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Fuel Cell Systems Explained

Second Edition

James Larminie

Oxford Brookes University, UK

Andrew Dicks

University of Queensland, Australia

(Former Principal Scientist, BG Technology, UK)

Copyright  2003 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, England Telephone (+44) 1243 779777 Email (for orders and customer service enquiries): cs-books@wiley.co.uk Visit our Home Page on www.wileyeurope.com or www.wiley.com All Rights Reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except under the terms of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London W1T 4LP, UK, without the permission in writing of the Publisher. Requests to the Publisher should be addressed to the Permissions Department, John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO 8SQ, England, or emailed to permreq@wiley.co.uk, or faxed to (+44) 1243 770620. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold on the understanding that the Publisher is not engaged in rendering professional services. If professional advice or other expert assistance is required, the services of a competent professional should be sought.

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Library of Congress Cataloging-in-Publication Data Larminie, James. Fuel cell systems explained / James Larminie, Andrew Dicks. – 2nd ed. p. cm. Includes bibliographical references and index. ISBN 0-470-84857-X (alk. paper)

1. Fuel cells. I. Dicks, Andrew. II. Title. TK2931.L37 2003 621.31′^ 2429 – dc 2002192419 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 0-470-84857-X Typeset in 10/12pt Times by Laserwords Private Limited, Chennai, India Printed and bound in Great Britain by Antony Rowe Ltd, Chippenham, Wiltshire This book is printed on acid-free paper responsibly manufactured from sustainable forestry in which at least two trees are planted for each one used for paper production.

xiv Preface

We wish all readers well, and hope that our efforts here meet with success in helping you understand better this most interesting and potentially helpful technology.

James Larminie, Oxford, England Andrew Dicks, Brisbane, Australia January 2003

Foreword to the first edition

By Dr Gary Acres OBE, formerly Director of Research, Johnson

Matthey plc

A significant time generally elapses before any new technological development is fully exploited. The fuel cell, first demonstrated by Sir William Grove in 1839, has taken longer than most, despite the promise of clean and efficient power generation. Following Bacon’s pioneering work in the 1950s, fuel cells were successfully devel- oped for the American manned space programme. This success, together with a policy to commercialise space technology, led to substantial development programmes in America and Japan in the 1970s and the 1980s, and more recently in Europe. Despite these efforts that resulted in considerable technical progress, fuel cell systems were seen to be ‘always five years away from commercial exploitation’. During the last few years of the twentieth century, much changed to stimulate new and expanding interest in fuel cell technology. Environmental concerns about global warming and the need to reduce CO 2 emissions provided the stimulus to seek ways of improving energy conversion efficiency. The motor vehicle industry, apart from seeking higher fuel efficiencies, is also required to pursue technologies capable of eliminating emissions, the ultimate goal being the zero emission car. The utility industries, following the impact of privatisation and deregulation, are seeking ways to increase their competitive position while at the same time contributing to reduced environmental emissions. As these developments have occurred, interest in fuel cell technology has expanded. Increasing numbers of people from disciplines ranging from chemistry through engineer- ing to strategic analysis, not familiar with fuel cell technology, have felt the need to become involved. The need by such people for a single, comprehensive and up-to-date exposition of the technology and its applications has become apparent, and is amply provided for by this book. While the fuel cell itself is the key component and an understanding of its features is essential, a practical fuel cell system requires the integration of the stack with fuel processing, heat exchange, power conditioning, and control systems. The importance of each of these components and their integration is rightly emphasised in sufficient detail for the chemical and engineering disciplines to understand the system requirements of this novel technology. Fuel cell technology has largely been the preserve of a limited group consisting primar- ily of electro and catalyst chemists and chemical engineers. There is a need to develop

Acknowledgements

The point will frequently be made in this book that fuels cells are highly interdisciplinary, involving many aspects of science and engineering. This is reflected in the number and diversity of companies that have helped with advice, information, and pictures in con- nection with this project. The authors would like to put on record their thanks to the following companies or organisations that have made this book possible:

