Principles and Applications of Electrochemistry

Transcription

1 Principles and Applications of Electrochemistry Fourth edition D. R. CROW Professor of Electrochemistry and Dean of Research University of Wolverhampton BLACKIE ACADEMIC & PROFESSIONAL An Imprint of Chapman & Hall London Glasgow Weinheim New York Tokyo Melbourne Madras

2 Contents 1 The development and structure of electrochemistry 1.1 The ubiquitous nature of electrochemistry 1.2 The historical dimension 1.3 The domains of electrochemistry Part I Principles 2 lonic interaction: the ways in which ions affect each other in Solution 2.1 The nature of electrolytes Ion-ion and ion-solvent interactions Dissolution, solvation and heats of Solution 2.2 Ion activity Chemical and electrochemical potential Mean ion activity 2.3 The Debye-Hückel equation A theoretical model for calculating activity coefficients Limiting and extended forms of the Debye-Hückel equation 2.4 Ion association Ionization, dissociation and association The Bjerrum equation Problems 3 lonic equilibria: the behaviour of acids and bases 3.1 Classical theory. The Arrhenius dissociation model 3.2 The Brensted-Lowry concept of acids and bases The importance of solvent in generating acid-base properties Relative strengths of conjugate pairs Types of solvent and general acid-base theory 3.3 Strengths of acids and bases in aqueous Solution Dissociation constants of acids and the self-ionization constant of water Dissociation constants of bases Zwitterions The values of dissociation constants 3.4 Extent of acidity and the ph scale Calculation of ph for Solutions of strong acids and bases Calculation of ph for Solutions of weak acids and bases 3.5 Hydrolysis. Salt Solutions showing acid-base properties 3.6 Calculation of the ph of salt Solutions Salts derived from weak acids and strong bases Salts derived from weak bases and strong acids Salts derived from weak acids and weak bases

3 Vlll CONTENTS 3.7 Buffer Systems The Henderson-Hasselbalch equation Efficiency of buffer Systems: buffer capacity Operation and choice of Visual indicators Functioning of indicators Titrimetric practice 41 Problems 41 4 The conducting properties of electrolytes L The significance of conductivity data Measurement of conductivity Molar conductivity Empirical Variation of molar conductivity of electrolyte Solutions with concentration The independent migration of ions Conductivity and the transport properties of ions Diffusion and conductivity: the Nernst-Einstein equation Ion speeds and conductivity: the Einstein and Stokes-Einstein equations Rationalization of relationships between molar conductivity and electrolyte concentration Strong, completely dissociated electrolytes Weak, incompletely dissociated electrolytes Electrolyte Systems showing ion pairing Conductivity at high field strengths and high frequency of ahernation of the field Electrical migration and transport numbers 65 Problems Interfacial phenomena: double layers The interface between conducting phases The electrode double layer Polarized and non-polarized electrodes Electrocapillarity: the Lippmann equation Variation of Charge with applied potential at a mercury/solution interface Specific adsorption Models for the double layer Distribution of Charge according to Helmholtz, Gouy and Chapman, and Stern The diffuse double layer The zeta potential Electrokinetic phenomena Electro-osmosis Streaming potential Electrophoresis Behaviour of colloidal Systems Stability of colloidal dispersions Colloidal electrolytes Polyelectrolytes 86 Problems 87

4 CONTENTS IX 6 Electrode potentials and electrochemical cells Comparison of chemical and electrochemical reactions Electrode potentials: their origin and significance Types of potential operating at the electrode/solution interface Measurable and non-measurable quantities Electrode potentials and activity: the Nernst equation Disturbance of the electrode equilibrium Why electrons transfer The distinction between fast and slow Systems The hydrogen scale and the IUPAC Convention The Standard hydrogen electrode Electrode potential and cell emf sign Conventions Calculation of cell emf values from tabulated data Other reference electrodes Concentration cells and emf measurements Concentration cells without liquid junctions Cells with amalgam electrodes Cells with gas electrodes operating at different pressures Concentration cells without transference Concentration cells with liquid junctions Cells with a liquid junction potential Cells with eliminated liquid junction potentials Calculation of liquid junction potentials Membrane equilibria Membrane potentials Dialysis Ion-exchange resins 125 Problems Electrode processes Equilibrium and non-equilibrium electrode potentials Current-potential relationships for fast and slow Systems Mass transfer and electron-exchange processes Types of mass transfer The kinetics of electrode processes: the Butler-Volmer equation The relationship between current density and overvoltage: the Tafel equation The modern approach to the Interpretation of electrode reactions Electrolysis and overvoltage Activation overvoltage (rj A ) Resistance overvoltage (%) Concentration overvoltage (r/ c ) Summary of overvoltage phenomena and their distinguishing features Hydrogen and oxygen overvoltage Decomposition potentials and overvoltage Individual electrode overvoltages Theories of hydrogen overvoltage 151 Problems 152 Part II Applications 8 Determination and investigation of physical parameters Applications of the Debye-Hückel equation Determination of thermodynamic equilibrium constants Dependence of reaction rates on ionic strength 157

5 CONTENTS 8.2 Determination of equilibrium constants by conductivity measurements Solubilities of sparingly soluble salts The ionic product of self-ionizing solvents Dissociation constants of weak electrolytes, e.g. weak acids Thermodynamics of cell reactions Determination of Standard potentials and mean ion activity coefficients The determination of transport numbers Determination by the Hittorf method Determination by moving boundary methods Determination using cell emf Interpretation and application of transport numbers Determination of equilibrium constants by measurements of potential Dissociation constants of weak acids The ionization constant of water Solubility products Equilibrium constants of redox reactions Formation (stability) constants of metal complexes The experimental determination of ph The hydrogen electrode The glass electrode 185 Problems 186 Electroanalytical techniques What constitues electroanalysis? Conductimetric titrations Potentiometrie titrations Zero current potentiometry Constant current potentiometry Potentiometry with two indicator electrodes Classical voltammetric techniques Polarography Characteristics of diffusion-controlled Polarographie waves Amperometric titrations Wave characteristics and the mechanism of electrochemical processes Modern Polarographie methods Variation of current during the life of mercury drops Pulse polarography Differential pulse polarography Stripping voltammetry Voltammetry based on forced controlled convection Rotating disc voltammetry The ring-disc electrode Cyclic voltammetry Ultramicroelectrodes Electrogravimetry Coulometric methods 217 Problems 219 Electrochemical sensors Ion-selective electrodes Glass membrane electrodes Solid-state electrodes Liquid membrane electrodes Problems with ion-selective electrodes Chemically modified electrodes 225

6 CONTENTS XI 10.4 Gas-sensing electrodes Enzyme electrodes Sensors based on modified metal oxide field effect transistors (MOSFETs) The wall-jet ring-disc electrode (WJRDE) The exploitation of electrode processes Mixed Potentials and double electrodes Pourbaix diagrams Corrosion prevention Electrochemical processes as sources of energy Primarycells Secondary cells Fuel cells Electrocatalysis and electrosynthesis Anodically initiated process Cathodically initiated process Electrochemistry on an industrial scale 252 Problems 254 Further Reading 256 Solutions to problems 259 Appendix I 271 Appendix II 274 Appendix III 275 Appendix IV 277 Index 279