calibration results are given. The gas gain was found from the calibration spectra. The electric fields and the operation of this detector in two configurations are described. Our original idea was to measure the effect of electrons emitted from the cathode surface according to the difference in count rates in two configurations. We found the optimal potential difference between the first and second cathodes in the two configurations using the calibration measurements of the count rates. In addition, the advantage of using a multi-cathode counter for measuring the intensity of single-electron emission from a metal is explained.

Low-Turn-On-Voltage, High-Brightness, and Deep-Red Light-Emitting Electrochemical Cell Based on a New Blend of [Ru(bpy)3]2+ and Zn-Diphenylcarbazone.

Deep red light-emitting electrochemical cells were prepared based on a blend of [Ru(bpy)3]2+, a cationic complex, and a neutral Zn(II)-complex based on diphenylcarbazone ligands, named Zn(DPCO). The crystal structure of the Zn(DPCO)2 (bpy)] molecule revealed that the DPCO ligand has been deprotonated to form DPCO– and coordinated to the Zn center metal through the C=O and N=N moieties of DPCO. From the cyclic voltammetry results and controlled potential coulometry data of the diphenylcarbazide (DPC) ligand, it is possible to establish that DPC is oxidized in an irreversible process at +0.77 V, giving DPCO and later oxidized at a higher potential (+1.32 V) to produce diphenylcarbadiazone (DPCDO). A detailed assignment of UV–vis spectra futures to determine the origin of ground- and excited-state transitions was achieved by time-dependent density functional theory calculations, which showed good agreement with the experimental results. Using a simple device architecture, we obtained deep red electroluminescence (EL) with high brightness (740 cd m–2) and luminous efficiency of 0.39 cd/A at a low turn-on voltage of 2.5 V. The favorable configuration of the cell consists of only a blend of complexes of indium tin oxide as the anode electrode and molten alloy cathode (Ga/In) without any polymer as the transporting layer. The comparison between [Ru(bpy)3]2+ and [Ru(bpy)3]2+/Zn(DPCO) demonstrates a red shift in the EL wavelength from 625 to 700 nm in the presence of Zn(DPCO), revealing the importance of using blends for future systems.

Simultaneous SO2 removal and CO2 reduction in a nano-BiVO4|Cu-In nanoalloy photoelectrochemical cell

SO2 and CO2 emitted from using of fossil fuels are causing serious environmental issues. Herein we put forward a promising strategy to realize CO2 reduction and SO2 removal simultaneously through a photoelectrochemical (PEC) process based on nanoelectrodes. In the present work, SO2 was oxidized to SO42− on BiVO4 photoanode after being absorbed by NaHCO3 solutions. At the same time, CO2 reduction occurred on nanoflower-like copper-indium alloy cathode. The absorption efficiency of SO2 was greater than 95%, and SO32− was oxidized to SO42− with oxidation efficiency about 50% in 3 h. Moreover, the energy of SO2 was recycled to assist the CO2 reduction on the cathode, consequently, the photocurrent densities were increased at least 3 times after introducing SO2. CO2 reduction with CO and HCOOH as main products was improved significantly when SO2 removal was conducted simultaneously. In-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments were also performed to study the adsorption and conversion of SO2 on BiVO4 nanoparticles. The proposed approach could efficiently remove SO2 and recycle the energy of it to reduce CO2 into useful chemicals. This work provides a sustainable strategy for dealing with CO2 and SO2 in the flue gas by combining desulfurization and CO2 reduction in one PEC cell using nanoelectrodes.

