Fuel Cell Science E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Veröffentlichungsjahr: 2011

Beschreibung

A comprehensive survey of theoretical andexperimental concepts in fuel cell chemistry

Fuel cell science is undergoing significant development, thanks, in part, to a spectacular evolution of the electrocatalysis concepts, and both new theoretical and experimental methods. Responding to the need for a definitive guide to the field, Fuel Cell Science provides an up-to-date, comprehensive compendium of both theoretical and experimental aspects of the field.

Designed to inspire scientists to think about the future of fuel cell technology, Fuel Cell Science addresses the emerging field of bio-electrocatalysis and the theory of heterogeneous reactions in fuel cell science and proposes potential applications for electrochemical energy production. The book is thorough in its coverage of the electron transfer process and structure of the electric double layer, as well as the development of operando measurements. Among other subjects, chapters describe:

• Recently developed strategies for the design, preparation, and characterization of catalytic materials for fuel cell electrodes, especially for new fuel cell cathodes

• A wide spectrum of theoretical and computational methods, with?the aim of?developing?new fuel cell catalysis concepts and improving existing designs to increase their performance.?

Edited by two leading faculty, the book:

• Addresses the emerging fields of bio-electrocatalysis for fuel cells and theory of heterogeneous reactions for use in fuel cell catalysis

• Provides a survey of experimental and theoretical concepts in these new fields

• Shows the evolution of electrocatalysis concepts

• Describes the chemical physics of fuel cell reactions

• Forecasts future developments in electrochemical energy production and conversion

Written for electrochemists and electrochemistry graduate students, electrocatalysis researchers, surface and physical chemists, chemical engineers, automotive engineers, and fuel cell and energy-related researchers, this modern compendium can help today's best minds meet the challenges in fuel science technology.

Leseprobe

Contents

Cover

Wiley Series on Electrocatalysis and Electrochemistry

Title Page

Copyright

Foreword

Is there a common “activity yardstick” that applies to all fuel cell electrocatalysts?

References

Preface

References

Preface to the Wiley Series on Electrocatalysis and Electrochemistry

Contributors

Chapter 1: Hydrogen Reactions on Nanostructured Surfaces

1.1 Introduction

1.2 Fundamentals of Hydrogen Reactions

1.3 Fundamental Studies of Hydrogen Reactions onExtended Single-Crystal Surfaces

1.4 Theoretical Studies of Hydrogen Catalysis

1.5 Fundamental Studies of Nanoparticles on Single Crystals

1.6 Investigations of Hydrogen-Related Reactions on Single Pd Particles

1.7 Studies of Hydrogen-Related Reactions on Carbon-Based Systems

References

Chapter 2: Comparison of Electrocatalysis and Bioelectrocatalysis of Hydrogen and Oxygen Redox Reactions

2.1 Introduction

2.2 Hydrogen Oxidation And Evolution Reaction

2.3 Oxygen Reduction Reaction

2.4 Oxygen Evolution Reaction

2.5 Concluding Remarks

References

Chapter 3: Design of Palladium-Based Alloy Electrocatalysts for Hydrogen Oxidation Reaction in Fuel Cells

3.1 Introduction

3.2 Promotional Effect of Pd on Hydrogen Oxidation Reaction at a Pt–Pd Alloy Electrode

3.3 Hydrogen Oxidation Reaction at a Ir–Pd Alloy Electrode

3.4 Summary

Acknowledgement

References

Chapter 4: Mechanism of an Enhanced Oxygen Reduction Reaction at Platinum-Based Electrocatalysts: Identification and Quantification of Oxygen Species Adsorbed on Electrodes by X-Ray Photoelectron Spectroscopy

