Unveiling Electrochemical Surface Processes with in situ Vibrational Spectroscopy Restricted; Files Only

Abstract

This thesis is a comprehensive summary of the studies into the electrochemical interfaces on different processes with in situ/operando vibrational spectroscopies, such as Surface-enhanced Raman Spectroscopy (SERS), Shell-isolated nanoparticle enhanced Raman Spectroscopy (SHINERS) and Sum Frequency Generation Spectroscopy (SFGS).

First, the thesis focuses on characterizing the electric double layer at interfaces. Chapter 4 is the SERS investigation of the electric double layer structure in a model electrocatalysis system. The study focuses on utilizing the Stark probe of the adsorbed CO on Au, revealing the unique double layer structure of the system by its ionic strength dependency under the electric fields at the interfaces. Chapter 5 extends the investigation to assess how surface nanoparticles influence surface static electric fields, addressing a controversial question in the field. Utilizing a combination of SHINERS and SFGS, the study compares the effects of nanoparticle proximity on interfacial electric fields across different distances to the surface by various molecular probes. These findings in the two chapters offer a deeper molecular understanding of the electric double layer in electrochemical systems.

The thesis also pioneers a novel approach to control hydrogen bonding at electrochemical interfaces, as detailed in Chapter 6. Through potential-dependent SERS spectra, this research offers a detailed mechanistic study on electrochemical controlling hydrogen bonding between 4-mercaptobenzoic acid and aniline on Au electrode, providing insights into the application of the electro-induction effect and electrolyte interactions in forming and destabilizing hydrogen bond at electrochemical interfaces.

Lastly, in Chapters 7 and 8, the thesis provides more insights into the electrochemical CO2 reduction reaction (CO2RR). Chapter 7 highlights the competitive adsorption of carbonate ions on Cu surfaces during CO2RR, using in situ SHINERS. This work sheds light on optimizing CO onset potentials by managing electrolyte composition and providing molecular understanding in this fine-tuning process. Chapter 8 explores the effects of light on electrochemical CO2RR, revealing significant findings about light-induced photoelectrochemical CO production and the interplay between surface morphology and reaction enhancement.

Overall, this thesis aims to study the electrochemical interfaces from the molecular aspects, trying to offer a deeper understanding of molecular interactions at electrochemical interfaces. 

Table of Contents

1.    Chapter 1 Introduction. 1

1.1.     Motivation. 1

1.2.     Outline. 4

1.3.     References. 8

2.    Chapter 2 Basic Theoretical Background. 9

2.1.     Electrochemical Interfaces and electrochemical reactions. 9

2.1.1.      Overview of the electrochemical interfaces. 9

2.1.2.      Background of the electric double layer at electrochemical interfaces. 10

2.1.3.      Background of energy conversions at interfaces—CO2RR.. 12

2.2.     Background of SERS and SHINERS. 15

2.2.1.      Background of Raman scattering and Raman spectroscopy. 15

2.2.2.      The feature of SERS effects. 18

2.2.3.      Mechanism of SERS effects. 19

2.2.4.      The development of “borrowing” method and SHINERS. 22

2.3.     Basics of VSFGS. 26

2.4.     References. 29

3.    Chapter 3 Methodology. 36

3.1.     Spectroscopic setups. 36

3.1.1.      Raman setup and signal processing. 36

3.1.2.      SFG setup and signal processing. 37

3.2.     Electrochemical setups and materials. 41

3.2.1.      Electrochemical workstations and electrochemical cells. 41

3.2.2.      Chemicals and other materials. 44

3.3.     Preparation for electrochemical electrodes. 45

3.3.1.      Electrochemical polishing of the electrodes. 45

3.3.2.      Electrochemical roughening electrodes for SERS measurements. 45

3.3.3.      Electrochemical deposition. 45

3.4.     Preparation for materials and characterizations. 48

3.4.1.      Au nanoparticles synthesis for SERS. 48

3.4.2.      Au@SiO2 nanoparticles synthesis for SHINERS 48

3.4.3.      SAM on electrode preparation. 49

3.5.     References. 50

4.    Chapter 4 Vibrational Spectroscopic Stark probe of the interfacial electric double layer of CO on Au. 50

4.1.     Introduction and background. 50

4.2.     Experimental design of CO on Au and spectra fitting 53

4.3.     Raman result analysis— CO on Au as a Stark probe 55

4.4.     Raman result analysis— Ionic strength effect on CO Stark tuning rate. 58

4.5.     The theoretical model of the electric double layer of CO on Au and the discussion. 63

4.6.     Conclusion. 70

4.7.     Reference. 71

5.    Chapter 5 Vibrational Spectroscopic Probing the impact of Nanoparticle Proximity on Interfacial Electric Fields. 74

