The Experts below are selected from a list of 2304 Experts worldwide ranked by ideXlab platform
Dennis Y C Leung - One of the best experts on this subject based on the ideXlab platform.
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parametric study of solid oxide steam electrolyzer for hydrogen production
International Journal of Hydrogen Energy, 2007Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:Abstract A theoretical model was developed to study the electrical characteristics of a solid oxide steam electrolyzer (SOSE) for hydrogen production. The activation and concentration overpotentials at the electrodes as well as the ohmic overpotential at the electrolyte were considered as the main sources of voltage loss. The Butler–Volmer Equation, Fick's model, and Ohm's law were applied to characterize the overpotentials. The theoretical model was validated as the simulation results agreed well with the experimental data from the literature. In the study of the component thickness effect, anode-support SOSE configuration was identified as the most favorable design. Further parametric analyses were performed to study the effects of material properties and operating conditions on the anode-supported SOSE cell performance. The results have shown that increasing electrode porosity and pore size can reduce the voltage loss. In the operation, both temperature and steam molar fraction can be increased to enhance the SOSE electrical efficiency. The pressure should be regulated depending on the current density. The electrochemistry model can be used to perform more analyses to gain insightful understanding of the SOSE hydrogen production principles and to optimize the SOSE cell and system designs.
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mathematical modeling of the coupled transport and electrochemical reactions in solid oxide steam electrolyzer for hydrogen production
Electrochimica Acta, 2007Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:Abstract A mathematical model was developed to simulate the coupled transport/electrochemical reaction phenomena in a solid oxide steam electrolyzer (SOSE) at the micro-scale level. Ohm's law, dusty gas model (DGM), Darcy's law, and the generalized Butler Volmer Equation were employed to determine the transport of electronic/ionic charges and gas species as well as the electrochemical reactions. Parametric analyses were performed to investigate the effects of operating parameters and micro-structural parameters on SOSE potential. The results substantiated the fact that SOSE potential could be effectively decreased by increasing the operating temperature. In addition, higher steam molar fraction would enhance the operation of SOSE with lower potential. The effect of particle sizes on SOSE potential was studied with due consideration on the SOSE activation and concentration overpotentials. Optimal particle sizes that could minimize the SOSE potential were obtained. It was also found that decreasing electrode porosity could monotonically decrease the SOSE potential. Besides, optimal values of volumetric fraction of electronic particles were found to minimize electrode total overpotentials. In order to optimize electrode microstructure to minimize SOSE electricity consumption, the concept of “functionally graded materials (FGM)” was introduced to lower the SOSE potential. The advanced design of particle size graded SOSE was found effective for minimizing electrical energy consumption resulting in efficient SOSE hydrogen production. The micro-scale model was capable of predicting SOSE hydrogen production performance and would be a useful tool for design optimization.
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parametric study of solid oxide fuel cell performance
Energy Conversion and Management, 2007Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:Abstract An electrochemical model was developed to study the current–voltage ( J – V ) characteristics of a solid oxide fuel cell (SOFC). The Butler–Volmer Equation, Fick’s model and Ohm’s law were used to determine the activation, concentration and ohmic overpotentials, respectively. One important feature of this model is that both the exchange current density and gas diffusion coefficients were dependent on the cell microstructures (porosity and pore size) and operational parameters (temperature, pressure and gas composition). The simulation results were compared with experimental data from the literature, and good agreement was obtained. The subsequent parametric modeling analyses determined how individual overpotentials were related to the geometric and operational parameters. It was found that there existed optimal values of electrode pore size and porosity for maximum cell performance. Both the activation and ohmic overpotentials decreased significantly with increasing temperature. However, the concentration overpotential was found to increase with increasing temperature. This unexpected phenomenon was caused by the reduced gas density at elevated temperature despite the increase in diffusion coefficient with increasing temperature. Besides, increasing the hydrogen content in the fuel stream and increasing the operating pressure were possible ways to enhance the SOFC power output. The parametric analyses provided insights in the operation of SOFCs and clarified some ambiguous understanding of SOFC overpotentials. The present model could also serve as a valuable tool for SOFC optimization design.
