White Modern Aspects of Electrochemistry 40

1. Auflage 2010
ISBN: 978-0-387-46106-9
Verlag: Springer
Format: PDF
Kopierschutz: 1 - PDF Watermark

E-Book, Englisch, Band 40, 352 Seiten

Reihe: Modern Aspects of Electrochemistry

This volume in the acclaimed series Modern Aspects of Electrochemistry starts with a dedication to the late Professor Brian Conway who for 50 years helped to guide this series to its current prominence. The remainder of the volume is then devoted to the following topics: PEM fuel cells; the use of graphs in electrochemical reaction newtworks; nanomaterials in Lithium-ion batteries; direct methanolf fuel cells (two chapters); fuel cell catalyst layers. The book is for electrochemists, electrochemical engineers, fuel cell workers and energy generation workers.

Autoren/Hrsg.

White, Ralph E.

Inhaltsverzeichnis

1;Preface;7
2;Memories of Brian Evans Conway Editor 1955-2005;9
3;Table of Contents;14
4;1 PEM Fuel Cell Bipolar Plates;20
4.1;I. INTRODUCTION;20
4.1.1;1. NAFION MEA Based Bipolar Plate Problems;21
4.1.2;2. Polybenzimldazole/H3PO4;22
4.2;II. DEFINITION;22
4.2.1;1. Separator Plate;23
4.2.2;2. FlowField;24
4.2.3;3. Port and Port Bridges;25
4.2.4;4. Seals;26
4.2.5;5. Frame;27
4.3;III. BIPOLAR PLATE FEATURES;27
4.3.1;1. Tolerances;28
4.3.2;2. Thermal Management;28
4.3.3;3. Electrical Conduction;29
4.3.4;4. Water Management;30
4.3.5;5. Low Cost;32
4.3.6;6. Stable, Free from Corrosion Products;32
4.3.6.1;(i) Galvanic Corrosion;32
4.4;IV. MATERIALS AND PROCESSES;34
4.4.1;1. Comparison of Carbon and Metal;34
4.4.1.1;(i) Operational;35
4.4.1.2;(ii) Forming Cost;35
4.4.2;2. Carbon;37
4.4.2.1;(i) Molded Graphite;37
4.4.2.2;(ii) Paper;38
4.4.2.3;(iii) Stamped Exfoliated Graphite iGrafoil, Graflex);38
4.4.3;3. Metal;38
4.4.3.1;(i) Forming Metal BipolarPlates;39
4.4.3.2;(ii) Intrinsically Corrosion Resistant Metals;40
4.4.3.3;(iii) Direct Coatings;40
4.4.3.3.1;(a) Plating;40
4.4.3.3.2;(b) Cladding;41
4.4.3.3.3;(c) Vapor deposition plasma, jet spray, CVD, laser ablation, LAFAD;41
4.4.3.3.4;(d) Flame spraying;41
4.4.3.3.5;(e) Thermal vapor deposition;41
4.4.3.3.6;(f) Thermally activated CVD;42
4.4.3.3.7;(g) Fast CVD;42
4.4.3.3.8;(h) Thermal laser assisted CVD (LCVD);42
4.4.3.3.9;(i) Reactive ion beam-assisted electron beam-physical vapor deposition;42
4.4.3.3.10;(j) Reactive plasma spraying (RPS);42
4.4.3.3.11;(k) Pulsed laser deposition (PLD);43
4.4.3.4;(iv) Conductive Polymer Grafting;43
4.4.3.4.1;(a) Aluminum coupling;44
4.4.3.4.2;(b) Polymer matrix;48
4.4.3.4.3;(c) Accelerators;49
4.4.3.4.4;(d) Crosslinkers;50
4.4.3.4.5;(e) Graft initiators and regenerators;50
4.4.3.4.6;(f) Solvents;50
4.4.3.4.7;(g) Conductive fillers;52
4.5;REFERENCES;52
5;2 Basic Applications of the Analysis of Variance and Covariance in Electrochemical Science and Engineering;55
5.1;I. INTRODUCTION;55
5.2;II. BASIC PRINCIPLES AND NOTIONS;56
5.3;III. ANOVA: ONE-WAY CLASSIFICATION;58
5.3.1;1. Completely Randomized Experiment (CRE);60
5.3.2;2. Randomized Block Experiment (RBE);60
5.3.2.1;(i) Example 1: A Historical Perspective of Caustic Soda Production;61
