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Full-Text Articles in Engineering
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 …
Development Of Method For Synthesis Of Pt–Co Cathode Catalysts For Pem Fuel Cells, Xuguang Li, Héctor R. Colón-Mercado, Gang Wu, Jong-Won Lee, Branko N. Popov
Development Of Method For Synthesis Of Pt–Co Cathode Catalysts For Pem Fuel Cells, Xuguang Li, Héctor R. Colón-Mercado, Gang Wu, Jong-Won Lee, Branko N. Popov
Faculty Publications
A procedure was developed to synthesize a platinum–cobalt (Pt–Co) alloy electrocatalyst for oxygen reduction using Co/C composite as a support. The Pt–Co/C catalysts were synthesized through: (i) chemical oxidation of carbon black, (ii) Co deposition on the oxidized carbon using a chelation method, (iii) chemical treatment in an acidic medium to remove excess of Co on the carbon surface, (iv) Pt deposition onto the Co/C support, and (v) postheat treatment to form the Pt–Co alloy catalyst. The synthesized Pt–Co/C catalyst showed improved activity and long-term stability in polymer electrolyte membrane …
Moving Boundary Model For The Discharge Of A Licoo2 Electrode, Qi Zhang, Ralph E. White
Moving Boundary Model For The Discharge Of A Licoo2 Electrode, Qi Zhang, Ralph E. White
Faculty Publications
A moving boundary model in a spherical LiCoO2 particle is presented to account for the diffusion controlled phase transition in LiCoO2 solid particles, and this model is incorporated into a porous electrode model for the LiCoO2 electrode. The simulation results agree well with the experimental data of a LiCoO2 electrode. A study of the flux distribution in the porous electrode shows that the phase transition phenomenon in the LiCoO2particles has a significant effect on the flux distribution by changing the solid phase diffusion resistance in the particles.
Simulation Of Polarization Curves For Oxygen Reduction Reaction In 0.5 M H2So4 At A Rotating Ring Disk Electrode, Qingbo Dong, Shriram Santhanagopalan, Ralph E. White
Simulation Of Polarization Curves For Oxygen Reduction Reaction In 0.5 M H2So4 At A Rotating Ring Disk Electrode, Qingbo Dong, Shriram Santhanagopalan, Ralph E. White
Faculty Publications
A cylindrical two-dimensional model based on the Nernst–Planck equations, the Navier–Stokes equation, and the continuity equation is used to simulate the oxygen reduction reaction in 0.5MH2SO4 at a rotating ring disk electrode. Concentration distributions and a potential profile are obtained as a function of the axial and radial distances from the center of the electrode surface. Polarization curves are simulated to interpret experimental results by studying various reaction mechanisms, i.e., the four-electron-transfer reduction of oxygen, the two-electron-transfer reduction of oxygen, a combination of the above two reactions, mechanisms with reduction of peroxide to water, and/or the heterogeneous …
Modeling Volume Changes In Porous Electrodes, Parthasarathy M. Gomadam, John W. Weidner
Modeling Volume Changes In Porous Electrodes, Parthasarathy M. Gomadam, John W. Weidner
Faculty Publications
A three-dimensional mathematical model is presented to describe volume changes in porous electrodes occurring during operation. Material conservation equations are used to derive governing relationships between electrode dimensions and porosity for deposition/precipitation, intercalation, and ionomer-based electrodes. By introducing a parameter, called the swelling coefficient, the relative magnitudes of the change in electrode dimensions and the change in porosity are determined. The swelling coefficient is design-dependent and measured experimentally for a given cell design. The model is general and forms a critical addition required to extend the existing porous electrode models to include volume change effects. For the special case of …
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 …
Cubic Spline Regression For The Open-Circuit Potential Curves Of A Lithium-Ion Battery, Qingzhi Guo, Ralph E. White
Cubic Spline Regression For The Open-Circuit Potential Curves Of A Lithium-Ion Battery, Qingzhi Guo, Ralph E. White
Faculty Publications
A cubic spline regression model was used to fit the experimental open-circuit potential (OCP) curves of two intercalation electrodes of a lithium-ion battery. All the details of an OCP curve were accurately predicted by the resulting model. The number of regression intervals used to fit an OCP curve was determined in a way such that in each regression interval the OCP exhibits a profile predictable by a third-order polynomial. The locations of the data points used to separate regression intervals were optimized. Compared to a polynomial model with the same number of fitting parameters, the cubic spline regression model is …
Effect Of Porosity On The Capacity Fade Of A Lithium-Ion Battery: Theory, Godfrey Sikha, Branko N. Popov, Ralph E. White
Effect Of Porosity On The Capacity Fade Of A Lithium-Ion Battery: Theory, Godfrey Sikha, Branko N. Popov, Ralph E. White
Faculty Publications
A mathematical model is presented to predict the performance of a lithium-ion battery. It includes the changes in the porosity of the material due to the reversible intercalation processes and the irreversible parasitic reaction. The model was also extended to predict the capacity fade in a lithium-ion battery based on the unwanted parasitic reaction that consumes Li+ along with the changes in the porosities of the electrodes with cycling due to the continuous parasitic side reaction. The model can be used to predict the drop in the voltage profile, change in the state of charge, and the effects of …
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.
