Understanding Voltammetry

by Compton, Richard G.; Banks, Craig E.

• ISBN13: 9781848165861
• ISBN10: 1848165862
• Edition: 2nd
• Format: Paperback
• Copyright: 2011-01-31
• Publisher: Imperial College Pr

Summary

The power of electrochemical measurements in respect of thermodynamics, kinetics and analysis is widely recognized but the subject can be unpredictable to the novice even if they have a strong physical and chemical background, especially if they wish to pursue the study of quantitative measurements further. Accordingly, some significant experiments are perhaps wisely never attempted while the literature is sadly replete with flawed attempts at rigorous voltammetry. This textbook considers how to go about designing, explaining and interpreting experiments centered around various forms of voltammetry (cyclic, microelectrode, hydrodynamic, etc.). The reader is assumed to have attained a knowledge equivalent to Master's level of physical chemistry but no exposure to electrochemistry in general, or voltammetry in particular. While the book is designed to "stand alone", references to important research papers are given to provide an introductory entry into the literature. In comparison to the first edition, two new chapters - transport via migration and nanoelectrochemistry - are added. Minor changes and updates are also made throughout the textbook to facilitate enhanced understanding and greater clarity of exposition.

Table of Contents

Preface	p. vii
Equilibrium Electrochemistry and the Nernst Equation	p. 1
Chemical Equilibrium	p. 1
Electrochemical Equilibrium: Introduction	p. 5
Electrochemical Equilibrium: Electron Transfer at the Solution-Electrode Interface	p. 9
Electrochemical Equilibrium: The Nernst Equation	p. 11
Walther Hermann Nernst	p. 17
Reference Electrodes and the Measurement of Electrode Potentials	p. 19
The Hydrogen Electrode as a Reference Electrode	p. 26
Standard Electrode Potentials and Formal Potentials	p. 27
Formal Potentials and Experimental Voltammetry	p. 30
Electrode Processes: Kinetics vs. Thermodynamics	p. 32
Electrode Kinetics	p. 35
Currents and Reaction Fluxes	p. 35
Studying Electrode Kinetics Requires Three Electrodes	p. 37
Butler-Volmer Kinetics	p. 40
Standard Electrochemical Rate Constants and Formal Potentials	p. 43
The Need for Supporting Electrolyte	p. 45
The Tafel Law	p. 46
Julius Tafel	p. 47
Multistep Electron Transfer Processes	p. 49
Tafel Analysis and the Hydrogen Evolution Reaction	p. 52
B. Stanley Pons	p. 57
Cold Fusion - The Musical!	p. 58
Why Are Some Standard Electrochemical Rate Constants Large but Others Slow? The Marcus Theory of Electron Transfer: An Introduction	p. 60
Marcus Theory: Taking it Further. Inner and Outer Sphere Electron Transfer	p. 66
Marcus Theory: Taking it Further. Adiabatic and Non-Adiabatic Reactions	p. 67
Marcus Theory: Taking it Further. Calculating the Gibbs Energy of Activation	p. 70
Relationship between Marcus Theory and Butler-Volmer Kinetics	p. 73
Marcus Theory and Experiment. Success!	p. 74
Diffusion	p. 77
Fick's 1st Law of Diffusion	p. 77
Fick's 2nd Law of Diffusion	p. 79
The Molecular Basis of Fick's Laws	p. 81
How Did Fick Discover His Laws?	p. 83
The Cottrell Equation: Solving Fick's 2nd Law	p. 88
The Cottrell Problem: The Case of Unequal Diffusion Coefficients	p. 92
The Nernst Diffusion Layer	p. 94
Mass Transfer vs. Electrode Kinetics: Steady-State Current-Voltage Waveshapes	p. 97
Mass Transport Corrected Tafel Relationships	p. 100
Cyclic Voltammetry at Macroelectrodes	p. 107
Cyclic Voltammetry: The Experiment	p. 107
Cyclic Voltammetry: Solving the Transport Equations	p. 109
Cyclic Voltammetry: Reversible and Irreversible Kinetics	p. 111
What Dictates 'Reversible' and 'Irreversible' Behaviour?	p. 119
Reversible and Irreversible Behaviour: The Effect of Voltage Scan Rate	p. 120
Reversible versus Irreversible Voltammetry: A Summary	p. 126
The Measurement of Cyclic Voltammograms: Three Practical Considerations	p. 127
The Effect of Unequal Diffusion Coefficients, DA ≠ DB	p. 129
Multiple Electron Transfer: Reversible Electrode Kinetics	p. 133