X-Ray Scattering Characterization of Advanced Low-Loading Oxygen Reduction Reaction Catalysts and Electrodes

While high oxygen reduction reaction (ORR) activities for polymer electrolyte fuel cells (PEFCs) have been demonstrated for high surface area carbon-supported Pt alloy nanoparticle catalysts in aqueous cell rotating disk electrode tests and when operating on oxygen in membrane-electrode assemblies (MEAs), the performance improvement expected from the high intrinsic ORR activities is not realized at moderate to high current densities. 1 One possible reason may arise from the complex requirements for full utilization of the electrocatalytic sites and for adequate reactant transport in the cathode catalyst layer. Knowledge about the structural features of the catalyst layer, understanding the distribution in this porous layer and understanding the proton mobility in ionomer between structural elements of the catalyst could help to design more efficient electrodes for PEFCs. Small angle X-ray scattering (SAXS), which probes objects with dimensions of 1 to 100 nm, is emerging as a powerful tool for structural investigations of PEFC electrodes to estimate the size, shape, and structure of the catalyst and ionomer formulations as well as of fuel cell electrodes. 2 Ultra-small angle X-ray scattering (USAXS) is the scattering at ultra-low angles by structures up to several micrometers in size. USAXS combined with SAXS can probe the length scales relevant to the carbon structures in PEFC electrodes (10 nm to 6000 nm). 3, 4 This presentation will highlight X-ray scattering microstructural characterization of state-of-the-art alloy cathode catalysts including catalyst powders, catalyst-ionomer-solvent dispersions, optimized electrodes and MEAs at different stages of testing and using different testing protocols. The microstructural results will be compared with the physico-chemical properties of the electrode components, the electrode fabrication processes, as well as the fuel cell performance and in-cell diagnaotics to establish a relationship between electrode microstructure and electrode performance. Acknowledgments This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the support of the Fuel Cell Performance and Durability Consortium (FC-PAD). The Advanced Photon Source was supported by the U.S. Department of Energy, Office of Basic Energy Sciences. Argonne is a U.S. Department of Energy Office of Science Laboratory operated under Contract No. DE-AC-02-06CH11357 by UChicago Argonne, LLC. References Kongkanand, A.; Mathias and M. F., Phys. Chem. Lett. 2016, 7, 1127–1137.Khaneft, M.; Holderer, O.; Ivanova, O.; Luke, W.; Kentzinger, E; Appavou, M. S.; Zorn R.; Lehnert, W. Fuel Cells 2016, 16 (4), 406–413.Yang, F.; Xin, L.; Uzunoglu, A.; Qiu, Y.; Stanciu, L.; Ilavsky, J.; Li, W.; Xie, J., ACS Appl. Mater. Interfaces 2017, 9, 6530−6538.Xin, L.; Yang, F.; Xie, J.; Yang, Z.; Kariuki N. N.; Myers, D. J.; Peng, J-K; Wang, X.; Ahluwalia, R. K.; Yu, K.; Ferreira, P. J.; Bonastre, A. M.; Fongalland, D.; Sharman, J. Electrochem. Soc. 2017 164(6): F674-F684.

An intermediate temperature garnet-type solid electrolyte-based molten lithium battery for grid energy storage

Batteries are an attractive grid energy storage technology, but a reliable battery system with the functionalities required for a grid such as high power capability, high safety and low cost remains elusive. Here, we report a solid electrolyte-based molten lithium battery constructed with a molten lithium anode, a molten Sn–Pb or Bi–Pb alloy cathode and a garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZTO) solid electrolyte tube. We show that the assembled Li||LLZTO||Sn–Pb and Li||LLZTO||Bi–Pb cells can stably cycle at an intermediate temperature of 240 °C for about one month at current densities of 50 mA cm−2 and 100 mA cm−2 respectively, with almost no capacity decay and an average Coulombic efficiency of 99.98%. Furthermore, the cells demonstrate high power capability with current densities up to 300 mA cm−2 (90 mW cm−2) for Li||LLZTO||Sn–Pb and 500 mA cm−2 (175 mW cm−2) for Li||LLZTO||Bi–Pb. Our design offers prospects for grid energy storage with intermediate temperature operations, high safety margin and low capital and maintenance costs.

