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In the first part of the dissertation (Chapters 3-5), the effect of a cationic dispersant, polyethyleneimine (PEI) on the co-deposition of micro and nano SiC particles with nickel is characterized and modeled. A major challenge in Ni/SiC co-deposition for wear-resistant coatings is that the dispersants that are used to stabilize the particles in the electrolyte to ensure high and uniform particle incorporation into the deposit can significantly affect the electrodeposition kinetics. To overcome this challenge, studies of particle dispersion and electrodeposition are integrated. The effect of PEI on the electrodeposition of Ni/SiC composites is characterized as a function of SiC and PEI bath concentration, current density, rotation speed, molecular weight of PEI and particle size. A pre-coating procedure, in which SiC particles are pre-coated with PEI in a different electrolyte prior to plating, is described. With the pre-coating procedure, high particle stability in the plating bath is obtained.
Provides a comprehensive understanding of a wide range of systems and topics in electrochemistry This book offers complete coverage of electrochemical theories as they pertain to the understanding of electrochemical systems. It describes the foundations of thermodynamics, chemical kinetics, and transport phenomena—including the electrical potential and charged species. It also shows how to apply electrochemical principles to systems analysis and mathematical modeling. Using these tools, the reader will be able to model mathematically any system of interest and realize quantitative descriptions of the processes involved. This brand new edition of Electrochemical Systems updates all chapters while adding content on lithium battery electrolyte characterization and polymer electrolytes. It also includes a new chapter on impedance spectroscopy. Presented in 4 sections, the book covers: Thermodynamics of Electrochemical Cells, Electrode Kinetics and Other Interfacial Phenomena, Transport Processes in Electrolytic Solutions, and Current Distribution and Mass Transfer in Electrochemical Systems. It also features three appendixes containing information on: Partial Molar Volumes, Vectors and Tensors, and Numerical Solution of Coupled, Ordinary Differential Equations. Details fundamental knowledge with a thorough methodology Thoroughly updated throughout with new material on topics including lithium battery electrolyte characterization, impedance analysis, and polymer electrolytes Includes a discussion of equilibration of a charged polymer material and an electrolytic solution (the Donnan equilibrium) A peerless classic on electrochemical engineering Electrochemical Systems, Fourth Edition is an excellent resource for students, scientists, and researchers involved in electrochemical engineering.
Current imperatives of electrification and decarbonization entail significant improvements in energy density, performance, and cost metrics for battery technology. This has motivated active research into new materials, cell designs, and external controls to ensure safe and efficient operation. Modeling and simulation approaches have a powerful complementary function in this regard, most notably exemplified by the models for Lithium-ion batteries by Newman and co-workers. The overarching theme of this dissertation is thus the development and application of electrochemical modeling approaches at multiple scales in problems relevant to the abovementioned contexts. At the systems level, the development of more intelligent and powerful Battery Management Systems is enabled by fast electrochemical models, which must balance competing considerations of accuracy, computational efficiency, and ease of parameterization. To this end, we report a rigorous and generalized methodology for "upscaling" continuum electrochemical models. This approach, based on the visualization of a battery as Tanks-in-Series, has been demonstrated for both Lithium-ion and more complex Lithium-sulfur batteries. With respect to full models, voltage prediction errors below 20 mV are achieved for high-energy cells in most practical cases. 30 mV errors are achieved for aggressive conditions of high-rate operation at sub-zero ambient temperatures, illustrating their practical utility. This approach results in improved computational speed since each conservation law is replaced by a relatively simple volume-averaged differential or algebraic equation. For examples of large-scale problems, this leads to 10x savings in computation time over fast implementations of conventional models, illustrating competitiveness for real-time applications. In the development of next-generation chemistries, continuum models can serve as a framework for the analysis and interpretation of experimental data, while providing design guidance and helping determine desirable operating regimes. Electrochemical phenomena at different length and time scales are manifested during operation through voltage and temperature signatures, cycle life, and coulombic efficiency. Optimization of cell-level metrics is thus predicated on their correlation with the internal electrochemistry. This entails the integration of electrochemical models at different levels of detail in a computationally efficient and robust manner. To this end, the second half of this dissertation describes our efforts to develop a simulation framework for the modeling of Lithium-metal systems. We first describe a robust computational method to simulate Poisson Nernst Planck (PNP) models for Lithium symmetric cells characterized by thin double layers. This can be leveraged in applications where computational efficiency is of salience, such as cycling simulations and parameterization by coupling kinetic models of interest. This is demonstrated by a systems level method, enabling the quick evaluation of candidate mechanisms appropriately expressed as time-varying rate constants, making it useful for understanding the phenomena underpinning voltage transitions in Lithium symmetric cells. This is followed by a description of a preliminary electrochemical-mechanical model for Li metal interfaces, which is expected to serve as basis for more sophisticated electrochemical-mechanical models for Li metal systems operating under external pressure. We expect these approaches to advance fundamental understanding and design of Li-metal batteries, while creating accessible computational tools to complement experimental studies. Taken together, these contributions are envisaged to advance the knowledge base for model-based design as well as Battery Management Systems, particularly in anticipation of the commercialization of emerging battery chemistries.