Multiple Electron Transfer: Irreversible Electrode Kinetics	p. 142
The Influence of pH on Cyclic Voltammetry	p. 147
The Scheme of Squares	p. 151
Simultaneous Two-Electron Transfer in Electrode Kinetics?	p. 152
Voltammetry at Microelectrodes	p. 157
The Cottrell Equation for a Spherical or Hemispherical Electrode	p. 157
Potential Step Transients at Microdisc Electrodes	p. 162
Microelectrodes Have Large Current Densities and Fast Response Times	p. 163
Applications of Potential Step Chronoamperometry Using Microdisc Electrodes	p. 165
Double Potential Step Microdisc Chronoamperometry Exploring the Diffusion Coefficient of Electrogenerated Species	p. 168
Cyclic and Linear Sweep Voltammetry Using Microdisc Electrodes	p. 176
Steady-State Voltammetry at the Microdisc Electrode	p. 186
Microelectrodes versus Macroelectrodes	p. 187
Ultrafast Cyclic Voltammetry: Megavolts per Second Scan Rates	p. 191
Ultrasmall Electrodes: Working at the Nanoscale	p. 192
Voltammetry at Heterogeneous Surfaces	p. 197
Partially Blocked Electrodes	p. 197
Microelectrode Arrays	p. 213
Voltammetry at Highly Ordered Pyrolytic Graphite Electrodes	p. 219
Electrochemically Heterogeneous Electrodes	p. 223
Electrodes Covered with Porous Films	p. 226
Voltammetric Particle Sizing	p. 229
Scanning Electrochemical Microscopy (SECM)	p. 233
Cyclic Voltammetry: Coupled Homogeneous Kinetics and Adsorption	p. 239
Homogeneous Coupled Reactions: Notation and Examples	p. 239
Modifying Fick's Second Law to Allow for Chemical Reaction	p. 241
Cyclic Voltammetry and the EC Reaction	p. 242
How Do the Parameters K1 and ∧ Emerge?	p. 246
Cyclic Voltammetry and the EC2 Reaction	p. 249
Examples of EC and EC2 Processes	p. 252
ECE Processes	p. 260
ECE versus DISP	p. 268
The CE Mechanism	p. 270
The EC' (Catalytic) Mechanism	p. 272
Adsorption	p. 274
Voltammetric Studies of Droplets and Solid Particles	p. 283
Hydrodynamic Electrodes	p. 291
Convection	p. 291
Modifying Fick's Laws to Allow for Convection	p. 293
The Rotating Disc Electrode: An Introduction	p. 294
The Rotating Disc Electrode - Theory	p. 295
Osborne Reynolds (1842-1912)	p. 299
The Rotating Disc Electrode - Further Theory	p. 299
Chronoamperometry at the Rotating Disc Electrode: An Illustration of the Value of Simulation	p. 306
The Rotating Disc and Coupled Homogeneous Kinetics	p. 309
The Channel Electrode: An Introduction	p. 312
The Channel Electrode: The Levich Equation Derived	p. 315
Channel Flow Cells and Coupled Homogeneous Kinetics	p. 316
Chronoamperometry at the Channel Electrode	p. 322
The Channel Electrode is not 'Uniformly Accessible'	p. 324
Channel Microelectrodes	p. 325
Channel Microband Electrode Arrays for Mechanistic Electrochemistry	p. 327
The High Speed Channel Electrode	p. 331
Hydrodynamic Electrodes Based on Impinging jets	p. 333
Sonovoltammetry	p. 335
Voltammetry for Electroanalysis	p. 347
Potential Step Voltammetric Techniques	p. 347
Differential Pulse Voltammetry	p. 348
Square Wave Voltammetry	p. 350
Stripping Voltammetry	p. 351
Sono-electroanalysis	p. 358
Voltammetry in Weakly Supported Media: Migration and Other Effects	p. 367
Potentials and Fields in Fully Supported Voltammetry	p. 367
The Distribution of Ions Around a Charged Electrode	p. 370
The Electrode-Solution Interface: Beyond the Gouy-Chapman Theory	p. 375
Double Layer Effect on Electrode Kinetics: Frumkin Effects	p. 379
A.N. Frumkin	p. 381
Transport by Diffusion and by Migration	p. 382
Measurement of Ion Mobilities	p. 384
Liquid Junction Potentials	p. 386
Chronoamperometry and Cyclic Voltammetry in Weakly Supported Media	p. 389
Voltammetry at the Nanoscale	p. 397
Transport to Particles Supported on an Electrode	p. 397
Nanoparticle Voltammetry: The Transport Changes as the Electrode Shrinks in Size	p. 405
Altered Chemistry at the Nanoscale	p. 414
Appendix: Simulation of Electrode Processes	p. 419
Fick's First and Second Laws	p. 419
Boundary Conditions	p. 420
Finite Difference Equations	p. 420
Backward Implicit Method	p. 421
Conclusion	p. 423
Index	p. 425
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