Electrochemistry

Carl H. Hamann:Following his studies in mathematics, physics, biology and economics in Hamburg and Bonn, graduating in 1966 as a physicist, Carl H. Hamann gained his doctorate in 1970, becoming Professor for Applied Physical Chemistry at the University of Oldenburg in 1975. He has since concentrated mainly on fuel cells, electrochemical metrology, passage and adsorption kinetics, turbulent flows, the thermodynamics of irreversible systems, preparative electroorganic chemistry and technical electrochemistry. Professor Hamann has thus far published some 80 articles in journals and books. Wolf Vielstich:As Heinz Gerischer's first student, in Gottingen in 1952/53, Wolf Vielstich was concerned with developing a fast Potentiostaten while determining exchange current densities. Upon starting work at the Institute for Physical Chemistry, Bonn University, in 1960 he demonstrated that, apart from mercury, reproducible cyclic voltamograms, such as for the oxidation of hydrogen and methanol, are contained in solid electrodes, including Pt, Ir, Rh, Au and Pd. There then followed experiments with methanol/air and NiMH cells, among others. He was always interested in developing novel methods, such as the rotating ring electrode, on-line MS (DEMS), in-situ FTIRS and UHV analysis of adsorbants. Between 1986 and 1993, Wolf Vielstich was the Coordinator of the first European project to develop a DMFC, and in 1998 he was awarded the Faraday Medal by the Royal Chemical Society. Since 1999 he has been working as a guest of the Universidade de Sao Paulo, and edited Wiley's Handbook of Fuel Cells (2003). Professor Hamnett graduated from the University of Oxford with a BA (Chemistry) in 1970 and a D.Phil. (Chemistry) in 1973. He has held research and academic positions at the University of British Columbia, Canada, and at Oxford and Newcastle Universities, England, before his appointment in January 2001 as Principal and Vice-chancellor of the University of Strathclyde. He has nearly 200 publications in books and scientific journals, covering areas of spectroscopy, quantum theory and electrochemistry. His primary academic interests in recent years include the development and utilisation of spectro-electrochemical techniques in electrochemistry, and the development of improved fuel cells and solar-energy conversion devices.

• Preface xiiiList of Symbols and Units xv1 Foundations, Definitions and Concepts 11.1 Ions, Electrolytes and the Quantisation of Electrical Charge 11.2 Transition from Electronic to Ionic Conductivity in an Electrochemical Cell 31.3 Electrolysis Cells and Galvanic Cells: The Decomposition Potential and the Concept of EMF 41.4 Faraday’s Laws 71.5 Systems of Units 92 Electrical Conductivity and Interionic Interactions 132.1 Fundamentals 132.1.1 The Concept of Electrolytic Conductivity 132.1.2 The Measurement of Electrolyte Conductance 142.1.3 The Conductivity 182.1.4 Numerical Values of Conductivity 192.2 Empirical Laws of Electrolyte Conductivity 212.2.1 The Concentration Dependence of the Conductivity 212.2.2 Molar and Equivalent Conductivities 222.2.3 Kohlrausch’s Law and the Determination of the Limiting Conductivities of Strong Electrolytes 232.2.4 The Law of Independent Migration of Ions and the Determination of the Molar Conductivity of Weak Electrolytes 262.3 Ionic Mobility and Hittorf Transport 272.3.1 Transport Numbers and the Determination of Limiting Ionic Conductivities 282.3.2 Experimental Determination of Transport Numbers 292.3.3 Magnitudes of Transport Numbers and Limiting Ionic Conductivities 312.3.4 Hydration of Ions 322.3.5 The Enhanced Conductivity of the Proton, the Structure of the H 3 O þ Ion and the Hydration Number of the Proton 342.3.6 The