Separate Cathode Research Articles

X‐ray Absorption Near‐Edge Structure and Nuclear Magnetic Resonance Study of the Lithium–Sulfur Battery and its Components

Understanding the mechanism(s) of polysulfide formation and knowledge about the interactions of sulfur and polysulfides with a host matrix and electrolyte are essential for the development of long-cycle-life lithium-sulfur (Li-S) batteries. To achieve this goal, new analytical tools need to be developed. Herein, sulfur K-edge X-ray absorption near-edge structure (XANES) and (6,7) Li magic-angle spinning (MAS) NMR studies on a Li-S battery and its sulfur components are reported. The characterization of different stoichiometric mixtures of sulfur and lithium compounds (polysulfides), synthesized through a chemical route with all-sulfur-based components in the Li-S battery (sulfur and electrolyte), enables the understanding of changes in the batteries measured in postmortem mode and in operando mode. A detailed XANES analysis is performed on different battery components (cathode composite and separator). The relative amounts of each sulfur compound in the cathode and separator are determined precisely, according to the linear combination fit of the XANES spectra, by using reference compounds. Complementary information about the lithium species within the cathode are obtained by using (7) Li MAS NMR spectroscopy. The setup for the in operando XANES measurements can be viewed as a valuable analytical tool that can aid the understanding of the sulfur environment in Li-S batteries.

Mikrobiyal Yakıt Hücrelerinde Anot ve Katot Bölmelerinin Birbirinden Ayrılmasında Kullanılan Bazı Yöntemler

Mikrobiyal Yakıt Hücrelerinde Anot ve Katot Bölmelerinin Birbirinden Ayrılmasında Kullanılan Bazı Yöntemler

Bench-scale demonstration of CO2 capture with electrochemically-mediated amine regeneration

Electrochemically-Mediated Amine Regeneration (EMAR) is a new strategy for CO2 separations that uses industrially relevant amine sorbents in a nearly isothermal capture process. The electric nature of the EMAR system offers significant practical advantages in retrofit applications and for installation in non-power generating facilities. EMAR systems are based on an electrochemical copper cycle where desorption is facilitated by oxidation of a copper anode to generate cupric ions that displace CO2 from the polyamine sorbents. The CO2 capacity of the sorbent solution is regenerated through electroplating of the cupric ions onto a separate copper cathode. Results from a bench-scale system demonstrate the potential of the technology for efficient low-energy capture of CO2. The importance of current density and sorbent flow rate are measured. The work of capture increases linearly with current density. For flow rate, however, there is an optimum value of about 1 cm s−1 of superficial velocity through the device. Different electrode geometries and different electrolytes are also examined. At ambient pressure and temperature, which are far from the ideal operating conditions, CO2 can be captured for 100 kJ per mol−1 at a membrane current density of 50 A m−2. The Faradaic (current) efficiencies reach 80% under some conditions with only minimal optimization of the design and materials. This level of performance already meets or exceeds the performance of other electrochemical systems.

Characterization and fabrication of LSCF tapes

Abstract In this work the manufacture of commercial La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3- δ (LSCF) by aqueous colloidal processing is presented. The surface behavior of LSCF as a function of pH and the effect of a polyelectrolyte (Duramax D3005) on the stability are studied using measurements of zeta potential. Concentrated suspensions were prepared to solid content as high as 35 vol.%. The best dispersing conditions were determined by means of rheological measurements for obtaining stable and fluid slurry for tape casting technique. Different relative densities of the tapes were obtained at different temperatures. The LSCF tapes are good candidates for using as gas separation membrane or cathode for SOFC.

Progress in Alkaline Membrane Fuel Cells and Regenerative Fuel Cells

The effect of anion functional group on the conductivity and performance of alkaline anion exchange membrane fuel cells (AAEMFCs) is reported. The functional groups used were trimethyl amine (TMA), 1,4-diazabicyclo[2.2.2]octane, dimethyl sulphide (DMS), diethyl sulphide, triethyl amine and N,N,N0,N0-tetramethyl-1,6- hexanediamine. Membranes and ionomer were characterised in terms of ionic conductivity and separate anode, cathode and cell performances. TMA functionalised (LDPE-co-VBC) or PVBC offered the highest conductivity amongst the various selections of amine/sulphide-based functional groups with conductivities values up to 0.25 (in plane) and 0.043 S cm-1 (through plane). Sulphide-based groups showed lower stability with temperature in comparison to amine-based groups. The increase in length of the chain in the aryl group (for example from methyl to ethyl) attached to the nitrogen (amine) or sulphur (sulphide) led to lower conductivity. TMA functionalised ionomer provided an improved oxygen reduction reaction with exchange current density some 300 times higher than that with DMS. TMA functionalized electrodes showed superior cell performance in comparison to the other functional groups with a current density of 0.72 A cm-2 at 0.6 V and a peak power density of 478 mW cm-2. The membrane exhibits good long term stability at temperatures up to 70°C. A study of a regenerative fuel cells with alkaline anion exchange membranes with CuxMn0.9−xCo2.1O4 (CuMnO) catalysts gave promising performance using a quaternary OH- ion ionomer binder based on polymethacrylate. Satisfactory stability of the membrane electrode assembly was observed from chronocoulometry.

