Method for Kinetic Analysis of a Recombination‐Controlled Reaction over a Wide Range of Current‐Densities from the Reversible Region up to the Limiting Current

1981 ◽  
Vol 128 (5) ◽  
pp. 1022-1027 ◽  
Author(s):  
B. E. Conway ◽  
D. M. Novak
Keyword(s):  
Kinetic Analysis ◽  
Limiting Current ◽  
Wide Range ◽  
Current Densities

scholarly journals PEM Single Cells under Differential Conditions: Full Factorial Parameterization of the ORR and HOR Kinetics and Loss Analysis

2021 ◽  
Author(s):  
Christophe Gerling ◽  
Matthias Hanauer ◽  
Ulrich Berner ◽  
Kaspar Andreas Friedrich
Keyword(s):  
Steady State ◽  
Electrochemical Impedance ◽  
Hydrogen Oxidation ◽  
Single Cells ◽  
Reduction Reaction ◽  
Limiting Current ◽  
Hydrogen Oxidation Reaction ◽  
Wide Range ◽  
Current Densities ◽  
Full Factorial

Abstract The anode and cathode kinetics are parameterized based on differential cell measurements. Systematic parameter variations are evaluated to disentangle the dependencies of the electrochemical impedance spectroscopy (EIS) signatures in H2/H2 mode. We introduce a new CO recovery protocol for both electrodes that enables to accurately characterize the hydrogen oxidation reaction (HOR) kinetics. Then, we demonstrate that a compact Tafel kinetics law captures the oxygen reduction reaction (ORR) kinetics for a full factorial grid of conditions, covering a wide range of relative humidities (rH), temperatures, oxygen partial pressures and current densities. This yields the characteristic activation energy and effective reaction order, and we reconcile models that make different assumptions regarding the rH dependency. Moreover, we analyze O2 transport contributions by steady-state and transient limiting current techniques and heliox measurements. Although the rising uncertainty of loss corrections at high current densities makes it impossible to unambiguously identify an intrinsic potential-dependent change of the Tafel slope, our data support that such effect needs not be considered for steady-state cathodic half-cell potentials above 0.8 V.

Compact and efficient gas diffusion electrodes based on nanoporous alumina membranes for microfuel cells and gas sensors

The Analyst ◽  
2020 ◽  
Vol 145 (1) ◽  
pp. 122-131 ◽  
Author(s):  
Wanda V. Fernandez ◽  
Rocío T. Tosello ◽  
José L. Fernández
Keyword(s):  
Response Times ◽  
Hydrogen Oxidation ◽  
Fast Response ◽  
Gas Diffusion ◽  
Limiting Current ◽  
Gas Diffusion Electrodes ◽  
Nanoporous Alumina ◽  
Alumina Membranes ◽  
Current Densities ◽  
Microfuel Cells

Gas diffusion electrodes based on nanoporous alumina membranes electrocatalyze hydrogen oxidation at high diffusion-limiting current densities with fast response times.

scholarly journals Stabilizing electrodeposition in elastic solid electrolytes containing immobilized anions

2016 ◽  
Vol 2 (7) ◽  
pp. e1600320 ◽  
Author(s):  
Mukul D. Tikekar ◽  
Lynden A. Archer ◽  
Donald L. Koch
Keyword(s):  
Elastic Solid ◽  
Present Theory ◽  
Metal Electrode ◽  
Mitigation Strategies ◽  
Factors Affecting ◽  
Wide Range ◽  
Current Densities ◽  
Morphological Instabilities ◽  
The Stability

Ion transport–driven instabilities in electrodeposition of metals that lead to morphological instabilities and dendrites are receiving renewed attention because mitigation strategies are needed for improving rechargeability and safety of lithium batteries. The growth rate of these morphological instabilities can be slowed by immobilizing a fraction of anions within the electrolyte to reduce the electric field at the metal electrode. We analyze the role of elastic deformation of the solid electrolyte with immobilized anions and present theory combining the roles of separator elasticity and modified transport to evaluate the factors affecting the stability of planar deposition over a wide range of current densities. We find that stable electrodeposition can be easily achieved even at relatively high current densities in electrolytes/separators with moderate polymer-like mechanical moduli, provided a small fraction of anions are immobilized in the separator.