Series Solution To The Transient Convective Diffusion Equation For A Rotating Disk Electrode, Shiriram Santhanagopalan, Ralph E. White
Series Solution To The Transient Convective Diffusion Equation For A Rotating Disk Electrode, Shiriram Santhanagopalan, Ralph E. White
Faculty Publications
A series solution to the transient convective diffusion equation for the rotating disc electrode system is presented and compared to previously reported solutions. The solution presented here is for the entire time domain and agrees well with both the short and long time solutions presented earlier in the literature.
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 …
A Steady-State Impedance Model For A Pemfc Cathode, Qingzhi Guo, Ralph E. White
A Steady-State Impedance Model For A Pemfc Cathode, Qingzhi Guo, Ralph E. White
Faculty Publications
A model for the simulation of the steady-state impedance response of a polymer electrolyte membrane fuel cell (PEMFC) cathode is presented. The catalyst layer of the electrode is assumed to consist of many flooded spherical agglomerate particles surrounded by a small volume fraction of gas pores. Stefan-Maxwell equations are used to describe the multicomponent gas-phase transport occurring in both the gas diffusion layer and the catalyst layer of the electrode. Liquid-phase diffusion of O2 is assumed to take place in the flooded agglomerate particles. Newman’s porous electrode theory is applied to determine over-potential distributions. © 2004 The Electrochemical Society. All …
Analysis Of Molten Carbonate Fuel Cell Performance Using A Three-Phase Homogeneous Model, N. Subramanian, B. S. Haran, P. Ganesan, Ralph E. White, Branko N. Popov
Analysis Of Molten Carbonate Fuel Cell Performance Using A Three-Phase Homogeneous Model, N. Subramanian, B. S. Haran, P. Ganesan, Ralph E. White, Branko N. Popov
Faculty Publications
In this study a three-phase homogeneous model was developed to simulate the performance of the molten carbonate fuel cell (MCFC) cathode. The homogeneous model is based on volume averaging of different variables in the three phases over a small volume element. This approach can be used to model porous electrodes as it represents the real system much better than the conventional agglomerate model. Using the homogeneous model the polarization characteristics of the MCFC cathode was studied under different operating conditions.
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.
A Mathematical Model Of Oxide/Carbon Composite Electrode For Supercapacitors, Hansung Kim, Branko N. Popov
A Mathematical Model Of Oxide/Carbon Composite Electrode For Supercapacitors, Hansung Kim, Branko N. Popov
Faculty Publications
A pseudo two-dimensional model is developed for the general application of supercapacitors consisting of an oxide/carbon composite electrode. The model takes into account the diffusion of protons in the oxide particle by employing the method of superposition. RuO2/carbon system is modeled as a specific example. From the simulation data, it is found that the oxide particle size and proton diffusion coefficient have an enormous effect on the performance at high discharge rate due to the limitation of proton transport into RuO2 particles. With increasing carbon ratio, the porosity of electrode increases, which causes the potential drop in …
Study Of Ionic Conductivity Profiles Of The Air Cathode Of A Pemfc By Ac Impedance Spectroscopy, Qingzhi Guo, Maria Cayetana, Yu-Min Tsou, Emory S. De Castro, Ralph E. White
Study Of Ionic Conductivity Profiles Of The Air Cathode Of A Pemfc By Ac Impedance Spectroscopy, Qingzhi Guo, Maria Cayetana, Yu-Min Tsou, Emory S. De Castro, Ralph E. White
Faculty Publications
A characterization of the ionic conduction of the active layer of a polymer electrolyte membrane fuel cell (PEMFC) cathode by ac impedance measurement at open-circuit potential conditions was conducted. Porous electrode theory was used to derive a compact equation, ∂2Φ̑2/∂y2+∂lnf(y)/∂y×∂Φ̑2/∂y−R/f(y)(1+jΩ)Φ̑2=0, to solve for the impedance response of a cathode at open-circuit potential conditions. This equation includes a parameter R, the ratio of an ionic resistance (evaluated at the active layer/membrane interface), to the total charge-transfer resistance of the active layer. The influence of an assumed ionic conductivity distribution profile f(y) on the error in the estimation of total double-layer …
Using Sputter Deposition To Increase Co Tolerance In A Proton-Exchange Membrane Fuel Cell, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang, Steven Shi, Narender Rana, Stephan Grunow, Timothy C. Stoner, Alain E. Kaloyeros
Using Sputter Deposition To Increase Co Tolerance In A Proton-Exchange Membrane Fuel Cell, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang, Steven Shi, Narender Rana, Stephan Grunow, Timothy C. Stoner, Alain E. Kaloyeros
