Physical Electrochemistry

Preface xvii Symbols and Abbreviations xix 1 Introduction 1 1.1 General Considerations 1 1.1.1 The Transition from Electronic to Ionic Conduction 1 1.1.2 The Resistance of the Interface can be Infinite 2 1.1.3 Mass-Transport Limitation 2 1.1.4 The Capacitance at the Metal/Solution Interphase 4 1.2 Polarizable and Nonpolarizable Interfaces 4 1.2.1 Phenomenology 4 1.2.2 The Equivalent Circuit Representation 5 Further Reading 7 2 The Potentials of Phases 9 2.1 The Driving Force 9 2.1.1 Definition of the Electrochemical Potential 9 2.1.2 Separability of the Chemical and the Electrical Terms 10 2.2 Two Cases of Special Interest 11 2.2.1 Equilibrium of a Species Between two Phases in Contact 11 2.2.2 Two Identical Phases not at Equilibrium 12 2.3 The Meaning of the Standard Hydrogen Electrode (SHE) Scale 13 Further Reading 15 3 Fundamental Measurements in Electrochemistry 17 3.1 Measurement of Current and Potential 17 3.1.1 The Cell Voltage is the Sum of Several Potential Differences 17 3.1.2 Use of a Nonpolarizable Counter Electrode 17 3.1.3 The Three-Electrode Setup 18 3.1.4 Residual jRS Potential Drop in aThree-Electrode Cell 18 3.2 Cell Geometry and the Choice of the Reference Electrode 19 3.2.1 Types of Reference Electrodes 19 3.2.2 Use of an Auxiliary Reference Electrode for the Study of Fast Transients 20 3.2.3 Calculating the Uncompensated Solution Resistance for a few Simple Geometries 21 3.2.3.1 Planar Configuration 21 3.2.3.2 Cylindrical Configuration 21 3.2.3.3 Spherical Symmetry 22 3.2.4 Positioning the Reference Electrode 22 3.2.5 Edge Effects 24 Further Reading 26 4 Electrode Kinetics: Some Basic Concepts 27 4.1 Relating Electrode Kinetics to Chemical Kinetics 27 4.1.1 The Relation of Current Density to Reaction Rate 27 4.1.2 The Relation of Potential to Energy of Activation 28 4.1.3 Mass-Transport Limitation Versus Charge-Transfer Limitation 30 4.1.4 The Thickness of the Nernst Diffusion Layer 31 4.2 Methods of Measurement 33 4.2.1 Potential Control Versus Current Control 33 4.2.2 The Need to Measure Fast Transients 35 4.2.3 Polarography and the Dropping Mercury Electrode (DME) 37 4.3 Rotating Electrodes 40 4.3.1 The Rotating Disk Electrode (RDE) 40 4.3.2 The Rotating Cone Electrode (RConeE) 44 4.3.3 The Rotating Ring Disk Electrode (RRDE) 45 Further Reading 47 5 Single-Step Electrode Reactions 49 5.1 The Overpotential, 𝜂 49 5.1.1 Definition and Physical Meaning of Overpotential 49 5.1.2 Types of Overpotential 51 5.2 Fundamental Equations of Electrode Kinetics 52 5.2.1 The Empirical Tafel Equation 52 5.2.2 The Transition-State Theory 53 5.2.3 The Equation for a Single-Step Electrode Reaction 54 5.2.4 Limiting Cases of the General Equation 56 5.3 The Symmetry Factor, 𝛽, in Electrode Kinetics 59 5.3.1 The Definition of 𝛽 59 5.3.2 The Numerical Value of 𝛽 60 5.4 The Marcus Theory of Charge Transfer 61 5.4.1 Outer-Sphere Electron Transfer 61 5.4.2 The Born–Oppenheimer Approximation 62 5.4.3 The Calculated Energy of Activation 63 5.4.4 The Value of 𝛽 and its Potential Dependence 64 5.5 Inner-Sphere Charge Transfer 65 5.5.1 Metal Deposition 65 Further Reading 66 6 Multistep Electrode Reactions 67 6.1 Mechanistic Criteria 67 6.1.1 The Transfer Coefficient, 𝛼, and its Relation to the Symmetry Factor, 𝛽 67 6.1.2 Steady State and Quasi-Equilibrium 69 6.1.3 Calculation of the Tafel Slope 71 6.1.4 Reaction Orders in Electrode Kinetics 74 6.1.5 The Effect of pH on Reaction Rates 77 6.1.6 The Enthalpy of Activation 79 Further Reading 81 7 Specific Examples of Multistep Electrode Reactions 83 7.1 Experimental Considerations 83 7.1.1 Multiple Processes in