Diffraction and Spectroscopic Methods in Electrochemistry

Series Preface V

Volume Preface XV

List of Contributors XVII

1 In-situ X-ray Diffraction Studies of the Electrode/Solution Interface 1
Christopher A. Lucas and Nenad M. Markovic

1.1 Introduction 1

1.2 Experimental 2

1.3 Adsorbate-induced Restructuring of Metal Substrates 4

1.3.1 Surface Relaxation 5

1.3.1.1 Pt Monometallic and Bimetallic Surfaces 5

1.3.1.2 Group IB Metals 12

1.3.2 Surface Reconstruction 16

1.4 Adlayer Structures 22

1.4.1 Anion Structures 23

1.4.2 CO Ordering on the Pt(111) Surface 28

1.4.3 Underpotential Deposition (UPD) 31

1.5 Reactive Metals and Oxides 36

1.6 Conclusions and Future Directions 41

Acknowledgments 42

References 42

2 UV-visible Reflectance Spectroscopy of Thin Organic Films at Electrode Surfaces 47
Takamasa Sagara

2.1 Introduction 47

2.2 The Basis of UV-visible Reflection Measurement at an Electrode Surface 49

2.3 Absolute Reflection Spectrum versus Modulated Reflection Spectrum 50

2.4 Wavelength-modulated UV-visible Reflectance Spectroscopy 53

2.5 Potential-modulated UV-visible Reflectance Spectroscopy 54

2.6 Instrumentation of the Potential-modulated UV-visible Reflection Measurement 55

2.7 ER Measurements for Redox-active Thin Organic Films 57

2.8 Interpretation of the Reflection Spectrum 62

2.9 Reflection Measurement at Special Electrode Configurations 65

2.10 Estimation of the Molecular Orientation on the Electrode Surface 68

2.10.1 Estimation of the Molecular Orientation on the Electrode Surface using the Redox ER Signal 69

2.10.2 Estimation of the Molecular Orientation on the Electrode Surface using the Stark Effect ER Signal 72

2.11 Measurement of Electron Transfer Rate using ER Measurement 73

2.11.1 Redox ER Signal in Frequency Domain 73

2.11.2 Examples of Electron Transfer Rate Measurement using ER Signal 76

2.11.3 Improvement in Data Analysis 78

2.11.4 Combined Analysis of Impedance and Modulation Spectroscopic Signals 79

2.11.5 Upper Limit of Measurable Rate Constant 82

2.11.6 Rate Constant Measurement using an ER Voltammogram 82

2.12 ER Signal Originated from Non-Faradaic Processes – a Quick Overview 83

2.13 ER Signal with Harmonics Higher than the Fundamental Modulation Frequency 84

2.14 Distinguishing between Two Simultaneously Occurring Electrode Processes 85

2.15 Some Recent Examples of the Application of ER Measurement for a Functional Electrode 87

2.16 Scope for Future Development of UV-visible Reflection Measurements 91

2.16.1 New Techniques in UV-visible Reflection Measurements 91

2.16.2 Remarks on the Scope for Future Development of UV-visible Reflection Measurements 92

Acknowledgments 93

References 93

3 Epi-fluorescence Microscopy Studies of Potential Controlled Changes in Adsorbed Thin Organic Films at Electrode Surfaces 97
Dan Bizzotto and Jeff L. Shepherd