Advanced Power Sources Ltd, UK Advantica plc (formerly BG Technology Ltd), UK Alstom Ballard GmbH, Armstrong International Inc, USA Ballard Power Systems Inc, Canada DaimlerChrysler Corporation DCH Technology Inc, USA Eaton Corporation, USA Epyx, USA GfE Metalle und Materialien GmbH, Germany International Fuel Cells, USA IdaTech Inc., USA Johnson Matthey plc, UK Hamburgische Electricit¨ats-Werke AG, Germany Lion Laboratories Ltd, UK MTU Friedrichshafen GmbH, Germany ONSI Corporation, USA Paul Scherrer Institute, Switzerland Proton Energy Systems, USA Siemens Westinghouse Power Corporation, USA Sulzer Hexis AG, Switzerland SR Drives Ltd, UK Svenska Rotor Maskiner AB, Sweden W.L. Gore and Associates Inc, USA Zytek Group Ltd, UK In addition, a number of people have helped with advice and comments to the text. In particular, we would like to thank Felix B¨uchi of the Paul Scherrer Institute; Richard Stone and Colin Snowdon, both from the University of Oxford; Ramesh Shah of the

xviii Acknowledgements

Rochester Institute; and Tony Hern and Jonathan Bromley of Oxford Brookes University, who have all provided valuable comments and suggestions for different parts of this work. Finally, we are also indebted to family, friends, and colleagues who have helped us in many ways and put up with us while we devoted time and energy to this project.

James Larminie, Oxford Brookes University, Oxford, UK Andrew Dicks, University of Queensland, Australia

xx Abbreviations

MEA Membrane electrode assembly MOSFET Metal oxide semiconductor field-effect transistor MWNT Multi-walled nanotube NASA National Aeronautics and Space Administration NL Normal litre, 1 L at NTP NTP Normal temperature and pressure (20◦C and 1 atm or 1.01325 bar) OCV Open circuit voltage PAFC Phosphoric acid (electrolyte) fuel cell PDA Personal digital assistant PEM Proton exchange membrane or polymer electrolyte membrane – different names for the same thing which fortunately have the same abbreviation. PEMFC Proton exchange membrane fuel cell or polymer electrolyte membrane fuel cell PFD Process flow diagram PM Permanent Magnet ppb Parts per billion ppm Parts per million PROX Preferential oxidation PURPA Public Utilities Regulatory Policies Act PTFE Polytetrafluoroethylene PSI Pounds per square inch PWM Pulse width modulation SCG Simulated coal gas SL Standard litre, 1 L at STP SOFC Solid oxide fuel cell SPFC Solid polymer fuel cell (= PEMFC) SPP Small power producer SRM Switched reluctance motor SRS Standard reference state (25◦C and 1 bar) STP Standard temperature and pressure (= SRS) SWNT Single-walled nano tube TEM Transmission electron microscope t/ha Tonnes per hectare annual yield THT Tetrahydrothiophene (C 4 H 8 O 2 S) TLV Threshold limit value TOU Time of use UL Underwriters’ Laboratory WTT Well to tank WTW Well to wheel YSZ Yttria-stabilised zirconia

Symbols

a Coefficient in base 10 logarithm form of Tafel equation, also Chemical activity ax Chemical activity of substance x A Coefficient in natural logarithm form of Tafel equation, also Area B Coefficient in equation for mass transport voltage loss C Constant in various equations, also Capacitance c (^) p Specific heat capacity at constant pressure, in J K−^1 kg−^1 c (^) p Molar specific heat capacity at constant pressure, in J K−^1 mol−^1 d separation of charge layers in a capacitor e Magnitude of the charge on one electron, 1. 602 × 10 −^19 Coulombs E EMF or open circuit voltage E^0 EMF at standard temperature and pressure, and with pure reactants F Faraday constant, the charge on one mole of electrons, 96,485 Coulombs G Gibbs free energy (or negative thermodynamic potential)
G^0 Change in Gibbs free energy at standard temperature and pressure, and with pure reactants
GTA Change in Gibbs free energy at ambient temperature g Gibbs free energy per mole g (^) f Gibbs free energy of formation per mole (g (^) f )X Gibbs free energy of formation per mole of substance X H Enthalpy h Enthalpy per mole hf Enthalpy of formation per mole (h (^) f )X Enthalpy of formation per mole of substance X I Current i Current density, current per unit area il Limiting current density in Crossover current within a cell io Exchange current density at an electrode/electrolyte interface ioc Exchange current density at the cathode ioa Exchange current density at the anode m Mass m ˙ Mass flow rate m (^) x Mass of substance x