4.1 Introduction

4.2 Methodology

4.3 Assignment of Oxygen Species (Surface Oxidation Process)

4.4 Intermediates of ORR

4.5 Mechanism of enhanced ORR at Pt-based electrodes

4.6 Summary

References

Chapter 5: Biocathodes for Dioxygen Reduction in Biofuel Cells

5.1 Introduction

5.2 Enzymes for Dioxygen Reduction Catalysis

5.3 Immobilization of the Enzyme on the Biocathode

5.4 Biocathodes Employing Mediated Electrocatalysis

5.5 Biocathodes Employing Mediatiorless Electrocatalysis

5.6 Summary and Outlook

References

Chapter 6: Platinum Monolayer Electrocatalysts: Improving Structure and Activity

6.1 Introduction to Pt Monolayer Electrocatalysts

6.2 Improving Activity and Stability of Pt Monolayer Electrocatalysts

6.3 Scaleup Synthesis, Structure, and Activity

6.4 Fuel Cell Performance and Stability

6.5 Summary

Acknowledgment

References

Chapter 7: The Importance of Enzymes: Benchmarks for Electrocatalysts

7.1 Introduction

7.2 Active Sites and Overall Structures of Fuel Cell Enzymes

7.3 Attaching and Electrically Connecting Enzymes to Anode and Cathode

7.4 Stability Issues

7.5 Conclusions

Acknowledgments

References

Chapter 8: Approach to Microbial Fuel Cells and Their Applications

8.1 Introduction

8.2 Microbial Fuel Cell Fundamentals

8.3 The Bacteria–Electrode Interface

8.4 Whole-Bacterium Cell Electrochemistry

8.5 MFC Applications

8.6 Concluding Remarks

References

Chapter 9: Half-Cell Investigations of Cathode Catalysts for PEM Fuel Cells: From Model Systems to High-Surface-Area Catalysts

9.1 Introduction

9.2 Experimental Considerations

9.3 Oxygen Reduction Reaction

9.4 Electrochemical Corrosion of Nanoparticles

Acknowledgment

References

Chapter 10: Nanoscale Phenomena in Catalyst Layers for PEM Fuel Cells: From Fundamental Physics to Benign Design

10.1 Introduction

10.2 Modeling of Nanoparticle Stability and Reactivity

10.3 Substrate Effects

10.4 Nanopore Confinement and Surface Roughness Effects in Catalyst Layers

10.5 Conclusions

References

Chapter 11: Fuel Cells with Neat Proton-Conducting Salt Electrolytes

11.1 Introduction

11.2 Salt Electrochemistry

11.3 General Characteristics of Salt Electrolytes

11.4 Conclusions

References

Chapter 12: Vibrational Spectroscopy for the Characterization of PEM Fuel Cell Membrane Materials

12.1 Introduction

12.2 Overview of PEM Materials

12.3 Experimental Approaches

12.4 Vibrational Spectroscopy of Nafion and Related Ionomer Membrane Materials

12.5 Outlook

12.6 Conclusions

Acknowledgments

References

Chapter 13: Ab Initio Electrochemical Properties of Electrode Surfaces

13.1 Introduction

13.2 Theory of Electrochemical Interfaces

13.3 Solvation Model

13.4 Conclusion

Acknowledgements

References

Chapter 14: Electronic Structure and Reactivity of Transition Metal Complexes

14.1 Introduction

14.2 Results

14.3 Conclusions

Acknowledgments

References

Chapter 15: Quantitative Description of Electron Transfer Reactions

15.1 Introduction

15.2 Electron Transfer Free-Energy Surfaces From Molecular Dynamics Simulations

15.3 Validation of the Penalty Functional

15.4 Ab Initio Calculations of Transfer Integral

15.5 Conclusion

Acknowledgment

References

Chapter 16: Understanding Electrocatalysts for Low-Temperature Fuel Cells

16.1 Introduction

16.2 Direct Methanol Fuel Cell Anode Catalysts

16.3 Oxygen Reduction Catalysts

16.4 Conclusion

References

Chapter 17: Operando XAS Techniques: Past, Present, and Future

17.1 Introduction

17.2 Selection of Experimental Setup

17.3 XAS Applications to Fuel Cells: The Past

17.4 XAS Methods

17.5 Operando XAS Studies in Fuel Cell Research: The Present

17.6 The Future of Operando XAS

Acknowledgment

References

Chapter 18: Operando X-Ray Absorption Spectroscopy of Polymer Electrolyte Fuel Cells