5.1.     Introduction and background. 74

5.2.     Impacts of NPs on EF probed by the comparison of SFG/SHINERS. 77

5.2.1.      Considerations for SHINERS/VSFGS comparison. 77

5.2.2.      Feasibility test on spectroscopic comparison — COad on Au. 78

5.2.3.      The impacts of NPs within OHP — PIC on Au 80

5.2.4.      The impacts of NPs within diffuse layer— 4-MBN on Au. 82

5.2.5.      The whole profile of the EF affected by the NPs —molecular Ruler on Au. 83

5.2.6.      The model of the electric double layer with NPs 85

5.3.     Conclusions. 89

5.4.     References. 90

6.    Chapter 6 Harness reversible interfacial hydrogen bonding at the interface with electro-induction effect 95

6.1.     Introduction and background. 95

6.2.     Results and discussion. 98

6.2.1.      The vibrational spectroscopic confirmation for hydrogen bonding formation. 98

6.2.2.      Reversible hydrogen bonding formation/dissociation at an electrochemical interface. 101

6.2.3.      Quantitative analysis of potential dependence on hydrogen bonding. 104

6.2.4.      Mechanistic understanding of the electrochemical hydrogen bonding at the interface. 112

6.3.     Conclusions. 118

6.4.     References. 120

7.    Chapter 7 In situ spectroscopic studies of electrochemical catalysis in CO2RR.. 124

7.1.     Introduction. 124

7.2.     Anion competitive binding effects in CO2 reduction on Cu electrodes. 126

7.2.1.      Raman measurements of CO2 reduction on Cu 127

7.2.2.      Key species assignments. 129

7.2.3.      Potential dependent adsorbate coverage during CO2 reduction. 131

7.2.4.      Competitive binding model for CO2 reduction on Cu. 135

7.2.5.      A new competitive binding model for CO2 reduction on Cu. 139

7.3.     Conclusions. 141

7.4.     Supporting Information. 143

7.4.1.      Extended description of experimental methods 143

7.4.2.      Extended results analysis and discussion. 143

7.4.2.1 Discussion on the background subtraction of Raman spectra. 143

7.4.2.2 Additional DFT calculated Raman spectra of key species. 146

7.4.2.3 Summary of the Raman peaks assignment 148

7.4.2.4 Additional discussion on *COO− peaks assignments. 152

7.4.2.5 Supplement discussion on Cu-OH-related species assignments. 155

7.4.2.6 Supplement electrochemical Raman spectra on *CO.. 159

7.4.2.7 Additional plot of potential dependent intensity. 160

7.4.2.8 Additional results on *CO3²⁻ population dependence. 161

7.4.2.9 Estimation of potentials of zero charge for systems. 163

7.4.2.10 DEMS Results Analysis. 164

7.4.2.11 Additional results on competitive binding control 166

7.4.2.12 Discussion on Cu2O reduction induced carbonate intensity change. 168

7.4.2.13 Additional discussions of other possible interpretations of the mechanism.. 170

7.5.     References. 173

8.    Chapter 8 Photo-enhanced Electrochemical CO2 reduction on Au electrodes. 178

8.1.     Introduction. 178

8.2.     Results and analysis. 179

8.2.1.      SFG observation of the photo-enhanced and photo-induced *CO on Au. 179

8.2.2.      Photocurrent measurements of PEEC CO2 reduction 183

8.2.3.      Evidence of solvated electrons species. 189

8.2.4.      Discussion on the mechanisms in PEEC CO2 193

8.3.     Conclusions. 195

8.4.     References. 196

About this Dissertation

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School	Laney Graduate School
Department	Chemistry
Degree	Ph.D.
Submission	Dissertation
Language	English
Research Field	Chemistry, Physical
Palabra Clave	Vibrational Spectroscopy Sum Frequency Generation Raman Electrochemistry Electrocatalysis
Committee Chair / Thesis Advisor	Tianquan(Tim) Lian, Emory University
Committee Members	Craig Hill, Emory University Brian Dyer, Emory University

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