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an electrochemical model of a solid oxide steam electrolyzer for hydrogen production
Chemical Engineering & Technology, 2006Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:An electrochemical model was developed to simulate the J-V characteristics of a solid oxide steam electrolyzer (SOSE) used for hydrogen production. Activation, concentration, and ohmic overpotentials were considered as the main factors for voltage loss. The Butler-Volmer Equation, Fick's model, and Ohm's law were applied to determine the overpotentials of a SOSE cell. The simulation results were compared with experimental data from the literature and good agreement was obtained. Additionally, parametric modeling analyses were conducted to study how the operating temperature and gas composition affected the electrical characteristics. It was found that the voltage loss could be reduced by increasing the operating temperature and steam molar fraction. It was also observed that an anode-supported SOSE cell exhibited a higher hydrogen production efficiency than electrolyte-supported and cathode-supported cells. The electrochemical model can be used to perform further analysis in order to further understand the principles of SOSE hydrogen production, and to optimize SOSE cell and system designs.
Meng Ni - One of the best experts on this subject based on the ideXlab platform.
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parametric study of solid oxide steam electrolyzer for hydrogen production
International Journal of Hydrogen Energy, 2007Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:Abstract A theoretical model was developed to study the electrical characteristics of a solid oxide steam electrolyzer (SOSE) for hydrogen production. The activation and concentration overpotentials at the electrodes as well as the ohmic overpotential at the electrolyte were considered as the main sources of voltage loss. The Butler–Volmer Equation, Fick's model, and Ohm's law were applied to characterize the overpotentials. The theoretical model was validated as the simulation results agreed well with the experimental data from the literature. In the study of the component thickness effect, anode-support SOSE configuration was identified as the most favorable design. Further parametric analyses were performed to study the effects of material properties and operating conditions on the anode-supported SOSE cell performance. The results have shown that increasing electrode porosity and pore size can reduce the voltage loss. In the operation, both temperature and steam molar fraction can be increased to enhance the SOSE electrical efficiency. The pressure should be regulated depending on the current density. The electrochemistry model can be used to perform more analyses to gain insightful understanding of the SOSE hydrogen production principles and to optimize the SOSE cell and system designs.
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mathematical modeling of the coupled transport and electrochemical reactions in solid oxide steam electrolyzer for hydrogen production
Electrochimica Acta, 2007Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:Abstract A mathematical model was developed to simulate the coupled transport/electrochemical reaction phenomena in a solid oxide steam electrolyzer (SOSE) at the micro-scale level. Ohm's law, dusty gas model (DGM), Darcy's law, and the generalized Butler Volmer Equation were employed to determine the transport of electronic/ionic charges and gas species as well as the electrochemical reactions. Parametric analyses were performed to investigate the effects of operating parameters and micro-structural parameters on SOSE potential. The results substantiated the fact that SOSE potential could be effectively decreased by increasing the operating temperature. In addition, higher steam molar fraction would enhance the operation of SOSE with lower potential. The effect of particle sizes on SOSE potential was studied with due consideration on the SOSE activation and concentration overpotentials. Optimal particle sizes that could minimize the SOSE potential were obtained. It was also found that decreasing electrode porosity could monotonically decrease the SOSE potential. Besides, optimal values of volumetric fraction of electronic particles were found to minimize electrode total overpotentials. In order to optimize electrode microstructure to minimize SOSE electricity consumption, the concept of “functionally graded materials (FGM)” was introduced to lower the SOSE potential. The advanced design of particle size graded SOSE was found effective for minimizing electrical energy consumption resulting in efficient SOSE hydrogen production. The micro-scale model was capable of predicting SOSE hydrogen production performance and would be a useful tool for design optimization.