18.1 Introduction

18.2 Parameters and Applications of Operando Spectroscopy

18.3 Conclusion

References

Chapter 19: New Concepts in the Chemistry and Engineering of Low-Temperature Fuel Cells

19.1 Introduction

19.2 Technology and Progress in Fuel Cell Development

19.3 Electrochemical Combustion in Fuel Cells: Concepts and Methods

19.4 New Methods for Studying Fuel Cell Catalysts

19.5 New Methods for Studying Fuel Cell Electrodes

19.6 Concluding Remarks

Acknowledgments

References

Color Plates

Index

Wiley Series on Electrocatalysis and Electrochemistry

Andrzej Wieckowski, Series Editor

Fuel Cell Catalysis: A Surface Science Approach, Marc T. M. Koper

Electrochemistry of Functional Supramolecular Systems, Margherita Venturi, Paola Ceroni, and Alberto Credi

Catalysis in Electrochemistry: From Fundamentals to Strategies for Fuel Cell Development, Elizabeth Santos and Wolfgang Schmickler

Fuel Cell Science: Theory, Fundamentals, and Biocatalysis, Andrzej Wieckowski and Jens Nrskov

Copyright © 2010 by John Wiley & Sons, Inc. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey

Published simultaneously in Canada

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Library of Congress Cataloging in-Publication Data:

Wieckowski, Andrzej

Fuel cell science : theory, fundamentals, and biocatalysis / edited by Andrzej Wieckowski and Jens Nrskov.

p. cm.

Includes bibliographical references and index.

ISBN 978-0-470-41029-5 (cloth)

Foreword

Is there a common “activity yardstick” that applies to all fuel cell electrocatalysts?

Thinking what should be the message in the foreword to a book that covers extensively a wide frontier of fuel cell catalysis work, a tempting, albeit somewhat risky, idea kept coming up in my mind: Is it possible to define a common “activity yardstick” that applies to a large number of, if not to all, fuel cell electrocatalysts? Is it possible to make such a generalization when considering the wide variety of catalytic surfaces studied and practiced in low-temperature fuel cells?

When examining the relevant literature, it appears that the more recent searches for active metal electrocatalysts and for active molecular electrocatalysts have had somewhat different priorities. In the case of metal electrocatalysts, the focus has been on tailoring the electronic properties of metal alloy surfaces to achieve an optimized bond strength between the metal surface and the relevant adsorbed intermediates [1]. Such studies have been supported by density functional theory (DFT) calculations, yielding the energies of the bonds between catalytically active surfaces and the likely reaction intermediates [2]. In all such studies, the assumption has been that a complete description of the electrocatalytic process requires consideration of a reactant molecule and a metal surface in contact with water, or aqueous electrolyte. The electro element of electrocatalysis has been covered all along by assuming that a change in the interfacial potential difference has an effect on, and only on, the activation energy of any reaction step involving electron transfer. Accordingly, the typical rate expression for an electrocatalytic process takes the form of a product of a preexponential term and a two-component exponential term, with the rate dependence on the electrode potential E fully covered in the exponential term. For a cathodic process within the so-called Tafel regime, the rate expression takes the following general form

