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Full-Text Articles in Engineering
Sr2Fe1.5Mo0.5O6 As Cathodes For Intermediate-Temperature Solid Oxide Fuel Cells With La0.8Sr0.2Ga0.87Mg0.13O3 Electrolyte, Guoliang Xiao, Qiang Liu, Fei Zhao, Lei Zhang, Changrong Xia, Fanglin Chen
Sr2Fe1.5Mo0.5O6 As Cathodes For Intermediate-Temperature Solid Oxide Fuel Cells With La0.8Sr0.2Ga0.87Mg0.13O3 Electrolyte, Guoliang Xiao, Qiang Liu, Fei Zhao, Lei Zhang, Changrong Xia, Fanglin Chen
Faculty Publications
The performance of Sr2Fe1.5Mo0.5O6 (SFMO) as a cathode material has been investigated in this study. The oxygen ionic conductivityof SFMO reaches 0.13 S cm-1 at 800°C in air. The chemical diffusion coefficient (Dchem) and surface exchange constant (kex) of SFMO at 750°C are 5.0 x 10-6 cm2 s-1 and 2.8 x 10-5 cm s-1, respectively, suggesting that SFMO may have good electrochemicalactivity for oxygen reduction. SFMO shows a thermal expansion coefficient (TEC) of 14.5 x 10-6 K-1 the …
Sulfur Dioxide Crossover During The Production Of Hydrogen And Sulfuric Acid In A Pem Electrolyzer, John A. Staser, John W. Weidner
Sulfur Dioxide Crossover During The Production Of Hydrogen And Sulfuric Acid In A Pem Electrolyzer, John A. Staser, John W. Weidner
Faculty Publications
A proton exchange membrane (PEM) electrolyzer has been investigated as a viable system for the electrolysis step in the thermochemical conversion of sulfur dioxide to sulfuric acid for the large-scale production of hydrogen. Unfortunately, during operation, sulfur dioxide can diffuse from the anode to the cathode. This has several negative effects, including reduction to sulfur that could potentially damage the electrode, consumption of current that would otherwise be used for the production of hydrogen, introduction of oxygen and SO2 to the hydrogen stream, and loss of sulfur to the cycle. However, proper water management can reduce or eliminate the …
Enhanced Dielectric Properties In Single Crystal-Like Bifeo3 Thin Films Grown By Flux-Mediated Epitaxy, S.-H. Lim, M. Murakami, J. H. Yang, S.-Y. Young, Jason R. Hattrick-Simpers, M. Wuttig, L. G. Salamanca-Riba, I. Takeuchi
Enhanced Dielectric Properties In Single Crystal-Like Bifeo3 Thin Films Grown By Flux-Mediated Epitaxy, S.-H. Lim, M. Murakami, J. H. Yang, S.-Y. Young, Jason R. Hattrick-Simpers, M. Wuttig, L. G. Salamanca-Riba, I. Takeuchi
Faculty Publications
We have fabricated single crystal-like BiFeO3 (BFO) thin films by flux-mediated epitaxy using pulsed laser deposition(PLD). The Bi–Cu–O flux composition and its thickness were optimized using composition spread, thickness gradient, and temperature gradient libraries. The optimized BFO thin films grown with this technique showed larger grain size of ∼2μm and higher dielectric constant in the range of 260–340 than those for standard PLD grown films. In addition, the leakage current density of the films was reduced by two orders of magnitude compared to that of standard PLD grown films.
