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Abstract
This thesis investigates the structure and electrochemical reactivity of underpotentially deposited (upd) modified Au(111) electrodes. The upd-modified electrodes are known to catalyze small molecule reactions. Poisons are used to interrogate the electrochemical reactivity and determine the corresponding structural changes.
STM investigations revealed that the catalytically active structure towards nitrate reduction is a (1 x 1) Cd structure for Cd upd on Au(111). Although SCN− does not affect the Cd upd/Au(111) catalyzed nitrate reduction reaction, ethanethiol is a partial inhibitor towards this reaction. STM images also suggest that nitrate is associated with the (1 x 1) Cd adlattice at the electroreduction potential. This association, based on the special properties of the nitrate anion, is necessary before electroreduction can occur.
Reactivity studies of the effect of I− on the peroxide reduction catalyzed by Pb underpotential deposition (upd) on Au(111) revealed that I− decreases the catalytic peroxide reduction activity. The change in activity upon addition of I− was modeled via a Tempkin isotherm. Analysis of STM images suggests that the active site for peroxide reduction is at the edge of the circular Pb islands. STM studies further show that at high I− concentrations, oblong PbI 2 islands are observed throughout potentials where a smooth Pb monolayer was present in the system absent KI.
Reactivity studies of the effect of SCN−, a weaker anion than I−, on the peroxide reduction catalyzed by Pb underpotential deposition (upd) on Au(111) revealed that SCN− decreases the catalytic peroxide reduction activity. The decrease in reactivity due to SCN− exhibited Langmuir behavior. STM studies reveal that islands of two different heights emerge following addition of SCN−. One type of islands is of the same composition prior to SCN− addition. The other type of island exhibits open Pb structures resulting from Pb and SCN− interactions. The open Pb structure exhibits a linear motif, a pattern that is uncommon among upd systems on hexagonal substrates.