(1)

where F is the Faraday constant, k0 is a frequency factor, is the overall catalyst surface area per unit electrode cross-sectional area, Cr is the concentration of the reactant molecule at the electrode surface, γ is the reaction order is the chemical component of the activation energy, and b is the so-called Tafel slope. In the case of molecular electrocatalysts, the more recent achievements in preparation of highly oxygen reduction reaction (ORR)-active, carbon-supported iron complexes [3], resulted from efforts to maximize the overall surface density of effective redox centers, N*. Lefevre et al. [3] showed that an effective center formed when the iron complex was located on a specific, pretailored carbon surface site. The mechanism of electrocatalytic processes taking place at such active surface sites is described in terms of redox mediation, where the electrocatalytic activity at a potential E is expected to involve a fraction of N*, Nactive (E), defined by

(2)

For example, in the specific case of ORR catalyzed by a molecular iron complex, a plausible mechanism of ORR at the active complex of iron, X–Fe(II), where X is a surface anchor site and the iron complex is in its reduced form, has been described [3] with a first step involving bonding of dioxygen to the active form of the iron complex, X–Fe(II), assisted by electron transfer from the Fe(II) center:

(3a)

This step is followed by the completion of the 4e reduction process with regeneration of the active form of the redox system, written in simplified form as follows:

(3b)

This mechanism implies that only at a cathode potential sufficiently negative to generate a significant population of the reduced form of the surface redox couple, X–Fe(II), can the rate of the process in Equations (3a) and (3b) rise to a measurable level. In an ideal case where the steady-state population of X–Fe(II) depends on potential according to a simple Nernst equation, the number of active sites at an electrode potential E will be given, for a cathodic process, as

(4)

where . Inserting in Equation (1) this dependence of active-site population on electrode potential, the rate expression will take the form

(5)

where in the simplest case,

The significant difference between Equations (5) and (1) is the appearance in (5) of two sources of rate dependence on electrode potential, associated with two different values of E°. One is the dependence of the activation energy at an active surface site on the overpotential, , and the second is a dependence of active-site population on . The former appears in the exponential term of the rate expression, whereas the latter appears in the preexponential term [4].

The tacit assumption behind the use of the simpler expression [Eq. (1)] for processes at metal surfaces is that availability of active sites on metal surfaces does not depend on the electrode potential. This assumption misses, however, a key element of electrocatalysis at metal surfaces [4]. For example, examination of the value of for metal and metal alloy electrocatalysts of high ORR activity, reveals that “ignition” of the ORR process is tied consistently with the onset of cathodic generation of some minimum surface population (e.g., 1%) of free metal sites on a surface that is fully covered under open-circuit conditions by oxygen species that block ORR. Recognizing that such change in surface composition is required for the onset of the process, one can describe the ORR process at Pt in terms of surface redox mediation, involving the Pt/PtOx surface redox system [4]. ORR ignition requires reduction of a Pt surface oxide, or hydroxide species, for example, according to

(6a)

followed next by reaction of O2 at Pt and with metal sites that become available beyond a threshold potential determined by according to

(6b)

Continuous repetition of (6a) + (6b) sustains a steady-state rate of a 4e ORR process, taking place at the active (metal) surface sites, with the active site continuously regenerated beyond a threshold potential determined by .

Mediation by a surface redox system is apparently a common feature of a wide variety of electrocatalysts, whether molecular or metallic, and this insight can lead to an attempted definition of a “general key to active electrocatalysts.” From Equation (5), an optimum value of will maximize the product of the preexponential and exponential-terms at an electrode potential of technical interest, that is, at a low overpotential-versus-. Consequently, must not be too far from , to electroactivate the mediating surface system and thereby ignite the faradaic process at a low overpotential. However, too small a difference between the two standard potentials will mean a small free-energy drive for the reaction of the reactant molecule with the active form of the surface redox system [e.g., reaction (6b)], because the standard free-energy change in that reaction is . The activation energy of a process like (6b) is expected to be lower, the higher the difference and, conversely, very close proximity of the two standard potentials will likely result in excessive . We are looking, therefore, at a need to optimize the gap between and , to satisfy the conflicting requirements of a low overpotantial for electrode surface activation and a sufficient free-energy drive for the reaction of the reactant molecule with the active surface site.