Novel Pemfc Cathodes Prepared By Pulse Deposition, Subasri M. Ayyadurai, Yoon-Seok Choi, Prabhu Ganesan, Swaminatha P. Kumaraguru, Branko N. Popov
Novel Pemfc Cathodes Prepared By Pulse Deposition, Subasri M. Ayyadurai, Yoon-Seok Choi, Prabhu Ganesan, Swaminatha P. Kumaraguru, Branko N. Popov
Faculty Publications
A pulse electrodeposition method of preparing thin platinum catalyst layers for polymer electrolyte membrane fuel cell (PEMFC) cathodes has been developed through surface activation of the gas diffusion layer (GDL) by a wetting agent. The performance of the catalyst layer was optimized by wetting agent type, immersion time in the wetting agent, and pulse deposition parameters such as total charge density, peak current density, and duty cycle ratio. The Toff time played a more important role than the Ton time in determining the electrode characteristics such as high concentration of Pt, smaller particle size, and loading. Pt cathodes …
Short-Time Transient Analysis Of Intercalation Of An Ion Into A Sphere, Sheba Devan, Ralph E. White
Short-Time Transient Analysis Of Intercalation Of An Ion Into A Sphere, Sheba Devan, Ralph E. White
Faculty Publications
A short-time transient analysis is presented for a sinusoidal input potential for a spherical particle. The objective of this work was to extract accurate values of the parameters associated with an intercalation into a spherical particle. These parameters are exchange current density, double-layer capacitance, and diffusion coefficient. The effects of these parameters on the response were examined using a sensitivity analysis, which indicated that optimum frequency values of the input perturbation exist for estimation of these parameters. A procedure is presented to obtain all these parameters using the short-time response. The results show that the short-time analysis is a useful …
Transient Analysis Of A Porous Electrode, Sheba Devan, Venkat R. Subramanian, Ralph E. White
Transient Analysis Of A Porous Electrode, Sheba Devan, Venkat R. Subramanian, Ralph E. White
Faculty Publications
An analytical expression is presented for the voltage response including the transient voltage for a simple (i.e., no concentration gradients) porous electrode model subject to a sinusoidal input current density. The transient voltage response as a function of the frequency, exchange current density, and double layer capacitance is studied independent of the periodic (steady state) voltage response. The change in the voltage response in the transient region is compared to that of the periodic voltage response with respect to the parameters. The physical properties of the porous electrode can be estimated using the voltage response in the transient …
Development Of First Principles Capacity Fade Model For Li-Ion Cells, P. Ramadass, Bala Haran, Parthasarathy M. Gomadam, Ralph E. White, Branko N. Popov
Development Of First Principles Capacity Fade Model For Li-Ion Cells, P. Ramadass, Bala Haran, Parthasarathy M. Gomadam, Ralph E. White, Branko N. Popov
Faculty Publications
A first principles-based model has been developed to simulate the capacity fade of Li-ion batteries. Incorporation of a continuous occurrence of the solvent reduction reaction during constant current and constant voltage (CC-CV) charging explains the capacity fade of the battery. The effect of parameters such as end of charge voltage and depth of discharge, the film resistance, the exchange current density, and the over voltage of the parasitic reaction on the capacity fade and battery performance were studied qualitatively. The parameters that were updated for every cycle as a result of the side reaction were state-of-charge of the electrode materials …
Development Of Novel Method For Preparation Of Pemfc Electrodes, Hansung Kim, Branko N. Popov
Development Of Novel Method For Preparation Of Pemfc Electrodes, Hansung Kim, Branko N. Popov
Faculty Publications
A method based on pulse electrodeposition technique was developed for preparation of membrane electrode assemblies (MEAs). In this approach, platinum is deposited directly on the surface of the carbon electrode. The method ensures most of the platinum to be in close contact with the membrane. Using this method it is possible to increase the Pt/C ratio up to 75 wt % near the surface of the electrode resulting in a 5 µm thick catalyst layer. The MEA prepared by pulse electrodeposition exhibits a current density of 0.33 A/cm2 at 0.8 V with platinum loading of 0.25 mg of Pt/cm …
Analytical Solution For The Impedance Of A Porous Electrode, Sheba Devan, Venkat R. Subramanian, Ralph E. White
Analytical Solution For The Impedance Of A Porous Electrode, Sheba Devan, Venkat R. Subramanian, Ralph E. White
Faculty Publications
A macrohomogeneous model is presented for a porous electrode that includes coupled potential and concentration gradients with linear kinetics. The equations are solved to obtain an analytical expression for the impedance of a porous electrode. Complex plane plots are presented that illustrate two well-defined arcs: a kinetic arc and a diffusion arc with their time constants far apart. The effects of parameters such as exchange current density, porosity, diffusion coefficient, thickness, and interfacial area on the impedance spectra are presented. The usefulness of the analytical solution in investigating the effect of solution phase diffusion is also presented.