3.1 Introduction 97

3.2 Fluorescence Microscopy and Fluorescence Probes 99

3.3 Fluorescence near Metal Surfaces 100

3.4 Description of a Fluorescence Microscope for Electrochemical Studies 101

3.4.1 Microscope Resolution 103

3.4.2 Image Analysis 104

3.5 Electrochemical Systems Studied with Fluorescence Microscopy 106

3.5.1 Adsorption of C18OH on Au(111) 108

3.5.2 The Adsorption and Dimerization of 2-(2_-Thienyl)pyridine (TP) on Au(111) 114

3.5.3 Fluorescence Microscopy of the Adsorption of DOPC onto an Hg Drop 115

3.5.4 Fluorescence Microscopy of Liposome Fusion onto a DOPC-coated Hg Interface 118

3.5.5 Fluorescence Imaging of the Reductive Desorption of an Alkylthiol SAM on Au 120

3.6 Conclusions and Future Considerations 122

Structures and Abbreviations 123

Acknowledgments 124

References 124

4 Linear and Non-linear Spectroscopy at the Electrified Liquid/Liquid Interface 127
David J. Fermín

4.1 Introductory Remarks and Scope of the Chapter 127

4.2 Linear Spectroscopy 128

4.2.1 Total Internal Reflection Absorption/Fluorescence Spectroscopy 128

4.2.2 Potential-modulated Reflectance/Fluorescence in TIR 134

4.2.3 Quasi-elastic Laser Scattering (QELS) 139

4.2.4 Other Linear Spectroscopic Studies at the Neat Liquid/Liquid Interface 142

4.3 Non-linear Spectroscopy 146

4.3.1 Second Harmonic Generation 146

4.3.2 Vibrational Sum Frequency Generation 151

4.4 Summary and Outlook 154

Acknowledgments 157

Symbols 157

Abbreviations 158

References 159

5 Sum Frequency Generation Studies of the Electrified Solid/Liquid Interface 163
Steven Baldelli and Andrew A. Gewirth

5.1 Introduction 163

5.1.1 Theoretical Background 163

5.1.2 SFG Intensities 164

5.1.3 Resonant Term 165

5.1.4 Non-resonant Term 166

5.1.5 Phase Interference 167

5.1.6 Orientation Information in SFG 168

5.1.7 Phase Matching 169

5.1.8 Surface Optics 169

5.1.9 Data Analysis Reference 171

5.1.10 Experimental Designs 172

5.1.11 Spectroscopy Cell 173

5.2 Applications of SFG to Electrochemistry 174

5.2.1 CO Adsorption 176

5.2.1.1 Polarization Studies 178

5.2.1.2 Potential Dependence 178

5.2.1.3 CO on Alloys 179

5.2.1.4 Solvent Effects 180

5.2.2 Adsorption of upd and opd H 180

5.2.3 CN on Pt and Au Electrodes 180

5.2.3.1 CN/Pt 180

5.2.3.2 CN/Au 183

5.2.4 OCN and SCN 183

5.2.5 Pyridine and Related Derivatives 183

5.2.6 Dynamics of CO and CN Vibrational Relaxation 185

5.2.7 Solvent Structure 187

5.2.7.1 Nonaqueous Solvents 187

5.2.7.2 Aqueous Solvents 191

5.2.8 Monolayers and Corrosion 193

5.3 Conclusion 193

Acknowledgments 194

References 195

6 IR Spectroscopy of the Semiconductor/Solution Interface 199
Jean-Noël Chazalviel and François Ozanam

6.1 Introduction 199

6.2 IR Spectroscopy at an Interface 200

6.2.1 Basic Principles of IR Spectroscopy 200

6.2.2 External versus Internal Reflection 201

6.3 Practical Aspects at an Electrochemical Interface 203

6.3.1 How Potential can Affect IR Absorption 204

6.3.2 How to Isolate Potential-sensitive IR Absorption 205

6.4 What can be Learnt from IR Spectroscopy at the Interface 207

6.4.1 Vibrational Absorption of Interfacial and Double-Layer Species 208

6.4.2 Vibrational Absorption of Species outside the Double-Layer 211

6.4.3 Electronic Absorption 213

6.5 Effect of Light Polarization in ATR Geometry 217

6.5.1 Selection Rules for a Polarized IR Beam 218

6.5.2 Case of Strongly Polar Species: LO-TO Splitting 218

6.5.3 Polarization Modulation 222

6.6 Dynamic Information from a Modulation Technique 222

6.7 Case of Rough or Complex Interfaces 224

6.7.1 Surface Roughness 225

6.7.2 Composite Interface Films 226

6.8 Conclusion 229

References 230

7 Recent Advances in in-situ Infrared Spectroscopy and Applications in Single-crystal Electrochemistry and Electrocatalysis 233
Carol Korzeniewski

