A trimethoprim-selective membrane electrode

An electrode selective for trimethoprim is based on the ion-pair complex of trimethoprim with silicotungstate, and gives rapid response to change in trimethoprim concentration over the range 3 × 10⁻⁵−2 × 10⁻² M with a response slope of 51.0 ± 1.5 mV/decade. No significant interferences are caused by sulpha-drugs. The electrode can be used for the potentiometric determination of trimethoprim.     

Cathode catalysts degradation mechanism from liquid electrolyte to membrane electrode assembly

Single-cell and half-cell degradation test procedures were evaluated for carbon-supported Pt/C, PtCo/C and PtNi/C catalysts. Half-cell analyses were employed to understand the effect of the number of cycles and of the scan rate over the cathode catalysts degradation under potential cycling from 0.6 to 1.2 V. The data suggested a time-dependent degradation for all three catalytic systems. Single-cell measurements were used to evaluate the impact of catalyst degradation on fuel cell performance. The measurements in both setups showed similar ECSA and ORR mass activity losses. Specific degradation mechanisms related to Pt dissolution, Pt agglomeration, and transitional metal leaching were quantified and correlated with performance losses.     

A novel membrane electrode assembly for improving the efficiency of the unitized regenerative fuel cell

A novel membrane electrode assembly (MEA) for unitized regenerative fuel cell (URFC) has been developed. The MEA was fabricated to improve the efficiency of the URFC by a Nafion-pyrolyzed method. The polarization curves for fuel cell and water electrolysis modes of URFC operation both were investigated. The MEA improved water management and minimized mass transport limitations. The URFC using the novel MEA exhibited a high water electrolysis performance and a much higher fuel cell performance than that of the URFC using the conventional MEA. The efficiency of fuel cell and round-trip enhanced 13.5% and 10.8% at 700 mA/cm² with the novel MEA respectively.     

A membrane electrode assembly with high fuel coulombic efficiency for passive direct borohydride fuel cells

Here, we report the development of a new membrane electrode assembly (MEA) structure for passive direct borohydride fuel cells (DBFCs). The anode of this type of MEA includes upper and lower parts for the electro-oxidation of borohydride and hydrogen, respectively. In comparison to conventional MEAs, the maximum power of this MEA is increased by 28.1%, and the anode polarization is decreased due to the current contribution of hydrogen electro-oxidation. The hydrogen generated from borohydride hydrolysis can be oxidized inside the cell, and the fuel coulombic efficiency reaches 100%. Therefore, high fuel utilization and cell safety can be obtained by employing this novel MEA in DBFCs.     

Characteristic simulation with various anode support thicknesses of membrane electrode assembly in SOFC

This study focuses on the research of solid oxide fuel cell (SOFC) and proposes reasonably practical designs, analyses, and numerical analyses with coupling software in physics, COMSOL Multiphysics, as the analysis tool to discuss the effects on the SOFC performance. This research applies the design of electrode support (anode support) to substitute the original electrolyte support, Yttria-stabilized zirconia, so that the electrolyte membrane could form a membrane to reduce ohmic resistance and increase power density. This study further discusses the effects of various flow fields (counterflow and co-flow) on internal mass transfer and SOFC performance. The findings show that the cell performance of SOFC with co-flow is better than counterpart with counterflow under anode support thickness 1,000 μm. Regarding the analyses of porosity effect with the porosity 0.7 and tortuosity 4.5, the power density reaches the maximum that could enhance the cell performance.     

Study of a highly durable low-humidification membrane electrode assembly using crosslinked polyvinyl alcohol for polymer electrolyte membrane fuel cells

A low-humidification membrane electrode assembly (MEA) for polymer electrolyte membrane fuel cells (PEMFCs) is prepared by adding the hydrophilic polymer: polyvinyl alcohol (PVA) to the anode catalyst layer. Glutaraldehyde (GA) is employed as a crosslinking agent for PVA to prevent washing from the anode during cell operation. This is confirmed by an immersion test in deionized water for 2 h. A single cell test is conducted at 80 °C, ambient pressure, and 50 % relative humidity. Although MEA containing 1 wt% non-crosslinked PVA shows the best initial performance (788 mA cm^?2 at 0.6 V), a considerable performance decrease of 41 % is observed following a 100-h durability test. However, MEA containing 5 wt% crosslinked PVA demonstrates enhanced durability, with little performance decline after 100 h of constant current operation. This strongly suggests that crosslinked PVA plays a crucial role in a low-humidification MEA at low humidity levels.     