Parallel 83 7.1.2 The Level of Impurity that can be Tolerated 84 7.2 The Hydrogen Evolution Reaction (HER) 87 7.2.1 Hydrogen Evolution on Mercury 87 7.2.2 Hydrogen Evolution on Platinum 89 7.3 Possible Paths for the Oxygen Evolution Reaction 91 7.4 The Role and Stability of Adsorbed Intermediates 94 7.5 Adsorption Energy and Catalytic Activity 95 Further Reading 96 8 The Electrical Double Layer (EDL) 97 8.1 Models of Structure of the EDL 97 8.1.1 Phenomenology 97 8.1.2 The Parallel-Plate Model of Helmholtz 99 8.1.3 The Diffuse Double Layer Model of Gouy and Chapman 100 8.1.4 The Stern Model 103 8.1.5 The Role of the Solvent at the Interphase 105 Further Reading 107 9 Electrocapillary 109 9.1 Thermodynamics 109 9.1.1 Adsorption and Surface Excess 109 9.1.2 The Gibbs Adsorption Isotherm 111 9.1.3 The Electrocapillary Equation 112 9.2 Methods of Measurement and Some Results 114 9.2.1 The Electrocapillary Electrometer 114 9.2.2 Some Experimental Results 119 9.2.2.1 The Adsorption of Ions 119 9.2.2.2 Adsorption of NeutralMolecules 120 Further Reading 122 10 Intermediates in Electrode Reactions 123 10.1 Adsorption Isotherms for Intermediates Formed by Charge Transfer 123 10.1.1 General 123 10.1.2 The Langmuir Isotherm and its Limitations 123 10.1.3 Application of the Langmuir Isotherm for Charge-Transfer Processes 125 10.1.4 The Frumkin Adsorption Isotherms 126 10.2 The Adsorption Pseudocapacitance Cϕ 127 10.2.1 Formal Definition of Cϕ and its Physical Understanding 127 10.2.2 The Equivalent-Circuit Representation 129 10.2.3 Calculation of Cϕ as a function of 𝜃 and E 130 Further Reading 133 11 Underpotential Deposition and Single-Crystal Electrochemistry 135 11.1 Underpotential Deposition (UPD) 135 11.1.1 Definition and Phenomenology 135 11.1.2 UPD on Single Crystals 139 11.1.3 Underpotential Deposition of Atomic Oxygen and Hydrogen 141 Further Reading 142 12 Electrosorption 145 12.1 Phenomenology 145 12.1.1 What is Electrosorption? 145 12.1.2 Electrosorption of Neutral Organic Molecules 147 12.1.3 The Potential of Zero Charge, Epzc, and its Importance in Electrosorption 148 12.1.4 TheWork Function and the Potential of Zero Charge 151 12.2 Adsorption Isotherms for Neutral Species 152 12.2.1 General Comments 152 12.2.2 The Parallel-Plate Model of Frumkin et al. 153 12.2.3 The Water Replacement Model of Bockris et al. 155 Further Reading 157 13 Fast Transients, the Time-Dependent Diffusion Equation,and Microelectrodes 159 13.1 The Need for Fast Transients 159 13.1.1 General 159 13.1.2 Small-Amplitude Transients 161 13.1.3 The Sluggish Response of the Electrochemical Interphase 162 13.1.4 How can the Slow Response of the Interphase be Overcome? 162 13.1.4.1 Galvanostatic Transients 162 13.1.4.2 The Double-Pulse GalvanostaticMethod 163 13.1.4.3 The Coulostatic (Charge-Injection) Method 164 13.2 The Diffusion Equation 167 13.2.1 The Boundary Conditions of the Diffusion Equation 167 13.2.1.1 Potential Step, Reversible Case (Chrono-Amperometry) 168 13.2.1.2 Potential Step, High Overpotential Region (Chrono-Amperometry) 171 13.2.1.3 Current Step (Chronopotentiometry) 172 13.3 Microelectrodes 174 13.3.1 The Unique Features of Microelectrodes 174 13.3.2 Enhancement of Diffusion at a Microelectrode 175 13.3.3 Reduction of the Solution Resistance 176 13.3.4 The Choice between Single Microelectrodes and Large Ensembles 176 Further Reading 178 14 Linear Potential Sweep and Cyclic Voltammetry 181 14.1 Three Types of Linear Potential Sweep 181 14.1.1 Very Slow Sweeps 181 14.1.2 Studies of Oxidation or Reduction of Species in the Bulk of the Solution 182 14.1.3 Studies of Oxidation or Reduction of Species