Corrosion Properties of Dissimilar Friction Stir Welded 6061 Aluminum and HT590 Steel

Corrosion properties of dissimilar friction stir welded 6061 aluminum and HT590 steel were investigated to understand effects of galvanic corrosion. As cathode when coupled, HT590 was cathodically protected. However, the passivation of AA6061 made the aluminum alloy cathode temporarily, which leaded to corrosion of HT590. From the EIS analysis showing Warburg diffusion plot in Nyquist plots, it can be inferred that the stable passivation layer was formed on AA6061. However, the weld as well as HT590 did not show Warburg diffusion plot in Nyquist plots, suggesting that there was no barrier for corrosion or even if it exists, the barrier had no function for preventing and/or retarding charge transport through the passivation layer. The open circuit potential measurements showed that the potential of the weld was similar to that of HT590, which lied in the pitting region for AA6061, making the aluminum alloy part of the weld keep corrosion state. That resulted in the cracked oxide film on AA6061 of the weld, which could not play a role of corrosion barrier.

Experimental Study on Four Cation Exchange Membranes in Electrosynthesis of Ammonium Persulfate

In order to improve current efficiency and decrease energy consumption in the electrosynthesis of ammonium persulfate, electrolytic properties of four cation exchange membranes, namely, the JCM-II® membrane, Nafion® 324 membrane CMI-7000® membrane and a self-made perfluorosulfonic ion exchange membrane (PGN membrane) were investigated using a sintered platinized titanium anode and a Pb-Sb-Sn alloy cathode in a self-made electrolytic cell. The effect of cell voltage and electrolyte flow rate on the current efficiency and the energy consumption were investigated. The results indicated that the PGN membrane could improve current efficiency to 94.85% and decrease energy consumption to 1119 kWh t-1 (energy consumption per ton of the ammonium persulfate generated) under the optimal operating conditions and the highest current efficiency of the JCM-II® membrane, Nafion® 324 membrane and CMI-7000® membrane were 80.73%, 77.76% and 73.22% with their lowest energy consumption of 1323 kWh t-1, 1539 kWh t-1 and 2256 kWh t-1, respectively. The PGN membrane has the advantages of high current efficiency and energy power consumption and has sufficient mechanical strength with the reinforced mesh. Therefore the PGN membrane will has good value in popularization in the industrial electrosynthesis of ammonium persulfate in the future. Keywords: Electrosynthesis, Ammonium persulfate, Current efficiency, Energy consumption, PGN membrane

Capacity extended bismuth-antimony cathode for high-performance liquid metal battery

Li-Bi based liquid metal batteries (LMBs) have attracted interest due to their potential for solving grid scale energy storage problems. In this study, the feasibility of replacing the bismuth cathode with a bismuth-antimony alloy cathode in lithium based LMBs is investigated. The influence of the Bi:Sb ratio on voltage characteristics is evaluated via the constant current discharge method and electrochemical titration. On observing the cross section of the electrode at various stages of discharge, it is determined that both Sb and Bi form solid intermetallics with Li on the cathode. Additionally, the addition of Bi not only reduces the melting temperature of the Bi:Sb intermetallic but also actively contributes to the electrode capacity. Thereafter, a Li|LiCl-LiF|Sb-Bi liquid metal battery with 3 A h nameplate capacity, assembled and cycled at 1 C rate, is found to possess a stable capacity for over 160 cycles. The overall performance of this battery is discussed in the context of cost effectiveness, energy and coulombic efficiencies.

Experimental Study on Two Anion Exchange Membranes in Electrosynthesis of Ammonium Persulfate

In order to improve current efficiency and reduce energy consumption in the electrosynthesis of ammonium persulfate, electrolytic properties of the AMI-7001 anion exchange membrane (AMI-7001 membrane) and one quatemary ammonium HDJAM anion exchange membrane (HDJAM membrane) were investigated using a sintered platinized titanium anode and a Pb-Sb-Sn alloy cathode in a self-made electrolytic cell. The effect of the cell voltage, the electrolyte flow rate and the SO42− concentration in the catholyte on the current efficiency and the energy consumption were investigated. The results indicated that the HDJAM membrane could obtain current efficiency of 90.9% and energy consumption of 1034 kWh t−1 (energy consumption per ton of the ammonium persulfate generated) and the AMI-7001 could get current efficiency of 74.8% and energy consumption of 1570 kWh t−1 under the optimal operating conditions. The experimental results show that the HDJAM membrane can significantly improve the current efficiency and reduce the energy consumption compared with the AMI-7001 membrane and will has good value in popularization in the electrosynthesis of ammonium persulfate, which expands the scope of the membrane in the electrosynthesis of ammonium persulfate because the cation membranes are the main membranes investigated in the electrosynthesis of ammonium persulfate.

