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PEM Fuel Cells

Book Description

Polymer Electrolyte Membrane (PEM) fuel cells convert chemical energy in hydrogen into electrical energy with water as the only by-product. Thus, PEM fuel cells hold great promise to reduce both pollutant emissions and dependency on fossil fuels, especially for transportation—passenger cars, utility vehicles, and buses—and small-scale stationary and portable power generators. But one of the greatest challenges to realizing the high efficiency and zero emissions potential of PEM fuel cells technology is heat and water management. This book provides an introduction to the essential concepts for effective thermal and water management in PEM fuel cells and an assessment on the current status of fundamental research in this field. The book offers you: • An overview of current energy and environmental challenges and their imperatives for the development of renewable energy resources, including discussion of the role of PEM fuel cells in addressing these issues; • Reviews of basic principles pertaining to PEM fuel cells, including thermodynamics, electrochemical reaction kinetics, flow, heat and mass transfer; and • Descriptions and discussions of water transport and management within a PEM fuel cell, including vapor- and liquid-phase water removal from the electrodes, the effects of two-phase flow, and solid water or ice dynamics and removal, particularly the specialized case of starting a PEM fuel cell at sub-freezing temperatures (cold start) and the various processes related to ice formation.

Table of Contents

  1. Cover
  2. Half Title
  3. Title Page
  4. Copyright Page
  5. Contents
  6. Preface
  7. List of Figures
  8. List of Tables
  9. Nomenclature
  10. 1 Introduction
    1. 1.1 Energy Challenges
    2. 1.2 Fuel Cells and their Roles in Addressing the Energy Challenges
    3. 1.3 PEM Fuel Cells
      1. 1.3.1 PEM Fuel Cell Operation
      2. 1.3.2 Current Status of PEM Fuel Cells
      3. 1.3.3 Thermal and Water Management
  11. 2 Basics of PEM Fuel Cells
    1. 2.1 Thermodynamics
      1. 2.1.1 Internal Energy and the First Law of Thermodynamics
      2. 2.1.2 Enthalpy Change
      3. 2.1.3 Entropy Change and the Second Law of Thermodynamics
      4. 2.1.4 Gibbs Free Energy and Thermodynamic Voltage
      5. 2.1.5 Chemical Potential and Nernst Equation
      6. 2.1.6 Relative Humidity and Phase Change
    2. 2.2 Electrochemical Reaction Kinetics
      1. 2.2.1 Electrochemical Kinetics
      2. 2.2.2 Electrochemical Mechanisms in PEM Fuel Cells
      3. 2.2.3 Linear Approximation and Tafel Equation
    3. 2.3 Voltage Loss Mechanisms and a Simplified Model
      1. 2.3.1 Open Circuit Voltage (OCV)
      2. 2.3.2 Activation Loss
      3. 2.3.3 Ohmic Loss
      4. 2.3.4 Transport Voltage Loss
      5. 2.3.5 Current-Voltage (I-V) Curve and Operation Efficiency
      6. 2.3.6 Role of Water and Thermal Management
    4. 2.4 Chapter Summary
  12. 3 Fundamentals of Heat and Mass Transfer
    1. 3.1 Introduction
    2. 3.2 Conservation Equations
      1. 3.2.1 General Forms
      2. 3.2.2 Mass and Momentum Conservation
      3. 3.2.3 Energy Equation
      4. 3.2.4 Species Transport Equation
    3. 3.3 Constitutive Equations
      1. 3.3.1 A Lattice Model
      2. 3.3.2 Fourier’s Law and Fick’s Law
    4. 3.4 Scaling and Dimensionless Groups
      1. 3.4.1 Scaling and Dimensionless Equations
      2. 3.4.2 Dimensionless Groups
    5. 3.5 Chapter Summary
  13. 4 Water and Its Transport in the Polymer Electrolyte Membrane