Cycle Life Modeling Of Lithium-Ion Batteries, Gang Ning, Branko N. Popov
Cycle Life Modeling Of Lithium-Ion Batteries, Gang Ning, Branko N. Popov
Faculty Publications
A first-principles-based charge-discharge model was developed to simulate the capacity fade of Li-ion batteries. The model is based on the loss of active lithium ions due to solvent reduction reaction and on the rise of the anode film resistance. The effect of parameters such as exchange current density, depth of discharge (DOD), end of charge voltage, film resistance, and the overvoltage of parasitic reaction were studied quantitatively. The model controls the required DOD by controlling the discharge time and estimates the end of discharge voltages as a function of cycle number.
Parameter Estimates For A Pemfc Cathode, Qingzhi Guo, Vijay A. Sethuraman, Ralph E. White
Parameter Estimates For A Pemfc Cathode, Qingzhi Guo, Vijay A. Sethuraman, Ralph E. White
Faculty Publications
Five parameters of a model of a polymer electrolyte membrane fuel cell (PEMFC) cathode (the volume fraction of gas pores in the gas diffusion layer, the volume fraction of gas pores in the catalyst layer, the exchange current density of the oxygen reduction reaction, the effective ionic conductivity of the electrolyte, and the ratio of the effective diffusion coefficient of oxygen in a flooded spherical agglomerate particle to the square of that particle radius) were determined by least-squares fitting of experimental polarization curves. The values of parameters obtained in this work indicate that ionic conduction and gas-phase transport are two …
Polyetheretherketone Membranes For Elevated Temperature Pemfcs, Balasubramanian Lakshmanan, Wayne Huang, David Olmeijer, John W. Weidner
Polyetheretherketone Membranes For Elevated Temperature Pemfcs, Balasubramanian Lakshmanan, Wayne Huang, David Olmeijer, John W. Weidner
Faculty Publications
Membrane electrode assemblies ~MEAs! made from polyetheretherketone ~PEEK! showed excellent fuel cell performance and thermal stability in the presence of substantial CO at elevated temperatures ~i.e., 120°C! in proton exchange membrane fuel cells ~PEMFCs!. For example, the current from a MEA made from PEEK membrane at 0.6 V and 120°C was 0.50 A/cm2 when run on pure hydrogen and 0.45 A/cm2 when run on reformate ~50% H2 , 1300 ppm CO, and balance N2). The current density from a MEA made from Nafion at 0.6 V and 120°C was 0.61 A/cm2 when run on pure hydrogen. The main difference between …
Theoretical Analysis For Obtaining Physical Properties Of Composite Electrodes, Parthasarathy M. Gomadam, John W. Weidner, Thomas A. Zawodzinski, Andrew P. Saab
Theoretical Analysis For Obtaining Physical Properties Of Composite Electrodes, Parthasarathy M. Gomadam, John W. Weidner, Thomas A. Zawodzinski, Andrew P. Saab
Faculty Publications
A theoretical analysis is presented that allows in situ measurements of the physical properties of a composite electrode, namely, the electronic conductivity, the ionic conductivity, the exchange-current density, and the double-layer capacitance. Use is made of the current-voltage responses of the composite electrode to dc and ac polarizations under three different experimental configurations. This analysis allows the physical properties to be obtained even when the various resistances in the composite (e.g., ionic, electronic, and charge-transfer) are of comparable values.
