The Experts below are selected from a list of 27 Experts worldwide ranked by ideXlab platform
Gunther G Scherer - One of the best experts on this subject based on the ideXlab platform.
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in situ Membrane Resistance measurements in polymer electrolyte fuel Cells by fast auxiliary current pulses
Journal of The Electrochemical Society, 1995Co-Authors: Felix N Buchi, Alois Marek, Gunther G SchererAbstract:A solid-state current Pulse generator for in situ Membrane Resistance measurements by superimposed square current pulses in polymer electrolyte fuel Cells was designed and built. The choice of the measuring technique and of parameters of the instrumentation was based on a critical analysis of the relevant electrochemical and physical processes. The inductance of the current pulse path is very low ({approx}5 nH), because the last stage of the generator is directly attached to the fuel Cell. This low inductance -permits the generation of 5 A pulses with extremely fast (decay time {<=}5 ns) trailing edges (accompanied by a moderate ringing), which in turn makes it possible to measure the voltage transient induced by the current decay, with gigahertz resolution. The voltage transient is analyzed in a time window of 200 to 700 ns after the end of the pulse. By measurements in this time window, it is possible to separate accurately the ohmic series Resistance of the Cell (Membrane Resistance) from the other over potentials at the electrochemical interfaces. Because the pulse current path is independent of the dc loop, the Resistance can be measured independently of the dc value, i.e., at open circuit and under high current density conditions.more » The instrument was tested, and the results were analyzed for accuracy. Resistances down to 2 m{Omega} can be measured with an error of <5%. The influence of the pulse length and pulse amplitude on the Cell voltage response was also investigated. For Cell Resistances in the order of few milliohms, a current pulse amplitude of 5 A is the minimum requirement for accurate measurements.« less
Felix N Buchi - One of the best experts on this subject based on the ideXlab platform.
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in situ Membrane Resistance measurements in polymer electrolyte fuel Cells by fast auxiliary current pulses
Journal of The Electrochemical Society, 1995Co-Authors: Felix N Buchi, Alois Marek, Gunther G SchererAbstract:A solid-state current Pulse generator for in situ Membrane Resistance measurements by superimposed square current pulses in polymer electrolyte fuel Cells was designed and built. The choice of the measuring technique and of parameters of the instrumentation was based on a critical analysis of the relevant electrochemical and physical processes. The inductance of the current pulse path is very low ({approx}5 nH), because the last stage of the generator is directly attached to the fuel Cell. This low inductance -permits the generation of 5 A pulses with extremely fast (decay time {<=}5 ns) trailing edges (accompanied by a moderate ringing), which in turn makes it possible to measure the voltage transient induced by the current decay, with gigahertz resolution. The voltage transient is analyzed in a time window of 200 to 700 ns after the end of the pulse. By measurements in this time window, it is possible to separate accurately the ohmic series Resistance of the Cell (Membrane Resistance) from the other over potentials at the electrochemical interfaces. Because the pulse current path is independent of the dc loop, the Resistance can be measured independently of the dc value, i.e., at open circuit and under high current density conditions.more » The instrument was tested, and the results were analyzed for accuracy. Resistances down to 2 m{Omega} can be measured with an error of <5%. The influence of the pulse length and pulse amplitude on the Cell voltage response was also investigated. For Cell Resistances in the order of few milliohms, a current pulse amplitude of 5 A is the minimum requirement for accurate measurements.« less
Alois Marek - One of the best experts on this subject based on the ideXlab platform.
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in situ Membrane Resistance measurements in polymer electrolyte fuel Cells by fast auxiliary current pulses
Journal of The Electrochemical Society, 1995Co-Authors: Felix N Buchi, Alois Marek, Gunther G SchererAbstract:A solid-state current Pulse generator for in situ Membrane Resistance measurements by superimposed square current pulses in polymer electrolyte fuel Cells was designed and built. The choice of the measuring technique and of parameters of the instrumentation was based on a critical analysis of the relevant electrochemical and physical processes. The inductance of the current pulse path is very low ({approx}5 nH), because the last stage of the generator is directly attached to the fuel Cell. This low inductance -permits the generation of 5 A pulses with extremely fast (decay time {<=}5 ns) trailing edges (accompanied by a moderate ringing), which in turn makes it possible to measure the voltage transient induced by the current decay, with gigahertz resolution. The voltage transient is analyzed in a time window of 200 to 700 ns after the end of the pulse. By measurements in this time window, it is possible to separate accurately the ohmic series Resistance of the Cell (Membrane Resistance) from the other over potentials at the electrochemical interfaces. Because the pulse current path is independent of the dc loop, the Resistance can be measured independently of the dc value, i.e., at open circuit and under high current density conditions.more » The instrument was tested, and the results were analyzed for accuracy. Resistances down to 2 m{Omega} can be measured with an error of <5%. The influence of the pulse length and pulse amplitude on the Cell voltage response was also investigated. For Cell Resistances in the order of few milliohms, a current pulse amplitude of 5 A is the minimum requirement for accurate measurements.« less
Terumi Nakajima - One of the best experts on this subject based on the ideXlab platform.