Durability of Pt-Co Alloy Polymer Electrolyte Fuel Cell Cathode Catalysts under Accelerated Stress Tests

The durability of Pt-Co alloy cathode catalysts supported on high surface area carbon is investigated by subjecting them to accelerated stress tests (ASTs). The catalysts had different initial Co contents and nanoparticle morphologies: a “spongy” porous morphology for the high-Co (H) content catalyst, and a fully alloyed crystalline morphology for the medium-Co (M) and low-Co (L) content catalysts. The specific activity of the catalysts depends on their initial Co content, morphology and nanoparticle size, and remained higher than 1000 μA/cm2-Pt after 27–50% Co loss. The H-catalyst electrode showed the smallest kinetic overpotentials (ηcs) due to higher initial Pt loading than the other two electrodes, but it had the fastest increase in ηcs with AST cycling due to lower Co retention; the L-catalyst electrode showed higher ηcs due to a lower initial Pt loading, but had a smaller increase in ηcs with aging due to higher Co retention; the M-catalyst electrode showed a similar increase in ηcs with aging, but this increase was due to the combined effects of Co dissolution and electrochemically active surface area (ECSA) loss. The modeled increase in mass transfer overpotentials with aging correlates with the initial Pt loading, ECSA loss and the initial catalyst morphology.

Influence of manganese on the electrochemical behavior of an aluminum cathode used in zinc electrowinning

Pure aluminum is commonly used as the cathode electrode in the traditional hydrometallurgy applications of zinc electrowinning. However, with the decrease of zinc concentrate grade and increase of the impurity ions in the electrolyte, the corrosion consumption of the cathode material increases gradually. To further improve the corrosion resistance and electrocatalytic activity of the aluminum cathode, the electrochemical behavior of manganese as an additive for pure Al cathode material, such as Al-Mn alloy, was studied herein. Using the analysis methods of electrochemical impedance spectroscopy, cathodic polarization, galvanostatic polarization, and Tafel curves, the effect of Mn content on the electrochemical behavior of Al-Mn alloy in 40℃ constant temperature conditions and a solution containing Zn2+ at 65 g·L-1 and H2SO4 at 150 g·L-1 was investigated. The results show that the corrosion resistance of Al alloy containing Mn increases obviously compared to that of pure Al electrodes, and the increase of the Mn content could decrease the corrosion current. Moreover, the corrosion potential and the Mn content do not exhibit obvious change trends. When the Mn content reaches 1.5%, the corrosion current reaches the lowest value of 1.11 mA·cm-2 and the corrosion potential reaches the minimum of -1.0954 V. When the electrical potential of cathode becomes zero, the exchange current density is influenced by the Mn content and the exchange current density i0 exhibits an initial increasing trend and then declines with the increase of the Mn content. When the Mn content is 1.5%, the exchange current density of the Al alloy cathode reaches the maximum of 3.7462×10-16 mA·cm-2; this value is much higher than that of the pure Al electrode (4.8027×10-33 mA·cm-2). The overall change amplitude is obvious, and the electrocatalytic activity of the Al-Mn electrodes is much improved compared with a pure Al electrode. The electrochemical process is controlled by the electrochemical mass transfer. Considering the corrosion resistance and electrocatalytic activity of the electrode material, the Al-Mn alloy containing 1.5% of Mn can be used as an ideal electrolytic zinc cathode.