On the basis of experimental results reported to date, the optimum value of for requiring electrocatalytic processes in low-temperature fuel cells is in the range of 300–400 mV. In the case of ORR at unalloyed Pt, for example, () is near 400 mV and can be lowered further by about 100 mV by alloying [1], resulting in enhanced ORR activity. The rate enhancement derived in this case from lowering of indicates that the beneficial effect of Pt alloying originates from lowering of the ignition overpotential, resulting in an increase in the value of the preexponential term in Equation (5) at some given cathode potential E. A metal surface where () is either significantly smaller than 300 mV or significantly higher than 400 mV exhibits ORR activity that is lower than that of Pt because it is associated with either high (in the former case), or an excessive ignition overpotential (in the latter case). An aggressive goal for the future would be to minimize further the difference between the two E° values. A surface redox system with removed less than 300 mV from , while, at the same time, securing a low for reaction of the reactant molecule with the active surface site, will enable the onset of significant current at overpotentials lower than those demonstrated to date. The reduction to practice of such a desirable surface function is highly challenging, however, because of the low rates typically associated with processes driven by small changes in free energy.

In summary, at a risk typical for all generalizations, a general rule for active fuel cell electrocatalysts is proposed here, in the hope that it can provide a common ground for the evaluation and development of new electrocatalysts. The rule is based on the recognition that a wide variety of electrocatalytic processes, taking place at either redox-functionalized or metal surfaces, are surface-redox-mediated, leading, in turn, to the pursuit of an optimum value for () as the guideline for maximizing the electrocatalytic activity. An optimized gap between these two standard potentials best addresses the conflicting demands of a minimum overpotential for surface activation and a high rate of the reaction between the reactant molecule and the active surface site. Since the maximum rate is expected at an optimal gap between the E° values, a plot of the rate of the electrocatalytic process versus () will obviously take the famous form of a “volcano”; however, this typical shape is now projected and explained in terms of a redox mediation mechanism and the need to optimize the value of () to achieve high rates at low overpotential. Enjoy the book!

S. Gottesfeld

References

1. H. A. Gasteiger and N. M. Markovi, Science324 (5923), 48–49 (2009).

2. J. Rossmeisel et al., in Fuel Cell Catalysis: A Surface Science Approach, M. T. M. Koper, ed., Wiley, Hoboken, NJ, 2009, pp. 57–93.

3. M. Lefevre et al., Science324 (5923), 71 (2009).

4. S. Gottesfeld, in Fuel Cell Catalysis: A Surface Science Approach, M. T. M. Koper, ed., Wiley, Hoboken, NJ, 2009, pp. 1–30.

Preface

The book covers some essential topics in the science of fuel cell electrocatalysis [1, 2]. It shows an increase in importance of theory and modeling, and the emerging new field of electrocatalysis science: bioelectrocatalysis. It shows a spectacular evolution of the electrocatalysis concepts, from a simple statement of hydrogen evolution/oxidation on platinum to reactions involving advanced nanoengineering and single-crystal surfaces, new methods to study, and complicated chemical moieties (up to enzymes). It is basically a materials/theory volume of chemical physics of fuel cell reactions, including the electron transfer process and structure of the electric double layer, as seen by a new generation of scientists, not necessarily electrochemists. It also shows that operando measurements became possible because of the availability of synchrotron light. It forecasts the work for the future for the current and incoming generation of fuel cell scientists, namely, to use theory and understanding of the process involved (see Chapter 19 and the Foreword), use the operando (advanced in situ) approach, and expect the unexpected from the emerging new field of bioelectrocatalysis. The future is bright and exciting; the combination of the intellectual, high technology, and energy issues makes us strong. We are looking forward.

AW acknowledges the splendid support by the National Science Foundation and the US Army Research Office toward his research in the preparation of this book.

