Electrochemistry: Principles, Methods, And Applications

Notation and Units xxi
 Main Symbols xxii
 Subscripts xxvi
 Abbreviations xxvii
 Fundamental physical constants xxix
 Mathematical constants xxix
 Useful relations at 25°C (298.15 K) involving fundamental constants xxix
 1 INTRODUCTION 1
 1.1 The scope of electrochemistry 1
 1.2 The nature of electrode reactions 1
 1.3 Thermodynamics and kinetics 2
 1.4 Methods for studying electrode reactions 5
 1.5 Applications of electrochemistry 5
 1.6 Structure of the book 6
 1.7 Electrochemical literature 7
 PART I Principles
 2 ELECTROCHEMICAL CELLS: THERMODYNAMIC PROPERTIES AND ELECTRODE POTENTIALS 13
 2.1 Introduction 13
 2.2 The cell potential of an electrochemical cell 14
 2.3 Calculation of cell potential: activities or concentrations? 16
 2.4 Calculation of cell potential: electrochemical potential. 18
 2.5 Galvanic and electrolytic cells 20
 2.6 Electrode classification 21
 2.7 Reference electrodes 22
 2.8 Movement of ions in solution: diffusion and migration . 25
 2.9 Conductivity and mobility 26
 2.10 Liquid junction potentials 32
 2.11 Liquid junction potentials, ion-selective electrodes, and biomembranes 33
 2.12 Electrode potentials and oxidation state diagrams. 34
 References 38
 xii Contents
 3 THE INTERFACIAL REGION 39
 3.1 Introduction 39
 3.2 The electrolyte double layer: surface tension, charge density, and capacity 39
 3.3 Double layer models 44
 the first models: Helmholtz, Gouy-Chapman, Stern,and Grahame 45
 Bockris, Devanathan, and Muller model 51
 chemical models 52
 3.4 Specific adsorption 54
 3.5 The solid metallic electrode: some remarks 56
 3.6 The semiconductor electrode: the space-charge region . 58
 3.7 Electrokinetic phenomena and colloids: the zeta potential 64
 electrophoresis 66
 sedimentation potential 67
 electroosmosis 67
 streaming potential 68
 limitations in the calculation of the zeta potential 68
 References 68
 4 FUNDAMENTALS OF KINETICS AND MECHANISM OF ELECTRODE REACTIONS 70
 4.1 Introduction 70
 4.2 The mechanism of electron transfer at an electrode 70
 4.3 The mechanism of electron transfer in homogeneous solution 71
 4.4 An expression for the rate of electrode reactions 72
 4.5 The relation between current and reaction rate: the exchange current 76
 4.6 Microscopic interpretation of electron transfer 77
 References 81
 5 MASS TRANSPORT 82
 5.1 Introduction 82
 5.2 Diffusion control 83
 5.3 Diffusion-limited current: planar and spherical electrodes 85
 5.4 Constant current: planar electrodes 90
 5.5 Microelectrodes 92
 5.6 Diffusion layer 94
 Contents xiii
 5.7 Convection and diffusion: hydrodynamicsystems 95
 5.8 Hydrodynamicsystems: some useful parameters 97
 5.9 An example of a convective-diffusion system: the rotating disk electrode
 References 102
 KINETICS AND TRANSPORT INELECTRODE REACTIONS 103
 6.1 Introduction 103
 6.2 The global electrode process: kinetics and transport 103
 6.3 Reversible reactions 106
 6.4 Irreversible reactions 109
 6.5 The general case Ill
 6.6 The Tafel law 113
 6.7 The Tafel law corrected for transport 115
 6.8 Kinetic treatment based on exchange current 115
 6.9 The effect of the electrolyte double layer on electrode kinetics 116
 6.10 Electrode processes involving multiple electron transfer 119
 6.11 Electrode processes involving coupled homogeneous reactions 122
 References 126
 PART II Methods
 ELECTROCHEMICAL EXPERIMENTS 129
 7.1 Introduction 129
 7.2 Electrode materials for voltammetry 129
 metals 130
 carbon 130
 other solid materials 133
 mercury 133
 7.3 The working electrode: preparation and cleaning 134
 7.4 The cell: measurements at equilibrium 136
 7.5 The cell: measurements away from equilibrium 137
 electrodes 137
 supporting electrolyte 138
 removal of oxygen 140
 7.6 Calibration of electrodes and cells 142
 7.7 Instrumentation: general 142
 xiv Contents
