Robert M. Darling

Bio: Robert M. Darling is an academic researcher from Argonne National Laboratory. The author has contributed to research in topics: Flow battery & Membrane. The author has an hindex of 21, co-authored 58 publications receiving 2170 citations. Previous affiliations of Robert M. Darling include University of California, Berkeley & United Technologies.

A Critical Review of Modeling Transport Phenomena in Polymer-Electrolyte Fuel Cells

Abstract: aLawrence Berkeley National Laboratory, Berkeley, California 94720, USA bLos Alamos National Laboratory, Los Alamos, New Mexico 87545, USA cUnited Technologies Research Center, East Hartford, Connecticut 06118, USA dSchool of Mechanical and Systems Engineering, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom eChemical and Biomolecular Engineering Department, University of California, Berkeley, California 94720, USA fFuel Cell Research and Development, General Motors, Pontiac, Michigan 48340, USA gBallard Power Systems, Burnaby, British Columbia V5J 5J8, Canada hFuel Cell Research Centre, Queens University, Kingston, Ontario K7L 3N6, Canada iDepartment of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA jDepartment of Mechanical Aerospace and Biomedical Engineering, University of Tennessee at Knoxville, Knoxville, Tennessee 37996, USA kDepartment of Mechanical Engineering Technology, SUNY Alfred State College, Alfred, New York 14802, USA lDepartment of Mechanical Engineering, University of Alberta, Edmonton, Alberta T6G 2G, Canada

The Impedance Response of a Porous Electrode Composed of Intercalation Particles

Abstract: A mathematical model is developed to describe the impedance response of a porous electrode composed of spherical intercalation particles. The model considers a porous electrode without solution‐phase diffusion limitations. The model is developed by first deriving the impedance response of a single intercalation particle, obtained by solving a set of governing equations which describe charge‐transfer and double‐layer charging at the surface, solid‐phase diffusion inside the particle, and an open‐circuit potential which varies as a function of intercalant concentration. The model also considers the effect of an insulating film surrounding the particle. The governing equations are linearized to take advantage of the small amplitude of the perturbing current in impedance analysis. Once the impedance of a single particle is determined, this result is incorporated into a model which describes a porous electrode limited by ohmic drop in the solution and solid phases, and by the impedance of the particles of which the porous electrode is composed. The model can be used to examine the effect of physical properties and particle‐size distributions in the porous electrode, and the usefulness of impedance analysis to measure solid‐phase diffusion coefficients is scrutinized. © 2000 The Electrochemical Society. All rights reserved.

Mathematical Modeling of Lithium Batteries

Abstract: Author(s): Thomas, Karen E.; Newman, John; Darling, Robert M. | Abstract: Early work on modeling lithium batteries, performed prior to the ready availability of high-speed digital computers, used simplified models neglecting kinetic or cencentration effects, assuming constant properties, or neglecting the separator, in order to obtain a close approximation to battery behavior within the limits of computational power available at the time. Today's computers can easily simulate the entire cell sandwich model, and simply present the model in the best form developed to date in section 3, followed by considerations of special situations which are not essential to the basic modeling framework. Simplifying cases which have contributed to our understanding of the lithium battery are presented in section 5. Finally, we discuss applications of modeling, such as interpreting experimental data and optimizing geometric parameters.

Modeling side reactions in composite LiYMn2O4 electrodes

Abstract: A Li/1 M LiClO 4 in propylene carbonate (PC)/Li y Mn 2 O 4 cell is used to investigate the influence of side reactions on the current-potential behavior of intercalation electrodes. Slow cyclic voltammograms and self-discharge data are combined to estimate, simultaneously, the reversible potential vs state-of-charge curve for the host material and the kinetic parameters for the side reaction. This information is then used, together with estimates of the solid-state diffusion coefficient and main reaction exchange current density, in a mathematical model of the system. Predictions from the model compare favorably with continuous cycling results and galvanostatic experiments with periodic current interruptions.

Modeling a Porous Intercalation Electrode with Two Characteristic Particle Sizes

Abstract: A mathematical model of a complete cell containing a porous intercalation electrode with two characteristic particle sizes is presented. Galvanostatic cycling and relaxation phenomena on open-circuit are compared to a cell with a single particle size. Electrodes with a particle-size distribution show modestly inferior capacity-rate behavior in all cases considered in this work. The cycling results exhibit a mismatch in the states-of-charge of the surfaces of the different particle sizes located at the same position in the electrode. The magnitude of this mismatch correlates with the slope of the open-circuit potential vs. state-of-charge curve of the intercalation material. The relaxation on open circuit is substantially faster when the particles are uniformly sized. Asymptotic solutions were developed to aid in the description of the open-circuit behavior in the cases with nonuniform particle sizes. The particle-size distribution has a more pronounced influence on the open-circuit results than on the galvanostatic results.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

New Insights into Perfluorinated Sulfonic-Acid Ionomers

Abstract: In this comprehensive review, recent progress and developments on perfluorinated sulfonic-acid (PFSA) membranes have been summarized on many key topics. Although quite well investigated for decades, PFSA ionomers’ complex behavior, along with their key role in many emerging technologies, have presented significant scientific challenges but also helped create a unique cross-disciplinary research field to overcome such challenges. Research and progress on PFSAs, especially when considered with their applications, are at the forefront of bridging electrochemistry and polymer (physics), which have also opened up development of state-of-the-art in situ characterization techniques as well as multiphysics computation models. Topics reviewed stem from correlating the various physical (e.g., mechanical) and transport properties with morphology and structure across time and length scales. In addition, topics of recent interest such as structure/transport correlations and modeling, composite PFSA membranes, degradat...