J. NORSKOV

A. WIECKOWSKI

References

1. S.-G. Sun, P.A. Christensen, and A. Wieckowski, eds., In-Situ Spectroscopic Studies of Adsorption at the Electrode and Electrocatalysis, Elsevier, Amsterdam, 2007.

2. A. Wieckowski, E. Savinova, and C. Vayenas, eds., Catalysis and Electrocatalysis at Nanoparticle Surfaces, Marcel Dekker, New York, 2003.

Note: Color versions of selected figures are available on ftp://ftp.wiley.com/sci_tech_med/fuel_cell_catalysis.

Preface to the Wiley Series on Electrocatalysis and Electrochemistry

The Wiley Series on Electrocatalysis and Electrochemistry covers recent advances in electrocatalysis and electrochemistry and depicts prospects for their contribution to the industrial world. The series illustrates the transition of electrochemical sciences from its beginnings in physical electrochemistry (covering mainly electron transfer reactions, concepts of electrode potentials, and structure of the electrical double layer) to a field in which electrochemical reactivity is shown as a unique aspect of heterogeneous catalysis, is supported by high-level theory, connects to other areas of science, and focuses on electrode surface structure, reaction environments, and interfacial spectroscopy.

The scope of this series ranges from electrocatalysis (practice, theory, relevance to fuel cell science and technology) to electrochemical charge transfer reactions, biocatalysis and photoelectrochemistry. While individual volumes may appear quite diverse, the series promises up-to-date and synergistic reports on insights to further the understanding of properties of electrified solid/liquid systems. Readers of the series will also find strong reference to theoretical approaches for predicting electrocatalytic reactivity by high-level theories such as DFT. Beyond the theoretical perspective, further vehicles for growth are provided by the sound experimental background and demonstration of the significance of such topics as energy storage, syntheses of catalytic materials via rational design, nanometer-scale technologies, prospects in electrosynthesis, new research instrumentation, surface modifications in basic research on charge transfer, and related interfacial reactivity. In this context, one might notice that new methods that are being developed for one specific field are readily adapted for application in another.

Electrochemistry has benefited from numerous monographs and review articles due to its applicability in the practical world. Electrocatalysis has also been the subject of individual reviews and compilations. The Wiley Series on Electrocatalysis and Electrochemistry hopes to address the current activity in both of these complementary fields by containing volumes that individually focus on topics of current and potential interest and application. At the same time, the chapters intend to demonstrate the connections of electrochemistry to areas in addition to chemistry and physics, such as chemical engineering, quantum mechanics, chemical physics, surface science, biochemistry, and biology, and thereby bring together a vast range of literature that covers each topic. While the title of each volume informs of the specific concentration chosen by the volume editors and chapter authors, the integral outcome of the series aims is to offer a broad-based analysis of the total development of the field. The progress of the series will provide a global definition of what electrocatalysis and electrochemistry are concerned with now and how these fields will evolve overtime. The purpose is twofold; to provide a modern reference for graduate instruction and for active researchers in the two disciplines, and to document that electrocatalysis and electrochemistry are dynamic fields that are ever-expanding and ever-changing in their scientific profiles.

Creation of each volume required the editor involvement, vision, enthusiasm and time. The Series Editor thanks all the individual volume editors who graciously accepted the invitations. Special thanks are for Ms. Anita Lekhwani, the Series Acquisitions Editor, who extended the invitation to the Series Editor and is a wonderful help in the assembling process of the Series.