This page has been reformatted by Knovel to provide easier navigation. v

Contents

Preface ............................................................................................ xiii

Foreword to the First Edition ........................................................... xv

Acknowledgements ......................................................................... xvii

Abbreviations ................................................................................... xix

Symbols ........................................................................................... xxi

1. Introduction ............................................................................. 1

1.1 Hydrogen Fuel Cells – Basic Principles ..................................... 1 1.2 What Limits the Current? ........................................................... 5 1.3 Connecting Cells in Series – the Bipolar Plate .......................... 6 1.4 Gas Supply and Cooling ............................................................ 10 1.5 Fuel Cell Types .......................................................................... 14 1.6 Other Cells – Some Fuel Cells, Some Not ................................ 16 1.6.1 Biological Fuel Cells ...................................................... 17 1.6.2 Metal/Air Cells ................................................................ 17 1.6.3 Redox Flow Cells or Regenerative Fuel Cells ............... 18 1.7 Other Parts of a Fuel Cell System ............................................. 19 1.8 Figures Used to Compare Systems ........................................... 21 1.9 Advantages and Applications .................................................... 22 References ......................................................................................... 24

2. Efficiency and Open Circuit Voltage ..................................... 25

2.1 Energy and the EMF of the Hydrogen Fuel Cell ........................ 25

vi Contents

viii Contents

Contents ix

Contents xi

xii Contents

• 2.2 The Open Circuit Voltage of Other Fuel Cells and Batteries This page has been reformatted by Knovel to provide easier navigation.
• 2.3 Efficiency and Efficiency Limits
• 2.4 Efficiency and the Fuel Cell Voltage
• 2.5 The Effect of Pressure and Gas Concentration
  • 2.5.1 The Nernst Equation
  • 2.5.2 Hydrogen Partial Pressure
  • 2.5.3 Fuel and Oxidant Utilization
  • 2.5.4 System Pressure
  • 2.5.5 An Application – Blood Alcohol Measurement
• 2.6 Summary
• References
• 3. Operational Fuel Cell Voltages
  • 3.1 Introduction
  • 3.2 Terminology
  • 3.3 Fuel Cell Irreversibilities – Causes of Voltage Drop
  • 3.4 Activation Losses
    • 3.4.1 The Tafel Equation
    • 3.4.2 The Constants in the Tafel Equation
    • 3.4.3 Reducing the Activation Overvoltage
    • 3.4.4 Summary of Activation Overvoltage
  • 3.5 Fuel Crossover and Internal Currents
  • 3.6 Ohmic Losses
  • 3.7 Mass Transport or Concentration Losses
  • 3.8 Combining the Irreversibilities
  • 3.9 The Charge Double Layer
  • 3.10 Distinguishing the Different Irreversibilities
  • References
• 4. Proton Exchange Membrane Fuel Cells
  • 4.1 Overview
  • 4.2 How the Polymer Electrolyte Works
  • 4.3 Electrodes and Electrode Structure
• 4.4 Water Management in the PEMFC This page has been reformatted by Knovel to provide easier navigation. - 4.4.1 Overview of the Problem - 4.4.2 Airflow and Water Evaporation - 4.4.3 Humidity of PEMFC Air - 4.4.4 Running PEM Fuel Cells without Extra Humidification - 4.4.5 External Humidification – Principles - 4.4.6 External Humidification – Methods