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parametric study of solid oxide fuel cell performance
Energy Conversion and Management, 2007Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:Abstract An electrochemical model was developed to study the current–voltage ( J – V ) characteristics of a solid oxide fuel cell (SOFC). The Butler–Volmer Equation, Fick’s model and Ohm’s law were used to determine the activation, concentration and ohmic overpotentials, respectively. One important feature of this model is that both the exchange current density and gas diffusion coefficients were dependent on the cell microstructures (porosity and pore size) and operational parameters (temperature, pressure and gas composition). The simulation results were compared with experimental data from the literature, and good agreement was obtained. The subsequent parametric modeling analyses determined how individual overpotentials were related to the geometric and operational parameters. It was found that there existed optimal values of electrode pore size and porosity for maximum cell performance. Both the activation and ohmic overpotentials decreased significantly with increasing temperature. However, the concentration overpotential was found to increase with increasing temperature. This unexpected phenomenon was caused by the reduced gas density at elevated temperature despite the increase in diffusion coefficient with increasing temperature. Besides, increasing the hydrogen content in the fuel stream and increasing the operating pressure were possible ways to enhance the SOFC power output. The parametric analyses provided insights in the operation of SOFCs and clarified some ambiguous understanding of SOFC overpotentials. The present model could also serve as a valuable tool for SOFC optimization design.
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an electrochemical model of a solid oxide steam electrolyzer for hydrogen production
Chemical Engineering & Technology, 2006Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:An electrochemical model was developed to simulate the J-V characteristics of a solid oxide steam electrolyzer (SOSE) used for hydrogen production. Activation, concentration, and ohmic overpotentials were considered as the main factors for voltage loss. The Butler-Volmer Equation, Fick's model, and Ohm's law were applied to determine the overpotentials of a SOSE cell. The simulation results were compared with experimental data from the literature and good agreement was obtained. Additionally, parametric modeling analyses were conducted to study how the operating temperature and gas composition affected the electrical characteristics. It was found that the voltage loss could be reduced by increasing the operating temperature and steam molar fraction. It was also observed that an anode-supported SOSE cell exhibited a higher hydrogen production efficiency than electrolyte-supported and cathode-supported cells. The electrochemical model can be used to perform further analysis in order to further understand the principles of SOSE hydrogen production, and to optimize SOSE cell and system designs.
Michael K H Leung - One of the best experts on this subject based on the ideXlab platform.
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parametric study of solid oxide steam electrolyzer for hydrogen production
International Journal of Hydrogen Energy, 2007Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:Abstract A theoretical model was developed to study the electrical characteristics of a solid oxide steam electrolyzer (SOSE) for hydrogen production. The activation and concentration overpotentials at the electrodes as well as the ohmic overpotential at the electrolyte were considered as the main sources of voltage loss. The Butler–Volmer Equation, Fick's model, and Ohm's law were applied to characterize the overpotentials. The theoretical model was validated as the simulation results agreed well with the experimental data from the literature. In the study of the component thickness effect, anode-support SOSE configuration was identified as the most favorable design. Further parametric analyses were performed to study the effects of material properties and operating conditions on the anode-supported SOSE cell performance. The results have shown that increasing electrode porosity and pore size can reduce the voltage loss. In the operation, both temperature and steam molar fraction can be increased to enhance the SOSE electrical efficiency. The pressure should be regulated depending on the current density. The electrochemistry model can be used to perform more analyses to gain insightful understanding of the SOSE hydrogen production principles and to optimize the SOSE cell and system designs.
-
mathematical modeling of the coupled transport and electrochemical reactions in solid oxide steam electrolyzer for hydrogen production
Electrochimica Acta, 2007Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:Abstract A mathematical model was developed to simulate the coupled transport/electrochemical reaction phenomena in a solid oxide steam electrolyzer (SOSE) at the micro-scale level. Ohm's law, dusty gas model (DGM), Darcy's law, and the generalized Butler Volmer Equation were employed to determine the transport of electronic/ionic charges and gas species as well as the electrochemical reactions. Parametric analyses were performed to investigate the effects of operating parameters and micro-structural parameters on SOSE potential. The results substantiated the fact that SOSE potential could be effectively decreased by increasing the operating temperature. In addition, higher steam molar fraction would enhance the operation of SOSE with lower potential. The effect of particle sizes on SOSE potential was studied with due consideration on the SOSE activation and concentration overpotentials. Optimal particle sizes that could minimize the SOSE potential were obtained. It was also found that decreasing electrode porosity could monotonically decrease the SOSE potential. Besides, optimal values of volumetric fraction of electronic particles were found to minimize electrode total overpotentials. In order to optimize electrode microstructure to minimize SOSE electricity consumption, the concept of “functionally graded materials (FGM)” was introduced to lower the SOSE potential. The advanced design of particle size graded SOSE was found effective for minimizing electrical energy consumption resulting in efficient SOSE hydrogen production. The micro-scale model was capable of predicting SOSE hydrogen production performance and would be a useful tool for design optimization.