Andrzej Wieckowski

Series Editor

Contributors

Radoslav R. Adzic, Brookhaven National Laboratory, Upton, NY 11973

Matthias Arenz, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark

Fraser A. Armstrong, Department of Chemistry, Oxford University, South Parks Road, Oxford OX1 3QR, United Kingdom

Renata Bilewicz, Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland

Nicéphore Bonnet, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

Fikile R. Brushett, Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana—Champaign, Urbana, IL 61801

Juan Pablo Busalmen, Laboratorio de Bioelectroquímica, INTEMA(CONICET), UNMdP. Juan B. Justo 4302, B7608FDQ, Mar del Plata, Argentina

Karen Chan, Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada

Ismaila Dabo, Université Paris-Est, CERMICS, Projet Micmac ENPC-INRIA, 6-8 Avenue Blaise Pascal, 77455 Marne-la-Vallée Cedex 2, France

Michael Eikerling, Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada

Abraham Esteve-Nuñez, Departamento de Química Analítica e Ingeniería Química, Universidad de Alcalá, Madrid, Spain

Juan Miguel Feliu, Instituto de Electroquímica, Universidad de Alicante, Apartado de Correos 99, 03080 Alicante, Spain

Peter Ferrin, Department of Chemical and Biological Engineering, University of Wisconsin—Madison, Madison, WI 53706

Dominic Gervasio, Department of Chemical and Environmental Engineering, University of Arizona, Tucson, AZ 85721

Hendrik A. Heering, Leiden Institute of Chemistry, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands

Paul J. A. Kenis, Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana—Champaign, Urbana, IL 61801

Michael L. Klein, Institute for Computational Molecular Science, College of Science and Technology, Temple University, Philadelphia, PA 19122

Marc T. M. Koper, Leiden Institute of Chemistry, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands

Carol Korzeniewski, Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409

Heather J. Kulik, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

Yanli Li, Université Paris-Est, CERMICS, Projet Micmac ENPC-INRIA, 6-8 Avenue Blaise Pascal, 77455 Marne-la-Vallée Cedex 2, France

Nenad M. Markovic, Materials Science Division Argonne National Laboratory, Argonne, IL 60439

Nicola Marzari, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139

Manos Mavrikakis, Department of Chemical and Biological Engineering, University of Wisconsin—Madison, Madison, WI 53706

Agostino Migliore, Center for Molecular Modeling, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104

Jens K. Nørskov, Department of Physics, Center for Atomic-Scale Materials Design, Technical University of Denmark, DK-2800, Lyngby, Denmark

Marcin Opallo, Institute of Physical Chemistry, Polish Academy of Sciences, ul. Kasprzaka 44/52, 01-224 Warsaw, Poland

Odysseas Paschos, Department of Physics, Technische Universität München, James Franck Strasse 1, D-85748, Garching, Germany

David E. Ramaker, Chemistry Department, George Washington University, Washington, DC 20052

Jan Rossmeisl, Department of Physics, Center for Atomic-Scale Materials Design, Technical University of Denmark, DK-2800, Lyngby, Denmark

Christina Roth, Institute for Materials Science, Technische Universität, Darmstadt, Germany

Ata Roudgar, Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada

Kotaro Sasaki, Brookhaven National Laboratory, Upton, NY 11973

Carlo U. Segre, Physics Division, Illinois Institute of Technology, 3101 S. Dearborn St., Chicago, IL 60616

Patrick H.-L. Sit, Center for Molecular Modeling, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104 and Institute for Computational Molecular Science, College of Science and Technology, Temple University, Philadelphia, PA 19122

Eugene S. Smotkin, Department of Chemistry and Chemical Biology, 417 Hurtig Hall, Northeastern University, Boston, MA 02116

Ulrich Stimming, Department of Physics, Technische Universität München, James Franck Strasse 1, D-85748 Garching, Germany and ZAE Bayern Division 1, Walther Meissner Strasse 6, D-85748 Garching, Germany

Yung-Eun Sung, World Class University Program of Chemical Convergence for Energy and Environment, School of Chemical and Biological Engineering, Seoul National University, Seoul 151-744, Korea

Hiroyuki Uchida, Clean Energy Research Center, University of Yamanashi, 4 Takeda, Kofu 400-8510, Japan