7.1 Introduction 233

7.2 Experimental 234

7.2.1 Spectrometer Systems 234

7.2.2 Spectrometer Throughput Considerations 234

7.2.3 Detectors 235

7.2.4 Signal-to-Noise Ratio Considerations 236

7.2.5 Signal Digitization 236

7.2.6 Signal Modulation and Related Data Acquisition Methods 237

7.3 Applications 238

7.3.1 Adsorption and Reactivity at Well-defined Electrode Surfaces 238

7.3.1.1 Adsorption on Pure Metals 238

7.3.1.2 Electrochemistry at Well-defined Bimetallic Electrodes 241

7.3.2 SEIRAS 244

7.3.3 Infrared Spectroscopy as a Probe of Surface Electrochemistryat Metal Catalyst Particles 249

7.3.4 Nanostructured Electrodes and Optical Considerations 253

7.3.5 Emerging Instrumental Methods and Quantitative Approaches 254

7.3.5.1 Step-scan Interferometry 254

7.3.5.2 Two-dimensional Infrared Correlation Analysis 256

7.3.5.3 Quantitation of Molecular Orientation 259

7.4 Summary 262

Acknowledgments 263

References 263

8 In-situ Surface-enhanced Infrared Spectroscopy of the Electrode/Solution Interface 269
Masatoshi Osawa

8.1 Introduction 269

8.2 Electromagnetic Mechanism of SEIRA 271

8.3 Experimental Procedures 273

8.3.1 Electrochemical Cell and Optics 273

8.3.2 Preparation of Thin-film Electrodes 276

8.4 General Features of SEIRAS 279

8.4.1 Comparison of SEIRAS with IRAS 279

8.4.2 Surface Selection Rule and Molecular Orientation 281

8.4.3 Comparison of SEIRA and SERS 284

8.4.4 Baseline Shift by Adsorption of Molecules and Ions 285

8.5 Selected Examples 287

8.5.1 Reactions of a Triruthenium Complex Self-assembled on Au 288

8.5.2 Cytochrome c Electrochemistry on Self-assembled Monolayers 290

8.5.3 Molecular Recognition at the Electrochemical Interface 293

8.5.4 Hydrogen Adsorption and Evolution on Pt 296

8.5.5 Oxidation of C1 Molecules on Pt 298

8.6 Advanced Techniques for Studying Electrode Dynamics 302

8.6.1 Rapid-scan Millisecond Time-resolved FT-IR Measurements 302

8.6.2 Step-scan Microsecond Time-resolved FT-IR Measurements 303

8.6.3 Potential-modulated FT-IR Spectroscopy 308

8.7 Summary and Future Prospects 309

Acknowledgments 310

References 310

9 Quantitative SNIFTIRS and PM IRRAS of Organic Molecules at Electrode Surfaces 315
Vlad Zamlynny and Jacek Lipkowski

9.1 Introduction 315

9.2 Reflection of Light from Stratified Media 316

9.2.1 Reflection and Refraction of Electromagnetic Radiation at a Two-phase Boundary 317

9.2.2 Reflection and Refraction of Electromagnetic Radiation at a Multiple-phase Boundary 323

9.3 Optimization of Experimental Conditions 325

9.3.1 Optimization of the Angle of Incidence and the Thin-cavity Thickness 327

9.3.2 The Effect of Incident Beam Collimation 330

9.3.3 The Choice of the Optical Window Geometry and Material 331

9.4 Determination of the Angle of Incidence and the Thin-cavity Thickness 336

9.5 Determination of the Isotropic Optical Constants in Aqueous Solutions 338

9.6 Determination of the Orientation of Organic Molecules at the Electrode Surface 343

9.7 Development of Quantitative SNIFTIRS 344

9.7.1 Description of the Experimental Set-up 344

9.7.2 Fundamentals of SNIFTIRS 347

9.7.3 Calculation of the Tilt Angle from SNIFTIRS Spectra 348

9.7.4 Applications of Quantitative SNIFTIRS 349

9.8 Development of Quantitative in-situ PM IRRAS 356

9.8.1 Introduction 356

9.8.2 Fundamentals of PM IRRAS and Experimental Set-up 357

9.8.3 Principles of Operation of a Photoelastic Modulator 360

9.8.4 Correction of PM IRRAS Spectra for the PEM Response Functions 364

9.8.5 Background Subtraction 366

9.8.6 Applications of Quantitative PM IRRAS 368

9.9 Summary and Future Directions 373

Acknowledgments 373

References 374

10 Tip-enhanced Raman Spectroscopy – Recent Developments and Future Prospects 377
Bruno Pettinger

10.1 General Introduction 377

10.2 SERS at Well-defined Surfaces 379

10.3 Single-molecule Raman Spectroscopy 384

10.4 Tip-enhanced Raman Spectroscopy (TERS) 391

10.4.1 Near-field Raman Spectroscopy with or without Apertures 391

10.4.2 First TERS Experiments 395

10.4.3 TERS on Single-crystalline Surfaces 401

10.5 Outlook 409

10.5.1 Recent Results 409

10.5.2 New Approaches on the Horizon 409

Acknowledgment 410

References 411

Subject Index 419