This thesis presents the one-dimensional equations, numerical method and simulations of a model to characterize the dynamical operation of an electrochemical cell. This model extends the current state-of-the art in that it accounts, in a primitive way, for the physics of the electrolyte/electrode interface and incorporates diffuse-charge dynamics, temperature coupling, surface coverage, and polarization phenomena. The one-dimensional equations account for a system with one or two mobile ions of opposite charge, and the electrode reaction we consider (when one is needed) is a one-electron electrodeposition reaction. Though the modeled system is far from representing a realistic electrochemical device, our results show a range of dynamics and behaviors which have not been observed previously, and explore the numerical challenges required when adding more complexity to a model. Furthermore, the basic transport equations (which are developed in three spatial dimensions) can in future accomodate the inclusion of additional physics, and coupling to more complex boundary conditions that incorporate two-dimensional surface phenomena and multi-rate reactions. In the model, the Poisson-Nernst-Planck equations are used to model diffusion and electromigration in an electrolyte, and the generalized Frumkin-Butler-Volmer equation is used to model reaction kinetics at electrodes. An energy balance equation is derived and coupled to the diffusion-migration equation. The model also includes dielectric polarization effects by introducing different values of the dielectric permittivity in different regions of the bulk, as well as accounting for surface coverage effects due to adsorption, and finite size "crowding", or steric effects. Advection effects are not modeled but could in future be incorporated. In order to solve the coupled PDE's, we use a variable step size second order scheme in time and finite differencing in space. Numerical tests are performed on a simplified system and the scheme's stability and convergence properties are discussed. While evaluating different methods for discretizing the coupled flux boundary condition, we discover a thresholding behaviour in the adaptive time stepper, and perform additional tests to investigate it. Finally, a method based on ghost points is chosen for its favorable numerical properties compared to the alternatives. With this method, we are able to run simulations with a large range of parameters, including any value of the nondimensionalized Debye length epsilon. The numerical code is first used to run simulations to explore the effects of polarization, surface coverage, and temperature. The code is also used to perform frequency sweeps of input signals in order to mimic impedance spectroscopy experiments. Finally, in Chapter 5, we use our model to apply ramped voltages to electrochemical systems, and show theoretical and simulated current-voltage curves for liquid and solid thin films, cells with blocking (polarized) electrodes, and electrolytes with background charge. Linear sweep and cyclic voltammetry techniques are important tools for electrochemists and have a variety of applications in engineering. Voltammetry has classically been treated with the Randles-Sevcik equation, which assumes an electroneutral supported electrolyte. No general theory of linear-sweep voltammetry is available, however, for unsupported electrolytes and for other situations where diffuse charge effects play a role. We show theoretical and simulated current-voltage curves for liquid and solid thin films, cells with blocking electrodes, and membranes with fixed background charge. The analysis focuses on the coupling of Faradaic reactions and diffuse charge dynamics, but capacitive charging of the double layers is also studied, for early time transients at reactive electrodes and for non-reactive blocking electrodes. The final chapter highlights the role of diffuse charge in the context of voltammetry, and illustrates which regimes can be approximated using simple analytical expressions and which require more careful consideration.
Atomic-Scale Modelling of Electrochemical Systems A comprehensive overview of atomistic computational electrochemistry, discussing methods, implementation, and state-of-the-art applications in the field The first book to review state-of-the-art computational and theoretical methods for modelling, understanding, and predicting the properties of electrochemical interfaces. This book presents a detailed description of the current methods, their background, limitations, and use for addressing the electrochemical interface and reactions. It also highlights several applications in electrocatalysis and electrochemistry. Atomic-Scale Modelling of Electrochemical Systems discusses different ways of including the electrode potential in the computational setup and fixed potential calculations within the framework of grand canonical density functional theory. It examines classical and quantum mechanical models for the solid-liquid interface and formation of an electrochemical double-layer using molecular dynamics and/or continuum descriptions. A thermodynamic description of the interface and reactions taking place at the interface as a function of the electrode potential is provided, as are novel ways to describe rates of heterogeneous electron transfer, proton-coupled electron transfer, and other electrocatalytic reactions. The book also covers multiscale modelling, where atomic level information is used for predicting experimental observables to enable direct comparison with experiments, to rationalize experimental results, and to predict the following electrochemical performance. Uniquely explains how to understand, predict, and optimize the properties and reactivity of electrochemical interfaces starting from the atomic scale Uses an engaging “tutorial style” presentation, highlighting a solid physicochemical background, computational implementation, and applications for different methods, including merits and limitations Bridges the gap between experimental electrochemistry and computational atomistic modelling Written by a team of experts within the field of computational electrochemistry and the wider computational condensed matter community, this book serves as an introduction to the subject for readers entering the field of atom-level electrochemical modeling, while also serving as an invaluable reference for advanced practitioners already working in the field.