 7.8 Analogue instrumentation 143
 potentiostat 146
 galvanostat 147
 compensation of cell solution resistance 148
 7.9 Digital instrumentation 148
 References 149
 8 HYDRODYNAMIC ELECTRODES 151
 8.1 Introduction 151
 8.2 Limiting currents at hydrodynamic electrodes 155
 8.3 A special electrode: the dropping mercury electrode 157
 8.4 Hydrodynamic electrodes in the study of electrode processes 163
 reversible reaction 163
 the general case 164
 8.5 Double hydrodynamic electrodes 165
 8.6 Multiple electron transfer: the use of the RRDE 167
 consecutive reactions 168
 parallel reactions 168
 consecutive and parallel reactions 169
 8.7 Hydrodynamic electrodes in the investigation of coupled
 homogeneous reactions 169
 8.8 Hydrodynamic electrodes and non-stationary techniques 171
 References 172
 9 CYCLIC VOLTAMMETRY AND LINEAR
 SWEEP TECHNIQUES 174
 9.1 Introduction 174
 9.2 Experimental basis 175
 9.3 Cyclic voltammetry at planar electrodes 176
 reversible system 177
 irreversible system 181
 quasi-reversible system 183
 adsorbed species 185
 9.4 Spherical electrodes 187
 9.5 Microelectrodes 188
 9.6 Systems containing more than one component 188
 9.7 Systems involving coupled homogeneous reactions 189
 9.8 Convolution linear sweep voltammetry 191
 9.9 Linear potential sweep with hydrodynamic electrodes 193
 9.10 Linear potential sweep in thin-layer cells 194
 References 197
 Contents xv
 10 STEP AND PULSE TECHNIQUES 199
 10.1 Introduction 199
 10.2 Potential step: chronoamperometry 200
 reversible system 202
 quasi-reversible and irreversible systems 203
 more complex mechanisms 205
 10.3 Double potential step 205
 10.4 Chronocoulometry 206
 10.5 Current step: chronopotentiometry 208
 reversible system 209
 quasi-reversible and irreversible systems 211
 10.6 Double current step 212
 10.7 Methods using derivatives of chronopotentiograms 213
 10.8 Coulostatic pulses 214
 10.9 Pulse voltammetry 214
 tast polarography 215
 normal pulse voltammetry (NPV) 216
 differential pulse voltammetry (DPV) 217
 square wave voltammetry (SWV) 219
 other pulse techniques 221
 applications of pulse techniques 222
 References 222
 11 IMPEDANCE METHODS 224
 11.1 Introduction 224
 11.2 Detection and measurement of impedance 225
 a.c. bridges 225
 phase-sensitive detectors and transfer function
 analysers 227
 direct methods 228
 11.3 Equivalent circuit of an electrochemical cell 229
 11.4 The faradaic impedance for a simple electrode process 230
 11.5 The faradaic impedance, Zf, and the total impedance: how to calculate Zf from experimental measurements 232
 11.6 Impedance plots in the complex plane 233
 11.7 Admittance and its use 236
 11.8 A.c. voltammetry 238
 11.9 Second-order effects 240
 higher harmonics 240
 other second-order methods 241
 faradaic rectification 242
 demodulation 242
 xvi Contents
 11.10 More complex systems, porous electrodes, and fractals 244
 11.11 Нуdrodynamic electrodes and impedance 248
 11.12 Transforms and impedance 249
 References 251
 12 NON-ELECTROCHEMICAL PROBES OF ELECTRODES AND ELECTRODE PROCESSES 253
 12.1 Introduction 253
 12.2 In situ spectroscopic techniques 254
 transmission 254
 reflectance, electroreflectance and ellipsometry 255
 internal reflection 258
 Raman spectroscopy 259
 electron spin resonance (ESR) spectroscopy 260
 X-ray absorption spectroscopy 261
 second harmonic generation (SHG) 263
 12.3 Ex situ spectroscopic techniques 263
 photoelectron spectroscopy (XPS) 263
 Auger electron spectroscopy (AES) 264
 electron energy loss spectroscopy (EELS) 266
 electrochemical mass spectrometry (ECMS)
 and secondary ion mass spectrometry (SIMS) 266
 low-energy and reflection high-energy electron
 diffraction (LEED and RHEED) 267
 12.4 In situ microscopic techniques 268
 scanning tunnelling microscopy (STM) 269
 atomic force microscopy (AFM) 270
 scanning electrochemical microscopy (SECM) 272
