In situ characterization of electrode-solution interfacial processes by surface vibrational spectroscopies
Abstract
Vibrational spectroscopic methods are particularly valuable for in-situ molecular characterization of the electrode-solution interface, which involve surface-enhanced Raman spectroscopy (SERS) and several variants of infrared reflection-absorption spectroscopy (IRRAS). The majority of this research effort has focussed on the application of SERS and IRRAS to the investigation of potential-dependent phenomena, such as adsorption-desorption and redox processes, that are of particular electrochemical significance. We have demonstrated that the frequencies and intensities of the vibrational bands observed in SERS and IRRAS yield valuable information concerning adsorbate configuration/orientation, adsorbate-adsorbate interaction (dipole-dipole coupling) and adsorbate-surface interaction for aromatic molecules, including pyridine, benzene, and benzene derivatives. Information regrading the nature of adsorbate-surface bonding for halides, pseudohalides, and aromatic molecules was also provided by SER studies. These in-situ vibrational spectroscopies have also been utilized to yield information on the molecular identity (as well as detailed physical state) of electrogenerated species and hence yield mechanistic information for multistep electrode processes. Emphasis has been placed on approaches in which time-resolved spectra are acquired in conjunction with conventional electrochemical techniques, enabling simultaneous vibrational and electrochemical kinetic (current-potential-time) information to be obtained during the evolution of irreversible electrode processes. Coupled with linear sweep voltammetry, SERS can yield sensitive, information primarily on the changes of interfacial composition and structure accompanying electrode reactions. Several systems have been investigated in detail including the electroreduction of nitrobenzene, azoxybenzene, and related species as well as the electrooxidation of aniline, benzidine, and related species. Reaction mechanisms are proposed based on these observations. The "single potential-alteration infrared" (SPAIR) procedure is used to identify solution intermediates and products. The oxidation of simple alcohols has been examined using this technique, enabling kinetic and mechanistic information to be obtained.
Degree
Ph.D.
Advisors
Weaver, Purdue University.
Subject Area
Analytical chemistry
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