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oxyopinins large amphipathic peptides isolated from the venom of the wolf spider oxyopes kitabensis with cytolytic properties and positive insecticidal cooperativity with spider neurotoxins
Journal of Biological Chemistry, 2002Co-Authors: Gerardo Corzo, Elba Villegas, Froylan Gomezlagunas, Lourival D Possani, Olga S Belokoneva, Terumi NakajimaAbstract:Abstract Five amphipathic peptides with antimicrobial, hemolytic, and insecticidal activity were isolated from the crude venom of the wolf spider Oxyopes kitabensis. The peptides, named oxyopinins, are the largest linear cationic amphipathic peptides from the venom of a spider that have been chemically characterized at present. According to their primary structure Oxyopinin 1 is composed of 48 amino acid residues showing extended sequence similarity to the ant insecticidal peptide ponericinL2 and to the frog antimicrobial peptide dermaseptin. Oxyopinins 2a, 2b, 2c, and 2d have highly similar sequences. At least 27 out of 37 amino acid residues are conserved. They also show a segment of sequence similar to ponericinL2. Circular dichroism analyses showed that the secondary structure of the five peptides is essentially α-helical. Oxyopinins showed disrupting activities toward both biological Membranes and artificial vesicles, particularly to those rich in phosphatidylcholine. Electrophysiological recordings performed on insect Cells (Sf9) showed that the oxyopinins produce a drastic reduction of Cell Membrane Resistance by opening non-selective ion channels. Additionally, a new paralytic neurotoxin named Oxytoxin 1 was purified from the same spider venom. It contains 69 amino acid residue cross-linked by five disulfide bridges. Application of mixtures containing oxyopinins and Oxytoxin 1 to insect larvae showed a potentiation phenomenon, by which an increase lethality effect is observed. These results suggest that the linear amphipathic peptides in spider venoms and neuropeptides cooperate to capture insects efficiently.
Aimy Bazylak - One of the best experts on this subject based on the ideXlab platform.
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Hydrophilic microporous layer coatings for polymer electrolyte Membrane fuel Cells operating without anode humidification
Journal of Power Sources, 2018Co-Authors: Pranay Shrestha, Daniel Muirhead, Jongmin Lee, Andrew Kai Cheung Wong, Benzhong Zhao, Hang Liu, Nan Ge, David Ouellette, Rupak K Banerjee, Aimy BazylakAbstract:Abstract In this study, a hydrophilic microporous layer (MPL) coating was applied to a commercial hydrophobic bi-layer gas diffusion layer (GDL). We investigated the effect of the hydrophilic MPL coating on Membrane hydration and liquid water distribution within the GDLs during fuel Cell operation without anode humidification, using fuel Cell performance monitoring and simultaneous synchrotron X-ray visualization. The application of the hydrophilic coating was found to enhance performance of the fuel Cell. Specifically, the application of the hydrophilic MPL coating led to an increase in Cell potential of up to 14% (0.07 V at 1.5 A/cm2) and a decrease in fuel Cell Membrane Resistance. The decrease in Membrane Resistance was attributed to improved Membrane hydration. This improvement in Membrane hydration was caused by the increase in liquid water retention at the catalyst layer-MPL interfaces. At high current densities, the application of the hydrophilic MPL coating led to increased liquid water accumulation within the cathode GDL, which subsequently led to increased oxygen transport Resistance. Our study demonstrates that the wettability of the GDL can be tailored to enhance fuel Cell performance for a desired range of operating conditions by balancing Membrane hydration and oxygen transport.