5.3.2.2;(ii) Example 2: Metallic Corrosion;63
5.4;IV. ANOVA: TWO-WAY CLASSIFICATION;64
5.4.1;1. Null and Alternative Hypotheses;64
5.4.2;2. Illustration of Two-Way Classification: Specific Energy Requirement for an Electrolytic Process;65
5.5;V. ANOVA: THREE-WAY CLASSIFICATIONS;67
5.6;VI. ANOVA: LATIN SQUARES (LS);69
5.7;VII. APPLICATIONS OF THE ANALYSIS OF COVARIANCE (ANCOVA);71
5.7.1;1. ANCOVA with Velocity as Single Concomitant Variable;71
5.7.1.1;(i) Pattern A (CRE);71
5.7.1.2;(ii) Pattern B(RBE);74
5.7.2;2. ANCOVA with Velocity and Pressure Drop Acting as Two Concomitant Variables;76
5.7.3;3. Two Covariate-Based ANCOVA of Product Yields in a Batch and in a Flow Electrolyzer;76
5.7.4;4. Covariance Analysis for a Two-Factor, Single Cofactor CRE;78
5.8;VIII. MISCELLANEOUS TOPICS;80
5.8.1;1. Estimation of the Type II Error in ANOVA;80
5.8.2;2. Hierarchical Classification;82
5.8.3;3. ANOVA-Related Random Effects;84
5.8.4;4. Introductory Concepts of Contrasts Analysis;87
5.9;IX. FINAL REMARKS;89
5.10;ACKNOWLEDGMENTS;90
5.11;LIST OF PRINCIPAL SYMBOLS;90
5.11.1;Subscripts;90
5.11.2;Greek Symbols;91
5.12;REFERENCES;91
6;3 Nanomaterials in Li-Ion Battery Electrode Design;93
6.1;I. INTRODUCTION;93
6.2;II. TEMPLATES USED;96
6.2.1;1. Track-Etch Membranes;96
6.2.2;2. Alumina Membranes;98
6.2.3;3. Other Templates;99
6.3;II. NANOSTRUCTURED CATHODIC ELECTRODE MATERIALS;101
6.3.1;1. Electrode Fabrication;102
6.3.1.1;(i) Nanostructured Electrode;102
6.3.1.2;(ii) Control Electrodes;103
6.3.2;2. Structural Investigations;104
6.3.3;3. Electrochemical Characterization;105
6.3.3.1;(i) Cyclic Voltammetry;105
6.3.3.2;(ii) Rate Capabilities;107
6.4;III. NANOSTRUCTURED ANODIC ELECTRODES;109
6.4.1;1. Electrode Fabrication;110
6.4.1.1;(i) Nanostructured Electrodes;110
6.4.1.2;(ii) Control Electrodes;110
6.4.2;2. Structural Investigations;111
6.4.3;3. Electrochemical Investigations;113
6.5;V. NANOELECTRODE APPLICATIONS;115
6.5.1;1. Low-Temperature Performance;115
6.5.1.1;(i) Electrode Fabrication;115
6.5.1.2;(ii) Strategy;116
6.5.1.3;(iii) Electrochemical Results;117
6.5.1.4;(iv) Electronic Conductivity;119
6.5.1.5;(v) Cycle Life;120
6.5.2;2. Variations on a Synthetic Theme;120
6.5.2.1;(i) Nanocomposite of LiFePO4/Carbon;120
6.5.2.1.1;(a) Electrode fabrication;121
6.5.2.1.2;(b) Methods;122
6.5.2.1.3;(c) Imaging;122
6.5.2.1.4;(d) Carbon analysis;124
6.5.2.1.5;(e) Electrochemistry;125
6.5.2.2;(ii) Improving Volumetric Capacity;127
6.5.2.2.1;(a) Strategy;128
6.5.2.2.2;(b) Electrode morphology;129
6.5.2.2.3;(c) Rate capabilities;132
6.6;VI. CARBON HONEYCOMB;135
6.6.1;1. Preparation of Honeycomb Carbon;136
6.6.2;2. Electrochemical Characterization;139
6.7;VII. CONCLUSIONS;141
6.8;ACKNOWLEDGEMENTS;141
6.9;REFERENCES;142
7;4 Direct Methanol Fuel Cells: Fundamentals, Problems and Perspectives;145
7.1;I. INTRODUCTION;145
7.2;II. OPERATING PRINCIPLE OF THE SPE-DMFC;146
7.3;III. ELECTRODE REACTION MECHANISMS IN SPE-DMFCS;150
7.3.1;1. Anodic Oxidation of Methanol;150
7.3.2;2. Cathodic Reduction of Oxygen;157
7.4;IV. MATERIALS FOR SPE-DMFCS;158
7.4.1;1. Catalyst Materials;158