Determination of Ionic Mobilities and Ionic Radii: Walden’s Rule 362.4 The Theory of Electrolyte Conductivity: The Debye-Hückel-Onsager Theory of Dilute Electrolytes 382.4.1 Introduction to the Model: Ionic Cloud, Relaxation and Electrophoretic Effects 382.4.2 The Calculation of the Potential due to the Central Ion and its Ionic Cloud: Ionic Strength and Radius of the Ionic Cloud 392.4.3 The Debye-Onsager Equation for the Conductivity of Dilute Electrolyte Solutions 442.4.4 The Influence of Alternating Electric Fields and Strong Electric Fields on the Electrolyte Conductivity 462.5 The Concept of Activity from the Electrochemical Viewpoint 462.5.1 The Activity Coefficient 462.5.2 Calculation of the Concentration Dependence of the Activity Coefficient 482.5.3 Extensions to More Concentrated Electrolytes 512.6 The Properties of Weak Electrolytes 612.6.1 The Ostwald Dilution Law 612.6.2 The Dissociation Field Effect 632.7 The Concept of pH and the Idea of Buffer Solutions 642.8 Non-aqueous Solutions 662.8.1 Ion Solvation in Non-aqueous Solvents 672.8.2 Electrolytic Conductivity in Non-aqueous Solutions 682.8.3 The pH-Scale in Protonic Non-aqueous Solvents 702.9 Simple Applications of Conductivity Measurements 712.9.1 The Determination of the Ionic Product of Water 712.9.2 The Determination of the Solubility Product of a Slightly Soluble Salt 722.9.3 The Determination of the Heat of Solution of a Slightly Soluble Salt 722.9.4 The Determination of the Thermodynamic Dissociation Constant of a Weak Electrolyte 732.9.5 The Principle of Conductivity Titrations 733 Electrode Potentials and Double-Layer Structure at Phase Boundaries 773.1 Electrode Potentials and their Dependence on Concentration, Gas Pressure and Temperature 773.1.1 The EMF of Galvanic Cells and the Maximum Useful Energy from Chemical Reactions 773.1.2 The Origin of Electrode Potentials, Galvani Potential Difference and the Electrochemical Potential 783.1.3 Calculation of the Electrode Potential and the Equilibrium Galvani Potential Difference between a Metal and a Solution of its Ions – The Nernst Equation 813.1.4 The Nernst Equation for Redox Electrodes 823.1.5 The Nernst Equation for Gas-electrodes 833.1.6 The Measurement of Electrode Potentials and Cell Voltages 843.1.7 Schematic Representation of Galvanic Cells 863.1.8 Calculation of Cell EMF’s from Thermodynamic Data 883.1.9 The Temperature Dependence of the Cell Voltage 903.1.10 The Pressure Dependence of the Cell Voltage – Residual Current for the Electrolysis of Aqueous Solutions 913.1.11 Reference Electrodes and the Electrochemical Series 933.1.12 Reference Electrodes of the Second Kind 983.1.13 The Electrochemical Series in Non-aqueous Solvents 1023.1.14 Reference Electrodes in Non-aqueous Systems and Usable Potential Ranges 1043.2 Liquid-junction Potentials 1053.2.1 The Origin of Liquid-junction Potentials 1053.2.2 The Calculation of Diffusion Potentials 1063.2.3 Concentration Cells with and without Transference 1083.2.4 Henderson’s Equation 1093.2.5 The Elimination of Diffusion Potentials 1113.3 Membrane Potentials 1123.4 The Electrolyte Double-Layer and Electrokinetic Effects 1153.4.1 Helmholtz and Diffuse Double Layer: the Zeta-Potential 1163.4.2 Adsorption of Ions, Dipoles and Neutral Molecules – the Potential of Zero Charge 1203.4.3 The Double-Layer Capacity 1213.4.4 Some Data for Electrolytic Double Layers 1233.4.5 Electrocapillarity 1243.4.6 Electrokinetic Effects – Electrophoresis, Electro-osmosis, Dorn-effect and Streaming Potential 1283.4.7 Theoretical Studies of the Double Layer 1303.5 Potential and Phase Boundary Behaviour at Semiconductor Electrodes 1333.5.1 Metallic Conductors. Semiconductors and Insulators 1333.5.2 Electrochemical Equilibria on