Durability of Pt-Co Alloy Cathode Catalysts for PEM Fuel Cells Under Cyclic Potentials

Alloying Pt with transition metals, such as Co and Ni, enhances the catalytic activity for the oxygen reduction reaction (ORR) at cathodes of polymer electrolyte fuel cells (PEFCs). The alloying process necessarily involves a high-temperature thermal annealing step that grows the size of catalyst nanoparticles above 4-5 nm. Particles of this size are known to be more stable under cyclic potentials as they are less prone to Pt dissolution and coalescence than finer scale 2-3 nm Pt particles. However, transition metals are unstable at operating fuel cell potentials and can leach out of the catalyst in the cathode and into the ionomer, resulting in loss of ORR activity. Three formulations of Pt-Co alloy catalysts supported on high surface area carbon were subjected to accelerated stress tests (ASTs) in H2-N2 environment. The AST protocol consisted of repeated square waves with 0.6 V lower potential limit (LPL), 0.95 V upper potential limit (UPL), and 3-s holds at LPL and UPL. Changes in cell performance were monitored by measuring polarization in H2-air, high frequency resistance (HFR), electrochemical surface area (ECSA), impedance in air and helox (79% He, 21% O2), and mass activity. These measurements were made at beginning of life (BOL) and after 1000 (1k), 20,000 (20k) and 30,000 (30k) cycles. The three catalysts had a different initial Co content (34%, 20%, and 15%) and electrode microstructure. At BOL, transmission electron microscopy (TEM) analysis of the high-Co content (H) catalyst electrode, 0.2 mg/cm2 Pt loading, showed a “spongy” porous (hollow) catalyst nanoparticle morphology with ~6.7 nm median Pt-Co particle size after conditioning. The BOL medium-Co content (M) catalyst electrode, 0.1 mg/cm2 Pt loading, showed a crystalline fully alloyed catalyst nanparticle morphology with ~4.4 nm particle size after conditioning. The BOL low-Co content (L) catalyst electrode, 0.1 mg/cm2 Pt loading, also showed catalysts with a fully alloyed crystalline morphology with ~4.5 nm median particle size.Post-mortem TEM analysis of aged electrode specimens showed different amounts of Co dissolution from the nanoparticles. There is an apparent direct relationship between the initial alloy Co content the amount of Co dissolved after potential cycles. WAXS analysis confirms significant Co loss from the nanoparticles and also indicates that the Pt-Pt d-spacing in Pt-Co alloy approaches the values typical of pure Pt particles. The effect of Co dissolution on the loss in specific activity for ORR is summarized in Fig. 1a. The data suggest that the specific activity depends not only on the initial Co content but also on the catalyst nanoparticle morphology and size. Even with 27-50% Co loss, the specific activity of Pt-Co alloy remains higher than 1000 mA/cm2-Pt, and exceeds the activity (650 mA/cm2-Pt) of pure Pt of similar particle size. The measured specific activities are consistent with a kinetic model and catalyst-specific choice of kinetic parameters.The modeled ORR kinetic losses depend on specific activity, ECSA, catalyst loading, and kinetic parameters (electrode morphology). As shown in Fig. 1b, the H-catalyst electrode shows the smallest kinetic overpotentials (ηc s) due to high Pt loading, but has the fastest increase in ηc s with ageing because of low Co retention in the electrode. The L-catalyst electrode shows higher ηc s due to lower Pt loading but has a smaller increase in ηc s with ageing because of high Co retention. For this catalyst, increase in is mostly due to loss of ECSA with ageing. The M-catalyst electrode shows similar increase in ηc s with ageing as the L-catalyst electrode, but this increase is due to the combined effects of Co dissolution and ECSA loss. The modeled increase in mass transfer overpotentials (ηm) with ageing correlates with Pt loading and ECSA loss and depends on the initial electrode morphology. There is no clear evidence of a relationship between Co dissolution (i.e., effect of Co2+ on O2 permeability in ionomer film) and the resulting increase in ηm. AcknowledgmentsThe authors wish to acknowledge the financial support of the Fuel Cell Technologies Office and Fuel Cell Component R&D Team Lead, Dr. Dimitrios Papageorgopoulus, and Technology Development Manager, Dr. Nancy Garland. The authors also wish to acknowledge General Motors, IRD and Umicore for supplying materials used in this study. The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. Figure 1

