ELECTROCHEMISTR Y

Principles, Methods, and Applications

CHRISTOPHER M . A . BRETT

ANA MARIA OLIVEIRA BRETT

Notation and Units xxi

Main Symbols xxii

Subscripts xxvi

Abbreviations xxviiFundamental physical constants xxixMathematical constants xxixUseful relations at 25°C (298 .15 K) involving fundamentalconstants 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 AN DELECTRODE POTENTIALS 13

2.1 Introduction 132.2 The cell potential of an electrochemical cell 142.3 Calculation of cell potential : activities or

concentrations? 1 62.4 Calculation of cell potential : electrochemical potential

1 82 .5 Galvanic and electrolytic cells 202.6 Electrode classification 212.7 Reference electrodes 222 .8 Movement of ions in solution : diffusion and migration 252 .9 Conductivity and mobility 262 .10 Liquid junction potentials 322 .11 Liquid junction potentials, ion-selective electrodes, an d

biomembranes 332 .12 Electrode potentials and oxidation state diagrams 34

References 38

3 THE INTERFACIAL REGION 3 93 .1 Introduction 3 93 .2 The electrolyte double layer : surface tension, charge

density, and capacity 393 .3 Double layer models 44

the first models : Helmholtz, Gouy-Chapman, Stern ,and Grahame 45Bockris, Devanathan, and Müller model 5 1`chemical' models 52

3 .4 Specific adsorption 543.5 The solid metallic electrode: some remarks 563.6 The semiconductor electrode : the space-charge region

583.7 Electrokinetic phenomena and colloids : the zeta

potential 64electrophoresis 66sedimentation potential 67electroosmosis 67streaming potential 68limitations in the calculation of the zeta potential .

68References 68

4 FUNDAMENTALS OF KINETICS AN DMECHANISM OF ELECTROD EREACTIONS 704.1 Introduction 704.2 The mechanism of electron transfer at an electrode .

704.3 The mechanism of electron transfer in homogeneous

solution 714 .4 An expression for the rate of electrode reactions 724.5 The relation between current and reaction rate : the

exchange current 764 .6 Microscopic interpretation of electron transfer .

77References 8 1

5 MASS TRANSPORT 825.1 Introduction 825.2 Diffusion control 8 35.3 Diffusion-limited current : planar and spherical

electrodes 8 55.4 Constant current : planar electrodes 9 05 .5 Microelectrodes 925.6 Diffusion layer 94

5 .7 Convection and diffusion: hydrodynamic systems .

955 .8 Hydrodynamic systems : some useful parameters . .

975 .9 An example of a convective-diffusion system : the

rotating disc electrode 98References 102

6 KINETICS AND TRANSPORT I NELECTRODE REACTIONS 103

6.1 Introduction 1036 .2 The global electrode process: kinetics and transport .

1036 .3 Reversible reactions 1066.4 Irreversible reactions 1096.5 The general case 11 16.6 The Tafel law 11 36.7 The Tafel law corrected for transport 1156 .8 Kinetic treatment based on exchange current 1156 .9 The effect of the electrolyte double layer on electrod e

kinetics 1166 .10 Electrode processes involving multiple electron transfer 1196.11 Electrode processes involving coupled homogeneous

reactions 122References 126

PART II Methods .

7 ELECTROCHEMICAL EXPERIMENTS . .

129

7.1 Introduction 1297 .2 Electrode materials for voltammetry 129

metals 130carbon 130other solid materials 133mercury 133

7.3 The working electrode : preparation and cleaning .

1347.4 The cell : measurements at equilibrium 1367.5 The cell : measurements away from equilibrium

137electrodes 137supporting electrolyte 138removal of oxygen 140

7.6 Calibration of electrodes and cells 1427.7 Instrumentation : general 142

7 .8 Analogue instrumentation 143potentiostat 146galvanostat 147compensation of cell solution resistance 148

7.9 Digital instrumentation 148References 149

8 HYDRODYNAMIC ELECTRODES 15 1

8 .1 Introduction 15 18 .2 Limiting currents at hydrodynamic electrodes 1558.3 A special electrode: the dropping mercury electrode