    1. 4.1 Introduction to the Polymer Electrolyte Membrane
    2. 4.2 Ion Transport and Ionic Conductivity
      1. 4.2.1 Proton Transport
      2. 4.2.2 Ionic Conductivity Correlations
      3. 4.2.3 Ionic Conductivity Measurement
    3. 4.3 Water Transport in Polymer Electrolyte Membranes
      1. 4.3.1 Transport Mechanisms
      2. 4.3.2 Water Holding Capacity
    4. 4.4 Water Quantification Using Neutron Radiography
    5. 4.5 Ion Transport in Cathode Catalyst Layers
      1. 4.5.1 Variation in Water Content in Catalyst Layers
      2. 4.5.2 Proton Transport in Cathode Catalyst Layers
      3. 4.5.3 Multiple-Layered Cathode Catalyst Layers
    6. 4.6 Chapter Summary
  14. 5 Vapor-Phase Water Removal and Management
    1. 5.1 Mass Transport Overview
    2. 5.2 Diffusion
      1. 5.2.1 Diffusivity
      2. 5.2.2 Molecular Versus Knudsen Diffusion
      3. 5.2.3 Diffusion in GDLs
    3. 5.3 Species Convection
      1. 5.3.1 Flow Modeling with Constant-Flow Assumption
      2. 5.3.2 Flow Formulation Without the Constant-Flow Assumption
      3. 5.3.3 Convection in GDLs
    4. 5.4 Pore-Scale Transport
      1. 5.4.1 Stochastic Material Reconstruction
      2. 5.4.2 Pore-Scale Transport Modeling
      3. 5.4.3 Pore-Level Phenomena
    5. 5.5 Transient Phenomena
      1. 5.5.1 Transient Terms and Time Constants
      2. 5.5.2 Transient Undergoing Constant Voltage or Step Change in Voltage
      3. 5.5.3 Transient Undergoing Constant Current or Step Change in Current
    6. 5.6 Water Management Between a PEM Fuel Cell and Fuel Processor
      1. 5.6.1 Water Balance Model
      2. 5.6.2 Effect of the Steam-to-Carbon Ratio
    7. 5.7 Chapter Summary
  15. 6 Liquid Water Dynamics and Removal
    1. 6.1 Multiphase Flow Overview
      1. 6.1.1 Modeling Multi-Phase Flows
    2. 6.2 Multiphase Flow in GDLS/CLS
      1. 6.2.1 Experimental Visualization
        1. 6.2.1.1 X-ray Imaging
        2. 6.2.1.2 Neutron Radiography
      2. 6.2.2 MultiPhase Mixture (M2) Formulation
        1. 6.2.2.1 Flow Equations
        2. 6.2.2.2 Species Transport
        3. 6.2.2.3 Model Prediction
      3. 6.2.3 Carbon Paper (CP) Versus Carbon Cloth (CC)
      4. 6.2.4 Spatially Varying Properties
        1. 6.2.4.1 Through-Plane Variation in The GDL Property
        2. 6.2.4.2 In-Plane Property Variation and the Effect of Land Compression
        3. 6.2.4.3 Microporous Layers (MPLs)
    3. 6.3 Multiphase Flow in Gas Flow Channels (GFCS)
      1. 6.3.1 Experimental Visualization
      2. 6.3.2 Two-Phase Flow Patterns
      3. 6.3.3 Modeling Two-Phase Flow
        1. 6.3.3.1 The Mixture Model
        2. 6.3.3.2 Two-Fluid Modeling
    4. 6.4 Water Droplet Dynamics at the GDL/GFC Interface
      1. 6.4.1 Force Balance on a Spherical-Shape Droplet
      2. 6.4.2 Droplet Deformation
      3. 6.4.3 Droplet Detachment
        1. 6.4.3.1 Control Volume Method
        2. 6.4.3.2 Derivation Using the Drag Coefficient (CD)
    5. 6.5 Chapter Summary
  16. 7 Ice Dynamics and Removal
    1. 7.1 Subfreezing Operation-Overview
    2. 7.2 Ice Formation
      1. 7.2.1 Water Transport and Conservation
      2. 7.2.2 Three Cold-Start Stages
      3. 7.2.2.1 First Stage: Membrane Hydration
      4. 7.2.2.2 Second Stage: Ice Formation
      5. 7.2.2.3 Third Stage: Ice Melting
    3. 7.3 Voltage Loss Due to Ice Formation
      1. 7.3.1 Spatial Variation of the Oxygen Reduction Reaction (ORR)
      2. 7.3.2 The ORR Rate Under Subfreezing Temperature
      3. 7.3.3 Oxygen Profile in the Catalyst Layer