Adsorbed on the Surface 182 14.1.4 Double-Layer Charging Currents 183 14.1.5 The Form of the Current–Potential Relationship 185 14.2 Solution of the Diffusion Equations 186 14.2.1 The Reversible Region 186 14.2.2 The High-Overpotential Region 187 14.3 Uses and Limitations of the Linear Potential Sweep Method 188 14.4 Cyclic Voltammetry for Monolayer Adsorption 190 14.4.1 Reversible Region 190 14.4.2 The High-Overpotential Region 192 Further Reading 193 15 Electrochemical Impedance Spectroscopy (EIS) 195 15.1 Introduction 195 15.2 Graphical Representations 200 15.3 The Effect of Diffusion Limitation –TheWarburg Impedance 203 15.4 Advantages, Disadvantages, and Applications of EIS 206 Further Reading 211 16 The Electrochemical Quartz Crystal Microbalance (EQCM) 213 16.1 Fundamental Properties of the EQCM 213 16.1.1 Introduction 213 16.1.2 The EQCM 214 16.1.3 The Effect of Viscosity 217 16.1.4 Immersion in a Liquid 218 16.1.5 Scales of Roughness 218 16.2 Impedance Analysis of the EQCM 219 16.2.1 The Extended Equation for the Frequency Shift 219 16.2.2 Other Factors Influencing the Frequency Shift 220 16.3 Uses of the EQCM as a Microsensor 220 16.3.1 Advantages and Limitations 220 16.3.2 Some Applications of the EQCM 222 Further Reading 225 17 Corrosion 227 17.1 The Definition of Corrosion 227 17.2 Corrosion Costs 230 17.3 Thermodynamics of Corrosion 232 17.3.1 Introduction and Important Terms 232 17.3.2 Electrode Potentials and the Standard Electromotive Force (EMF) Series 236 17.3.3 The Dependence of Free Energy on the Equilibrium Constant and Cell Potential 241 17.3.4 The Nernst Equation 241 17.3.5 The Potential–pH (Pourbaix) Diagrams 242 17.4 Kinetics of Corrosion 252 17.4.1 Introduction and Important Terms 252 17.4.2 Two Limiting Cases of the Butler–Volmer Equation: Tafel Extrapolation and Polarization Resistance 255 17.4.3 Corrosion Rate 257 17.4.4 The Mixed-Potential Theory and the Evans Diagrams 257 17.4.5 Passivation and its Breakdown 264 17.5 Corrosion Measurements 270 17.5.1 Non-Electrochemical Tests 270 17.5.2 Electrochemical Tests 272 17.5.2.1 Open-Circuit Potential (OCP) Measurements 272 17.5.2.2 Polarization Tests 273 17.5.2.3 Linear Polarization Resistance (LPR) 277 17.5.2.4 Zero-Resistance Ammetry (ZRA) 277 17.5.2.5 Electrochemical Noise (EN) Measurements 278 17.5.2.6 Electrochemical Hydrogen Permeation Tests 279 17.5.3 Complementary Surface-Sensitive Analytical Characterization Techniques 284 17.6 Forms of Corrosion 286 17.6.1 Uniform (General) Corrosion 286 17.6.2 Localized Corrosion 289 17.6.2.1 Crevice Corrosion 289 17.6.2.2 Filiform Corrosion 291 17.6.2.3 Pitting Corrosion 291 17.6.3 Intergranular Corrosion 293 17.6.3.1 Sensitization 293 17.6.3.2 Exfoliation 294 17.6.4 Dealloying 295 17.6.5 Galvanic (Bimetallic) Corrosion 295 17.6.6 Environmentally Induced Cracking (EIC)/Environment-Assisted Cracking (EAC) 297 17.6.6.1 Hydrogen Embrittlement (HE) 297 17.6.6.2 Hydrogen-Induced Blistering 299 17.6.6.3 Hydrogen Attack 299 17.6.6.4 Stress Corrosion Cracking (SCC) 300 17.6.6.5 Corrosion Fatigue (CF) 303 17.6.7 Erosion Corrosion 304 17.6.8 Microbiological Corrosion (MIC) 305 17.7 Corrosion Protection 308 17.7.1 Cathodic Protection 308 17.7.1.1 Cathodic Protection with Sacrificial Anodes 308 17.7.1.2 Impressed-Current Cathodic Protection (ICCP) 310 17.7.2 Anodic Protection 312 17.7.3 Corrosion Inhibitors 313 17.7.4 Coatings 315 17.7.5 Other Mitigation Practices 320 Further Reading 321 18 Electrochemical Deposition 323 18.1 Electroplating 323 18.1.1 Introduction 323 18.1.2 The Fundamental Equations of Electroplating 324 18.1.3 Practical Aspects of Metal Deposition 