1578 .4 Hydrodynamic electrodes in the study of electrode

processes 16 3reversible reaction 16 3the general case 164

8.5 Double hydrodynamic electrodes 16 58.6 Multiple electron transfer: the use of the RRDE

167consecutive reactions 16 8parallel reactions 16 8consecutive and parallel reactions 169

8.7 Hydrodynamic electrodes in the investigation of coupledhomogeneous reactions 169

8.8 Hydrodynamic electrodes and non-stationary techniques 17 1References 172

9 CYCLIC VOLTAMMETRY AND LINEA RSWEEP TECHNIQUES 174

9.1 Introduction 1749.2 Experimental basis 17 59.3 Cyclic voltammetry at planar electrodes 176

reversible system 17 7irreversible system 18 1quasi-reversible system 18 3adsorbed species 18 5

9.4 Spherical electrodes 18 79.5 Microelectrodes 18 89.6 Systems containing more than one component 18 89.7 Systems involving coupled homogeneous reactions .

18 99.8 Convolution linear sweep voltammetry 19 19.9 Linear potential sweep with hydrodynamic electrodes

19 39.10 Linear potential sweep in thin-layer cells 194

References 197

10 STEP AND PULSE TECHNIQUES 19 9

10 .1 Introduction 19 910.2 Potential step : chronoamperometry 20 0

reversible system 202quasi-reversible and irreversible systems 203more complex mechanisms 205

10.3 Double potential step 20510.4 Chronocoulometry 20610.5 Current step : chronopotentiometry 208

reversible system 209quasi-reversible and irreversible systems 21 1

10 .6 Double current step 21210.7 Methods using derivatives of chronopotentiograms .

21310 .8 Coulostatic pulses 21 410 .9 Pulse voltammetry 21 4

tast polarography 21 5normal pulse voltammetry (NPV) 21 6differential pulse voltammetry (DPV) 21 7square wave voltammetry (SWV) 21 9other pulse techniques 22 1applications of pulse techniques 222

References 222

11 IMPEDANCE METHODS 22411 .1 Introduction 22411 .2 Detection and measurement of impedance 225

a.c . bridges 225phase-sensitive detectors and transfer functio nanalysers 227direct methods " 22 8

11 .3 Equivalent circuit of an electrochemical cell 22 911 .4 The faradaic impedance for a simple electrode process 23011 .5 The faradaic impedance, Zf, and the total impedance :

how to calculate Z f from experimental measurements 23211 .6 Impedance plots in the complex plane 23311 .7 Admittance and its use 23611 .8 A.c. voltammetry 23811.9 Second-order effects 240

higher harmonics 240other second-order methods 24 1

faradaic rectification 242demodulation 242

11 .10 More complex systems, porous electrodes, and fractals 24411 .11 Hydrodynamic electrodes and impedance 24811 .12 Transforms and impedance 249

References 251

12 NON-ELECTROCHEMICAL PROBES O FELECTRODES AND ELECTROD EPROCESSES 253

12.1 Introduction 25312 .2 In situ spectroscopic techniques 254

transmission 25 4reflectance, electroreflectance and ellipsometry .

255internal reflection 258Raman spectroscopy 259electron spin resonance, (ESR) spectroscopy . .

260X-ray absorption spectroscopy 26 1second harmonic generation (SHG) 263

12 .3 Ex situ spectroscopic techniques 26 3photoelectron spectroscopy (XPS) 263Auger electron spectroscopy (AES) 264electron energy loss spectroscopy (EELS) 266electrochemical mass spectrometry (ECMS )

and secondary ion mass spectrometry (SIMS) .

266low-energy and reflection high-energy electron

diffraction (LEED and RHEED) 26712 .4 In situ microscopic techniques 268

scanning tunnelling microscopy (STM) 269atomic force microscopy (AFM) 270scanning electrochemical microscopy (SECM) . .

272scanning ion conductance microscopy (SICM) . .