A compact electrode assembly for voltammetric measurements with solid electrodes

Summary An electrode assembly is presented consisting of a cell compartment of plexiglass and an electronic circuit for automatic performance. It was especially designed for the use with polarographs PAR 264, 264 A, 384 and 384 B when working with solid electrodes. A special attempt was made to reduce the metallic parts of the assembly to a minimum in order to avoid contamination risks when analyzing heavy metals.

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Kompakter Elektrodenstand für voltammetrische Messungen mit Festkörperelektroden

Zusammenfassung Ein Elektrodenstand wird beschrieben, der aus einer Meßzelleneinheit aus Plexiglas und einem elektronischen Schaltkreis für automatischen Betrieb besteht. Er wurde speziell für die Polarographen-PAR-Modelle 264 und 384 für voltammetrische Messungen mit Festkörperelektroden konzipiert. Um bei Schwermetallanalysen das Kontaminationsrisiko möglichst gering zu halten, wurden metallische Teile der Zelle weitgehendst vermieden.

     

Improvement of the proton exchange membrane fuel cell performances by optimization of the hot pressing process for membrane electrode assembly

The present study deals with PEM fuel cells, namely with the optimization of the hot pressing process for membrane electrode assembly (MEA) fabrication. Designs of experiments (DoE) have been used for evaluating the effect of hot pressing parameters (pressure, temperature, and time) on the MEA electrical performances. Full factorial 2³ DoE showed that the most important parameter is the pressing temperature. Surface response methodology indicated a non-monotonous behavior of the MEA electrical performances with respect to the pressing temperature. The MEA electrical performances increased with the pressing temperature in the temperature range from 100 to 115 °C, and decreased significantly in the temperature range from 115 to 130 °C. This behavior was attributed to drastic changes of the Nafion® 112 membrane properties and membrane/electrode interface over this temperature range. Observations of the MEA cross-section structure by scanning electron microscopy confirmed such hypotheses. Thermo-mechanical properties of Nafion® as determined by dynamic scanning calorimetry allowed estimating the glass transition temperature at ca. T _g?≈?117 °C in the conditions of the present study. The higher H₂/air fuel cell performance of ca. 0.8 W cm^?2 was obtained with the optimized pressing temperature for MEA fabrication of ca. 115 °C close to the T _g temperature of Nafion® 112, whereas for higher temperature the structure of the Nafion® membrane and of the membrane–electrode interface is damaged.     

A chloroquine membrane electrode with low detection limit

A PVC membrane electrode for chloroquine [7-chloro-4-(4-diethylamine-1-methylbutylamino)-quinoline] based on a chloroquine/dinonylnaphthalene sulphonic acid ion-pair is described. The electrode shows near-Nernstian response in the 10^?2–10^?6 M range and a detection limit of 2 × 10^?7 M. Its selectivity relative to various inorganic ions, amino acids, neurotransmitters, drugs, and some excipients is reported. Direct potentiometry is used to determine chloroquine in pharmaceutical preparations with good results.     

A polystyrene-based membrane electrode sensitive to molybdate ions

A polystyrene-based zirconium oxide membrane has been used to determine the concentration of molybdate ions in the range 0.5-10(-3)M and pH range 7-11. The response time is about 20 sec and the electrode remains usable for at least 6 months. It can also be used as an indicator electrode for titrations involving molybdate ions. Univalent anions interfere more strongly than bivalent and multivalent anions.     

A urea-sensing membrane electrode for whole blood measurements

The construction and properties of a new urea-sensing membrane electrode capable of making direct urea measurements in whole blood are described. The electrode has a layered structure in which a small quantity of EDTA-stabilized urease enzyme solution is held between an external dialysis membrane and the gas-permeable membrane of a conventional ammonia selective electrode. It is shown that the electrode functions reliably in whole blood samples, used with minimal pretreatment, as well as in serum or aqueous solutions. The range, dynamic response, lifetime, precision, and accuracy of the electrode system are appropriate for clinical measurements in whole blood or serum, and promise to simplify such analyses with an attendant reduction in costs.     