Semiconductor Electrodes 1363.6 Simple Applications of Potential Difference Measurements 1393.6.1 The Experimental Determination of Standard Potentials and Mean Activity Coefficients 1393.6.2 Solubility Products of Slightly Soluble Salts 1413.6.3 The Determination of the Ionic Product of Water 1413.6.4 Dissociation Constants of Weak Acids 1423.6.5 The Determination of the Thermodynamic State Functions (r G 0 , r H 0 and r S 0) and the Corresponding Equilibrium Constants for Chemical Reactions 1443.6.6 pH Measurement with the Hydrogen Electrode 1453.6.7 pH Measurement with the Glass Electrode 1483.6.8 The Principle of Potentiometric Titrations 1534 Electrical Potentials and Electrical Current 1574.1 Cell Voltage and Electrode Potential during Current Flow: an Overview 1574.1.1 The Concept of Overpotential 1594.1.2 The Measurement of Overpotential; the Current-Potential Curve for a Single Electrode 1604.2 The Electron-transfer Region of the Current-Potential Curve 1624.2.1 Understanding the Origin of the Current-Potential Curve in the Electrontransfer-limited Region with the Help of the Arrhenius Equation 1624.2.2 The Meaning of the Exchange Current Density j 0 and the Asymmetry Parameter b 1664.2.3 The Concentration Dependence of the Exchange-current Density 1694.2.4 Electrode Reactions with Consecutive Transfer of Several Electrons 1704.2.5 Electron Transfer with Coupled Chemical Equilibria; the Electrochemical Reaction Order 1734.2.6 Further Theoretical Considerations of Electron Transfer 1794.2.7 Determination of Activation Parameters and the Temperature Dependence of Electrochemical Reactions 1844.3 The Concentration Overpotential – The Effect of Transport of Material on the Current-Voltage Curve 1854.3.1 The Relationship between the Concentration Overpotential and the Butler-Volmer Equation 1864.3.2 Diffusion Overpotential and the Diffusion Layer 1874.3.3 Current-Time Behaviour at Constant Potential and Constant Surface Concentration c s 1894.3.4 Potential-Time Behaviour at Constant Current: Galvanostatic Electrolysis 1914.3.5 Transport by Convection, Rotating Electrodes 1924.3.6 Mass Transport Through Migration – The Nernst-Planck Equation 1994.3.7 Spherical Diffusion 2004.3.8 Micro-electrodes 2014.4 The Effect of Simultaneous Chemical Processes on the Current Voltage Curve 2034.4.1 Reaction Overpotential, Reaction-limited Current and Reaction Layer Thickness 2044.5 Adsorption Processes 2074.5.1 Forms of Adsorption Isotherms 2084.5.2 Adsorption Enthalpies and Pauling’s Equation 2114.5.3 Current-Potential Behaviour and Adsorption-limited Current 2114.5.4 Dependence of Exchange Current Density on Adsorption Enthalpy, the Volcano Curve 2124.6 Electrocrystallisation – Metal Deposition and Dissolution 2134.6.1 Simple Model of Metal Deposition 2144.6.2 Crystal Growth in the Presence of Screw Dislocations 2184.6.3 Under-potential Deposition 2194.6.4 The Kinetics of Metal Dissolution and Metal Passivation 2204.6.5 Electrochemical Materials Science and Electrochemical Surface Technology 2224.7 Mixed Electrodes and Corrosion 2254.7.1 Mechanism of Acid Corrosion 2264.7.2 Oxygen Corrosion 2274.7.3 Potential-pH Diagrams or Pourbaix Diagrams 2274.7.4 Corrosion Protection 2284.8 Current Flows on Semiconductor Electrodes 2314.8.1 Photoeffects in Semiconductors 2334.8.2 Photoelectrochemistry 2344.8.3 Photogalvanic Cells 2354.8.4 Solar Energy Harvesting 2364.8.5 Detoxification using Photoelectrochemical Technology 2404.9 Bioelectrochemistry 2414.9.1 The Biochemistry of Glucose Oxidase as a Typical Redox Enzyme 2424.9.2 The Electrochemistry of Selected Biochemical Species 2445 Methods for the Study of the Electrode/Electrolyte Interface 2515.1 The Measurement of Stationary Current-Potential