-
parametric study of solid oxide fuel cell performance
Energy Conversion and Management, 2007Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:Abstract An electrochemical model was developed to study the current–voltage ( J – V ) characteristics of a solid oxide fuel cell (SOFC). The Butler–Volmer Equation, Fick’s model and Ohm’s law were used to determine the activation, concentration and ohmic overpotentials, respectively. One important feature of this model is that both the exchange current density and gas diffusion coefficients were dependent on the cell microstructures (porosity and pore size) and operational parameters (temperature, pressure and gas composition). The simulation results were compared with experimental data from the literature, and good agreement was obtained. The subsequent parametric modeling analyses determined how individual overpotentials were related to the geometric and operational parameters. It was found that there existed optimal values of electrode pore size and porosity for maximum cell performance. Both the activation and ohmic overpotentials decreased significantly with increasing temperature. However, the concentration overpotential was found to increase with increasing temperature. This unexpected phenomenon was caused by the reduced gas density at elevated temperature despite the increase in diffusion coefficient with increasing temperature. Besides, increasing the hydrogen content in the fuel stream and increasing the operating pressure were possible ways to enhance the SOFC power output. The parametric analyses provided insights in the operation of SOFCs and clarified some ambiguous understanding of SOFC overpotentials. The present model could also serve as a valuable tool for SOFC optimization design.
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an electrochemical model of a solid oxide steam electrolyzer for hydrogen production
Chemical Engineering & Technology, 2006Co-Authors: Meng Ni, Michael K H Leung, Dennis Y C LeungAbstract:An electrochemical model was developed to simulate the J-V characteristics of a solid oxide steam electrolyzer (SOSE) used for hydrogen production. Activation, concentration, and ohmic overpotentials were considered as the main factors for voltage loss. The Butler-Volmer Equation, Fick's model, and Ohm's law were applied to determine the overpotentials of a SOSE cell. The simulation results were compared with experimental data from the literature and good agreement was obtained. Additionally, parametric modeling analyses were conducted to study how the operating temperature and gas composition affected the electrical characteristics. It was found that the voltage loss could be reduced by increasing the operating temperature and steam molar fraction. It was also observed that an anode-supported SOSE cell exhibited a higher hydrogen production efficiency than electrolyte-supported and cathode-supported cells. The electrochemical model can be used to perform further analysis in order to further understand the principles of SOSE hydrogen production, and to optimize SOSE cell and system designs.
T M Jahns - One of the best experts on this subject based on the ideXlab platform.
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Modeling of low-temperature operation of a hybrid energy storage system with a Butler-Volmer Equation based battery model
2016 IEEE Energy Conversion Congress and Exposition (ECCE), 2016Co-Authors: Phillip J Kollmeyer, Anantharaghavan Shridar, T M JahnsAbstract:Lithium-ion battery performance is significantly reduced at low temperatures, where substantially increased resistance reduces power capability and lithium plating causes charging limitations. To reduce the low-temperature limitations of an electric vehicle battery pack, a hybrid energy storage system consisting of a battery pack, an ultracapacitor pack, and a dc/dc converter is investigated. A low-temperature battery model that includes a nonlinear resistance based on the Butler-Volmer Equation and an ultracapacitor model are developed, and the model parameters are experimentally measured for temperatures from -20°C to 25°C. The models are then appropriately scaled for a full-size electric vehicle and paired with a dc/dc converter loss model. The optimal power split is determined for various drive cycles using a dynamic programming optimization algorithm. It is shown, using both analytical and experimental results, that the hybrid energy storage system is an excellent approach for substantially reducing the total energy storage system losses at low temperatures, as well as increasing regenerative braking energy capture, reducing output power limiting, and increasing vehicle range.