Faculty Publications
Placing a layer of Ru atop a Pt anode increases the carbon monoxide tolerance of proton-exchange membrane fuel cells when oxygen is added to the fuel stream. Sputter-deposited Ru filter anodes composed of a single Ru layer and three Ru layers separated by Nafion-carbon ink, respectively, were compared to Pt, Pt:Ru alloy, and an ink-based Ru filter anodes. The amount of Pt in each anode was 0.15 mg/cm2 and the amount of Ru in each Ru-containing anode was 0.080 mg/cm2. For an anode feed consisting of hydrogen, 200 ppm CO, and 2% O2 (in the form …
Study Of Sn-Coated Graphite As Anode Material For Secondary Lithium-Ion Batteries, Basker Veeraraghavan, Anand Durairajan, Bala Haran, Branko N. Popov, Ronald Guidotti
Study Of Sn-Coated Graphite As Anode Material For Secondary Lithium-Ion Batteries, Basker Veeraraghavan, Anand Durairajan, Bala Haran, Branko N. Popov, Ronald Guidotti
Faculty Publications
Tin-graphite composites have been developed as an alternate anode material for Li-ion batteries using an autocatalytic deposition technique. The specific discharge capacity, coulombic efficiency, rate capability behavior, and cycle life of Sn-C composites has been studied using a variety of electrochemical methods. The amount of tin loading and the heating temperature have a significant effect on the composite performance. The synthesis conditions and Sn loading on graphite have been optimized to obtain the maximum reversible capacity for the composite electrode. Heating the composite converts it from amorphous to crystalline form. Apart from higher capacity, Sn-graphite composites possesses higher coulombic efficiency, …
Estimation Of Diffusion Coefficient Of Lithium In Carbon Using Ac Impedance Technique, Qingzhi Guo, Venkat R. Subramanian, John W. Weidner, Ralph E. White
Estimation Of Diffusion Coefficient Of Lithium In Carbon Using Ac Impedance Technique, Qingzhi Guo, Venkat R. Subramanian, John W. Weidner, Ralph E. White
Faculty Publications
The validity of estimating the solid phase diffusion coefficient, Ds, of a lithium intercalation electrode from impedance measurement by a modified electrochemical impedance spectroscopy (EIS) method is studied. A macroscopic porous electrode model and concentrated electrolyte theory are used to simulate the synthetic impedance data. The modified EIS method is applied for estimating Ds. The influence of parameters such as the exchange current density, radius of active material particle, solid phase conductivity, porosity, volume fraction of inert material, and thickness of the porous carbon intercalation electrode, the solution phase diffusion coefficient, and transference number, on the …
Development Of A Novel Co Tolerant Proton Exchange Membrane Fuel Cell Anode, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang
Development Of A Novel Co Tolerant Proton Exchange Membrane Fuel Cell Anode, Andrew T. Haug, Ralph E. White, John W. Weidner, Wayne Huang
Faculty Publications
Typically Pt is alloyed with metals such as Ru, Sn, or Mo to provide a more CO-tolerant, high-performance proton exchange membrane fuel cell (PEMFC) anode. In this work, a layer of carbon-supported Ru is placed between the Pt catalyst and the anode flow field to form a filter. When oxygen is added to the fuel stream, it was predicted that the slow H2 kinetics of Ru in this filter would become an advantage compared to Pt and Pt:Ru alloy anodes, allowing a greater percentage of O2 to oxidize adsorbed CO to CO2. With an anode feed …
Studies On Capacity Fade Of Spinel-Based Li-Ion Batteries, Ramadass Premanand, Anand Durairajan, Bala Haran, Ralph E. White, Branko N. Popov
Studies On Capacity Fade Of Spinel-Based Li-Ion Batteries, Ramadass Premanand, Anand Durairajan, Bala Haran, Ralph E. White, Branko N. Popov
Faculty Publications
The performance of Cell-Batt® Li-ion cells using nonstoichiometric spinel as the positive electrode material has been studied at different charging rates. The capacity of the cell was optimized based on varying the charging current and the end potential. Subsequent to this, the capacity fade of these batteries was studied at different charge currents. During cycling, cells were opened at intermittent cycles and extensive material and electrochemical characterization was done on the active material at both electrodes. For all charge currents, the resistance of both the electrodes does not vary significantly with cycling. This result is in contrast with cells …
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 …
Modeling Of A Nickel-Hydrogen Cell: Phase Reactions In The Nickel Active Material, B. Wu, Ralph E. White
Modeling Of A Nickel-Hydrogen Cell: Phase Reactions In The Nickel Active Material, B. Wu, Ralph E. White
Faculty Publications
No abstract provided.