Curves 2515.1.1 The Potentiostat 2525.1.2 Determination of Kinetic Data by Potential Step Methods 2535.1.3 Measurements with Controlled Mass Transport 2555.1.4 Stationary Measurement of Very Rapid Reactions with Turbulent Flow 2575.2 Quasi-Stationary Methods 2605.2.1 Cyclic Voltammetry: Studies of Electrode Films and Electrode Processes – Electrochemical Spectroscopy 2605.2.2 AC Measurements 2785.3 Electrochemical Methods for the Study of Electrode Films 2915.3.1 Measurement of Charge Passed 2925.3.2 Capacitance Measurements 2945.4 Spectroelectrochemical and other Non-classical Methods 2955.4.1 Introduction 2955.4.2 Infra-Red Spectroelectrochemistry 2975.4.3 Electron-spin Resonance 3055.4.4 Electrochemical Mass Spectroscopy 3095.4.5 Additional Methods of Importance 3195.4.6 Scanning Microscope Techniques 3215.5 Preparation of Nanostructures, Combination of STM and UHV-Transfer 3265.5.1 Use of an STM-tip in SECM Experiments for the Preparation of Definite Nanostructure 3265.5.2 Combination of STM and UHV Transfer 3265.6 Optical Methods 3285.6.1 Ellipsometry 3295.6.2 XAS, SXS and XANES 3346 Electrocatalysis and Reaction Mechanisms 3396.1 On Electrocatalysis 3396.2 The Hydrogen Electrode 3416.2.1 Influence of Adsorbed Intermediates on i-V Curves 3426.2.2 Influence of the pH-value of the Solution and the Catalyst Surface 3446.2.3 Hydrogen Oxidation at Platinum and Chemisorbed Oxygen 3456.3 The Oxygen Electrode 3466.3.1 Investigation of the Oxygen Reduction Reaction with Rotating Ring-Disc Electrode 3476.4 Methanol Oxidation 3486.4.1 Parallel Pathways of Methanol Oxidation in Acid Electrolyte 3506.4.2 Methanol Adsorption 3506.4.3 Reaction Products and Adsorbed Intermediates of Methanol Oxidation 3526.4.4 Effects of Surface Structure and Adsorbed Anions 3546.4.5 On the Mechanism of Methanol Oxidation 3556.4.6 Catalyst Promoters for Methanol Oxidation 3566.5 Carbon Monoxide Oxidation at Platinum Surfaces 3586.5.1 Identification of Surface Structures for CO Adsorbed on Pt(111) 3586.5.2 Oxidation of CO in the Presence of Dissolved CO 3596.5.3 The Oxidation of Carbon Monoxide: Langmuir-Hinshelwood Mechanism 3616.5.4 CO Oxidation at Higher Overpotentials, Influence of Mass Transfer and Oxygen Coverage 3636.6 Conversion of Chemical Energy of Ethanol into Electricity 3646.7 Reaction Mechanisms in Electro-organic Chemistry 3666.7.1 General Issues 3666.7.2 Classification of Electrode Processes 3676.7.3 Oxidation Processes: Potentials, Intermediates and End Products 3696.7.4 Reduction Processes: Potentials, Intermediates and Products 3716.7.5 Further Electroorganic Reactions and the Influence of the Electrode Surface 3726.7.6 Electrochemical Polymerisation 3736.8 Oscillations in Electrochemical Systems 3757 Solid and Molten-salt Ionic Conductors as Electrolytes 3817.1 Ionically Conducting Solids 3817.1.1 Origins of Ionic Conductivity in Solids 3817.1.2 Current/Voltage Measurements on Solid Electrodes 3857.2 Solid Polymer Electrolytes (SPE’s) 3867.2.1 Current/Voltage Measurements with SPE’s 3887.2.2 Other Polymeric Membranes 3887.3 Ionically-conducting Melts 3927.3.1 Conductivity 3927.3.2 Current-Voltage Studies 3937.3.3 Further Applications of High-temperature Melts 3947.3.4 Room Temperature Melts 3958 Industrial Electrochemical Processes 3978.1 Introduction and Fundamentals 3978.1.1 Special Features of Electrochemical Processes 3978.1.2 Classical Cell Designs and the Space-Time Yield 3998.1.3 Morphology of Electrocatalysts 4018.1.4 The Activation Overpotential 4038.2 The Electrochemical Preparation of Chlorine and NaOH 4048.2.1 Electrode Reactions during the Electrolysis of Aqueous NaCl 4048.2.2 The Diaphragm Cell 4058.2.3 The Amalgam Cell 4068.2.4 The Membrane Process 4088.2.5 Membrane