Enhanced azo dye removal through anode biofilm acclimation to toxicity in single-chamber biocatalyzed electrolysis system

Azo dye is widely used in printing and dyeing process as one of refractory wastewaters for its high chroma, stable chemical property and toxicity for aquatic organism. Biocatalyzed electrolysis system (BES) is a new developed technology to degrade organic waste in bioanode and recover recalcitrant contaminants in cathode with effective decoloration. The ion exchange membrane (IEM) separate anode and cathode for biofilm formation protection. Azo removal efficiency was up to 60.8%, but decreased to 20.5% when IEM was removed. However, expensive ion exchange membrane (IEM) not suitable for further practical application, bioelectrochemical activity of bioanode is sensitive to the toxicity of azo dye. A gradient increase of azo dye concentration was used to acclimate anode biofilm to pollutant toxicity. The azo removal efficiency can be enhanced to 73.3% in 10h reaction period after acclimation. The highest removal efficiency reached 83.7% and removal rates were increased to 8.37 from 3.04 g/h/L of dual-chamber. That indicated the feasibility for azo dye removal by single-chamber BES. The IEM cancellation not only decreased the internal resistance, but increased the current density and azo dye removal.

Kinetics of the electrochemical oxidation of 1,1-bis-hydroperoxy-4-methylcyclohexane on platinum

The electrochemical synthesis of 3,12-dimethyl-7,8,15,16-tetraoxadispiro[5.2.5.2]hexadecane (1,2,4,5-tetraoxane) from 1,1-bis-hydroperoxy-4-methylcyclohexane on platinum electrode in a cell with separated and unseparated cathode and anode space in an aprotic solvent is conducted. The kinetics of electrochemical oxidation of 1,1-bis(hydroperoxy)-4-methylcyclohexane is studied. The current yield of the reaction is determined.

The point spread function of the human head and its implications for transcranial current stimulation

Rational development of transcranial current stimulation (tCS) requires solving the ‘forward problem’: the computation of the electric field distribution in the head resulting from the application of scalp currents. Derivation of forward models has represented a major effort in brain stimulation research, with model complexity ranging from spherical shells to individualized head models based on magnetic resonance imagery. Despite such effort, an easily accessible benchmark head model is greatly needed when individualized modeling is either undesired (to observe general population trends as opposed to individual differences) or unfeasible. Here, we derive a closed-form linear system which relates the applied current to the induced electric potential. It is shown that in the spherical harmonic (Fourier) domain, a simple scalar multiplication relates the current density on the scalp to the electric potential in the brain. Equivalently, the current density in the head follows as the spherical convolution between the scalp current distribution and the point spread function of the head, which we derive. Thus, if one knows the spherical harmonic representation of the scalp current (i.e. the electrode locations and current intensity to be employed), one can easily compute the resulting electric field at any point inside the head. Conversely, one may also readily determine the scalp current distribution required to generate an arbitrary electric field in the brain (the ‘backward problem’ in tCS). We demonstrate the simplicity and utility of the model with a series of characteristic curves which sweep across a variety of stimulation parameters: electrode size, depth of stimulation, head size and anode–cathode separation. Finally, theoretically optimal montages for targeting an infinitesimal point in the brain are shown.

Effect of anion functional groups on the conductivity and performance of anion exchange polymer membrane fuel cells

A study of the effect of anion functional group on the conductivity and performance of alkaline anion exchange membrane fuel cells (AAEMFCs) is reported.Membranes and ionomer were characterised in terms of ionic conductivity and separate anode, cathode and cell performances. TMA functionalised (LDPE-co-VBC) or PVBC offered the highest conductivity amongst the various selections of amine/sulphide-based functional groups with conductivities values up to 0.25 (in plane) and 0.043Scm−1 (through plane). Sulphide-based groups showed lower stability with temperature in comparison to amine-based groups. The increase in length of the chain in the aryl group attached to the nitrogen or sulphur led to lower conductivity. The high OH− conductivity in membranes functionalised with TMA is reflected by its low activation energy of 12kJmol−1; close to the reported value for H+ conductivity in Nafion.The ionomer functional groups affected oxygen permeability, the activation energy and the exchange current density for oxygen reduction. TMA functionalised ionomer provided an improved medium for the oxygen reduction reaction with exchange current density some 300 times higher than that with DMS. Anode flooding appeared to severely restrict cell performance and was determined by the type of functional group used for the ionomer. TMA functionalized electrodes showed superior cell performance with a current density of 0.722Acm−2 at 0.6V and a peak power density of 478mWcm−2.