7.4.1.1;(i) Anode Catalysts;158
7.4.1.2;(ii) Oxygen Reduction Catalysts;167
7.4.1.3;(iii) Membrane Materials;174
7.5;V. DIRECT METHANOL FUEL CELL PERFORMANCE;181
7.5.1;1. DMFC Stack Performance;193
7.5.2;2. Alternative Catalysts and Membranes in the DMFC;196
7.5.3;3. Alkaline Conducting Membrane and Alternative Oxidants;201
7.6;VI. CONVENTIONAL VS. MIXED-REACTANT SPE-DMFCS;203
7.7;VII. MATHEMATICAL MODELLING OFTHEDMFC;210
7.7.1;1. Methanol Oxidation;213
7.7.2;2. Empirical Models for Cell Voltage Behaviour;216
7.7.3;3. Membrane Transport;220
7.7.4;4. Effect of Methanol Crossover on Fuel Cell Performance;222
7.7.5;5. Mass Transport and Gas Evolution;223
7.7.6;6. DMFC Electrode Modelling;227
7.7.7;7. Cell Models;228
7.7.8;8. Single Phase Flow;230
7.7.9;9. Two- and Three-Dimensional Modelling;231
7.7.10;10. Dynamics and Modelling;233
7.7.11;11. Stack Hydraulic and Thermal Models;233
7.8;VIII. CONCLUSIONS;234
7.9;LIST OF SYMBOLS;235
7.9.1;Superscripts and Subscripts;235
7.9.2;Greek Symbols;236
7.10;REFERENCES;236
8;5 Review of Direct Methanol Fuel Cells;246
8.1;I. INTRODUCTION;246
8.2;II. ANODE KINETICS;249
8.2.1;1. Reaction Mechanism;249
8.2.2;2. Methanol Oxidation Catalysts;250
8.2.3;(i) Platinum and Platinum Catalyst Structure;250
8.2.4;(ii) Platinum and Platinum Alloy Catalyst Performance;257
8.3;III. OXYGEN REDUCTION REACTION CATALYSTS;264
8.4;IV. HIGH TEMPERATURE MEMBRANES;265
8.5;V. METHANOL CROSSOVER;270
8.5.1;1. Magnitude of Crossover;270
8.5.2;2. Effect of CO2 Crossover;275
8.5.3;3. Mixed-Potential Effects;277
8.5.4;4. Novel Membranes to Reduce Methanol Crossover;278
8.6;VI. DMFC MODELING REVIEW;281
8.6.1;1. One-Dimensional Models;282
8.6.2;2. Two-Dimensional and Three-Dimensional Models;290
8.7;VII. SUMMARY;295
8.8;REFERENCES;297
9;6 Direct Numerical Simulation of Polymer Electrolyte Fuel Cell Catalyst Layers;302
9.1;I. INTRODUCTION;302
9.2;II. DIRECT NUMERICAL SIMULATION (DNS) APPROACH;305
9.2.1;1. Advantages and Objectives of the DNS Approach;306
9.2.2;2. DNS Model- Idealized 2-D Microstructure;307
9.2.3;3. Three-Dimensional Regular Microstructure;310
9.2.4;4. Results and Discussion;316
9.2.4.1;(i) 2-D Model: Kinetics- vs. Transport-Limited Regimes;316
9.2.4.2;(ii) Comparison ofthe Polarization Curves between 2-D and 3-D Simulations;321
9.3;III. THREE-DIMENSIONAL RANDOM MICROSTRUCTURE;322
9.3.1;1. Random Structure;323
9.3.2;2. Structural Analysis and Identification;324
9.3.3;3. Governing Equations;328
9.3.4;4. Boundary Conditions;331
9.3.5;5. Results and Discussion;333
9.4;IV. DNS MODEL - WATER TRANSPORT;337
9.4.1;1. Water Transport Mechanism;338
9.4.2;2. Mathematical Description;340
9.4.3;3. Results and Discussion;344
9.4.3.1;(i) Inlet-Air Humidity Effect;344
9.4.3.2;(ii) Water Crossover Effect;347
9.4.3.3;(iii) Optimization of Catalyst Layer Compositions;348
9.5;V. 3-D CORRELATED MICROSTRUCTURE;350
9.5.1;1. Stochastic Generation Method;350
9.5.2;2. Governing Equations, Boundary Conditions and Numerical Procedure;351
9.5.3;3. Results and Discussion;354
9.6;VI. CONCLUSIONS;357
9.7;ACKNOWLEDGEMENTS;357
9.8;REFERENCES;358
10;Index;359