 scanning ion conductance microscopy (SICM) 273
 12.5 Ex situ microscopic techniques: electron microscopy 273
 12.6 Other in situ techniques 276
 measurement of mass change: the quartz crystal
 microbalance (QCM) 276
 measurement of absorbed radiation: thermal changes 277
 12.7 Photoelectrochemistry 278
 12.8 Electrochemiluminescence 282
 References 282
 PART III Applications
 13 POTENTIOMETRIC SENSORS 289
 13.1 Introduction 289
 Contents xvii
 13.2 Potentiometric titrations 290
 13.3 Functioning of ion-selective electrodes 294
 13.4 Glass electrodes and pH sensors 295
 13.5 Electrodes with solid state membranes 297
 13.6 Ion-exchange membrane and neutral carrier membrane electrodes 301
 13.7 Sensors selective to dissolved gases 303
 13.8 Enzyme-selective electrodes 303
 13.9 Some practical aspects 304
 13.10 Recent developments: miniaturization 305
 ISFETs 305
 coated wire electrodes 306
 hybrid sensors 307
 13.11 Potentiometric sensors in flow systems 307
 13.12 Electroanalysis with potentiometric sensors 308
 References 309
 14 AMPEROMETRIC AND VOLTAMMETRIC
 SENSORS 310
 14.1 Introduction 310
 14.2 Amperometric titrations 311
 simple amperometric titrations 311
 biamperometric titrations 312
 amperometric titrations with double hydrodynamic
 electrodes 313
 14.3 Membrane and membrane-covered electrodes 314
 14.4 Modified electrodes .316
 14.5 Increase of sensitivity: pre-concentration techniques 318
 14.6 Amperometric and voltammetric electroanalysis 322
 References 324
 15 ELECTROCHEMISTRY IN INDUSTRY 326
 15.1 Introduction 326
 15.2 Electrolysis: fundamental considerations 327
 15.3 Electrochemical reactors 328
 15.4 Porous and packed-bed electrodes 331
 15.5 Examples of industrial electrolysis and electrosynthesis 332
 the chlor-alkali industry 332
 metal extraction: aluminium 336
 water electrolysis 338
 organic electrosynthesis: the Monsanto process 339
 15.6 Electrodeposition and metal finishing 341
 15.7 Metal processing 345
 xvjjj Contents
 15.8 Batteries 346
 15.9 Fuel cells 349
 15.10 Electrochemistry in water and effluent treatment 350
 References 351
 16 CORROSION 353
 16.1 Introduction 353
 16.2 Fundamentals 353
 thermodynamic aspects 354
 kinetic aspects 354
 16.3 Types of metallic corrosion 361
 16.4 Electrochemical methods of avoiding corrosion 363
 electrochemically produced protective barriers 364
 sacrificial anodes 364
 methods of impressed current/potential 365
 corrosion inhibitors 365
 References 366
 17 BIOELECTROCHEMISTRY 367
 17.1 Introduction 367
 17.2 The electrochemical interface between biomolecules: cellular membranes, transmembrane potentials, bilayer lipid membranes, electroporation 368
 17.3 Nerve impulse and cardiovascular electrochemistry 373
 the nerve impulse 374
 cardiovascular problems 376
 17.4 Oxidative phosphorylation 378
 17.5 Bioenergetics 379
 17.6 Bioelectrocatalysis 381
 17.7 Bioelectroanalysis 387
 17.8 Future perspectives 391
 References 391
 Appendices
 Al USEFUL MATHEMATICAL RELATIONS . . 395
 Al.l The Laplace transform 395
 introduction 395
 the transform 395
 important properties 397
 A1.2 The Fourier transform 398
 Contents xix
 A1.3 Other useful functions and mathematical expressions 399
 the Airy function 399
 the gamma function 399
 the error function 400
 Taylor and Maclaurin series 401
 hyperbolic functions 403
 Reference 404
 A2 PRINCIPLES OF A.C. CIRCUITS 405
 A2.1 Introduction 405
 A2.2 Resistance 406
 A2.3 Capacitance 406
 A2.4 Representation in the complex plane 406
 A2.5 Resistance and capacitance in series 407
 A2.6 Resistance and capacitance in parallel 408
 A2.7 Impedances in series and in parallel 410
 A2.8 Admittance 410
 A2.9 The Kramers-Kronig relations 410
 References 411
 A3 DIGITAL SIMULATION 412
 A3.1 Introduction 412
 A3.2 Simulation models 412
 A3.3 Implicit methods 414
 References 414
 A4 STANDARD ELECTRODE POTENTIALS . . 416
 INDEX 419