Modeling Lithium Intercalation In A Porous Carbon Electrode, Gerardine G. Botte, Ralph E. White
Modeling Lithium Intercalation In A Porous Carbon Electrode, Gerardine G. Botte, Ralph E. White
Faculty Publications
No abstract provided.
Proton Diffusion In Nickel Hydroxide: Prediction Of Active Material Utilization, Sathya Motupally, Christopher C. Streinz, John W. Weidner
Proton Diffusion In Nickel Hydroxide: Prediction Of Active Material Utilization, Sathya Motupally, Christopher C. Streinz, John W. Weidner
Faculty Publications
Galvanostatic charge and discharge experiments reveal that the active material in nickel electrodes cannot be fully accessed at high currents or for thick films. It has been proposed that the utilization of the active material is controlled by the diffusion rate of protons through the film. This hypothesis is supported by the good agreement between mathematical simulations of material utilization and experimental data over a range of charge and discharge currents and film thicknesses. Furthermore, the fraction of material utilized is larger on charge than on discharge. The asymmetry on charge and discharge is due to a diffusion coefficient that …
The Role Of Oxygen At The Second Discharge Plateau Of Nickel Hydroxide, Sathya Motupally, Mukul Jain, Venkat Srinivasan, John W. Weidner
The Role Of Oxygen At The Second Discharge Plateau Of Nickel Hydroxide, Sathya Motupally, Mukul Jain, Venkat Srinivasan, John W. Weidner
Faculty Publications
It was shown that the appearance of a secondary discharge plateau approximately 400 mV below the primary plateau can result from the reduction of oxygen. During the galvanostatic discharge of planar nickel-hydroxide films at room temperature and in 3 weight percent KOH solutions, the second discharge plateau was observed only in the presence of dissolved oxygen in the electrolyte. When the solution was deoxygenated, no residual capacity could be extracted from the films even at low discharge rates or from overcharged films. In addition, the duration of the second plateau is inversely proportional to the square of the discharge current, …
Electrochemical Investigations Of Cobalt-Doped Limn2O4 As Cathode Material For Lithium-Ion Batteries, P. Arora, Branko Popov, Ralph E. White
Electrochemical Investigations Of Cobalt-Doped Limn2O4 As Cathode Material For Lithium-Ion Batteries, P. Arora, Branko Popov, Ralph E. White
Faculty Publications
A wide range (y = 0.05–0.33) of Co-doped LiCoyMn2–yO4 spinels were synthesized and electrochemically characterized. These Co-doped spinels showed improved specific capacity and capacity retention over pure spinels. Electrochemical impedance spectroscopy and the linear polarization resistance technique were used to determine the transport and electrochemical kinetic parameters of Co-doped spinels. The presence of Co in the spinel inhibits the passivation process occurring on the surface of the cathode. Also, Co increases the exchange current density and facilitates the charge-transfer reaction of the active material. The lower self-discharge observed for Co-doped spinels was attributed …
Theoretical Analysis Of Metal Hydride Electrodes: Studies On Equilibrium Potential And Exchange Current Density, Bala S. Haran, Branko N. Popov, Ralph E. White
Theoretical Analysis Of Metal Hydride Electrodes: Studies On Equilibrium Potential And Exchange Current Density, Bala S. Haran, Branko N. Popov, Ralph E. White
Faculty Publications
A theoretical model for the metal hydride electrode has been developed assuming that hydrogen diffusion in the alloy and charge-transfer at the surface control the discharge process. Theoretical equations for the dependence of equilibrium potential and exchange current density on the surface hydrogen concentration have been derived. These parameters have been used to correlate experimental data with the theoretical electrode discharge model. Analysis of both the experimental and theoretical discharge curves reveals a potential plateau determined by the magnitude of the interactions between the hydrogen in the alloy and the unhydrided metal. Neglecting these hydrogen-metal site interactions results in simulations …