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improved nonlinear model for electrode voltage current relationship for more consistent online battery system identification
Energy Conversion Congress and Exposition, 2011Co-Authors: Larry W Juang, Phillip J Kollmeyer, T M Jahns, Robert D LorenzAbstract:An improved nonlinear model for the electrode voltage-current relationship for online battery system identification is proposed. In contrast with the traditional linear-circuit model, the new approach employs a more accurate model of the battery electrode nonlinear steady-state voltage drop based on the Butler-Volmer Equation. The new form uses an inverse hyperbolic sine approximation for the Butler-Volmer Equation. Kalman filter-based system identification is proposed for determining the model parameters based on the measured voltage and current. Both models have been implemented for lead-acid batteries and exercised using test data from a Corbin Sparrow electric vehicle. A comparison of predictions for the two models demonstrates the improvements that can be achieved using the new nonlinear model. The results include improved battery voltage predictions that provide the basis for more accurate state-of-function (SOF) readings.
Martin Z Bazant - One of the best experts on this subject based on the ideXlab platform.
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Modeling of the Interactions of Uniformly Sized
2016Co-Authors: Bernardo Orvananos, Martin Z Bazant, Todd Ferguson, Katsuyo ThorntonAbstract:In this talk, we will present a model and simulations developed to study inter-particle phase separation dynamics in an electrode consisting of intercalation-compound nanoparticles aimed to understand the charge-discharge processes in LixFePO4. The electrochemical simulation is carried out using a numerical method based on the Smoothed Boundary Method (SBM) [1]. The details of Li transport in the particles and electrolyte, electrostatics in the liquid, as well as the reaction at particle-electrolyte interfaces, are considered in this model. We assume that the nanoparticles (40 nm in diameter) are small enough such that two-phase coexistance within a particle is inhibited and that the nanoparticles are electrically well connected such that the electrostatic potential remains uniform in all particles. In order to calculate the Li insertion/extraction flux at the particle surface, we employed the modified Butler-Volmer Equation proposed by Bai et al. [2], where the equilibrium chemical potential is derived from the regular-solution double-well energy function. In this study, we focused on the effect of particle arrangement in the electrode. To this end, we chose a very narrow but long computational domain, a 64x64x1152 nm3 in size, where the long dimension is parallel to the cell direction (anode to cathode). The domain embeds 26 spherical particles in a body center cubic arrangement, and represents a portion of a cell near the separator. The dynamics is simulated in the approximately 1-micron long cell, of which the cathode spans 876 nm. A constant current into the cell is imposed on the bottom boundary, and periodic boundary conditions are imposed at long, rectangular box faces. The configuration of the computational domain is show
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charge transfer kinetics at the solid solid interface in porous electrodes
Nature Communications, 2014Co-Authors: Peng Bai, Martin Z BazantAbstract:Electrochemical kinetics are usually described by the Butler–Volmer Equation. Bai and Bazant propose a method to extract reaction rates for porous electrodes from experiments and show the necessity of using Marcus charge transfer theory in place of the conventional kinetics.
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theory of chemical kinetics and charge transfer based on nonequilibrium thermodynamics
Accounts of Chemical Research, 2013Co-Authors: Martin Z BazantAbstract:Advances in the fields of catalysis and electrochemical energy conversion often involve nanoparticles, which can have kinetics surprisingly different from the bulk material. Classical theories of chemical kinetics assume independent reactions in dilute solutions, whose rates are determined by mean concentrations. In condensed matter, strong interactions alter chemical activities and create variations that can dramatically affect the reaction rate. The extreme case is that of a reaction coupled to a phase transformation, whose kinetics must depend not only on the order parameter but also on its gradients at phase boundaries. Reaction-driven phase transformations are common in electrochemistry, when charge transfer is accompanied by ion intercalation or deposition in a solid phase. Examples abound in Li-ion, metal–air, and lead–acid batteries, as well as metal electrodeposition–dissolution. Despite complex thermodynamics, however, the standard kinetic model is the Butler–Volmer Equation, based on a dilute s...