Full Cell Mathematical Model Of A Mcfc, N. Subramanian, B. S. Haran, Ralph E. White, Branko N. Popov
Full Cell Mathematical Model Of A Mcfc, N. Subramanian, B. S. Haran, Ralph E. White, Branko N. Popov
Faculty Publications
A theoretical model for the molten carbonate fuel cell was developed based on the three-phase homogeneous approach. Using this model, the contribution of different cell components to losses in cell performance has been studied. In general, at low current densities, the electrolyte matrix contributed to the major fraction of potential losses. Mass transfer effects became important at high current densities and were more prominent at the cathode. Electrolyte conductivity and cathode exchange current density seemed to play a limiting role in determining cell performance. Using the model, the maximum power density from a single cell for different cell thicknesses was …
Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn
Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn
Faculty Publications
This work presents a mathematical model for charge/discharge of electrochemical capacitors that explicitly accounts for particle-packing effects in a composite electrochemical capacitor consisting of hydrous RuO2 nanoparticles dispersed within porous activated carbon. The model is also used to investigate the effect of nonuniform distributions of salt in the electrolyte phase of the electrode in the context of dilute solution theory. We use the model to compare the performance of capacitors with electrodes made from different activated carbons and to investigate the effects of varying carbon content and discharge current density. Even at low discharge current density, concentration polarization in …
Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn
Modeling The Effects Of Electrode Composition And Pore Structure On The Performance Of Electrochemical Capacitors, Changqing Lin, Branko N. Popov, Harry J. Ploehn
Faculty Publications
This work presents a mathematical model for charge/discharge of electrochemical capacitors that explicitly accounts for particle-packing effects in a composite electrochemical capacitor consisting of hydrous RuO2 nanoparticles dispersed within porous activated carbon. The model is also used to investigate the effect of nonuniform distributions of salt in the electrolyte phase of the electrode in the context of dilute solution theory. We use the model to compare the performance of capacitors with electrodes made from different activated carbons and to investigate the effects of varying carbon content and discharge current density. Even at low discharge current density, concentration polarization in …
Approximate Solutions For Galvanostatic Discharge Of Spherical Particles I. Constant Diffusion Coefficient, Venkat R. Subramanian, James A. Ritter, Ralph E. White
Approximate Solutions For Galvanostatic Discharge Of Spherical Particles I. Constant Diffusion Coefficient, Venkat R. Subramanian, James A. Ritter, Ralph E. White
Faculty Publications
Approximate models are developed, based on second, fourth, and sixth order polynomials, that describe the concentration profile of an electrochemically active species in a spherical electrode particle. Analytical expressions are obtained that describe the way the concentration profiles, surface concentrations, and electrode utilization change during the galvanostatic discharge of an electrode particle. Based on a comparison with an exact analytical model over a wide range of dimensionless current densities, all three approximate models performed extremely well in predicting these quantities. Quantitative criterion for the validity of these models is also developed and shows that the sixth order, four parameter approximate …
Modeling The Effects Of Ion Association On Direct-Current Polarization Of Solid Polymer Electrolytes, Changqing Lin, Ralph E. White, Harry J. Ploehn
Modeling The Effects Of Ion Association On Direct-Current Polarization Of Solid Polymer Electrolytes, Changqing Lin, Ralph E. White, Harry J. Ploehn
Faculty Publications
Considerable experimental evidence indicates that ion association occurs in solid polymer electrolytes. This work provides a thorough theoretical analysis of the effect of ion association on the conductivity, general current-potential behavior, and limiting current density in a solid polymer electrolyte. The model employs dilute solution theory to describe the fluxes of cations, anions, and ion pairs in a motionless continuum but neglects higher order association. The predictions of the model highlight the effects of the relative diffusion coefficients and dimensionless association constant on concentration distributions of simple ions and ion pairs, the limiting current density, and the potential drop required …
A Semianalytical Method For Predicting Primary And Secondary Current Density Distributions: Linear And Nonlinear Boundary Conditions, Dhanwa Thirumalai, Ralph E. White
A Semianalytical Method For Predicting Primary And Secondary Current Density Distributions: Linear And Nonlinear Boundary Conditions, Dhanwa Thirumalai, Ralph E. White
Faculty Publications
No abstract provided.