scholarly journals Electrical Discharges in Oil-Lubricated Rolling Contacts and Their Detection Using Electrostatic Sensing Technique

Sensors ◽  
2022 ◽  
Vol 22 (1) ◽  
pp. 392
Author(s):  
Kamran Esmaeili ◽  
Ling Wang ◽  
Terry J. Harvey ◽  
Neil M. White ◽  
Walter Holweger
Keyword(s):  
High Current Density ◽  
Rolling Contact ◽  
Voltage Measurement ◽  
Electrical Discharges ◽  
Steel Rolling ◽  
Bearing Life ◽  
Wide Range ◽  
Robust Techniques ◽  
Rolling Elements ◽  
Current Densities

The reliability of rolling element bearings has been substantially undermined by the presence of parasitic and stray currents. Electrical discharges can occur between the raceway and the rolling elements and it has been previously shown that these discharges at relatively high current density levels can result in fluting and corrugation damages. Recent publications have shown that for a bearing operating at specific mechanical conditions (load, temperature, speed, and slip), electrical discharges at low current densities (<1 mA/mm2) may substantially reduce bearing life due to the formation of white etching cracks (WECs) in bearing components, often in junction with lubricants. To date, limited studies have been conducted to understand the electrical discharges at relatively low current densities (<1 mA/mm2), partially due to the lack of robust techniques for in-situ quantification of discharges. This study, using voltage measurement and electrostatic sensors, investigates discharges in an oil-lubricated steel-steel rolling contact on a TE74 twin-roller machine under a wide range of electrical and mechanical conditions. The results show that the discharges events between the rollers are influenced by temperature, load, and speed due to changes in the lubricant film thickness and contact area, and the sensors are effective in detecting, characterizing and quantifying the discharges. Hence, these sensors can be effectively used to study the influence of discharges on WEC formation.

scholarly journals An Investigation of Direct Hydrocarbon (Propane) Fuel Cell Performance Using Mathematical Modeling

2018 ◽  
Vol 2018 ◽  
pp. 1-18
Author(s):  
Bhavana Parackal ◽  
Hamidreza Khakdaman ◽  
Yves Bourgault ◽  
Marten Ternan
Keyword(s):  
Fuel Cells ◽  
Current Density ◽  
Reaction Rate ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Polarization Curves ◽  
Limiting Current ◽  
Fuel Cell Performance ◽  
Limiting Current Density ◽  
Current Densities

An improved mathematical model was used to extend polarization curves for direct propane fuel cells (DPFCs) to larger current densities than could be obtained with any of the previous models. DPFC performance was then evaluated using eleven different variables. The variables related to transport phenomena had little effect on DPFC polarization curves. The variables that had the greatest influence on DPFC polarization curves were all related to reaction rate phenomena. Reaction rate phenomena were dominant over the entire DPFC polarization curve up to 100 mA/cm2, which is a value that approaches the limiting current densities of DPFCs. Previously it was known that DPFCs are much different than hydrogen proton exchange membrane fuel cells (PEMFCs). This is the first work to show the reason for that difference. Reaction rate phenomena are dominant in DPFCs up to the limiting current density. In contrast the dominant phenomenon in hydrogen PEMFCs changes from reaction rate phenomena to proton migration through the electrolyte and to gas diffusion at the cathode as the current density increases up to the limiting current density.