27312 .5 Ex situ microscopic techniques : electron microscopy

27312 .6 Other in situ techniques

276measurement of mass change : the quartz crysta lmicrobalance (QCM) 276measurement of absorbed radiation : thermal changes 277

12.7 Photoelectrochemistry 27812 .8 Electrochemiluminescence 282

References 282

PART III Applications

13 POTENTIOMETRIC SENSORS 28913 .1 Introduction 289

13.2 Potentiometric titrations 290

13 .3 Functioning of ion-selective electrodes 29413.4 Glass electrodes and pH sensors 29 513 .5 Electrodes with solid state membranes 29 713 .6 Ion-exchange membrane and neutral carrier membrane

electrodes 30113 .7 Sensors selective to dissolved gases 30 313 .8 Enzyme-selective electrodes 30313 .9 Some practical aspects 30 413 .10 Recent developments : miniaturization 30 5

ISFETs 30 5coated wire electrodes 30 6hybrid sensors 30 7

13 .11 Potentiometric sensors in flow systems 30713 .12 Electroanalysis with potentiometric sensors 30 8

References 30 9

14 AMPEROMETRIC AND VOLTAMMETRI CSENSORS 310

14.1 Introduction 31 014 .2 Amperometric titrations 31 1

simple amperometric titrations 31 1biamperometric titrations 31 2amperometric titrations with double hydrodynami celectrodes 31 3

14 .3 Membrane and membrane-covered electrodes 31 414 .4 Modified electrodes 31 614 .5 Increase of sensitivity : pre-concentration techniques

31 814 .6 Amperometric and voltammetric electroanalysis . .

322References 324

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15 ELECTROCHEMISTRYIN INDUSTRY 326

15 .1 Introduction 32615 .2 Electrolysis : fundamental considerations 32715.3 Electrochemical reactors 32815 .4 Porous and packed-bed electrodes 33 115 .5 Examples of industrial electrolysis and electrosynthesis

332the chlor-alkali industry 332metal extraction: aluminium 336water electrolysis 338organic electrosynthesis : the Monsanto process .

33915 .6 Electrodeposition and metal finishing 34 115 .7 Metal processing 345

15.8 Batteries 346

15 .9 Fuel cells 349

15 .10 Electrochemistry in water and effluent treatment .

350References 351

16 CORROSION 353

16.1 Introduction 35316.2 Fundamentals 353

thermodynamic aspects 354kinetic aspects 354

16 .3 Types of metallic corrosion 36116 .4 Electrochemical methods of avoiding corrosion . .

363electrochemically produced protective barriers .

364sacrificial anodes 364methods of impressed current/potential 365corrosion inhibitors 365

References 366

17 BIOELECTROCHEMISTRY 367

17.1 Introduction 367

17 .2 The electrochemical interface between biomolecules :cellular membranes, transmembrane potentials, bilaye rlipid membranes, electroporation 368

17 .3 Nerve impulse and cardiovascular electrochemistry

373the nerve impulse 374cardiovascular problems 376

17.4 Oxidative phosphorylation 37817.5 Bioenergetics 37917.6 Bioelectrocatalysis !i 38117.7 Bioelectroanalysis 38717.8 Future perspectives 391

References 391

Appendice s

Al USEFUL MATHEMATICAL RELATIONS 39 5

A1.1 The Laplace transform 395introduction 395the transform 395important properties 397

A1 .2 The Fourier transform 398

A1 .3 Other useful functions and mathematical expressions 39 9the Airy function 39 9the gamma function 399the error function 400Taylor and Maclaurin series 40 1hyperbolic functions 403

Reference 404

A2 PRINCIPLES OF A .C . CIRCUITS 405

A2.1 Introduction 405A2.2 Resistance 406A2.3 Capacitance 406A2.4 Representation in the complex plane 406A2.5 Resistance and capacitance in series 407A2.6 Resistance and capacitance in parallel 408A2.7 Impedances in series and in parallel 410A2.8 Admittance 410A2.9 The Kramers-Kronig relations 410

References 411

A3 DIGITAL SIMULATION 412

A3.1 Introduction 412A3.2 Simulation models 412A3 .3 Implicit methods 414

References 41 4

A4 STANDARD ELECTRODE POTENTIALS 41 6

INDEX 41 9f1i