A new membrane electrode system with iodide-selective properties

The strongly basic anion-exchange resin Dowex 2 when saturated with triiodide and placed in a gel layer in a glass tube acts as an electrode for iodine, as does a platinum wire electrode. When the gel membrane is placed with a platinum electrode in an iodide solution, the anion-exchange resin adsorbs iodide selectively, and a decrease in the potential of the membrane electrode is caused. The arrangement can be used as an iodide-selective electrode, which shows a linear response over the pI^-range 1–5 and an excellent selectivity for iodide over other halides.     

Chitosan-mediated in situ biomolecule assembly in completely packaged microfluidic devices

We report facile in situ biomolecule assembly at readily addressable sites in microfluidic channels after complete fabrication and packaging of the microfluidic device. Aminopolysaccharide chitosan's pH responsive and chemically reactive properties allow electric signal-guided biomolecule assembly onto conductive inorganic surfaces from the aqueous environment, preserving the activity of the biomolecules. A transparent and nonpermanently packaged device allows consistently leak-free sealing, simple in situ and ex situ examination of the assembly procedures, fluidic input/outputs for transport of aqueous solutions, and electrical ports to guide the assembly onto the patterned gold electrode sites within the channel. Both in situ fluorescence and ex situ profilometer results confirm chitosan-mediated in situ biomolecule assembly, demonstrating a simple approach to direct the assembly of biological components into a completely fabricated device. We believe that this strategy holds significant potential as a simple and generic biomolecule assembly approach for future applications in complex biomolecular or biosensing analyses as well as in sophisticated microfluidic networks as anticipated for future lab-on-a-chip devices.     

New cocaine-selective membrane electrode

The sensitivity and selectivity of a cocaine-selective membrane electrode have been improved with the use of sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate as an ion-exchanger and tetrakis(2-ethylhexyl) pyromellitate (TEHPY) as a solvent mediator. The use of TEHPY suppressed the responses to lipophilic quaternary ammonium ions and strengthened the response to cocaine. The electrode exhibited a near-Nernstian response over a concentration range of 10⁻²to 10⁻⁶ M cocaine with a slope of 56 mV per decade. The lower limit of detection was 4 × 10⁻⁷ M cocaine. Interference by other drugs (morphine and codeine) and a stimulant (methamphetamine) was negligible. This electrode was applied for the determination of cocaine in a drug mixture containing cocaine and morphine, which is widely used to suppress acute pain in cancer patients. The concentration of cocaine, different in each patient, was measured precisely with an average recovery of 99.9% and a mean relative standard deviation of 0.56%.     

A new selenite selective membrane electrode and its application

A new membrane ion selective electrode sensitive to selenite ion has been developed. The electrode consisted of 1,2-phenylenediamine selen complex PIS (piaselenol) as the active material, PVC or SR (silicon rubber) as membrane matrix and DBF (dibutylphtalate) as plasticizer. This electrode showed linear response for selenite ion in the 10(-5)-10(-1)M concentration range. The slope of the linear portion was 21 mV/10-fold change in selenite concentration. The effect of membrane composition and membrane thickness on electrode response was studied and the electrode which contains 2% PIS, 49% PVC and 49% DBF was found to be the most sensitive one to selenite. The slope of the electrode did not change for 2 months and the pH change did not affect the response of the electrode in pH range of 3-9. The interferences of SO(4)(2-), SO(3)(2-), S(2-), HPO4(2-), CI(-), Br(-), and I(-) are investigated and while no interference was observed for SO(4)(2-), SO(3)(2-), S(2-) and I(-), a very small interference was observed for CI(-) and Br(-). The selenium present in anodic slime is determined using this electrode.     

A membrane electrode for nitrate and other univalent anions

A membrane electrode has been developed which is responsive to nitrate and other univalent anions but non-responsive to sulphate and other multivalent anions and to cations other than hydrogen. The membrane is prepared by polymerizing a mixture of phenol, formaldehyde, ammonia and nickel nitrate directly to a film for mounting in the usual cell-with-membrane assembly. Response to hydrogen ion is 0.30 mV per pH unit, to nitrate 0.60 mV per pNO(3) (activity) unit. Based on chemical composition and behaviour, physical properties, and electrical response, a structure and mechanism for exchange with hydrogen ion and nitrate ion and for internal electrical conduction has been postulated. Applications have been made to the determination of nitrate and to the detection of end-points.