This book presents peer reviewed articles from The International Conference on Metallurgical Engineering and Centenary Celebration (METCENT 2023), held at Indian Institute of Technology (BHU) Varanasi, India from the 26-28th of October 2023. It covers wide areas of metallurgical and materials science, highlighting recent advancements in these areas, including but not limited to Advanced Steels, Computational Material Science, Recent Ferrous/Non-Ferrous Metallurgy Processes, Green Iron and Steel Making Technologies and others. METCENT 2023 provides a unique opportunity to all the Metallurgists, Materials Scientists, Academicians and Industry experts to share their experiences on this special occasion.
Complexity and Complex Chemo-Electric Systems presents an analysis and synthesis of chemo-electric systems, providing insights on transports in electrolytes, electrode reactions, electrocatalysis, electrochemical membranes, and various aspects of heterogeneous systems and electrochemical engineering. The book describes the properties of complexity and complex chemo-electric systems as the consequence of formulations, definitions, tools, solutions and results that are often consistent with the best performance of the system. The book handles cybernetics, systems theory and advanced contemporary techniques such as optimal control, neural networks and stochastic optimizations (adaptive random search, genetic algorithms, and simulated annealing). A brief part of the book is devoted to issues such as various definitions of complexity, hierarchical structures, self-organization examples, special references, and historical issues. This resource complements Sieniutycz’ recently published book, Complexity and Complex Thermodynamic Systems, with its inclusion of complex chemo-electric systems in which complexities, emergent properties and self-organization play essential roles. Covers the theory and applications of complex chemo-electric systems through modeling, analysis, synthesis and optimization Provides a clear presentation of the applications of transport theory to electrolyte solutions, heterogeneous electrochemical systems, membranes, electro-kinetic phenomena and interface processes Includes numerous explanatory graphs and drawings that illustrate the properties and complexities in complex chemo-electric systems Written by an experienced expert in the field of advanced methods in thermodynamics and related aspects of macroscopic physics
The present study investigates transport and electrochemical phenomena in electrochemical capacitors (ECs) for electrical energy storage applications. Modeling of such systems is made difficult by the complex multidimensional and multiscale porous electrode structures along with the coupled physical phenomena and redox reactions. This study is unique in that it presents rigorous development of physical models for electric double layers and redox reactions in ECs. These models were used to gain insights into the coupled transport and electrochemical phenomena involved. Finally, the results were used to identify the dominant design parameters. First, this study identified the important physical phenomena that must be accounted for when simulating electric double layer capacitors (EDLCs). It established that the Stern and diffuse layers, the finite ion sizes, and the field-dependent electrolyte permittivity must all be accounted for. To account for the Stern layer for 3D electrode structures along with all the other phenomena, a new set of boundary conditions was derived. In fact, this study presents the first simulations of EDLCs with 3D electrode structures including (i) ordered mesoporous carbon sphere arrays and (ii) ordered bimodal mesoporous carbons, respectively. The model and numerical tools were validated successfully against experimental data. Second, this study derives a scaling law for the integral areal capacitance of carbon-based EDLCs supported by rigorous analysis and experimental data for various mesoporous carbon electrodes with different electrolytes. It establishes that the integral areal capacitance of porous electrodes can be expressed as the product of the capacitance of planar electrodes and a semi-empirical function to correct for the porous electrode morphology. To maximize the integral areal capacitance, the electrolyte should have small ion effective diameter and large dielectric constant. The electrode pore diameter should be tailored as monodispersed as possible to match the ion diameter. Third, this study presents dynamic modeling of EDLCs accounting for charge transport in both the electrode and electrolyte. It provides rigorous physical interpretations of experimental observations from electrochemical impedance spectroscopy and cyclic voltammetry (CV) experiments based on physics-based numerical simulations. Moreover, a generalized modified Poisson-Nernst-Planck (GMPNP) model was derived from first principles to simulate electric double layer dynamics valid for asymmetric electrolytes and/or in the presence of multiple ion species. For the first time, a self-similar behavior was identified for the electric double layer integral capacitance estimated from CV measurement simulations. Finally, this study presents dynamic modeling of asymmetric supercapacitors in CV measurements by rigorously and simultaneously accounting for electric double layers and redox reactions as well as ion insertion in the electrode. It establishes that in CV measurements of pseudocapacitive materials: (i) the capacitive current varies linearly with scan rate v and (ii) the Faradaic current is proportional to $v1ʹ2 The models and results could help develop the optimum electrode architecture to achieve maximum energy and power densities. Moreover, these models will also be useful for simulating and designing various practical electrochemical, colloidal, and biological systems for a wide range of applications.