Sputtered Nanoporous PtNi Thin Film Cathodes with Improved Thermal Stability for Low Temperature Solid Oxide Fuel Cells

Nanoporous PtNi alloy thin film was demonstrated to effectively improve the thermal stability of cathode under high temperature fuel cell operation. The grain growth, which indicates the agglomeration of the nanoparticles, were constrained, as observed by comparing the surface morphologies and grain sizes in bulk of film between pure Pt and PtNi alloy cathodes. The constrained grain growth by alloying with Ni maintained the porosity in bulk of cathode film for sufficient cathode oxygen diffusion and adsorption/dissociation processes. Fuel cell using Pt67-Ni33 cathode better maintained the output current density than the cell using pure Pt cathode by 26% after 48hours of continuous operation.

Fabrication and characterization of YSZ/Al2O3 nano-composite coatings on Inconel by electrophoretic deposition

Abstract

Thermal Rayleigh-Marangoni convection in a three-layer liquid-metal-battery model.

The combined effects of buoyancy-driven Rayleigh-Bénard convection (RC) and surface tension-driven Marangoni convection (MC) are studied in a triple-layer configuration which serves as a simplified model for a liquid metal battery (LMB). The three-layer model consists of a liquid metal alloy cathode, a molten salt separation layer, and a liquid metal anode at the top. Convection is triggered by the temperature gradient between the hot electrolyte and the colder electrodes, which is a consequence of the release of resistive heat during operation. We present a linear stability analysis of the state of pure thermal conduction in combination with three-dimensional direct numerical simulations of the nonlinear turbulent evolution on the basis of a pseudospectral method. Five different modes of convection are identified in the configuration, which are partly coupled to each other: RC in the upper electrode, RC with internal heating in the molten salt layer, and MC at both interfaces between molten salt and electrode as well as anticonvection in the middle layer and lower electrode. The linear stability analysis confirms that the additional Marangoni effect in the present setup increases the growth rates of the linearly unstable modes, i.e., Marangoni and Rayleigh-Bénard instability act together in the molten salt layer. The critical Grashof and Marangoni numbers decrease with increasing middle layer thickness. The calculated thresholds for the onset of convection are found for realistic current densities of laboratory-sized LMBs. The global turbulent heat transfer follows scaling predictions for internally heated RC. The global turbulent momentum transfer is comparable with turbulent convection in the classical Rayleigh-Bénard case. In summary, our studies show that incorporating Marangoni effects generates smaller flow structures, alters the velocity magnitudes, and enhances the turbulent heat transfer across the triple-layer configuration.

Effect of Al:Ag alloy cathode on the performance of transparent organic light-emitting devices

Transparent organic light-emitting devices (TOLEDs) based on a stacked alloy cathode of LiF/Al:Ag are investigated. The devices have a structure of indium-tin-oxide (ITO)/4,4′,4″-Tris[2-naphthyl(phenyl)amino]triphenylamine (2T-NATA) (25 nm)/N,N′-Di-[(1-naphthyl)-N,N′-diphenyl]-1,1’-biphenyl-4,4′-diamine (NPB) (40 nm)/tris-(8-hydroxyquinoline) aluminum (Alq3) (50 nm)/LiF (1 nm)/Al:Ag (1:3) (x), where the thicknesses of cathode metal layers (Al:Ag) are adjusted, respectively, from 70 nm to 100 nm. In the experiment, it is found that the LiF (1 nm)/Al:Ag (1:3) (75 nm) has good electron injection efficiency. Compared with an Al-only cathode, the turn-on voltage is lowered. At the voltage of 10 V, the luminances for bottom emission from ITO anode side and top emission from metal cathode side are 2 459 cd/m2 and 1 729 cd/m2, respectively. Thanks to electron injection enhancement by using Al:Ag cathode, we can obtain a better energy level matching between the cathode and the organic layer, thus the devices have lower turn-on voltage and higher luminance. The total transmittance of the devices can achieve about 40% at the wavelength of 550 nm.