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Doctor of Philosophy




Application of square-wave hydrodynamically modulated voltammetry (QHMV) is discussed for the study of anodic reactions electrocatalyzed by surface oxides at noble metal electrodes. QHMV permits extraction of the convective-coupled faradaic component from the total electrode current by alternating the rotational velocity of a rotating disk electrode (RDE) about a non-zero value and computing the difference of the total current obtained for the two velocities. Since the anodic formation of surface oxides as well as the decomposition of H(,2)O to produce O(,2) are virtually independent of rotational velocity in aqueous solution, the positive potential limit for application of QHMV is observed to be 200-400 mV more positive than that for conventional cyclic voltammetry, depending on the electrode material. Therefore, small mass-transport coupled currents occurring simultaneously with oxide formation and O(,2) evolution can be characterized voltammetrically by application of QHMV;Results obtained by cyclic voltammetry and QHMV are described briefly for several anodic reactions at various noble metal electrodes. Major emphasis is placed on the anodic behavior of I('-) at a Pt electrode in acidic media. The convective components of the total electrode current include: (1) the mass-transport limited production of I(,2) (E > 0.55 V); (2) the mass-transport coupled oxidation of I('-) to IO(,3)('-) (1.0 V E > 1.1 V), which is catalyzed by the anodic formation of PtOH; and (3) the mass-transport limited formation of IO(,3)('-) (E > 1.5 V) which is concluded to be electrocatalyzed by an OH intermediate product of O(,2) evolution. In addition, the results obtained for the catalytic reduction of IO(,3)('-) at a Pt electrode are described briefly;Data obtained for the anodic detection of I('-) are presented for the application of constant and multi-step potential amperometry. Iodide can be detected by measuring the current resulting from: (1) the mass-transport limited production of I(,2)('-) from I('-), (2) the suppression of the anodic formation of Pt oxide, and (3) the electrocatalyzed oxidation of I('-) to IO(,3)('-). Enhanced sensitivity of the measured signal;is observed in the potential region where the electrocatalyzed oxidation of I('-) to IO(,3)('-) occurs; ('1)DOE Report IS-T-1129. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.



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Deborah S. Austin



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203 pages