CHARACTERIZATION OF TRANSIENT ELECTROCATALYTIC INTERMEDIATES BY SERS

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The net 6-electron, five point reduction of nitrite to ammonia is catalyzed by the enzyme nitrite reductase. Electrochemical studies have shown that a series of water soluble porphyrins are efficient electrocatalyst for the conversion of nitrite to ammonia. The proposed spectro-electrochemical study will couple a number of surface- spectroscopic and electrochemical techniques to obtain data on the molecular structure and lifetimes of the porphyrin intermediates, generated during the electrocatalytic reduction. From this data, a comprehensive mechanism for the porphyrin catalyzed electro-reduction of nitrite to ammonia will be developed. The specific spectroscopic techniques to be employed are solution Raman spectroscopy, surface-enhanced Raman spectroscopy, SERS, and its variant, time-resolved SERS, TRSERS, along with UV/Vis absorption spectroscopy. By linking the large enhancement afforded by SERS, with multi-channel detection, molecular structural information on electro-generated catalytic transients on a SERS active electrode surface will be obtained. Radiation chemical and photochemical studies will also be incorporated and these techniques will provide rat constraints for short-lived iron porphyrin intermediates generated by pulse photochemical processes. The electrochemical techniques to be employed include cyclic voltammetry, differential pulse voltammetry and constant potential electrolysis. Electrochemical techniques provide information regarding the rate of the reaction and the influence of diffusion, concentration and temperature. SERS spectroscopy provides information on the chemical identity, structure, configuration and orientation of the surface species. By coupling electrochemical experiments with SERS scattering spectroscopy, both kinetic and structural characteristics of the surface intermediates will be probed. The conclusion derived from this research will find application in the characterization and design of modified electrode surfaces. These modified surfaces possess potential applications in energy conversion processes, light driven reactions and the activation of small biological molecules.