Reconstitution of local Ca2+ signaling between cardiac L-type Ca2+ channels and ryanodine receptors: insights into regulation by FKBP12.6

2005 ◽  
Vol 289 (6) ◽  
pp. C1476-C1484 ◽  
Author(s):  
Sanjeewa A. Goonasekera ◽  
S. R. Wayne Chen ◽  
Robert T. Dirksen
Keyword(s):  
Voltage Dependence ◽  
Molecular Model ◽  
Ryanodine Receptors ◽  
Dihydropyridine Receptors ◽  
Wide Range ◽  
Fluorescence Change ◽  
Current Densities ◽  
Ca2 Channels

Ca+-induced Ca2+ release (CICR) in the heart involves local Ca2+ signaling between sarcolemmal L-type Ca2+ channels (dihydropyridine receptors, DHPRs) and type 2 ryanodine receptors (RyR2s) in the sarcoplasmic reticulum (SR). We reconstituted cardiac-like CICR by expressing a cardiac dihydropyridine-insensitive (T1066Y/Q1070M) α1-subunit (α1CYM) and RyR2 in myotubes derived from RyR1-knockout (dyspedic) mice. Myotubes expressing α1CYM and RyR2 were vesiculated and exhibited spontaneous Ca2+ oscillations that resulted in chaotic and uncontrolled contractions. Coexpression of FKBP12.6 (but not FKBP12.0) with α1CYM and RyR2 eliminated vesiculations and reduced the percentage of myotubes exhibiting uncontrolled global Ca2+ oscillations (63% and 13% of cells exhibited oscillations in the absence and presence of FKBP12.6, respectively). α1CYM/RyR2/FKBP12.6-expressing myotubes exhibited robust and rapid electrically evoked Ca2+ transients that required extracellular Ca2+. Depolarization-induced Ca2+ release in α1CYM/RyR2/FKBP12.6-expressing myotubes exhibited a bell-shaped voltage dependence that was fourfold larger than that of myotubes expressing α1CYM alone (maximal fluorescence change was 2.10 ± 0.39 and 0.54 ± 0.07, respectively), despite similar Ca2+ current densities. In addition, the gain of CICR in α1CYM/RyR2/FKBP12.6-expressing myotubes exhibited a nonlinear voltage dependence, being considerably larger at threshold potentials. We used this molecular model of local α1C-RyR2 signaling to assess the ability of FKBP12.6 to inhibit spontaneous Ca2+ release via a phosphomimetic mutation in RyR2 (S2808D). Electrically evoked Ca2+ release and the incidence of spontaneous Ca2+ oscillations did not differ in wild-type RyR2- and S2808D-expressing myotubes over a wide range of FKBP12.6 expression. Thus a negative charge at S2808 does not alter in situ regulation of RyR2 by FKBP12.6.

scholarly journals Kinetic Analysis of 2-[11C]Thymidine PET Imaging Studies of Malignant Brain Tumors: Preliminary Patient Results

2002 ◽  
Vol 1 (3) ◽  
pp. 153535002002021
Author(s):  
Joanne M. Wells ◽  
David A. Mankoff ◽  
Janet F. Eary ◽  
Alexander M. Spence ◽  
Mark Muzi ◽  
...  
Keyword(s):  
Brain Tumors ◽  
Kinetic Analysis ◽  
Cellular Proliferation ◽  
Response To Therapy ◽  
Response To Treatment ◽  
Normal Brain ◽  
Arterial Blood ◽  
Pet Tracer ◽  
Wide Range ◽  
Thymidine Transport

2-[11C]Thymidine (TdR), a PET tracer for cellular proliferation, may be advantageous for monitoring brain tumor progression and response to therapy. Kinetic analysis of dynamic TdR images was performed to estimate the rate of thymidine transport ( K1t) and thymidine flux ( KTdR) into brain tumors and normal brain. These estimates were compared to MRI and pathologic results. Methods: Twenty patients underwent sequential [11C]CO2 (major TdR metabolite) and TdR PET studies with arterial blood sampling and metabolite analysis. The data were fitted using the five-compartment model described in the companion article. Results: Comparison of model estimates with clinical and pathologic data shows that K1t is higher for MRI contrast enhancing tumors ( p > .001), and KTdR increases with tumor grade ( p > .02). On average, TdR retention was lower after treatment in high-grade tumors. The model was able to distinguish between increased thymidine transport due to blood–brain barrier breakdown and increased tracer retention associated with tumor cell proliferation. Conclusion: Initial analysis of model estimates of thymidine retention and transport show good agreement with the clinical and pathological features of a wide range of brain tumors. Ongoing studies will evaluate its role in measuring response to treatment and predicting outcome.

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