Bipolar Electrochemistry: Chemical Analysis Based on Electrochemiluminescence and Surface Enhanced Raman Spectroscopy

Abstract

Bipolar electrochemistry has a variety of applications ranging from chemical analysis, material modification and synthesis, to generate motions, etc, and it is also a very simple, cheap, useful technology. The main goal of this thesis is to analyze chemicals based on electrochemiluminescence (ECL) and surface enhanced Raman spectroscopy. Since bipolar electrochemistry does not have a direct readout in current, electrochemiluminescence is becoming a more and more useful technique for electroanalysis on bipolar electrochemistry. Small molecules like O2 capable of quenching ECL can be detected according to Stern−Volmer equation. A linear potential gradient was created going through the solution along the bipolar electrode when the external voltage is sufficient on the bipolar cell. As the redox reactions were relative to the potential applied, the extent of reaction on bipolar electrode was different due to the potential gradient, which can be observed by surface enhance Raman scattering. Consequently, the potential distribution was obtained. Chapter 1 presents a detailed literature review on the principle and application of bipolar electrochemistry including chemical analysis based on electrochemiluminescence and electrodissolution, material modification, synthesis and generating motions, concentration enrichment and separation. Additionally, a short introduction of electrochemiluminescence and Raman spectroscopy was given at the end of chapter 1. Chapter 2 describes the detection of small molecules like 1-ferrocenylmethanol (1-hydroxymethyl ferrocene) and oxygen capable of quenching the electrochemiluminescence via energy or electron transfer in terms of Stern−Volmer equation in a bipolar electrochemical cell. It opens a new area of research using ECL quenching to detect small molecules based on bipolar electrochemistry. Chapter 3 illustrates different quenching effect of halide ions (Cl–, Br–, and I–), indicating the quenching ability of the halides follows the order I– > Br– > Cl–, and the quenching rate constants are also related to their formal oxidation potential. Chapter 4 deals with the potential distribution on bipolar electrode by observing the Raman intensity change of a surface enhanced Raman scattering probe at the cathodic pole when the external voltage is sufficient to drive redox reactions. The Raman intensities of 2-AQS and 2-H2AQS corresponded to the amount of them on bipolar electrode, respectively, and the relative population of 2-AQS to 2-H2AQS will vary at different positions according to the potential gradient going through the solution along bipolar electrode. Chapter 5 gives a summary of my research work and the future work.