Mathematical Modeling Of Proton‐Exchange‐Membrane Fuel‐Cell Stacks, Dhanwa Thirumalai, Ralph E. White
Mathematical Modeling Of Proton‐Exchange‐Membrane Fuel‐Cell Stacks, Dhanwa Thirumalai, Ralph E. White
Faculty Publications
No abstract provided.
A Model For The Galvanostatic Deposition Of Nickel Hydroxide, Mahesh Murthy, Gowri S. Nagarajan, John W. Weidner, John W. Van Zee
A Model For The Galvanostatic Deposition Of Nickel Hydroxide, Mahesh Murthy, Gowri S. Nagarajan, John W. Weidner, John W. Van Zee
Faculty Publications
A mathematical model is presented for the galvanostatic deposition of Ni(OH)2 films in stagnant Ni(NO3)2 solutions. The objective is to quantify the anomalous deposition behavior reported previously in which the utilization of the electrochemically generated OH– species decreased drastically as the concentration of Ni(NO3)2 increased beyond 0.1 M. For example as the Ni(NO3)2 concentration increased from 0.1 to 2.0 M, the deposition rate decreased by a factor of ten at 2.5 mA/cm2. At this high ratio of concentration to current density, a comparison with Faraday's …
Anomalous Codeposition Of Fe-Ni Alloys And Fe-Ni-Sio2 Composites Under Potentiostatic Conditions, M. Ramasubramanian, S. N. Popova, Branko N. Popov, Ralph E. White, K. M. Yin
Anomalous Codeposition Of Fe-Ni Alloys And Fe-Ni-Sio2 Composites Under Potentiostatic Conditions, M. Ramasubramanian, S. N. Popova, Branko N. Popov, Ralph E. White, K. M. Yin
Faculty Publications
A mathematical model has been developed to describe the electrodeposition of Fe-Ni alloys and Fe-Ni-SiO2 composites under potentiostatic conditions. This model can be used to predict the polarization behavior, partial current densities, and alloy composition of each of the components as a function of the applied potential. Fe-Ni-SiO2 samples were deposited on platinum rotating disk electrodes from sulfate electrolytes under potentiostatic conditions, and the results obtained were compared to the model. The model predictions were found to agree well with the experimental observations for the Fe-Ni and Fe-Ni-SiO2 systems.
Determination Of Transport And Electrochemical Kinetic Parameters Of Bare And Copper-Coated Lani4.27Sn0.24 Electrodes In Alkaline Solution, G. Zheng, Branko N. Popov, Ralph E. White
Determination Of Transport And Electrochemical Kinetic Parameters Of Bare And Copper-Coated Lani4.27Sn0.24 Electrodes In Alkaline Solution, G. Zheng, Branko N. Popov, Ralph E. White
Faculty Publications
Electrochemical properties of bare and copper-coated LaNi4.27Sn0.24 electrodes were investigated in alkaline solution. The exchange current density, polarization resistance, and equilibrium potential were determined as functions of the state of charge in the electrodes. The symmetry factors for bare and copper-coated electrodes were estimated to be 0.53 and 0.52, respectively. By using a constant current discharge technique, the hydrogen diffusion coefficient in bare and coated LaNi4.27Sn0.24 was estimated to be 6.75 × 10–11 cm2/s.
Application Of Porous Electrode Theory On Metal Hydride Electrodes In Alkaline Solution, G. Zheng, Branko N. Popov, Ralph E. White
Application Of Porous Electrode Theory On Metal Hydride Electrodes In Alkaline Solution, G. Zheng, Branko N. Popov, Ralph E. White
Faculty Publications
Porous electrode theory was applied to estimate the exchange current density, the polarization resistance, and symmetry factor for LaNi4.27Sn0.24 hydride electrode in alkaline solution. The exchange current density, polarization resistance, and symmetry factor were determined from polarization curves which were obtained at low overpotentials.