Miomir B. Vukmirovic, Brookhaven National Laboratory, Upton, NY 11973

Mitsuru Wakisaka, Fuel Cell Nanomaterials Center, University of Yamanashi, 4 Takeda, Kofu 400-8510, Japan

Jia X. Wang, Brookhaven National Laboratory, Upton, NY 11973

Liya Wang, Department of Chemistry, Simon Fraser University, Burnaby, British Columbia, Canada

Masahiro Watanabe, Fuel Cell Nanomaterials Center, University of Yamanashi, 4 Takeda, Kofu 400-8510, Japan

Andrzej Wieckowski, Department of Chemistry, University of Illinois at Urbana—Champaign, Urbana, IL 61801

Holger Wolfschmidt, Department of Physics, Technische Universität München, James Franck Strasse 1, D-85748 Garching, Germany

Sung Jong Yoo, Fuel Cell Center, Korea Institute of Science and Technology, Seoul 136-791, Korea

Chapter 1

Hydrogen Reactions on Nanostructured Surfaces

Holger Wolfschmidt and Odysseas Paschos

Department of Physics, Technische Universität München, Garching Germany

Ulrich Stimming

Department of Physics, Technische Universität München and ZAE Bayern Division 1, Garching Germany

Hydrogen catalysis is an important scientific field since hydrogen reactions (e.g., hydrogen evolution and hydrogen oxidation) play a key role in electrochemical devices such as fuel cells and electrolyzers. The latter devices have the potential to provide clean and sustainable energy with high efficiencies. This chapter reviews hydrogen catalysis in detail. Details on hydrogen reaction studies from theoretical and experimental perspectives are presented. The former usually complement the results from experimental studies and are used to strengthen them. Various systems that have been explored throughout the years are reviewed. These include model surfaces as well as applied systems. Model catalyst systems comprise Pt and Pd nanoislands deposited on planar surfaces of inert supports, high-quality single-crystal materials, or single nanoparticles created with scanning tunneling microscopy tips. Applied systems consist of metallic nanoparticles deposited on high-surface-area carbon supports. Theory versus experiment, and model versus applied systems are reviewed in detail, and useful insights for hydrogen reactions in these systems are demonstrated

1.1 Introduction

Whereas the nineteenth century was the stage of the steam engine and the twentieth century was the stage of the internal-combustion engine, it is likely that the twenty-first century will be the stage of the fuel cell. Fuel cells have captured the interest of people around the world as one of the next great energy alternative. They are now on the verge of being introduced commercially, revolutionizing the present method of power production. Fuel cells can use hydrogen as fuel and oxygen or air as oxidant, offering the prospect of supplying the world with clean, sustainable electrical power, heat, and water.

This chapter focuses on hydrogen reactions such as the hydrogen oxidation reaction (HOR) and the hydrogen evolution reaction (HER). These reactions are of utmost importance in developing and improving fuel cell devices. The discussion here is directed principally toward hydrogen electrocatalysis from an experimental as well as theoretical perspective. Starting with an overview on the fundamentals of hydrogen reactions in Section 1.2, studies on single crystals as well-defined and high-quality surfaces are reviewed. An introduction to theoretical work calculating important fundamentals for hydrogen catalysis regarding material properties is then discussed. As predicted by theory, the behavior of nanostructured and bimetallic surfaces differs from that of bulk material. Similar findings supporting the theoretical predictions are shown for large nanostructured surfaces as well as single particles. The section concludes with a short overview of carbon-based catalysts.

The fundamentals of hydrogen reactions are reviewed in Section 1.2. Starting from the general reversible hydrogen reaction, the different reaction pathways suggested by Volmer, Heyrowsky, and Tafel are introduced. Because of the importance of the hydrogen adsorption mechanism and the important findings with new experimental techniques, a short overview of results obtained since the late 1990s is given. An introduction to the correlation between catalytic behavior and the catalyst material significance of this correlation, completes this section using experimental and theoretical calculations, with a conclusion regarding the long-range.