Detection of water vapor in cathode gas diffusion layer of polymer electrolyte fuel cell using water sensitive paper

Water management in cathode electrode of polymer electrolyte fuel cell (PEFC) is essential for high performance operation, because liquid water condensed in porous gas diffusion layer (GDL) and catalyst layer (CL) blocks oxygen transport to active reaction sites. In this study, the water vapor distribution inside the cathode GDL of a PEFC was detected by using water sensitive paper (WSP) to understand the water transport through the cathode electrode during the startup. Furthermore, the liquid water behavior at the cathode was directly visualized using an optical diagnostic, and the water distribution under the current-collecting ribs and gas channels of the cathode separator was investigated. It was found that the water vapor concentration within the cathode electrode begins to increase near the CL in the downstream region immediately after starting the operation. In the cathode upstream region, the water concentration becomes remarkably high under the current-collecting ribs of the cathode separator because the ribs block the water vapor exhaust from the cathode GDL.

Carbon steel corrosion under anaerobic–aerobic cycling conditions in near-neutral pH saline solutions. Part 2: Corrosion mechanism

A corrosion mechanism has been developed to describe tubercle formation along pipeline steels during successive anaerobic–aerobic cycles. Small concentrations of O 2 under nominally anaerobic conditions can lead to the separation of anodes and cathodes. Under subsequent aerobic conditions localized corrosion is then promoted by O 2 reduction on the general magnetite-covered surface. Subsequently, the conversion of magnetite to maghemite passivates the general surface, and focuses corrosion within one major tubercle-covered pit. On switching from aerobic to anaerobic conditions, corrosion is temporarily supported by the galvanic coupling of lepidocrocite (γ-FeOOH) reduction (to γ-Fe-OH·OH) to steel dissolution primarily within the tubercle-covered pit.

Polarized Electron Gun Development at the Brookhaven National Laboratoy

Development of two different polarized electron guns is ongoing at BNL. One aims at extremely high brightness at a moderate beam current. This design uses a superconducting RF gun and a test setup is built to show that a Gallium-Arsenide cathode with negative affinity has a sufficiently long quantum efficiency lifetime in such an environment. An electron injector using this technology may eliminate the need of the electron damping ring and a long transport line at the International Linear Collider. The other project aims at producing a high beam current with moderate emittance requirements, dubbed the "Gatling gun". In this DC gun, bunches are extracted from 20 separate cathodes and merged into a single beam using a rotating magnetic field. Such an electron gun could serve as an injector for the electron-ion collider eRHIC, which is planned at BNL. We will report on the status of these projects.

Screening defective lithium ion batteries of 0 V open-circuit voltage by a high current charge process in combination with in situ infrared thermal imaging technology

How to screen defective lithium ion batteries is of great importance to the producers and consumers, which has been a challenging problem, since some lithium ion batteries will not present evident different electrochemical behaviors at the initial use stage. Here, we found that defective lithium ion batteries of zero open-voltage could be differentiated from the good ones by charging at 1,800 mA (corresponding to 3 C) in combination with in situ infrared thermal imaging technology. During the charge process, the surface temperatures of the defective lithium ion batteries of zero open-voltage showed at least 10 °C higher than that of the good one. Results of the charge voltage, charge current, temperature rise, and the analysis of the cathode strip, separator, and anode strip after full-discharge process showed that this method was effective.

Lithium-6 stable isotope determination by atomic absorption spectroscopy and its application to pharmacokinetic studies in man.

No useful radioisotope of lithium exists to assist in the study of its biochemical pharmacology. A simple method has been developed for the determination of the stable isotope 6Li by atomic absorption spectroscopy (AAS). The technique is applicable in any laboratory equipped with simple AAS apparatus. Analysis of total lithium content (E) by flame emission spectroscopy is followed by separate determination (A6 and A7) of atomic absorption by the sample of the light emitted by separate hollow cathode lamps manufactured from the isotopes 6Li and 7Li. The standard curve of absorption ratio (A6/A7) against isotopic ratio (6Li/7Li) at any concentration (E) is an exponential which may be solved using a simple programmable calculator. Application of this method to the study of the pharmacokinetics of 6Li administered to 4 normal volunteers previously loaded with 7Li suggests that the rate of appearance of lithium in blood is unaffected by the previous state of lithium loading.