325 18.1.4 Hydrogen Evolution as a Side Reaction 326 18.1.5 Plating of Noble Metals 327 18.1.6 Current Distribution in Electroplating 328 18.1.6.1 Uniformity of Current Distribution 328 18.1.6.2 The Faradaic Resistance (RF) and the Solution Resistance (RS) 328 18.1.6.3 The DimensionlessWagner Number 329 18.1.6.4 Kinetically Limited Current Density 333 18.1.7 Throwing Power 334 18.1.7.1 Macro Throwing Power 334 18.1.7.2 Micro Throwing Power 334 18.1.8 The Use of Additives 336 18.1.9 The Microstructure of Electrodeposits and the Evolution of Intrinsic Stresses 339 18.1.10 Pulse Plating 341 18.1.11 Plating from Nonaqueous Solutions 343 18.1.11.1 Statement of the Problem 343 18.1.11.2 Methods of Plating Al 345 18.1.12 Electroplating of Alloys 346 18.1.12.1 General Observations 346 18.1.12.2 Some Specific Examples 349 18.1.13 The Mechanism of Charge Transfer in Metal Deposition 351 18.1.13.1 Metal Ions Crossing the Interphase Carry the Charge across it 351 18.2 Electroless Deposition of Metals 352 18.2.1 Some Fundamental Aspects of Electroless Plating of Metals and Alloys 352 18.2.2 The Activation Process 353 18.2.3 The Reducing Agent 353 18.2.4 The Complexing Agent 354 18.2.5 The Mechanism of Electroless Deposition 354 18.2.6 Advantages and Disadvantages of Electroless Plating Compared to Electroplating 357 18.3 Electrophoretic Deposition (EPD) 358 Further Reading 361 19 Electrochemical Nanotechnology 363 19.1 Introduction 363 19.2 Nanoparticles and Catalysis 363 19.2.1 Surfaces and Interfaces 364 19.2.2 The Vapor Pressure of Small Droplets and the Melting Point of Solid NPs 365 19.2.3 TheThermodynamic Stability andThermal Mobility of NPs 368 19.2.4 Catalysts 368 19.2.5 The Effect of Particle Size on Catalytic Activity 369 19.2.6 Nanoparticles Compared to Microelectrodes 370 19.2.7 The Need for High Surface Area 371 19.3 Electrochemical Printing 372 19.3.1 Electrochemical Printing Processes 373 19.3.2 Nanoelectrochemistry Using Micro- and Nano-Electrodes/Pipettes 379 Further Reading 384 20 Energy Conversion and Storage 387 20.1 Introduction 387 20.2 Batteries 388 20.2.1 Classes of Batteries 388 20.2.2 TheTheoretical Limit of Energy per UnitWeight 390 20.2.3 How is the Quality of a Battery Defined? 391 20.2.4 Primary Batteries 392 20.2.4.1 Why DoWe Need Primary Batteries? 392 20.2.4.2 The Leclanché and the Alkaline Batteries 392 20.2.4.3 The Li–Thionyl Chloride Battery 393 20.2.4.4 The Lithium–Iodine Solid-State Battery 395 20.2.5 Secondary Batteries 396 20.2.5.1 Self-Discharge and Specific Energy 396 20.2.5.2 Battery Stacks Versus Single Cells 396 20.2.5.3 Some Common Types of Secondary Batteries 397 20.2.5.4 The Li-ion Battery 402 20.2.5.5 Metal–Air Batteries 408 20.2.6 Batteries-Driven Electric Vehicles 409 20.2.7 The Polarity of Batteries 410 20.3 Fuel Cells 412 20.3.1 The Specific Energy of Fuel Cells 412 20.3.2 The Phosphoric Acid Fuel Cell (PAFC) 412 20.3.3 The Direct Methanol Fuel Cell (DMFC) 415 20.3.4 The Proton Exchange Membrane Fuel Cell (PEMFC) 418 20.3.5 The Alkaline Fuel Cell (AFC) 420 20.3.6 High-Temperature Fuel Cells 421 20.3.6.1 The Solid Oxide Fuel Cell (SOFC) 421 20.3.6.2 The Molten Carbonate Fuel Cell (MCFC) 422 20.3.7 Porous Gas Diffusion Electrodes 423 20.3.8 Fuel-Cell-Driven Vehicles 426 20.3.9 Criticism of the Fuel Cells Technology 427 20.4 Supercapacitors 428 20.4.1 Electrostatic Considerations 428 20.4.2 The Energy Stored in a Capacitor 429 20.4.3 The Essence of Supercapacitors 430 20.4.4 Advantages of Supercapacitors 432 20.4.5 Barriers for Supercapacitors 435 20.4.6 Applications of Supercapacitors 435 20.5 Hydrogen Storage 436 Further Reading 443 Index 445