      4. 7.3.4 Voltage Loss Due to Ice Formation
      5. 7.3.5 A Model of Cold-Start Cell Voltage
    4. 7.4 State of Subfreezing Water
    5. 7.5 Chapter Summary
  17. 8 Thermal Transport and Management
    1. 8.1 Heat Transfer Overview
      1. 8.1.1 Heat Transfer and Its Importance
      2. 8.1.2 Heat Transfer Modes
        1. 8.1.2.1 Heat Conduction
        2. 8.1.2.2 Convective Heat Transfer
        3. 8.1.2.3 Heat Radiation
      3. 8.1.3 Heat Transfer in Porous Media
    2. 8.2 Heating Mechanisms
      1. 8.2.1 The Entropic Heat
      2. 8.2.2 Irreversibility of the Electrochemical Reactions
      3. 8.2.3 The Joules Heat
    3. 8.3 Steady-State Heat Transfer
      1. 8.3.1 One-Dimensional (1D) Heat Transfer Analysis
      2. 8.3.2 Two-Dimensional (2D) Heat Transfer Analysis
      3. 8.3.3 Numerical Analysis
        1. 8.3.3.1 Macroscopic Model Prediction
        2. 8.3.3.2 Pore-Level Heat Transfer
    4. 8.4 Transient Phenomena
      1. 8.4.1 General Transient Operation
      2. 8.4.2 Transient Subfreezing Operation
        1. 8.4.2.1 Temperature Evolution and Voltage Loss
        2. 8.4.2.2 Activation Voltage Loss
        3. 8.4.2.3 Ohmic Voltage Loss
    5. 8.5 Experimental Measurement of Thermal Conductivity
    6. 8.6 Cooling Methods
      1. 8.6.1 Heat Spreaders Cooling
      2. 8.6.2 Cooling by Air or Liquid Flow
      3. 8.6.3 Phase-Change-Based Cooling
    7. 8.7 Example: A Thermal System of Automotive Fuel Cells
      1. 8.7.1 A Lumped-System Model of a PEM Fuel Cell
      2. 8.7.2 Bypass Valve
      3. 8.7.3 Radiator
      4. 8.7.4 Transport Delay
      5. 8.7.5 Fluid Mixer
      6. 8.7.6 Cathode Intercooler
      7. 8.7.7 Anode Heat Exchanger
    8. 8.8 Chapter Summary
  18. 9 Coupled Thermal-Water Management: Phase Change
    1. 9.1 Introduction to Phase Change
    2. 9.2 Vapor-Liquid Phase Change: Evaporation and Condensation
      1. 9.2.1 Vapor-Phase Water Diffusion and Heat Pipe Effect
      2. 9.2.2 GDL De-Wetting
      3. 9.2.3 GDL De-Wetting and Voltage Loss
      4. 9.2.4 A General Definition of the Damkohler Number, Da
        1. 9.2.4.1 Local Heating and Vapor-Phase Removal
        2. 9.2.4.2 A Specific Damkohler Number
        3. 9.2.4.3 Liquid-Free Passages
        4. 9.2.4.4 2D Numerical Simulation
    3. 9.3 Freezing/Thawing
      1. 9.3.1 Temperature Spatial and Temporal Variation
      2. 9.3.2 Non-Isothermal Cold Start
      3. 9.3.3 Freezing/Thawing and Degradation
    4. 9.4 System-Level Analysis of Coupled Thermal and Water Management
      1. 9.4.1 Flow Rates of Species and Two-Phase Flows
      2. 9.4.2 Energy Balance
    5. 9.5 Chapter Summary
  19. Appendix II A: Thermodynamic Properties of Air, Hydrogen Gas, and Water Vapor
  20. Appendix II B: Calculation of the Enthalpy, Entropy, and Gibbs Free Energy For a Substance and the PEM Fuel Cell Reaction
  21. Appendix III A: Mass, Momentum, and Energyconservation Equations in Thecartesian, Cylindrical and Spherical Coordinates
  22. Appendix III B: Mathematical Basics and Relations
  23. Appendix III C: Henry’s Constant For Selected Gases in Water at Moderate Pressure
  24. Appendix IV A: Membrane Materials
  25. Appendix IV B: Ion Transport in Electrolytes
  26. Appendix V A: Transport Properties of Typical Gases at Atmospheric Pressure
  27. Appendix VI A: Governing Equations of Multiphase Flow and Heat Transfer In Porous Media
  28. Appendix VI B: Multiphase Mixture Model in Porous Media
  29. Appendix VIII A: Thermal Properties of Selected Materials
  30. Index
  31. Ad Page
  32. Back Cover