Visualization of liquid water movement on the micro sub-channels of flow paths in a proton exchange membrane fuel cell cathode separator

This paper introduces micro sub-channels to manage the liquid water in cathode flow paths in order to enhance the performance of proton exchange membrane fuel cells (PEMFCs) under high current density operating conditions. By visualization experiments, the capillary force of the micro sub-channels proves its ability to spread the liquid water on the main flow path, and consequently the main flow path possesses the space required to deliver air. Also, the advantages and disadvantages of various patterns of micro sub-channels were analyzed by comparing the liquid water movements on the main flow paths and the micro sub-channels. Finally, measuring the performance of a test PEMFC with micro sub-channels, we verified the performance enhancement that occurs in PEMFCs through the use of micro sub-channels.

Examination of the Effect of System Pressure Ratio and Heat Recuperation on the Efficiency of a Coal-Based Gas Turbine Fuel Cell Hybrid Power Generation System With CO2 Capture

This paper examines two coal-based hybrid configurations that employ separated anode and cathode streams for the capture and compression of CO2. One configuration uses a standard Brayton cycle, and the other adds heat recuperation ahead of the fuel cell. Results show that peak efficiencies near 55% are possible, regardless of cycle configuration, including the cost in terms of energy production of CO2 capture and compression. The power that is required to capture and compress CO2 is shown to be approximately 15% of the total plant power.

Development of a planar μDMFC operating at room temperature

A co-planar micro Direct Methanol Fuel Cell (μDMFC) configuration was designed, developed and tested. The system geometry consisted of anodic and cathodic micro-channels arranged in the same plane. Firstly, micro-channels for a uniform distribution of oxygen and methanol were designed and realized on a polymeric substrate of polycarbonate. Then, the deposition of the catalytic elements inside the micro-channels by a spray-coating technique was carried out. Micro-channels were then covered by a catalyzed membrane containing separate anode and cathode layers. Different cell configurations were built, tested and evaluated. It was observed that the open circuit voltage varied significantly as a function of the membrane humidification degree and distance between anode and cathode channels in this planar design. In the presence of a large distance between the anode and cathode channel, the OCV reached 0.97 V. This high OCV reflected the absence of methanol cross-over due to the specific planar configuration. Regrettably, the overall cell impedance (ohmic and polarization resistance) limited the performance. A maximum power density of 1.3 mW cm −2 (active area) was achieved at room temperature with the smallest distance between anode and cathode (0.25 mm).

Polymer coatings as separator layers for microbial fuel cell cathodes

Membrane separators reduce oxygen flux from the cathode into the anolyte in microbial fuel cells (MFCs), but water accumulation and pH gradients between the separator and cathode reduces performance. Air cathodes were spray-coated (water-facing side) with anion exchange, cation exchange, and neutral polymer coatings of different thicknesses to incorporate the separator into the cathode. The anion exchange polymer coating resulted in greater power density (1167±135mWm−2) than a cation exchange coating (439±2mWm−2). This power output was similar to that produced by a Nafion-coated cathode (1114±174mWm−2), and slightly lower than the uncoated cathode (1384±82mWm−2). Thicker coatings reduced oxygen diffusion into the electrolyte and increased coulombic efficiency (CE=56–64%) relative to an uncoated cathode (29±8%), but decreased power production (255–574mWm−2). Electrochemical characterization of the cathodes ex situ to the MFC showed that the cathodes with the lowest charge transfer resistance and the highest oxygen reduction activity produced the most power in MFC tests. The results on hydrophilic cathode separator layers revealed a trade off between power and CE. Cathodes coated with a thin coating of anion exchange polymer show promise for controlling oxygen transfer while minimally affecting power production.

High‐efficiency power production from coal with carbon capture

AbstractA zero‐emissions power plant with high efficiency is presented. Syngas, produced by the gasification of coal, is shifted to produce H2 which in turn fuels stacks of solid oxide fuel cells. Because the fuel cells maintain separate anode and cathode streams, air can be used as the oxygen source without diluting the fuel exhaust with nitrogen. This enables recovery of CO2 from the exhaust with a very small energy penalty. As a result, an absorption‐based CO2 recovery process is avoided, as well as the production of large quantities of high‐purity O2, allowing a high overall thermal efficiency and essentially eliminating the energy penalty for carbon capture. © 2010 American Institute of Chemical Engineers AIChE J, 2010

Image reversal photoresist for small molecule organic light-emitting diode applications

We have developed an image reversal photoresist with high thermal stability and electric insulating properties for small molecule organic light-emitting diode (SMOLED) applications. The thermal stability and electric insulating properties were investigated and compared to those of the conventional insulation layer and cathode separator materials of SMOLEDs. Moreover, to verify its applicability and reliability, 1.17″ 96 × RGB (red, green, and blue subpixels) × 96 passive matrix SMOLEDs were fabricated using the image reversal photoresist. This image reversal photoresist makes a single isolation structure, where the insulation layer and cathode separators of SMOLEDs are simultaneously formed by a single layer of image reversal photoresist, applicable to SMOLEDs, thereby reducing the fabrication processes and cutting down the manufacturing cost.