Theory of porous electrodes—XVI. The nickel hydroxide electrode

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“…Furthermore, in Eq. 6 ji, is the electrochemical potential of species [2] i, according to = p., + r,F4) [8] [3]…”

Section: Modelmentioning

confidence: 99%

Electronic Network Modeling of Rechargeable Batteries: I. The Nickel and Cadmium Electrodes

Kruijt

Bergveld

Notten

1998

J. Electrochem. Soc.

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“…Since the microscale length k is assumed to be much smaller than the pore length L which the axial current must penetrate in a realistic porous electrode, I' may be assumed to be constant, and [1] and [3] ance (the term in brackets, which represents the resistance of an ideal cylindrical pore segment whose length and volume are identical to those of the real pore segment) multiplied by the factor <S> <l/S>. The factor arises specifically from the cross-sectional variations, that is, the constrictions and expansions, in the pore structure.…”

Section: Macroscopic Distribution In Constricted Pore Structuresmentioning

confidence: 99%

Effect of Pore Structure on Current and Potential Distributions in a Porous Electrode

Lanzi

Landau

1990

J. Electrochem. Soc.

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The effects of the detailed structure of porous electrodes on their macroscopic and microscopic current and potential distributions have been quantitatively analyzed. An analytical expression has been derived for the macroscopic pore resistance in terms of a constriction factor which can be related to the pore microstructure and takes the place of an empirical tortuosity. The model has been verified by comparing its predictions to results from numerical computations and experiment. Analysis of the current and concentration distributions within localized micropores indicates that the microporous area is fully accessible to charge and mass transfer. Thus the kinetics of interfacial processes is determined primarily by the micropore structure, while the ohmic and mass transport limitations throughout the volume of the electrode are imposed prineipally by the resistance of the macropores.Electrochemical cells are often restricted in the current density which may be practically applied. Where kinetic limitations may be significant, or where it is desirable to use the full volume of an electrode for electrochemical reactions, porous electrodes with their high surface areas are generally used to allow for the application of higher currents and greater utilization of reactants. Such is the case for many battery electrodes in which fast kinetics and large extents of reaction are required. The efficiency of utilization and associated voltage losses are intimately linked to the current and potential distributions within the porous structure.Most available models only consider the macroscopic structure of the electrode and assume it to be a superposition of homogeneous phases. Euler and Nonnemacher (1) developed a model to determine the current distributions within porous electrodes under linear kinetics. Newman and Tobias (2) extended this model to apply for Tafel kinetics, both with and without mass-transfer limitations. These authors treated the pore structure as a superposition of continuous phases without regard to the structural details within the electrode. This approach has been adapted by many workers in models for specific porous electrodes, such as nickel oxide electrodes (3, 4), gas-fed electrodes (5), and halogen electrodes for zinc-halogen batteries (6-8).White et al. (9) examined an effect of pore size distribution; they related this to gas-contacted area in gas-fed electrodes. These constitute only a few more recent examples; a more extensive review is provided by Newman and Tiedemann (10).Most of the authors cited above followed the precedent of Ref.(1, 2) by assuming that the electrode consists of a superposition of continuous phases. They did not attempt to relate the model parameters, particularly the tortuosity and specific area, to the structural characteristics of the pores. A numerical study based on a random network model by Kramer and Tomkiewicz (11) suggests that such relations can be found, since their results were found to agree qualitatively with those of a single-pore model. The purpose of our...

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“…Side reaction 2 OH 1 0, + H20 + 2e 2 During charging, the applied current is used to produce [2] hydrogen through reaction 4 and consume oxygen through reaction 5, whereas hydrogen is consumed by the applied current and the current from reaction 5 during discharging.…”

Section: Modelmentioning

confidence: 99%

A Multiphase Mathematical Model of a Nickel/Hydrogen Cell

Vidts

Delgado

White

1996

J. Electrochem. Soc.

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A mathematical model for a nickel/hydrogen cell is developed to investigate the dynamic performance of the cell's charge and discharge processes. Concentrated solution theory and the volume averaging technique are used to characterize the transport phenomena of the electrolyte and other species in the porous electrode and separaton Other physical fundamentals, such as Ohm's law, are employed to describe the electrical and other physical processes in the cell. The model is designed to predict the distribution of electrolyte, hydrogen, and oxygen concentrations within the cell, hydrogen and oxygen pressure, potential, current density, electrochemical reaction rates, and state of charge. The model can be used to evaluate the influences of all the physical, design, and operation parameters on the behavior of a nickel-hydrogen cell. The model simulations show excellent agreement with experimental data for charge and discharge operations. The model simulations show the formation of a secondary discharge plateau by the end of discharge. This plateau is caused by oxygen reduction at the nickel electrode. It is the first model that predicts this feature, which is a characteristic of the nickel electrode. The model simulations also show the existence of an optimum charge rate that maximizes the charge efficiency, which can be used for the implementation of optimal operating conditions. InfroductionIn this article we present a mathematical model for a nickel/hydrogen cell (NiOOH/H,) for charge and discharge operations. The nickel/hydrogen battery has several attractive features that make it the prime candidate for energy storage in many aerospace applications. Salient features of this battery are a long cycle lifetime that exceeds any other maintenance-free secondary battery system, high specific energy (energy/weight), high power density, and tolerance to overcharge.1

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Theory of porous electrodes—XVI. The nickel hydroxide electrode

Cited by 29 publications

References 8 publications

Electronic Network Modeling of Rechargeable Batteries: I. The Nickel and Cadmium Electrodes

Electronic Network Modeling of Rechargeable Batteries: I. The Nickel and Cadmium Electrodes

Effect of Pore Structure on Current and Potential Distributions in a Porous Electrode

A Multiphase Mathematical Model of a Nickel/Hydrogen Cell

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