Surface Treatment For Mitigation Of Hydrogen Absorption And Penetration Into Aisi 4340 Steel, G. Zheng, Branko N. Popov, Ralph E. White
Surface Treatment For Mitigation Of Hydrogen Absorption And Penetration Into Aisi 4340 Steel, G. Zheng, Branko N. Popov, Ralph E. White
Faculty Publications
The effectiveness of underpotential deposition of Pb onto a membrane made of AISI 4340 steel on the reduction of the hydrogen evolution reaction on the membrane and the degree of hydrogen ingress into the membrane was determined. In the presence of a monolayer coverage of Pb on the membrane surface, the hydrogen evolution currents were reduced by a factor of two compared with the values obtained on bare steel, and the steady-state hydrogen permeation flux through the steel membranes was reduced by 71%.
Mathematical Modeling Of An H2s Removal Electrolyzer, Z. Mao, P. Adanuvor, Ralph E. White
Mathematical Modeling Of An H2s Removal Electrolyzer, Z. Mao, P. Adanuvor, Ralph E. White
Faculty Publications
A mathematical model is presented for a high temperature H2S electrolyzer. It is shown that the maximum current in this type of a cell is determined entirely by the transport rate of sulfide ions through the separator. It is suggested that this model could be used to determine the feasibility of various designs for this electrolyzer.
A Two-Dimensional Mathematical Model Of A Porous Lead Dioxide Electrode In A Lead-Acid Cell, E. C. Dimpault-Darcy, T. V. Nguyen, Ralph E. White
A Two-Dimensional Mathematical Model Of A Porous Lead Dioxide Electrode In A Lead-Acid Cell, E. C. Dimpault-Darcy, T. V. Nguyen, Ralph E. White
Faculty Publications
A two-dimensional mathematical model is presented for a lead dioxide electrode in a lead-acid cell. It is used to simulate the time dependent behavior of the electrode during discharge. The model contains six dependent variables: the concentration of the acid electrolyte, the porosity, the electrical potentials of the solid and solution phases, and the two directional components of the current density in the electrolyte. The effect of the electrode grid was included by varying the conductivity of the solid. Parameters such as electrode conductivity, electrode dimensions, and temperature are investigated to understand their effects on electrode discharge performance.
Secondary Current Distributions Using Topaz2d And Linear Kinetics, E. C. Dimpault-Darcy, Ralph E. White
Secondary Current Distributions Using Topaz2d And Linear Kinetics, E. C. Dimpault-Darcy, Ralph E. White
Faculty Publications
Secondary current density distributions are of interest
to cell designers. The purpose of this note is to illustrate
how to use an existing numerical method to determine
these distributions for cells that contain conducting and
nonconducting bodies between the main anode and cathode.
A Mathematical Model For The Initial Corrosion Rate Of A Porous Layer On A Rotating Disk Electrode, William E. Ryan, Ralph E. White, S. L. Kelly
A Mathematical Model For The Initial Corrosion Rate Of A Porous Layer On A Rotating Disk Electrode, William E. Ryan, Ralph E. White, S. L. Kelly
Faculty Publications
A mathematical model is presented for the initial corrosion rate of a porous layer on a rotating disk electrode. The model is used to predict the corrosion potential and corrosion current density for a porous electrode made of pure iron in aerated caustic solutions. The dependence of these predictions on some of the properties of the porous layer is presented. It is shown that the corrosion rate depends significantly on the specific surface area of the porous electrode.
Modeling The Rotating Disk Electrode For Studying The Kinetics Of Electrochemical Reactions, P K. Adanuvor, Ralph E. White, S E. Lorimer
Modeling The Rotating Disk Electrode For Studying The Kinetics Of Electrochemical Reactions, P K. Adanuvor, Ralph E. White, S E. Lorimer
Faculty Publications
A general mathematical model for studying the kinetics of electrochemical reactions at a rotating disk electrode under steady-state potentiostatic conditions is presented. The model, apart from predicting the net and partial current densities at given values of the applied potential, the ohmic potential drop, and the concentration and potential profiles in the solution, also accounts for homogeneous reactions of any order in the solution and noncharge transfer reactions at the electrode surface. The versatility of the model is demonstrated by the application of the model to a variety of complex reaction schemes.