  • 4.5 PEM Fuel Cell Cooling and Air Supply
    • 4.5.1 Cooling Using the Cathode Air Supply
    • 4.5.2 Separate Reactant and Cooling Air
    • 4.5.3 Water Cooling of PEM Fuel Cells
  • 4.6 PEM Fuel Cell Connection – the Bipolar Plate
    • 4.6.1 Introduction
    • 4.6.2 Flow Field Patterns on the Bipolar Plates
    • 4.6.3 Making Bipolar Plates for PEM Fuel Cells
    • 4.6.4 Other Topologies
  • 4.7 Operating Pressure
    • 4.7.1 Outline of the Problem
      • Operating Pressures 4.7.2 Simple Quantitative Cost/Benefit Analysis of Higher
    • 4.7.3 Other Factors Affecting Choice of Pressure
  • 4.8 Reactant Composition
    • 4.8.1 Carbon Monoxide Poisoning
    • 4.8.2 Methanol and Other Liquid Fuels
    • 4.8.3 Using Pure Oxygen in Place of Air
  • 4.9 Example Systems
    • 4.9.1 Small 12-W System
    • 4.9.2 Medium 2-kW System
    • 4.9.3 205-kW Fuel Cell Engine
  • References
• 5. Alkaline Electrolyte Fuel Cells This page has been reformatted by Knovel to provide easier navigation.
  • 5.1 Historical Background and Overview - 5.1.1 Basic Principles - 5.1.2 Historical Importance - 5.1.3 Main Advantages
    • 5.2 Types of Alkaline Electrolyte Fuel Cell
      • 5.2.1 Mobile Electrolyte
      • 5.2.2 Static Electrolyte Alkaline Fuel Cells
      • 5.2.3 Dissolved Fuel Alkaline Fuel Cells
    • 5.3 Operating Pressure and Temperature
    • 5.4 Electrodes for Alkaline Electrolyte Fuel Cells
      • 5.4.1 Introduction
      • 5.4.2 Sintered Nickel Powder
      • 5.4.3 Raney Metals
      • 5.4.4 Rolled Electrodes
    • 5.5 Cell Interconnections
    • 5.6 Problems and Development
    • References
• 6. Direct Methanol Fuel Cells
     • 6.1 Introduction
     • 6.2 Anode Reaction and Catalysts
       • 6.2.1 Overall DMFC Reaction
       • 6.2.2 Anode Reactions in the Alkaline DMFC
       • 6.2.3 Anode Reactions in the PEM Direct Methanol FC
       • 6.2.4 Anode Fuel Feed
       • 6.2.5 Anode Catalysts
     • 6.3 Electrolyte and Fuel Crossover
       • 6.3.1 How Fuel Crossover Occurs
       • 6.3.2 Standard Techniques for Reducing Fuel Crossover
       • 6.3.3 Fuel Crossover Techniques in Development
     • 6.4 Cathode Reactions and Catalysts
  • 6.5 Methanol Production, Storage, and Safety This page has been reformatted by Knovel to provide easier navigation.
    • 6.5.1 Methanol Production
    • 6.5.2 Methanol Safety
    • 6.5.3 Methanol Compared to Ethanol
    • 6.5.4 Methanol Storage
  • 6.6 Direct Methanol Fuel Cell Applications
  • References
• 7. Medium and High Temperature Fuel Cells
  • 7.1 Introduction
  • 7.2 Common Features
    • 7.2.1 An Introduction to Fuel Reforming
    • 7.2.2 Fuel Utilization
    • 7.2.3 Bottoming Cycles
      • Technology 7.2.4 The Use of Heat Exchangers – Exergy and Pinch
  • 7.3 The Phosphoric Acid Fuel Cell (PAFC)
    • 7.3.1 How It Works
    • 7.3.2 Performance of the PAFC
    • 7.3.3 Recent Developments in PAFC
  • 7.4 The Molten Carbonate Fuel Cell (MCFC)
    • 7.4.1 How It Works
    • 7.4.2 Implications of Using a Molten Carbonate Electrolyte
    • 7.4.3 Cell Components in the MCFC
    • 7.4.4 Stack Configuration and Sealing
    • 7.4.5 Internal Reforming
    • 7.4.6 Performance of MCFCS
    • 7.4.7 Practical MCFC Systems
  • 7.5 The Solid Oxide Fuel Cell
    • 7.5.1 How It Works
    • 7.5.2 SOFC Components
      • SOFC 7.5.3 Practical Design and Stacking Arrangements for the
      • 7.5.4 SOFC Performance This page has been reformatted by Knovel to provide easier navigation.