Leseproben

"3 Nanomaterials in Li-Ion Battery Electrode Design (p. 75-76)

Charles R. Sides and Charles R. Martin*

I. INTRODUCTION

Li-ion batteries have generated great interest as lightweight, portable, rechargeable power sources over the last decade. Their introduction in 1990 by T. Nagaura and K. Tozawa of SonyTec Inc. fueled the explosion of personal electronic devices. Li-ion batteries are now the power source of choice for laptops, cell phones, and digital cameras. The public has quickly embraced this technology, which accounts for an approximately $3 billion annual market. 2 Despite (or perhaps as a result of) the commercial success of these batteries, a global research initiative exists to improve the existing design.

The goal of which is to apply this technology to more demanding and exotic uses, such as the electric component of hybrid vehicles, low-temperature applications, and power supplies for MEMs. However, the current design cannot adequately satisfy the power requirements of such systems, due to the inability to deliver a sufficient quantity of charge at high discharge currents. 3 This chapter will detail the efforts of laboratories, ours in particular, to incorporate the field of nanomaterials to improve upon Li-ion batteries.

Li-ion batteries operate by reversibly intercalating charge in each of two electrodes. Intercalation is the process by which a guest species (Li+) is able to reversibly enter/exit a host structure, causing little or no difference to the lattice of the host. These electrodes are separated by an ion-conductive electrolyte. Upon discharge, the Li-ions deintercalate from the low-potential electrode, migrate through the electrolyte, and insert into the highpotential electrode. The ions then rely on solid-state diffusion to fill the non-surface intercalation sites.

Obeying the governing laws of charge neutrality, electrons compensate for the movement of the ions. If current flow is reversed (from cathode to anode), Li-ions insert into the low-potential electrode and the system is charged. The low-potential electrode is the anode and the high-potential electrode is the cathode. This convention (adopted from the discharge process) is obeyed regardless of the direction of current flow. In the analysis of a battery system, both the ionic conductivity and electronic conductivity must be considered. Nanomaterials are advantageous in both regards.

The Martin research group has pioneered the nanofabrication strategy of template synthesis." This general method has been used to synthesize nanostructures of a variety of materials such as gold 5-8 carbon 9-11 semiconductors 12,13 polymers 14,15 and Li-ion battery electrodes,II,13,16-28 our focus here. In general, this method involves deposition of a precursor material into a micro- or nanoporous template. This template is typically commercially available track-etch polymer filters or anodized alumina, though others have been demonstrated. Depending on both the porediameter and the specific chemical interactions between the pore wall and the precursor, the resulting structures may be tubes (hollow) or wires (solid). These structures are referred to as "nano", if one or more of their dimensions are on the nanoscale « 100 nm). The aspect ratio (length / width), though, is often on the order of 10.

In this embodiment of Li-ion electrodes, a precursorimpregnated polycarbonate template membrane is attached to a section of metal foil. The foil has dual-functionality as it serves as a substrate during synthesis and as a common current collector during electrochemical characterization. The precursor is processed (typically, by aging or heating) into the desired product. Often in the case of battery materials, the template is then removed by plasma etching or dissolution. The result is an electrode that consists of structures that mirror the geometry (length, diameter, and number density) of the pores of the template."