Processes using an Oxygen Cathode 4108.3 The Electrochemical Extraction and Purification of Metals 4148.3.1 Extraction from Aqueous Solution 4148.3.2 Metal Purification in Aqueous Solution 4158.3.3 Molten Salt Electrolysis 4178.4 Special Preparation Methods for Inorganic Chemicals 4188.4.1 Hypochlorite, Chlorate and Perchlorate 4188.4.2 Hydrogen Peroxide and Peroxodisulphate 4198.4.3 Classical Water Electrolysis 4208.4.4 Modern Water Electrolysis and Hydrogen Technology 4208.5 Electro-organic Synthesis 4228.5.1 An Overview of Processes and Specific Features 4228.5.2 Adiponitrile – The Monsanto Process 4248.6 Modern Cell Designs 4258.7 Future Possibilities for Electrocatalysis 4288.7.1 Electrochemical Modification of Catalytic Activity in Heterogeneous Chemical Reactions – The NEMCA Effect 4298.8 Component Separation Methods 4318.8.1 Treatment of Waste Water 4318.8.2 Electrodialysis 4338.8.3 Electrophoresis 4348.8.4 Electrochemical Separation Procedures in the Nuclear Industry 4359 Galvanic Cells 4399.1 Basics 4409.2 Properties, Components and Characteristics of Batteries 4419.2.1 Function and Construction of Lead-Acid Batteries 4419.2.2 Function and Construction of Leclanché Cells 4429.2.3 Electrolyte and Self-discharge 4449.2.4 Open-circuit Voltage, Specific Capacity and Energy Density 4449.2.5 Current-Voltage Characteristics, Power Density and Power-density/Energy-density Diagrams 4469.2.6. Battery Discharge Characteristics 4479.2.7 Charge Characteristics, Current and Energy Yield and Cycle Number 4489.2.8 Cost of Electrical Energy and of Installed Battery Power 4499.3 Secondary Systems 4509.3.1 Conventional Secondary Batteries 4509.3.2 New Developments 4529.3.3 Summary of Data for Secondary Battery Systems 4619.4 Primary Systems other than Leclanché Batteries 4649.4.1 Alkaline-Manganese Cells 4649.4.2 The Zinc-Mercury Oxide Battery 4659.4.3 Lithium Primary Batteries 4669.4.4 Electrode and Battery Characteristics for Primary Systems 4669.5 Fuel Cells 4689.5.1 Fuel Cells with Gaseous Fuels 4699.5.2 Modern Developments 4729.5.3 Fuel Cells with Liquid Fuels 4819.6 Primary and Secondary Air Batteries 4839.6.1. Metal-Air Primary Batteries 4849.6.2. Metal-Air Secondary Systems 4859.7 Efficiency of Batteries and Fuel Cells 4869.8 Super-capacitors 48710 Analytical Applications 49110.1 Titration Processes using Electrochemical Indicators 49110.2 Electro-analytical Methods 49410.2.1 Polarography and Voltammetry 49410.2.2 Further Methods - Coulometry, Electrogravimetry and Chronopotentiometry 50210.3 Electrochemical Sensors 50510.3.1 Conductivity and pH Measurement 50510.3.2 Redox Electrodes 50610.3.3 Ion-sensitive Electrodes 50610.3.4 Sensors for the Analysis of Gases 510Subject Index 521

"The text is certainly comprehensive in its coverage, ranging from ionic mobilities and liquid junction potentials, through redox electrochemistry of proteins and surface spectroscopy of electrocatalytic reactions, to fuel cells, batteries and gas sensors." (Chromatographia, February 2010) "The renowned authorial team emphasize application in energy technology while covering the physicalchemical fundamentals, modern methods of investigation, electrochemical analysis and production methods, as well as fuel cells and micro-and nanotechnology." (Chimie Nouvelle, March 2010)"Both classical contents and modern developments of electrochemistry have been incorporated in this textbook to educate young modern electrochemists … .A very solid and useful textbook. I highly recommend it to students and researchers." (The Higher Education Academy Physical Sciences Centre, December 2008) "…an excellent introduction to the physical-chemical aspects of electrochemistry…and is strongly recommended." (CHOICE, December 2007)