        • Hybrid Systems 7.5.5 SOFC Combined Cycles, Novel System Designs and
      • 7.5.6 Intermediate Temperature SOFCs
    • References
• 8. Fuelling Fuel Cells
     • 8.1 Introduction
     • 8.2 Fossil Fuels
       • 8.2.1 Petroleum
         • Hydrates, and LPG 8.2.2 Petroleum in Mixtures: Tar Sands, Oil Shales, Gas
       • 8.2.3 Coal and Coal Gases
       • 8.2.4 Natural Gas
     • 8.3 Bio-Fuels
     • 8.4 The Basics of Fuel Processing
       • 8.4.1 Fuel Cell Requirements
       • 8.4.2 Desulphurization
       • 8.4.3 Steam Reforming
       • 8.4.4 Carbon Formation and Pre-Reforming
       • 8.4.5 Internal Reforming
       • 8.4.6 Direct Hydrocarbon Oxidation
       • 8.4.7 Partial Oxidation and Autothermal Reforming
         • Cracking of Hydrocarbons 8.4.8 Hydrogen Generation by Pyrolysis or Thermal
       • 8.4.9 Further Fuel Processing – Carbon Monoxide Removal
     • 8.5 Practical Fuel Processing – Stationary Applications
       • 8.5.1 Conventional Industrial Steam Reforming
         • PAFC Plants with Steam Reformers 8.5.2 System Designs for Natural Gas Fed PEMFC and
       • 8.5.3 Reformer and Partial Oxidation Designs
  • 8.6 Practical Fuel Processing – Mobile Applications - 8.6.1 General Issues
    • 8.6.2 Methanol Reforming for Vehicles This page has been reformatted by Knovel to provide easier navigation.
    • 8.6.3 Micro-Scale Methanol Reactors
    • 8.6.4 Gasoline Reforming
  • 8.7 Electrolysers
    • 8.7.1 Operation of Electrolysers
    • 8.7.2 Applications of Electrolysers
    • 8.7.3 Electrolyser Efficiency
    • 8.7.4 Generating at High Pressure
    • 8.7.5 Photo-Electrolysis
  • 8.8 Biological Production of Hydrogen
    • 8.8.1 Introduction
    • 8.8.2 Photosynthesis
    • 8.8.3 Hydrogen Production by Digestion Processes
  • 8.9 Hydrogen Storage I – Storage as Hydrogen
    • 8.9.1 Introduction to the Problem
    • 8.9.2 Safety
    • 8.9.3 The Storage of Hydrogen as a Compressed Gas
    • 8.9.4 Storage of Hydrogen as a Liquid
    • 8.9.5 Reversible Metal Hydride Hydrogen Stores
    • 8.9.6 Carbon Nanofibres
    • 8.9.7 Storage Methods Compared
  • 8.10 Hydrogen Storage II – Chemical Methods
    • 8.10.1 Introduction
    • 8.10.2 Methanol
    • 8.10.3 Alkali Metal Hydrides
    • 8.10.4 Sodium Borohydride
    • 8.10.5 Ammonia
    • 8.10.6 Storage Methods Compared
  • References
• Pumps 9. Compressors, Turbines, Ejectors, Fans, Blowers, and
• 9.1 Introduction - 9.2 Compressors – Types Used This page has been reformatted by Knovel to provide easier navigation. - 9.3 Compressor Efficiency - 9.4 Compressor Power - 9.5 Compressor Performance Charts - 9.6 Performance Charts for Centrifugal Compressors - 9.7 Compressor Selection – Practical Issues - 9.8 Turbines - 9.9 Turbochargers - 9.10 Ejector Circulators - 9.11 Fans and Blowers - 9.12 Membrane/Diaphragm Pumps
  • References
• 10. Delivering Fuel Cell Power
      • 10.1 Introduction
      • 10.2 DC Regulation and Voltage Conversion
        • 10.2.1 Switching Devices
        • 10.2.2 Switching Regulators
      • 10.3 Inverters
        • 10.3.1 Single Phase
        • 10.3.2 Three Phase
        • 10.3.3 Regulatory Issues and Tariffs
        • 10.3.4 Power Factor Correction
      • 10.4 Electric Motors
        • 10.4.1 General Points
        • 10.4.2 The Induction Motor
        • 10.4.3 The Brushless DC Motor
        • 10.4.4 Switched Reluctance Motors
        • 10.4.5 Motors Efficiency
        • 10.4.6 Motor Mass
      • 10.5 Fuel Cell/Battery or Capacitor Hybrid Systems
      • References